The Scuba GOAT Podcast

Simon Mitchell - Explaining Decompression Illness & Hyperbaric treatment

May 15, 2023 Matt Waters / Simon Mitchell Season 4 Episode 9
The Scuba GOAT Podcast
Simon Mitchell - Explaining Decompression Illness & Hyperbaric treatment
Show Notes Transcript Chapter Markers

Simon's correct title reads... Professor Simon Mitchell MB ChB, PhD, DipOccMed, DipAdvDHM (ANZCA), FUHM, FANZCA, Department of Anaesthesiology, University of Auckland.  This clearly does not fit in the title of this episode however, it goes a LONG way to explaining why Simon is one of the top dogs when it comes to being able to pour a healthy amount of clarity over the common confusions between decompression sickness, decompression illness, and arterial gas embolism.

Simon is a physician and scientist with specialist training in diving medicine and anesthesiology. He is widely published with over 150 papers or book chapters. He co-authored the 5th edition of 'Diving and Subaquatic Medicine' and has two chapters on decompression illness in the most recent edition of Bennett and Elliott. He has twice been Vice President of the Undersea and Hyperbaric Medicine Society (USA) and in 2010 received the society’s Behnke Award for contributions to the science of diving and hyperbaric medicine. In the past, Simon was a naval diving medical officer and medical director of the Wesley Centre for Hyperbaric Medicine in Brisbane. He now works as a consultant anaesthetist at Auckland City Hospital, and Professor in Anaesthesiology at the University of Auckland. He provides on-call cover for diving and hyperbaric emergencies at the North Shore Hospital Hyperbaric Unit in Auckland. Simon assumed the role of Editor of Diving and Hyperbaric Medicine in January 2019.

Simon’s diving career has included more than 6,000 dives spanning sport, scientific, commercial, and military diving. He has been a lead member of teams that were the first to dive and identify three deep wrecks of high historical significance in Australia and New Zealand. At the time of one of these dives (2002) the 180 m depth represented the deepest wreck dive ever undertaken. He was elected to Fellowship of the Explorers’ Club of New York in 2006, and was the DAN Rolex Diver of the Year in 2015.

Ref: www.dhmjournal.com. (n.d.). DHM, Simon Mitchell. [online] 

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SPEAKERS

Matt Waters, Simon Mitchell

Matt Waters  

Ladies and gentlemen, welcome to the Scuba Podcast where we explore the fascinating world of Scuba diving and ocean exploration. Today's guest is a highly accomplished physician and scientist who specialises in diving hyperbaric medicine, and anesthesiology. With over 160 published papers and book chapters. He is a recognised authority in his field, a co author of the fifth edition of diving and aquatic medicine, and the hyperbaric and diver medicine chapter for the last three editions of Harrison's Principles internal medicine, Professor Simon Mitchell was honoured with the bank award by the undersea and hyperbaric medicine society for his significant contributions to the science of diving and hyperbaric medicine. Simon is a consultant and a scientist at Auckland City Hospital, and a professor in anesthesiology at the University of Auckland. He provides anchal cover for diving and hyperbaric emergencies at the hyperbaric unit in Auckland. And he has also assumed the role of editor in chief of the diving and hyperbaric medicine journal in 2019. Aside from his academic and professional achievements, Simon has an impressive diving career with over 6000 dives spanning sport, scientific, commercial and military diving. elected to the fellowship of the Explorers Club of New York in 2006, and recipients of the Dan relics diver of the year in 2015. Simon's most recent expeditions were truck in November 2019, the purse resurgence cave in February 2020, and a New Zealand project to take arterial blood gas specimens from an elite freediver at 60 metres in February 21. With his vast experience and expertise in the field of diving and hyperbaric medicine Professor Simon Mitchell is a truly fascinating guest and I am delighted to welcome him on to the Scuba goat podcast. Simon. Good morning to you, sir. How you doing?

 

Simon Mitchell  

Yeah. Good morning, Matt. Yeah, nice to be here.

 

Matt Waters  

Oh, let's, let's just turn your volume down a little bit on your end. I think one of the very first things that we've got to kind of look at and chat about is you so why don't you just let us know where you first started to dive how did you get into donning a mask and fins and getting getting wet?

 

Simon Mitchell  

I was really lucky Matt. I grew up in a little seaside suburb in Wellington called Seatoun. Wellington in New Zealand has got this amazing rocky coastline where diving can literally be after work or after school activity. It was after school for me I was only about 10 or 11 When I started diving in. And of course it was snorkelling at first it was just what the kids did, you know, we all just got in the water and everything back then had this magical quality about it, you know, you got in the water, and you were just confronted with all these things that you'd never seen before. It was just fascinating. And, you know, I just I totally fell in love with and of course, as a boy. I wanted to catch stuff. So it wasn't long after that, that I graduated to spearfishing as a sort of extension of what we were doing. But you know, right back in those days, it was like we couldn't afford wetsuits. We had to wear jerseys with light a fire on the shore, get in the water freeze, get out of the water, heat up around the fire get packing. But it was a magical time, you know, and I remember it very clearly.

 

Matt Waters  

Yeah, yeah. And it's what point did you end up starting to train for the for the dive in then?

 

Simon Mitchell  

Yeah, well, it's pretty much as soon as I could I did an Open Water diver course it wasn't Paddy. In those days, it was the old sort of CMAs system. And I think I was 14 when I got my, what was called Basic Scuba, I think back then. And then, you know, I became an instructor as quickly as you could I think I was an instructor at the age of 19. And, and then it all just progressed from there. I mean, that's one of the amazing things about diving, Matt and I, you know, at this point, probably, again, is that you can you can make a kind of a career, what I mean a recreational career out of it, but reinvent yourself lots of different times. You know, like I say, snorkelling became spearfishing became Scuba diving became instruction and then combined with my job I my first degree was in marine biology and I was a science technician for our sort of equivalent organisation to the CSIRO and Australia or nowhere in the US. So doing marine biology stuff with diving, a bit of photography Krypton at that time, and then after that I did medicine went to the military, and was involved with the operational diving team there did rebreather diving and surface supply diving And when I left in the military, it became it morphed into technical diving and photography was back in the frame. So you know, it's it's kind of, I've had a lifetime of diving, but it's cycled through different activities.

 

Matt Waters  

Yeah, yeah. That's, that's a hell of a lot to unpack there.

 

Simon Mitchell  

Yeah, sorry. Well, we don't have to back all.

 

Matt Waters  

Yeah. When did you when you that first step into being an instructor was that in New Zealand? Or were you ever she's, yeah, it was different.

 

Simon Mitchell  

It was in New Zealand. And, again, it was under the old system, the old CMAs system. So it was quite a process, you know, like it. I mean, I don't think there's anything wrong with the way it's done these days, where you can progress to being an instructor relatively quickly, you know, the safety record of the industry speaks for itself. But back then it was perceived that, you know, becoming an instructor was a long and arduous, arduous thing. And, you know, it took a while. And then we crossed over into the petty system later on about 1985 I think it was, and, you know, I instructed diving instruction was how I paid my way through medical school. So even then it was, you know, diving was an integral part of my life, even when I was very distracted with the, you know, the rigorous process of doing a medical degree.

 

Matt Waters  

Yeah. So you did one degree in marine biology and then decided that animals weren't enough for your need to progress on to humans?

 

Simon Mitchell  

Well, the truth is, actually, and I, you know, maybe I'm torpedoing my sort of reputation in medicine here is that when I left school, I just simply wasn't good enough to go to med school. And in fact, it was something I'd always dreamed about. But there was no way I could have done it on my school record, I, I was diving too much when I should have been studying. And so I was a very average student at school. I like, you know, we used to have this thing called school school certificate. Back in the old days, which was the first public exam you set and I actually failed School Certificate science. And yet here I am, you know, Professor of anesthesiology at the medical school. I probably shouldn't say that in public, but, but look, it was nothing to do with fundamental ability, it was all to do with being obsessed with diving and not not studying like I should have at school. So it wasn't until I went, went and did other things like the marine biology that I started to become a good student and getting the sort of grades that would be necessary for getting into medical school.

 

Matt Waters  

So did you have any, any kind of idea at that time in your life that the two should meet, you know, the, with the medical training and, and the diving? Did you see that at an early stage?

 

Simon Mitchell  

Sort of, yeah, I mean, when I once I got into medical school, then it did crystallise in my head that when I left there, when I got through the course, I would like in some way to try to adapt my career to diving. And that was, it was in those years that I first encountered this guy called Dez Gorman, who actually is quite well known medical circles here in New Zealand, and was in in Australia, too. He he was a prominent diving physician at that time, head of the unit in Adelaide, the hyperbaric medicine unit, Royal Adelaide Hospital had a massive reputation. And I got in touch with him. And he encouraged me to think about diving medicine as a career. And in fact, serendipitously, he moved from Australia to New Zealand to the Royal New Zealand Navy about the time I graduated from medical school. So it was a natural thing to go from med school to working with deers in the Royal New Zealand Navy. And that was a terrific time. I mean, it was the early 90s. And we had this exuberant diving population here in New Zealand, who we, you know, weren't particularly good at following the rules. And we had a large number of decompression sickness cases. So it was a fantastic time for getting true experience based expertise and diving medicine. And so I worked I worked in the Navy with deers for about eight or nine years, which was a fantastic grounding and diving medicine. And it was later that I moved into anesthesiology after I left the Navy.

 

Matt Waters  

So, so you're actually enlisted. I assumed commissioned being a doctor.

 

Simon Mitchell  

Yes, I was. Yeah, I was a commissioned officer in the Royal New Zealand Navy Anna and look, you know, that was a fabulous time in my life. I I embraced the naval life. I had a lot of deployments overseas on ships had some wonderful experiences and I saw some things and did some things I never would have done if I wasn't in the Navy. There's no question about that. The problem with the New Zealand Navy and my ambitions is that the New Zealand Navy just a bit small to train you in the specialist fields that you wanted to go into, you know, whereas in the United States, so they will try and the UK, even Australia, they will change train their doctors and specialties like anaesthesia, surgery, everything pretty much the New Zealand Navy doesn't do that. And in order to become an anaesthetist I needed to leave the Navy. So that's what I ended up doing.

 

Matt Waters  

Yeah, it's a shame. Because obviously, they they lose a lot of people doing it that way. But they do. You've got to follow your goals. Ultimately. Yeah.

 

Simon Mitchell  

Yeah, well, that's one of the reasons the New Zealand Navy, I think, is and kind of understaffed from a medical point of view, because there's no, it's difficult to have a medical career unless you want to do it in a, an area that specifically aligned with Navy interests. And basically, they would train you and general practice or occupational medicine. But not, unfortunately, not the sort of sharping specialty that I wanted to go into anaesthesia.

 

Matt Waters  

I remember looking at the New Zealand, New Zealand military, probably late 90s, early 2000s Because I was in the UK military. And I was considering jumping ship over to Australia, New Zealand. But But even as a you know, I think you call them black handover here, whether the same down in New Zealand proportions engineer, it was never high on the list. It was always the GPS and the dentists that they wanted that. So I was just in the wrong trade.

 

Simon Mitchell  

Well, so I look, no, I don't wish in any way shape or form to sound like I'm disparaging my time in the Navy. I I'm not at all. And indeed it was what got me started. And you know, dears was a high level academic who supervise my PhD, they, they actually allowed me the time to do a PhD while I was in the Navy. And that's what got me started my academic career, my research interests in diving medicine, and all that clinical experience with SEC divers? Well, you know, in 1995, we treated 100 cases of decompression sickness, which, you know, which is a lot, you know, I remember pretty much living at the hyperbaric unit in January, we treated 30 of those cases in January that year. And you know, all the years around then mid 90s, it was a bit like that, not quite 100, but up there. So, as a young doctor, trying to get genuine experience based expertise, it was terrific. And it's hard now, you know, like, the numbers of decompression sickness cases have fallen off substantially, certainly the number that we treat, and and now someone coming into the field, like me would really struggle to find the experience, they need to call themselves, you know, genuine experience diving physician.

 

Matt Waters  

Yeah, yeah, I can imagine. And just to put that into concept context there, I was talking to a good friend of mine, who's based on Koh Tao in Thailand. And she is the manager of the hyperbaric chamber that they put in there recently. And that little island is one of the busiest locations on Earth for new for divers, divers wanting to do recreational diving and get into it. And I think last month, they only had two suspected cases where they put put them in the pot just to make sure. So to hear, what was it 30 cases in one month? You guys down there, we're really going for it.

 

Simon Mitchell  

We were but you know, it needs to be said that that has changed, you know, and it's not that way anymore. Like we now we would be lucky to treat 20 cases in a year. So, so it's really gone down. And there's all sorts of reasons for that, but which we can talk about later if you want. But there are still some places in Asia In fact, where they are treating large numbers of cases, but not usually recreational divers, they're usually indigenous sea harvesters. There's a few spots in Asia and China where people who are doing you know fishing at a sort of occupational level are getting sick quite often so so there are still some places in the world where they trade a lot of divers, but we're not one of them anymore. Yeah.

 

Matt Waters  

Yeah. That's good to hear. Not not too good. Like you're safe for people coming into the industry. But it's it's good to hear that people are being safe. I suppose over the years that you've been doing their shifts, you've obviously seen it a massive change in the understanding of the pressure on the body as divers. We do get many people come in listening to the show that are relative To be new to dive in. So would you mind just given us a background or a quick overview of the basics of what decompression sickness decompression illness is?

 

Simon Mitchell  

Sure. Well, decompression illness, it's often not appreciated. Foley is a collective term for two different disorders. One is decompression sickness, which creates some confusion because illness and sickness sound really similar. And the second problem that exists under the umbrella of decompression illness is what we call arterial gas embolism. And that's probably the quickest one to explain. So I'll deal with it first. So divers will all be familiar with the fact that they've been taught to breathe normally never hold their breath. And that's because if you hold your breath and ascend, then expanding gas can damage the lungs and introduce bubbles into the bloodstream, the arterial blood, and that's what is called arterial gas embolism. And those bubbles can travel to all places in the body, but the place we worry the most about is the brain, because they can produce stroke like symptoms, which can be serious or even fatal. So that's arterial gas embolism. And it's actually relatively rare. You know, just we talk about it a lot, particularly in diver training courses to try and prevent it appropriately. But it's actually not very common. The second problem decompression sickness, it's kind of completely different, even though it involves bubbles, just the same as arterial gas embolism, it's a very different mechanism. So that's the one where, when we dive, we're breathing compressed gas for a period of time, we absorb some of the inert gas. So if it's an air dive, that's nitrogen. And then as we come back to the surface, decompress that gas, wants to come out of solution. And what we want it to do is diffuse from tissues into the blood and be carried back to the lungs and be breathed out. But what it can do is actually form bubbles, especially if we come up too quickly or don't do an appropriate amount of decompression. Although it must be said that we most of us do actually form bubbles, even on dives where there's nothing gone wrong and where we don't get any symptoms. And those bubbles seem to be relatively harmless. But if there's enough of them, or if they're in the wrong place, then they can cause harm. So those little nitrogen bubbles, they can form in tissues. And classically, we talked about the bins because that's a manifestation of pain, bubbles forming in the pain sensitive structures and our musculoskeletal system. But the bubbles can get into the blood. And that they can, again, they can travel around the body and cause various symptoms, of course, we worry the most about neurological problems like spinal cord involvement, or the brain or the inner ear, which can produce quite dramatic and quite serious symptoms. But that that is a very different problem to arterial gas embolism like that lung damage. And arterial gas embolism can occur in incredibly shallow water, like you can do that in a swimming pool if you get it wrong. So even in like a metre deep, whereas it's impossible to get decompression sickness in that setting. Whereas decompression sickness requires that you go deeper and longer and the deeper and longer you go them, the higher the risk, obviously. So yeah, that's I mean, that's a quick walk through decompression sickness and arterial gas embolism collectively referred to as decompression illness. Is that what you were kind of getting at? Is that the sort of overview you want it?

 

Matt Waters  

It's perfect, perfect. Yeah, it's it is a very confusing subject for, for most people, especially, I mean, even for experienced divers, you know, it's good to refresh on these matters. Yeah. So obviously, when we go dive in, we've got the rstc medical forms and asking about pre med, pre existing medical conditions, etc, etc. Are there other key elements that you've seen over the years that may amplify the chances of being affected by decompression sickness?

 

Simon Mitchell  

Well, there are some medical predispositions to that. But mostly, those are not really things that you would typically pick up in a in a routine diving medical, so I speak specifically of a thing called paitent frame and oh Valley, which is a little communication between the two upper chambers of the heart, which we all have when we're in our mother's wombs, because it by it allows blood to bypass the lungs which you don't need when you're when you're not born yet. But in some people that persists after birth, in other words, it doesn't close like it's supposed to And that allows blood from the veins that have quite a few that has quite a few nitrogen bubbles in it to get across into the arterial side. Normally, those bubbles would be filtered by the lungs and removed and they don't get onto the arterial side of our circulation. But if they can do that, across a payment for m and o Valley, then that is a predisposition to certain forms of decompression sickness, including the more serious forms. Now, we can't pick that up on a routine diving medical, and we usually only discover after people do suffer, those relevant forms have decompression sickness, and we do a test for it. But it's probably worth pointing out with since you've raised the issue of of diving medicals, and the rstc form and the history we take there, that the most important element of that is not predispositions to decompression sickness, but more your general health. And it's blokes like you and me actually met that it's targeted most at because of all the diving fatalities. About a third of them are due to some kind of cardiac event as a, as a predisposing injury is that way, you know, so in other words, someone has a heart attack in the water and ends up drowning. And so the diving, medical is more focused on excluding those kinds of problems than it is the underlying predispositions for decompression sickness. And actually, one of the weaknesses in our system, one of the big weaknesses is that you and I can have a diving medical at the start of our career or have in fact, maybe not even have a medical, you know, you fill out the rstc form, it's a Screening Questionnaire, and there's nothing wrong with it, it works well. And I say that because I helped design it. And, and, you know, if there's no positive answers on the Screening Questionnaire, then you go into your diving course, and you do your diamond course. And from that point on, it's possible to have an entire diving career and never interface with the medical system, again, unless you do another course, or you're required to have a diving medical for some specific reason. But we're not very good at health surveillance. In other words, keeping an eye on our health over the years as we get older. I mean, I started diving with him when I was 14. That's, I have to admit, I'm going to admit on on air, but that's 50 years ago, right? So. So, you know, I could have gone that entire time with no interface with the medical system. As it happens, I go to a GP regularly, I have checkups, because I've seen too many friends get into trouble with cardiac issues over the years that are undetected. So those are the things that the diving medical tends to focus on, or the medical screening focuses on rather than the trying to identify underlying causes of decompression sickness.

 

Matt Waters  

Yeah. Which is why you've got that checkbox for anyone over 45 that that picks on me straightaway.

 

Simon Mitchell  

Absolutely. Right. You know, anyone who's over 45 should actually yeah, there's the form is quite sensible, like, you shouldn't see a doctor. But if you walk into a doctor surgery can give a convincing history of superb functional capacity. Like, met, I met waters. I go, I run a marathon once a week, I don't get any chest pain. And, you know, like, that would probably tell me that I don't need to do any more investigations on you. But if you're, you know, overweight, unfit, have a family history of, of cardiac problems and you're a smoker, then I would probably think very strongly about investigating you for cardiac issues further. So it's, it's getting people at that risk age into the system so that they don't miss something that's important and could result in their death and in a diving environment.

 

Matt Waters  

Yeah, yeah. Yeah. Hey, one thing I'd like to pick up on actually, you just mentioned, they're smokers. I'm an ex smoker. So I'm now Mr. Anti smoker and hate it. I can smell it 1000 metres away. But is it? Is there a mash out? Have you seen or got any kind of evidence of smoking being a major addition to issues when diving?

 

Simon Mitchell  

Yeah, look, the truth is? No, we don't have strong evidence that smoking is a risk factor for specifically for the things that I've been talking about. Yeah. However, there's, there's a massive evidence that smoking as a risk factor for heart disease and heart disease has been proven hard evidence. This is not speculation to be the disabling injury in 30% of diving fatalities. So right there, you've got a really good reason not to smoke if you're a diver. However, it's also almost certainly true that smoking predisposes you to lung conditions that might make pulmonary barotrauma more likely, but we have no real proof of that.

 

Matt Waters  

I find it quite interesting because obviously been an ex smoker. And I took that leap. I was a smoker for 3034 35 years. And then when I gave up, I couldn't believe how much better my lifestyle got particular in the water.

 

Simon Mitchell  

Oh, you know, diving aside, you know, in my role as a physician, I would say to anyone watching this, that if you're a smoker, the single most important step you can ever take to improve your general state of health is to give up smoking, and it will improve your financial situation. There's all sorts of benefits as well. But, you know, smoking, I would say that, in some point in the future, people will look back on the age of smoking and go, do they really do that? Like, that's just crazy. But I think people will, I think that that at some point in the future, people will look back on that, like, like, we look back on how they used to send kids up chimneys to clean them out. Or, you know, and they'll go, No way, like, like, puffing smoke into your lungs. You gotta be joking. Anyway. Yeah, that rant over.

 

Matt Waters  

That's okay. I keep ranting over my son about it, because he's, he does like part time cigarettes, but he's on vapes all the time, and it's just, it's in his mouth. 24/7 is ridiculous. And God knows what he's doing. Because there's no studies or no proof on what's going on with those things at the moment, but it's just all chemicals. It's just crazy. Yeah, not a good. I'll have my little rant on it as well. So Marcus, if you're listening, stop vaping. Oh, hey, one thing I wanted to ask or highlight, as well as the advantages of being underwater for people that are disabled and special needs, because I've been doing a fair bit of helping out with Lindy Leggett from the Scuba gym. And I think she's doing an absolutely outstanding job. But it led me to think with this chat coming up with you is about the larger roles of hyperbaric oxygen therapy. Can you talk about that at all on how it's used outside of diving as well? And the benefits?

 

Simon Mitchell  

Of course I can. Yeah, I look, first of all, let me just comment, or pick up on your comment about the special needs divers. You know, that has been quite controversial over the years. But I'm high as you know, as a physician, and you know, the sort of one of the so called gatekeepers in terms of fitness for diving, I think, a certain amount of cautious caution is necessary. When you're selecting people to do those kinds of programmes, you just need to make sure they don't have any major problems that would be associated with increased risk underwater, but I am 100% supportive of those programmes, they do a fantastic job for properly selected participants. And and in fact, there's published evidence now, you know, a number of publications in the journal that I'm editor of the psychological and physical benefits of participating in those kinds of programmes. So I, I am very, I'm very supportive of that. But yeah, jumping to hyperbaric oxygen. So yeah, as you've quite rightly pointed out, you know, re compression and breathing 100% Oxygen has been the gold standard therapy for treating decompression sickness for fairly obvious reasons, you know, you can press bubbles and you get rid of nitrogen more quickly if you compress someone and breathe oxygen. And it perhaps not so obvious mechanisms, but hyperbaric oxygen has some biochemical effects, which advantageous in treating bubble induced injury. So you know, that and that's obvious to any diver they they know about that literally from day one that, you know, decompression sickness or arterial gas embolism, you get re compressed, but hyperbaric oxygen, so the administration of oxygen under pressure is also used, as you quite rightly point out as a treatment in certain medical problems. And they're a relatively small number of those problems which have where the use of hyperbaric oxygen has been supported by good data. But you know, the most prominent one Is that we would use hyperbaric oxygen for, say, in Australia or New Zealand would be non healing wounds, particularly in diabetics, and particularly in the lower limbs, radiation tissue injury. So it's not a well known fact that when people have radiotherapy for cancer, they can develop tissue injury, which can last a very long time, and indeed can get worse over time, and produce quite disabling symptoms, depending on where it is. And hyperbaric oxygen is pretty much the only thing that encourages that tissue to develop new blood vessels and heal. So just those two things alone, quite prominent indications for hyperbaric oxygen, there's about 10 or 12, others that are also on the list of things that we would consider established by sufficient data to justify the use, the biggest problem with it is that hyperbaric oxygen is relatively easy to administer, you don't actually have to be a doctor to do it. And it's, it's been abused, all over the world, for the treatment of just about anything. And, you know, typically by people who will take money off you for putting you in a chamber and giving you what I would call false hope. And it's a major problem in the field. And I have written with one or two of my colleagues, I've written extensively about this, because it's a real blight on the field. And one of the problems with it, that's sometimes not recognised is that all of my non hyperbaric colleagues out there in the wider world, look at that, you know, so they'll see a list of 100 things that someone says they can treat in a hyperbaric chamber, and they just look at that and they go, that's just quackery, which it is, of course, but they form a judgement about the entire field based on seeing those kinds of things. And so drags the whole show down. So the patients that really would benefit from it, like the diabetic ulcers, the radiation tissue injury, patients don't get referred. Because the doctors looking after them think that the whole field is full of quacks. And, you know, it's, it's not something that they would subject their patients to. And that's tragic, because it does work for certain things. But there's an awful lot of misinformation. And of course, you know, the internet's the worst thing for that, you know, like, you'll find no shortage of people who trumpeting the benefits of hyperbaric oxygen for all sorts of things, typically, things that have some kind of cognitive, psychological overlay. As you think about it, Matt, if you were to design, the best placebo intervention in the world, it would be a hyperbaric chamber, right? You come there, once a day, massive commitment and expectation, you're greeted by all the staff who are lovely to you, and, and you meet other people, which might not be the case for a lot of patients, they have these social interactions, which might not be normal for them, they go into this chamber, that is sort of quite adventurous. And it's, it heats up on compression, and it and it cools down during decompression, and they breathe oxygen in there. And this whole, you know, milieu of stimulation, is a potent placebo if you're suffering from a problem that has any kind of cognitive overlay to it. So you know, it's no wonder that people who have, for example, chronic neurological disorders, like chronic fatigue, or, or multiple sclerosis, that fluctuates a bit or, you know, that any number of things, it's no wonder that when they go into a hyperbaric chamber and and have a course of treatment, that they believe that it's actually helping them. And in fact, there's been multiple studies looking at this now in various indications like chronic brain injury from trauma, we're the placebo, the, you know, where that basically they give to, they have two groups, they give one of them real hyperbaric oxygen, and another a sham, hyperbaric oxygen treatment. In other words, it's the same experience just without the hyperbaric oxygen, and both groups benefit. Both groups say they got better, but there's no difference between the groups. So anyway, that I don't want to go on about that for too long. But that is one of the problems in the field with hyperbaric oxygen that it gets abused by people who take money off patients for treatment with no real proof that it actually has beneficial.

 

Matt Waters  

So I mean, this is the first I've heard of this. These are private companies that are have LinkedIn to the medical care structure and get referred to and does the does the, you know, Medicare or the government assist in funding this stuff? Or is it completely on the back end of the patient to do it of their own accord?

 

Simon Mitchell  

Yeah, typically the letter. So in Australia, there are there are units, there are publicly funded units or units that can bill Medicare for certain indications, but they only will pay for the things that it actually does work for. So mostly, it it's, it's patients paying for it themselves, which is another thing that really offends me, you know, you're taking money off these people who can't afford it. You know, for a treatment that doesn't work. I mean, there's just for a physician. There's nothing worse, in my opinion, I just think it's terrible.

 

Matt Waters  

May I've literally just opened, I've just punched into Google hyperbaric chamber. And the very first page that I've opened, it's it's very first sentence is pressurised hyperbaric chamber is a non medical wellness device.

 

Simon Mitchell  

Yeah, well, you'll probably find that that advertisement is for what they call mild hyperbaric treatment or a chamber that doesn't pressurise you to very high pressures, and you may even just breathe air in it, and they'll be touting it, you know, like, it would be just the same as putting up a plastic oxygen mask on sitting in the corner of your living room, in terms of the oxygen dose. And yet, they'll sell you that or put you in one of those and charging money for it. claiming that it works for all sorts of medical problems. But yeah, it doesn't.

 

Matt Waters  

Yeah, I'm actually, yeah, I'm gonna stop looking at that page.

 

Simon Mitchell  

Why would well, you might be signing up for it.

 

Matt Waters  

You've just, I think you've just opened a big bag of worms that are not gonna be able to get there. That's,

 

Simon Mitchell  

look, I don't you know, I mean, I don't think we should spend too much time talking about hyperbaric treatment, except to say that it is a thing and it works for certain diseases and, and diving illnesses. You know, decompression sickness and arterial gas embolism is one of two of them. And then there's a limited range of other things. But there's an awful lot of bollocks out there on

 

Matt Waters  

ya know, I've literally just seen it. Okay, let's move away from the bollocks and the quacks. Now, one thing I do remember from my years instructing all the time, when he talks about DCS, DCI, the quantity of symptoms or the range of symptoms is just truly astounding. Either, can you narrow it down a little bit for you know, maybe people that might be quite nervous of do I have the bench is the obvious symptoms that would would stand out?

 

Simon Mitchell  

Yeah, it's really that's an interesting question. It is difficult to narrow down because the truth is that decompression sickness, so we're talking about the consequences of bubbles forming from dissolved gas coming out of solution. It does have a very wide range of symptoms. And one of the problems is that those symptoms are what we would refer to as nonspecific and other words, they can be symptoms of lots of other things, which makes it very confusing to make a diagnosis. And one of the biggest challenges and diving medicine is getting a call from someone who's in a remote location. They might even be on a liveaboard dive boat we're evacuating them would be a massive challenge and of course ruin the trip for everyone else on the boat, etc. And they've got these nonspecific symptoms that are quite hard to sort out anyway, that wasn't really your question. But the point is that the symptoms are varied and they, you know, they can be quite difficult to separate from other things. However, the most common symptoms are things like musculoskeletal pain, and I would say this that, you know, pain can arise from a whole lot of things, but the pain of decompression sickness is quite distinctive a lot. I've actually had musculoskeletal decompression sickness twice. And it's like this deep, boring ache that is a bit unlike you know, the pain you get when you strain a muscle or for a start movement doesn't usually make it worse and rubbing. It doesn't make it better. And it's like it's like you can't do anything about it both times I've had it was in my upper arm, not so much my shoulder, but can people talk about pain in the joints, but and I think this pain can kind of happen in lots of different places, but the most common places are upper arm, shoulders. hips, knees. So in association probably with the pains instead of structures around those major joints. So pain. And then another common problem is a rash, which can take multiple forms that can look like a sort of allergic rash. And then it can also present as a sort of a much more bruised looking appearance, quite a scary looking rash. We call it cutis marmorata. And it's fairly distinctive when you see it. So pain, a rash. Other common problems that were the most, those are the common, mild symptoms, and then the probably the most common serious symptom, weakness or numbness in the limbs, particularly the lower limbs, that would suggest that you've got spinal involvement. And that's probably the, that's the most feared symptom of decompression sickness that occurs moderately often, it's still compared to the pain and rash symptoms, it's actually quite uncommon. And then you can get other symptoms like very significant dizziness, or what we call vertigo, hearing loss after a dive, that that's because the bubbles are involving the inner ear. And there's a whole variety of other things. I mean, I think walking all through walking right through all of the symptoms of decompression sickness, we could spend a lot of time doing that. And I just, I would, I'd endorse your point that it's a disease with a wide variety of symptoms, many of which can be caused by other problems. And I think the thing thing I would say to divers is, look, when when you get symptoms after diving, then there's a good chance that they're diving related, right? Unless it's some kind of bizarre coincidence. So what I would, especially with the more serious symptoms, it's important that you don't rationalise and say, Okay, I've got this symptom, but I'm going to try and attribute it to something else, because I don't want the stigma or the blame for getting decompression sickness. And I actually, that's a very good an important point to make is that, you know, when we got into diving, especially in the older days, there was this thing that if you get decompression sickness, then you must have done something wrong. And now we have a much more sophisticated understanding of that it's not true people, especially in the more advanced forms of diving like technical diving, where they're doing decompressions it you know, these decompressions are just sort of estimates of what what puts your safety level at an acceptable level. They're not absolutes, they're not binary outcome. So if you do your decompression, you definitely won't get sick. And if you don't do it, you definitely will, it's not like that, it you you can do everything right and still get symptoms, and you can do everything wrong and not get symptoms. So don't rationalise just if you've got symptoms, especially the more significant ones after diving, you should contact the diving emergency service, whatever it is, and whatever country you're in, and, and talk to an expert, that's why those those services are available 24 hours, divers have this tendency to do this, you know, especially guys, they don't like to get that diagnosis. And so they'll you know, they get to the surface and they really dizzy and vomiting and they'll say I'm seasick and I'll go and lie down for you know, a couple of hours and when they finish lying down then they find they can't move their legs also you know like these are the things that can catch people out yeah

 

Matt Waters  

quick break May I need to pee okay this is a morning recording last time I did a recording it was with Pete Masley so it was beers and wine and it was stopping every 20 minutes so that one I've talked about that just picking up on what we were saying though I've got a good buddy of mine I won't I won't name him but he's a dive professional and years ago we were diving together and we come back up to the surface and just a standard recreational no decompression and is this Caitlyn? Do you get this as well and his skin you could literally feel it like like they popping wrapping bubble wrap like that. That's that's really not right. You need to get that checked out and unreturned to his home country. He brought it up with his doctor who then sends him on to a research team and he ended up doing I think 234 dives or something like that in a controlled environment with them. To find out what why he was getting? I think it was a subcutaneous hematoma. If that's right, yeah. But there was no there was no result there was they couldn't understand why he was getting this. And they checked him for PFR and all that kind of stuff. And, and he's an absolutely fantastic diver perfect trim perfect profile everything. And he's just, I think it's fair to say that he's a bit of a freak of nature. There's just been no, no understanding of why it occurs with him. But it's literally every dive he does.

 

Simon Mitchell  

It's really interesting. He may actually have contacted me to ask about that. I have had a couple of people raise those kinds of things with me. If you're asking me why I mean, I, you know, given that he's been extensively investigated, and no, no issues found, I'm maybe in no better position than while I certainly am not in a better position than the people who've investigated him to speculate on that. But subcutaneous emphysema, particularly, if you find it up around the base of the neck, in that skin in the sort of area or up in the neck itself, that can indicate that you've got some kind of leakage of gas out of the lungs that's getting into the sort of central chest area and migrating up into the tissues around here. And in fact, that's really the only circumstance under which I've ever felt what you know, like the bubble wrap. And it's vanishingly rare. I mean, you almost never see it. But why you would get there? I mean, where was the skin where you could feel it? Which one is on his on his phone on his forearm? Oh, yeah. Well, that that's very unusual. I mean, certainly what I was just discussing wouldn't cause that. So that suggests that he's getting bubble formation in his skin. And, I mean, that's a very unusual presentation, and probably is explained in some way by some kind of strange circulatory problem that, you know, like he's he's loading guests during the dive, and then getting vasoconstriction, which stops the guest, washing out of the tissues, which could conceivably form guess, you know, under the skin, so that you could feel it at but I've never seen that. I have heard of it. But I've never seen it in a very long diving medicine career, I've never actually seen that. I've certainly felt bubbles under the skin around the base of the neck from pulmonary Baron. But I've never seen that.

 

Matt Waters  

So on the on the back end of what you've just said there, and with your superior experience and knowledge in this, I'm going to confirm that I can still call him a freak of nature.

 

Simon Mitchell  

That's fair. Yeah. Definitely.

 

Matt Waters  

Okay, so moving on a little bit. And we you mentioned age earlier on arterial gas. Well, how is that the symptoms are significantly different, and what are the kinds of long term consequences of possible

 

Simon Mitchell  

arterial look, it's in many respects, a bit like a stroke. So, you know, the bubbles will go into the cerebral circulation, so the brain and they block if they're big enough, they'll block blood vessels which produces things like you see in a stroke. So, it can produce unconsciousness, it can produce a hemiplegia, so a paralysis down one side of the body, either upper limb, lower limb or both. It can produce visual changes, or loss of vision, speech difficulties, thinking difficulties, anything that can happen in a stroke. Now, the thing that separates arterial gas embolism from a typical stroke is that a stroke is caused by a clot or something solid. And unless you get that clot removed pretty quickly, you likely end up with some kind of permanent effect from your stroke. Bubbles are a little bit different in that they actually can redistribute and not block the blood vessel. However, if they're big enough, and they block it for long enough, just like a stroke, you can get permanent paralysis hemiplegia, as you can get permanent visual loss. Permanent cognitive function changes, permanent speech changes, but but the spectrum of long term effects goes right through to complete recovery. And indeed, it's not that uncommon for a diver to come to the surface. like a rat, you know, the classic situation is a rapid ascent where people forget to breathe or forget to breathe normally or hold their breath, they go rapidly unconscious wake up, and they're confused, and then everything goes away. And that certainly happens. So full recovery spontaneously, without even without any treatment is certainly possible. But at the other end of the spectrum, permanent disability or even death is certainly possible as well. So it's a very variable thing. And that probably depends very much on the size of the bubbles, the gas load that gets introduced into the circulation.

 

Matt Waters  

And presumably, when we're looking at a dive profile, if if the diver is working excessively, then that must increase the chances of getting symptoms of either

 

Simon Mitchell  

were working. Yes, so decompression sickness where you absorb nitrogen, and then it comes out of solution. As you come back to the surface. There's a whole bunch of things about a dive profile that we look at, in trying to make a judgement about how likely decompression sickness is for the diameter. Sometimes it's obvious that we're dealing with decompression sickness. But then other times when the symptoms are more subtle, or nonspecific, like, like I said before can be caused by other things. Sometimes we then focus a lot on the dive profile, and what happened on the dive in assessing the risk so that it gives us it gives us a mental picture or or a yardstick against which to judge the risk of the dive. So things like the profile itself is obviously critically important. So the deeper the longer, if you come up too quickly, or you miss a decompression stops, then obviously, those are all factors that point us towards a higher risk. But then you just mentioned, you know, working if you work hard, I mean, you think about a typical dive, right? You work hard, or at least you're working when you're swimming around the bottom. But during the ascent, particularly on a decompression dive, where you just kind of hanging out in the water, you're not working. And when you're working on the bottom, you've got lots of circulation, because your heart's pumping more the bloods flowing more, so you take up guests more quickly. But when you're resting on the decompression, that's the kind of the opposite. So your heart's not pumping as much your bloods not circulating as fast. And so washing, that gas that you've absorbed out of the tissues is actually a slower process. So that asymmetry in working between the bottom phase of the dive and the surfacing phase is a risk factor. And another classic example of that is temperature, right. So think about a typical dive, you'd jump in the water, you're warm at the start of the dive, you swimming around, you're warm, that's when you're absorbing the guest down at the bottom. But then during the decompression, when you're not moving so much and it's you know, times dragging on, that's when you get cold. And when you get cold, you get blood vessel constriction, that's exactly how your body defends against heat loss. So you get all this peripheral vasoconstriction so that your circulation through your tissues during the decompression isn't as good, again, a proven risk factor for decompression sickness. And let me say that, you know, this is not just theory that the, the risk associated with increased work at depth, and getting cold during decompression is well proven by hard data. And then there's, you know, there's a few other things that people talk about, like, you know, being dehydrated, and being fatter, you know, with a higher percentage of body fat and a few other things where the data are less convincing. But you know, certainly it's one of the things we look at Matt is you know, when someone contacts us, we are very interested in the diving they've done and the profile that they used and the circumstances the diving, it was a warm, Was it cold? Was it hard work? Was there not? You know, all those things? Are things we factor into assessing the risk of the dive?

 

Matt Waters  

Yeah, it's one hell of a rabbit hole to go down, isn't it?

 

Simon Mitchell  

Oh, it is. It is. And it brings me right back to some of the comments I made earlier about experience based expertise. It's really challenging for a practitioner who hasn't, isn't a diver themselves, perhaps and hasn't dealt with a lot of divers and hasn't seen enough cases to develop that pattern recognition that we rely on quite a lot in medicine. It's very challenging for them to confront a diver on the phone and will confront the wrong word but, you know, like speak to a diver on the phone and, and assess all these things that I'm talking about. And wrap it all up into a final decision about What to do with that person on the end of the phone? That is it's very challenging.

 

Matt Waters  

I suppose one of the difficulties, like you mentioned earlier on, as well as, especially with with men will be that, that bruised ego and just washing over, you know, if you're trying to get it from conversation on the phone, you're not getting that visual indicators of a bit of bullshit going on to try and

 

Simon Mitchell  

oh, no, for sure. For sure. And look, I'm always a little bit wary about about what I hear on the phone. So I, you know, any diver, any experience diving physician will tell you that they'll I've seen lots of cases where what you get told on the phone. And what you see when the diver ends up with you are two very different things. And often, they're a lot worse than what they implied they were on the phone. So the phone conversations, if I get any sense that I'm dealing with something that could be serious, I'll usually opt for a relatively conservative stance and evacuate the diver. Now there are there are exceptions we don't we certainly don't evacuate everyone we have a conversation with and indeed, that's one of the reasons we're treating less cases these days. Because we recognise we've defined a, we've made a definition of mild decompression sickness. And we have an international consensus that says, if the diver really does only have very mild symptoms, then it's okay to manage them without evacuating them and re compressing them. That of course, doesn't mean I wouldn't really compress someone like that. You know, if they were standing, if they were here in Auckland, of course I would. But if they're on bikini yet, oh, and it's going to take a $200,000 slightly hazardous evacuation. to evacuate someone who's got a bit of mild elbow pain and nothing else, then I would probably manage that person at Bikini Atoll rather than trying to evacuate them. So these days, we do make judgments on this. But if I getting back to my point, if I was nervous about what the person was telling me and I got any hint that they might be obfuscating, more serious symptoms, I usually opt for an evacuation.

 

Matt Waters  

Yeah, yeah. Well, speaking about the evacuation, you know, once you've decided that you're going to evacuate someone and and use the pot as it were. How do you go through the process of determining the appropriate treatment plan for that patient?

 

Simon Mitchell  

Do you mean in terms of the evacuation or what we do with them when they get to the hyperbaric chamber?

 

Matt Waters  

Yeah, when when you get back to putting them inside? Well,

 

Simon Mitchell  

look, the truth of it is it's a fairly generic process. We you know, we have one we have Well, there's several options for the RE compression profile. But there's one very generic option called the US Navy table six, which is a four and a four and three quarter hour recompression, that involves compressing them to 2.8 atmospheres or 18 metres of sea water equivalent for 320 minute oxygen breathing periods, and then decompressing over 30 minutes to nine metres sea water equivalent or 1.9 atmospheres. And there's a couple of one hour periods of oxygen breathing, they're separated by an air brake and then a final decompression to the to surface pressure now that can be modified a little bit, you can extend the period of time you spend at both of those pressures. But look, if all you ever did you know no matter who you are anywhere in the world, treating decompression sickness, or arterial gas embolism, if all you ever did was the US Navy table six, then you couldn't really be criticised for that. Because there's no real evidence that anything else is any better button in some places. And we've been we've indulged in this kind of thing over the years, we sometimes re compress to a slightly deeper depth, if we get someone very early with very serious symptoms will sometimes do that. Sometimes use different gases, especially when you go beyond 2.8 atmospheres or 18 metres of sea water equivalent in a chamber can't use 100% Oxygen anymore because it becomes too toxic. So you have to breathe something else. And we'd rather they didn't read there. So often we'll use heliox mixtures for those kinds of decompressions. But that's getting quite heroic, and there's no real evidence that it's any better than just doing that standard. US Navy table six, maybe making it a little bit longer if they've got very serious symptoms. So there's not a lot of variability in that. That's the truth. And it's, you know, it's not the most complicated intervention and medicine one would have to say

 

Matt Waters  

well, is there any, any cases that stand out to mind that you you can discuss that have Maybe piqued your, your interest or challenges?

 

Simon Mitchell  

Well, the the interesting cases are the ones that are, you know, like somewhat paradoxically, in terms of outcome for the diver the most interesting cases or the sickest ones. Because they're challenging, and they're interesting. And, you know, I hasten to add that one will prefer, they didn't happen to the diver. But when they do, those are the ones that are interesting. And one of the one of the fascinating things about diving in the last sort of 20 years, we've had this, you know, advent of technical diving, and because these divers are doing deep dives, and I'm, I'm obviously one of them, right. So in no way shape, or form as any sort of criticism, you know, I do it. But we are, so I might as well use the term we we do these deep dives that require decompression, often quite substantial amounts of decompression. And of course, that introduces the potential for things to go wrong in failure to complete the decompression, so you get people coming up too quickly from dives, where they were supposed to do a whole lot of decompression and, and what that creates is people who are very sick, so they get very what we might call fulminant decompression sickness. And so they, you know, in medical terms are shocked hypotensive, you know, their blood pressure's low that they have all sorts of biochemical and haematological derangements, they might be paralysed in all four limbs, and, you know, just very unstable intensive care type patients. And, you know, one, I mean, I was involved in a case, while I've had a number of these over the years, thankfully, they're not very common. But I do remember one in Sydney, a technical diver who a good friend who came up rapidly from a 110 metre dive, because of a fault with a rebreather, and he was incredibly sick, the sickest diver I've ever treated, who actually made a full recovery. And, you know, it's, I can talk about it, because we actually published it as a case report in diving and hybrid Medicine Journal, because it was so interesting, and he was so sick. And yet, he actually made a full recovery, you know, young fat guy and had a few things lined up for him, he got treated very quickly. It's diving off Sydney and the, the, when the when the accident unfolded, the rescue helicopter was actually in the air doing a retrieval exercise. When the guys put the phone down, and from bringing the ambulance service, they could actually see that helicopter flying towards them, you know, literally 30 seconds later. So that was a very lucky break, in that case. And it turned out that it Prince Wales Hospital, they were also running intensive care in the hyperbaric chamber exercise. So he arrived, you know, like, all these stars, other than the accident happening itself, obviously, which we would prefer didn't occur. All these stars aligned in his treatment. And he had a terrific outcome. But he was very sick.

 

Matt Waters  

He allowed to name the guy who was he stayed, I won't

 

Simon Mitchell  

name him, but but I'll certainly I can provide you a website address where you can actually look up the paper that describes the whole case, you can download it for free. Brilliant. So I'll provide that to you. And if your readers want to read about that case, they can

 

Matt Waters  

do that on this show notes for sure. Okay, so you're kind of bridging the gap between professional divers, recreational divers, sports divers, military divers, and in the medicine world? In your opinion, are we doing everything that's possible to promote safe diving practices? Or do you think there's more that we could do?

 

Simon Mitchell  

Oh, there's well, there's, you know, it's a difficult question, but you probably can never do enough. And I do think that the industry is reasonably good at self reflection and making appropriate recommendations where we see problems. Now, implementing those recommendations and getting compliance with them is another challenge. But I do think that I think we're pretty good at that. I mean, we've already seen one example in this podcast. So I talked before about how a cardiac event is the, you know, the disabling injury and 30% of diving fatalities. And the industry's response to that is to ensure that the Screening Questionnaire identifies those people who are at high risk of that and ensures that they have A medical evaluation before they go diving entirely appropriate. That's a good example of it. I mean, I've just come back from rebreather forum for in Malta, where we had three days of presentations. And then at the end, I actually chaired the consensus session where we pulled important points out of the out of the various presentations that had been made. And a lot of those were safety points. And you crafted them into a series of consensus statements, which are effectively recommendations for industry and divers. And you know, an example of that is, you know, a very strong advocacy for the use of pre jump checklists before rebreather divers jump in the water. I mean, like, if, if you look through the causes of rebreather deaths, probably more than half of them have occurred because the diver jumped into the water with the oxygen cylinder turned off, or their rebreather turned off, or their diluent cylinder turned off, or their dry suit, not connected to its inflator, just those four or five things, if everybody had checked those chicken response with someone else before, just before they jumped on the water takes about 45 seconds, then we probably would have had half the deaths we've had, because those things are incredibly common. So you know, we recognise that and the industry has strongly advocated the use of pre jump checklists, very simple killer item pre jump checklists. And it is another example of, you know, self correction by the buyer diving essentially a diving group, I mean, rebury the forum for was a collection of divers as much as anything else. But it, it has self recognise that these issues and has advocated for an intervention, the use of checklists that will help prevent those things. So, you know, I think, I think that we aren't bad at advocating for doing the right thing. Getting divers to do the right thing is another story, of course, and I have no magic wand to wave in that regard, Matt, I would say this, though, that where we want divers coming through to exhibit good practices, I can't overstate the importance of people like us, you and me and senior divers, so people that others modify their behaviour on setting a good example, you know, and I can tell you, I will not go onto a dive boat with my rebreather and not use a checklist before I get in the water. But I do not want people seeing me do that. For a start, I value safety, you know, so I don't want to make any of those mistakes. But you know, I just will not do that. Because it's critically important. If you know, other people who are, you know, influenceable can watch me, then I want to model good behaviour. And I do not want to set a bad example. And that's critically important in our industry instructors, you have to do the right thing.

 

Matt Waters  

Yeah. And it's not even under the teaching umbrella, either. It's, if you are. If you are an example of professionalism within our industry, as a dive professional, you should be very vocal and very clear about doing your pre jump checks, whether that's on a rebreather or just on a single tank recreationally.

 

Simon Mitchell  

Yeah, well, you're right, you know, that's right. So a buddy check, you know, and that that gets omitted a lot. You're in fact, you almost never see it done. And you know, I disagree with that, too. I think that we should be doing those checks. I cannot put my hand up and say that every time I've jumped in the water for a simple open circuit, Scuba dive, I always do a buddy check. And I should you're quite right. And, you know, taking my own previous comments on board. The reason I focused on rebreather divers in the way that I did is that we have hard evidence that those things are critically important in causation of rebreather fatalities. There's no question about that, slightly less of a well proven thing for you know, the efficacy of doing buddy checks. Having said that, there is no doubt that they will enhance safety and they should be done. I actually think we could do a better job at designing them. You know, like begin with review and friend. I mean, like an organisation like Patty with all its resources, couldn't they come up with a better mnemonic than that? I mean, we used to say we used to say botulism with runs and flatulence. I think we had a whole bunch like we tried to, you know, Make it a bit more interesting and spicy. But surely they could do a better job. You know what I mean? I think that those those checks are important. And we should be doing them in all forms of diving. You're absolutely right.

 

Matt Waters  

Yeah, yeah. I like, I mean, obviously, you're going to be an advocate of him as well. But the way Gareth lock is just kind of opening up that that kind of protection of embarrassment that people seem to feel about doing checks, and, you know, just being honest and open and getting shit done with checklists, and prayed, and honesty after a dive site with review and feedback, etc, etc. I think the more that that develops within our industry, then the safety factor is surely going to go up through the roof. In my opinion,

 

Simon Mitchell  

I think that there's good evidence from other industries. And aviation is a classic example. And medicine. My field is another classic example where chicklet the use of checklists, for example, as a proven strategy for reducing mortality and complications in the operating room. Now, you know, Gareth Yeah, absolutely. Right. You know, he, he is probably the most identifiable advocate for bringing the broader field of human factors into, into diving. And that's not just checklists, of course, checklist is an important part of it. But anything that any strategy that will reduce the chances of errors or omissions or violations where people make conscious choices to do bad things, is obviously welcomed and has advocacy for talking about accidents and being open and honest about them. You know, so a just culture where people don't get judged when they do this. That's all that's all really important stuff. And I totally agree Gareth does a great job of that. He he was at rebreather forum for and spoke about his passion for that over there as well.

 

Matt Waters  

Yeah, to see quite a few of his posts. It looks like he's saying on literally every presentation that was going on.

 

Simon Mitchell  

He did well, I know. Well, it was a single stream meeting. So you could but he didn't. I didn't see him duck out of any of them. He's pretty passionate about it.

 

Matt Waters  

Oh, hell yeah. Yeah, it's good. Okay. Let me just flick through a couple of these questions we've got here. Oh, I'll tell you what I didn't mention what I'd like to touch on briefly. When we first started to chat I touch base with you because I'd I'd had a law rango spasm 24 metres. And it was not long after I'd seen Steven Fordyce his presentation at ASA tech. Now for what you can explain what Allah rangos plasma is better than me, surely. But if you were to listen as if you were to look it up on Google and just check out the videos, you'll you'll see, it's a pretty horrific thing to go through, let alone be doing it underwater. If you are these pretty damn rare, or is it kind of struck out to me that, you know, for two people to be voicing and whether they're more common than what I thought?

 

Simon Mitchell  

Yeah, no good question. So just to be clear, for those listening at laryngospasm is when we're actually not let's step back. And so the larynx is what a lot of people commonly refer to as the voice box, you know, so it's, it's this organ that sits at the top of the airway, the trachea that goes down to the lungs. And it has multiple functions. It has the epiglottis, which flops down when you swallow and stops any food getting down into the airway, which you don't want. And it also contains the vocal cords which can tighten or loosen, and come together or move apart in order to make the various sounds that we make when we're speaking. So it's actually a vital organ and, you know, very important to our quality of life and our ability to communicate cetera. Now, one of the things that can occur with the larynx and the vocal cords, is that if the larynx gets a lot, what you might call a fright, or it gets stimulated in an egg in a noxious way the vocal cords can snap together, and that will block the airway. And that's what we call laryngospasm. And interestingly, when you get laryngospasm, the main, the bit of the breathing cycle, so breathing cycle is inspiration and expiration, the bit of the breathing cycle that gets impaired is inspiration. Expiration actually works because you're kind of forcing gas out through the cords from the chest, whereas inspiration tends to that pushes the cords apart the vocal cords apart, whereas inspiration sucks them together when you're trying to draw gas in. So it's inspiration that's worse and we get this thing called stride or which is when during inspiration, you get this sort of, either you can't inspire at all or if you can, the vocal cords are sort of very close together, you get this kind of this kind of high pitch noise, which, I mean, if if it happens to you, and you're awake, it's terrifying because you feel like you're being strangled or asphyxiated, which is effectively what you are being you know, you are being asphyxiated. It's just your hope that it's going to break before you become hypoxic and unconscious. Now the head you're right, that said, there's been several episodes of the securing underwater and to answer your original question i It's very rare. You know, I'm a diving physician well connected in the diving medicine community and the diving community. And I've only heard of a few episodes that I think a genuine luring a spasm under water. Why can it happen? I think one possibility is that if you get water into your airway, and you get water landing on the vocal cords, or you're unlucky enough to have a piece of bit of snot or something yet Centre at land directly on the vocal cords during breathing, that could precipitate luring a spasm. The interesting thing about the case you mentioned, Steven for dices case is that that almost certainly happened because of negative pressure inside his airway induced by wearing a rebreather on his side, a side mount rebreather, and going steep vertical head down to get through a passenger in a cave. So that the counter lung of the rebreather was way higher than his airway. So there might I mean, I don't know, but maybe 50 6070 centimetres of difference in water depth. So the counter lungs up here and the airways down here. And that means because the two are connected to each other, that means that the pressure in the airway was the same as the pressure up here higher, you know, because this is shallower. So the the sorry, the pressure in the airway is lower because the because the catalogue shallower, and that means that there's this negative pressure inside the airway, which during an inspiration might be enough to suck the vocal cords together, and then they'll go into spasm. And that's what it sounds like happened in Stephens amazing video scary video. And he was really lucky. I mean, it broke, as usually well. But it'd be terrifying while you're in that state of being almost unable to inhale, you can exhale, but not inhale. So you breathe out and then you can't actually breathe and again. So yeah, there have been several cases. And I think, you know, there's two broad classes of causes. One is some kind of irritation of the vocal cords or the larynx, like water or snot or something else, or regurgitated stomach contents, something like that. And the other cause the other potential cause is hydrostatic imbalance, where you you get this counter lung being at a very different shallower depth to your airway and on a on a, say, a side mount rebreather, which can possibly do it as well. Yeah, fascinating. Yeah. Really interesting. I'm really hoping Stephen will write that case up. We can publish it properly. And in a diving Medicine Journal.

 

Matt Waters  

Yeah, yeah, for sure. And we'll probably talk more about it. He was actually the first person I touch base with whenever when it occurred. Because I mean, when I heard his presentation, I was tech. I'd already had Ella rango spasm, but it was on the surface. It was just in between dives. I drink some water and actually say, I assume it was water that touched the vocal cords and caused and I assume underwater, it was water that got on the vocal cords as well. But you know, seeing his video and his presentation are like, holy shit. That's what it is because I never really paid any attention to what it's just yeah, yeah, yeah, I didn't bother looking into it. But it was the for me it was the the knock on effect that comes from it as well. Having that experience underwater was the first time and I won't lie. I was shitting Tiffany cufflinks. i It was the closest and the most understanding I've had a panicked divers just having that mental idea that I need to go. And I'm at 24 metres and then the professional side of me say no, don't be stupid, you've got to stay there and sit this out. And it only lasts about 30 seconds. But yeah, the knock on effect was, I think, probably 15 or 20 dives, before I could actually comfortably be in the water again and not be thinking shit, it's gonna happen again.

 

Simon Mitchell  

I know it would be terrifying, no question about it. Yeah.

 

Matt Waters  

hyperbaric medicine, what's it? What do you think the future is for it? I mean, you've obviously seen its growth over many, many years. Now. Where are we going?

 

Simon Mitchell  

Well, I think the key there is to properly research, the various things that it might be useful for. As I alluded to earlier, there are a couple of indications where there, there's pretty good data from studies that show that it works. So you know, I mentioned diabetic foot ulcers, and I mentioned radiation tissue injury. But I think the key to wider acceptance for further indications and other words, diseases you can treat is proper research. You know, not this Are we think it might work for this and more. So we'll just do it and charge people money, you need to do proper trials. So the future is identifying things where it makes biological sense, where maybe there's been a few cases that seemed to have responded well to it. So okay, let's do a proper trial, let's prove this. And therefore gain wider acceptance amongst you know, the medical community that this is a legitimate indication, that's the future. Now, whether we get there or not, because we haven't done a terrific job of that so far. But follow the money. That's the problem. You know, people just want to make money. So they're looking for things that they can charge money for, and that they can treat now. And there doesn't seem to be any shortage of people prepared to pay money for treatment for things where it hasn't got adequate proof. But the future if I could wave a magic wand, the future would be proper trials in us in a relatively limited number of conditions where it might work and establish those things as either established indications or not. Yep, good evidence or not. That's what we need. You know, the situation we have right now. I mean, the Getting back to the point I made before, if every diabetic foot ulcer and every radiation tissue injury in Auckland, that actually could benefit from hyperbaric oxygen got referred, it would keep two or three hyperbaric units, busy, full time, you know, 24/7, you don't need anything else. Actually, the problem is, those patients aren't getting referred. And the reason they're not getting referred, is all this bollocks activity by people who drag the reputation of the field down. And so the physicians looking after these patients are no, I'm not going to refer them for that. Because it's, you know, here's this advertisement for treating everything under the sun with hyperbaric oxygen, it must be bollocks. That's the point. If we stuck to it an evidence base, you know, ethical practice, then we would get the all the referrals you could possibly need to make your, you know, your hyperbaric units successful. But unfortunately, we're in this kind of vicious circle where there's too much an established practice out there. And that creates a poor reputation for the field.

 

Matt Waters  

Unfortunately, well, how about we bring it up the other way? What's, what's been some of the most rewarding aspects of the work that you've done over areas?

 

Simon Mitchell  

Well, in in terms of diving, you know, in recent years, I've become, you know, I've been a technical diver Well, in recent years, the last, since Alice left the Navy 30 years ago, I've been involved in technical diving, and since 2019 98, or 99, I've been a rebreather diver. And, you know, I've had the most amazing experiences as a as a diver, you know, I can, there's too many to kind of, to articulate but I would say that probably the single most rewarding thing for me and diving was way back in 22. Sorry, 2002 when Trevor Jackson and I dived, the wreck that was thought to be Australian hospital ships in core of Brisbane was 180 metres no one had ever dived at and at the time, actually, it was The deepest shipwreck dive that ever been done and we dived it because we obtained some video from when that ship had been discovered 10 years earlier that we thought made it look possible that it actually wasn't the right rig and yet this was gazetted on the government website is on charts as the centre, there was a church on the nearest point of land, there were trips out there for families to throw wreaths over the site on that site. And here we were thinking maybe it's not even the right ship. So we dived it, and indeed found that it wasn't the right ship, which created quite a lot of controversy at the time. 60 minutes made a programme about our dive, where they essentially shamed the government for accepting the report from 10 years earlier, that was done with an ROV. So someone would put an ROV down, got some sort of vague, it's a shipwreck, and they claimed it was the Centaur. And no one really questioned that. And yet, you know, 10 years later, we dived it's not the right rig. And it was a bit unsatisfying, because you know, we disenfranchised all these people who thought they knew where their loved ones were. But the good thing that came out of that was the Australian government funded a search for the real wreck, and that they actually chartered the ship that found the Bismarck and the Atlantic and HMS Sydney off Western Australia. And they found it about five miles or so further out than we were we were right on the edge of the continental shelf, they found it and 2000 metres of water, never be dived. No question, they found that with the bell on deck, hmm, I actually sent or, you know, the whole visit was extraordinary. And the cool thing about that is that, you know, after a few years, these people who were throwing wreaths on the wrong Rick got taken out there for the very first time, and three wreaths over the side on the right side. And look, you know, if I was visiting a grave site from my grandfather in France, who died in the war, and his body was really at another grave site, I'd actually want to know that, you know, and so in the end had a good outcome. And that's probably the single most satisfying thing I've ever done in diving was that dark, but I've had lots of amazing experiences. And just you know, recently I've been doing, you know, expeditions with the windmills guys. Here in New Zealand, the peace resurgence cave, we went there in 2020. Richard Harrison, Craig challen did, you know, extended their previous range in that cave, they did 245 metres in a 16 hour dive and six degree water. And just several months ago, Richard, and Craig did another dive this time, slightly less 230. But use hydrogen for the very first time in 30 years, very first time ever on a rebreather, to try and ameliorate the effects of the high pressure neurological syndrome while getting rid of the nitrogen out of the mix because of its density. And that was successful. So that was another really satisfying expedition to be part of. Yeah, and that was just just a couple of months ago. So you know, I've had some fabulous, fabulous times and diving. Yeah. And in terms of, I think you also asked about, you know, professionally? Well, we, you know, we've kind of over the last 20 years, or, yeah, the 20 years we've we've sort of made an art form out of identifying problems, or questions that the diving community has in relation to diving medicine or physiology, particularly around the use of rebreathers. And trying to answer those questions with relatively simple, small studies that are doable, but are of high practical relevance. And we've had a terrific time with that. Just lots of really interesting studies. Probably my single like, if you're asking me, my single biggest contributor to diving medicine, in my view, would be the consensus conference that we held in 2004 in Sydney, where we developed an international consensus on what mild decompression sickness is, and an acceptance that it's okay to not re compress patients with mild decompression sickness, if it's difficult to access, re compression. And that why is that important? It's important because that was the dawn of the age of travel to all these exotic locations that we're currently seeing or people going. People were wanting, you know, the most remote the most exotic you know, the To the new experience, and so they were going to increasingly remote locations all over the world. And it was creating problems because they ring Dan with these very mild nonspecific symptoms from places like Bikini Atoll. And then you're faced with this issue. Well, what do we do? Because at that point in time, it was pretty much a standard of care if someone had symptoms of decompression sickness, and you made the diagnosis, you kind of were obligated to evacuate them, no matter how serious or not, it was. Whereas once we, once we constructed this consensus, and we had an agreement on that, it, it really revolutionised the way divers were managed all over the world. And we're, you know, we're 20 years, almost 20 years down the track from that consensus. And although it was very controversial at the time, it's fair to say that no evidence or even compelling anecdote has emerged that would suggest we went too far with that, that it seems to have worked. And that was a big contribution to the way divers are managed all over the world that has persisted and, you know, become relatively entrenched in practice, I would say. So, you know, those are a couple of examples of really satisfying things that I've had in my career.

                                                                                                                                                                                                            

Matt Waters  

Just just a couple of good ones, though.

 

Simon Mitchell  

Oh, well, you know, it all sounds a bit sort of self congratulatory. I mean, you asked. So um,

 

 

yeah, it should be.

 

Simon Mitchell  

But yeah, a lot. Every divers got their best dive, you know. So mine just happened to be the central thing. I wouldn't say it was my best dive. But it was certainly the most satisfying dive project I've been involved with. But the you know, these recent things with the wit meals have been terrific as well, I must say.

 

Matt Waters  

Hey, I want to pick up on there as well. Just on a subject. What's your thoughts on on people doing the old fashioned kind of self administered? Re compression?

 

Simon Mitchell  

You mean in the water? Yeah, yeah. Well, that is an issue that's been around for a long time. It's been a big controversy. Typically, the medical community have been against it. However, again, this is another thing that the growth, the advent of technical diving has changed that LEMs landscape a bit. So just a few years ago, 2018, I was actually asked by the divers alert network in the US to review pre hospital management of decompression sickness, which included that mild definition revisiting that has it worked, do we need to change it? And one of the questions I asked was, What about in watery compression? Because the medical community considered it quite a few times and said, No, no, we don't want that. And yet, now we have this population of technical divers who are trained to plan and execute decompression stops and the water they're trained to use 100% oxygen in the water, they know the risks of doing that they know how to minimise those risks, they know how to do it safely. In other words, is this a group that we would be prepared to endorse using in watery compression under certain circumstances? And to cut a long story short, the consensus we came to is yes. So there is now a consensus of medical experts that says that properly selected divers with decompression sickness being treated by properly trained and equipped divers, and that is technical divers trained to at least decompression procedures level. So they know how to use oxygen can use in water decompression legitimately if a hyperbaric chamber is more than two hours away. So that's kind of where we've landed in terms of in watery compression. So it's not so let me be clear, it's not that every PADI divemaster can put a sign on their boat saying in water recompression provided here, you know, that is not the intent of it. And it's not in water compression on air, because that has been shown under multiple conditions to not be very successful. But in water recompression by properly trained divers using oxygen is definitely an option. And once again, I can provide you with a web link to a paper the paper that we essentially generated to justify that decision, one of the things we did is quite interesting, as part of part of that process, we dug out all the evidence that demonstrates that very, very rapid rate compression is effective, because that's the big advantage that embroidery compression gives you right, it's you can do it really quickly. And in fact, we found data from US Navy databases that David delete has access to we we were able to present a strong case, that very rapid rate compression does actually work. So that's point number one. And also we demonstrated we found data from early US Navy recompression. Table testing programmes that shorter, shallower re compressions, like you can do in water actually are effective, especially if you use them early. You can't do a table six in the water, right? You can't go to 2.8 atmospheres underwater and breathe 100% oxygen that's too dangerous. But you can go to 1.9 metres and there are some in water decompression treatment protocols that basically involve that, especially if you use a full face mask or mouthpiece retainer device as a safety factor. I'm just gonna have to plug my computer in here, because I think I'm gonna run out of power soon. I think we're all good. And I have power so no, that's that's fine. Yep. Sorry, you will just have to eat it at bed out.

 

Matt Waters  

That's fine. I might leave it in just for embarrassment. Okay, I tell you what let's do. Let's do another nine questions of the 10 questions. I've been asking every guest. We've just had one of those, because one of the questions was a memorable dive and I think 190 metres kind of covers that. And then we can get wrapped up and you can get on with your, you're married. Okay, so question number one, how do you describe your position as a diver and medical guru to people who are not familiar with the activity of diving?

 

Simon Mitchell  

Well, I would just say that I am a diver, you know, and like any person who has been passionate in a sport for a long time, I've evolved over a long period of time. And so as a diver, I'm now what people call a technical diver. And I use rebreathers, for deeper longer dives. That just gets me to places where I couldn't get to otherwise, I'm not a dip snob. By the way, you know, I'm still having to go for a nice shallow tropical reef dive. I love it, in fact, but the technical diving is a tool to get longer and deeper. And I've been very lucky to be able to wrap that passion up into my career, both as a clinician in treating other divers who are sick, but also in doing research work to answer questions that are relevant to the communities that I'm part of. So I've had a very all encompassing diving and medical career all wrapped together, both clinically, academically and recreationally. I don't know if that answers that question. But that's yeah, that's my that's my answer.

 

Matt Waters  

Well, you've actually fit in a hell of a lot into what you could arguably say, as a relatively short time over your lifespan, you know, to be able to do and achieve what you've done so far is just phenomenal.

 

Simon Mitchell  

Oh, that's really nice of you. I mean, it's like a long slow innings and cricket. Keep me like runs. Yeah. Yeah,

 

Matt Waters  

yeah. Hey, one thing I didn't ask, and I should cross my mind when I was speaking to Pete the other week. With the advent of a lot more tech divers, effectively recreational tech divers that are going on holidays to these remote locations, what do you think there's going to be an increase in issues with, you know, decompression sickness due to these people being qualified, and then not, not preparing for such a trip like Chuck lagoon or something like that, you know, I can only imagine people sitting at home for a long period of time not really doing dives to what you would call reasonable depths, and then all of a sudden going and doing 10 1215 days on a boat dive in every day. Yeah, that's got to increase problems,

 

Simon Mitchell  

I think. I'm not sure that it's the lack of preparation, although that, you know, could certainly contribute. It's not really what we see what, what we see on those expeditions. And I, you know, I've been on maybe six or seven of Pete's expeditions to either track or bikini actually more than that. And I'm going again, in December to what we see is divers who, it doesn't really matter whether they're active prior or not, they get to a place like that. And they're just blown away by how good it is. And because it's a trip of a lifetime, I spent a fortune getting there. They just want to squeeze out every single diving minute that they can. And so we see them doing patterns of diving that they probably wouldn't do, like, you know, two big dives a day, you know, decompression dive long deepish. And then it's usually day three or four, we start to see problems, you know, as this all accumulates, so it's not really the fact that they haven't prepared necessarily rather that they just get to an amazing place and, you know, dive their backsides off. And that just creates provocation. That's the main issue, I think, is it's not like I don't think it would have helped if you'd done a whole lot of diving before you arrived, I think you'd still be likely to have the same kind of problems. It's just this, you know, arrive in this amazing place and then just go ballistic with. Yeah, that's what that's typically what we see.

 

Matt Waters  

Okay. All right. So, if someone wanted to pursue a career similar to yours, what advice would you give them?

 

Simon Mitchell  

Well, there are quite a few people who are doing exactly that. And I get to talk to them quite often. I've got a young medical student from the United States staying at our home at the moment who's who's trying to do exactly what I've done. Well, you know, be a diver But then there's some hard yards that have to be done. And one of them is getting a medical degree. You know, if you really want to be a diving an academic diving physician, so getting a medical degree and and then one of the pieces of advice that I quite often give it to circumvent people trying to do what I did, which was make it all about diving medicine, is that you can't do that. Right? You, you, there's no such thing as someone who only does diving medicine. There's just no way we see enough divers to do that, well, well, there are some people who spend their entire lives doing diving medicals, but sorry, I'd rather rip my own head off. And, you know, you're just doing these endless medicals on people who are fitting well, that's not my idea of of satisfaction. So what I mean, what you need to do is do your medical degree, and then involve yourself in the activities of a diving Medicine Unit. So as an on call doctor and contribute to an on call roster. But at the same time, you need to train in another specialty that will pay the bills and hopefully have some compatible skills that you know, you can apply in your diving medicine career. So anesthesiology is absolutely perfect. You know, we we we become very good at managing critically ill people. We've got great airway skills, we know all there is to know about giving drugs that sustain life. And, and so anaesthesia is a great choice. And also there's quite a lot of cross fertilisation between diving medicine, physiology and anaesthesia, physiology, you know, gas physiology, all that kind of stuff. But emergency medicine is another good one. And like any medical specialty would do, but the ones that give you a skill mix, which translates in some practical way to diving medicine like out there in the field when I'm on one a pizza expeditions. The fact that someone could come to the surface and be drowned and need resuscitation as an anesthesiologist that doesn't faze me too much. That's not to say I wouldn't get distressed in a situation like that, of course I would, especially if the patient's doing badly, but but I know I've got the right set of skills to deal with a thing like that. Whereas if I was a dermatologist, maybe less so you get my point. So go to med school, maintain your interest in diving, do a compatible specialty, do it in a place where there is a diving Medicine Unit so that you can get involved in the activities of that unit. And then you have this parallel career going forward in your primary medical specialty, and diving medicine and that and of course, stay a diver and keep diving. That's how to do it. And if you really want to immerse yourself and become influential, then getting involved in diving medicine research is also a good thing to do. Because the truth of it is, people don't know me, because I'm good at treating decompression sickness. They know me because I've published a lot of stuff about diving and diving, medicine and diving physiology. And a lot of that comes out of the research that I do. So if you really want to become influential, and you talk a lot of conferences and all that kind of stuff, you need to start studying, diving and diving medicine. And that's a cool thing to do, too. You know, and, you know, I was very lucky, I got to do a PhD in a relevant subject area when I was in the Navy. There are other ways of doing that. But yeah, so go to med school, do a relevant specialty in parallel with some diving medicine activity. And so if you're doing if you want to do this in New Zealand, you'd either do it in Auckland or Christchurch, where there are chambers, you wouldn't do it and Wellington for example, because that you wouldn't be able to immerse yourself in the activities of a diving Medicine Unit. And stay at diver advanced your diving career and do some research that There you go. There's my formula for becoming somebody like me.

 

Matt Waters  

If you could change anything about the diving industry, or Scuba diving in general, what would it be?

 

Simon Mitchell  

I probably it probably goes back to that discussion we had earlier about human factors. I mean, because my natural gravitation is towards safety, you know, because of my role as a physician. And and the things that motivate me or that I would want to change are the things that promote safety. I mean, if I was eco warrior, I might give you a completely different answer to that question quite legitimately, you know, but for me in with my professional interests. You know, if I could wave a magic wand and get every rebreather diver to use a checklist, that would be something before they jumped on the water. That's probably something I would do. And so it's difficult to put my finger on any one thing, but I think there's an oops, there's an example, if you want one of something that would fit that sort of question.

 

Matt Waters  

Okay, thinking about green and conservation, what? What are your thoughts on ways for us as human beings to minimise our impact on the oceans?

 

Simon Mitchell  

Well, there's lots of ways, of course. But for me, there's two broad areas. One is even a pollution of the oceans and plastics in particular. And actually, you know, we're, we're moving in the right direction there, I think, you know, that if you think about the change in plastics use that you and I've witnessed in the last 10 years, there's definitely been a change, and people are on to that. But pollution of the oceans is a big one. But the other thing that I think is, is it like hits this is the big thing is exploitation. I mean, we are overfishing the oceans, there is absolutely no doubt about that. And you only have to look at places where you explicitly prevent that from happening to see what things could be like, if we didn't do that. Now, look, I get it. I mean, you know, people rely on the oceans for food, but some of the things we see and the exploitation that goes on, it just can't go on. I mean, we need to button off on that we need to find better ways, less damaging ways of feeding the population of the world, then strip mining it of all life and, and things that really offend me are these, you know, pictures of dead men to raise with their gills ripped out, or sharks with their fins chopped off, or, you know, like, if I could put a stop to that kind of stuff, but just at a high level, reducing exploitations to sustain the exploitation to fishing pressure to sustainable levels, which currently we're not doing, you know, there are places where we do but an isolated fisheries, which are exemplars of how things can be done. But across the world, we're not doing a very good job of it. And change.

 

Matt Waters  

Agreed, agreed. While senators were on the conservation bandwagon. So is there any kind of conservation efforts that you're particularly passionate about? And if so,

 

Simon Mitchell  

why? Ah. Well, lots of I mean, lots, you know, there's no sensible conservation effort that I wouldn't, that I wouldn't support. But I guess, I guess, one that springs to mind as a diver, because it's diving oriented is, and I think there are branches of this and lots of different countries. But here in New Zealand, we've got a group that, that focus, particularly on ghost net fishing, and getting rid of ghost nets out of the ocean. And I I am, like, there's nothing more heartbreaking than seeing a net sitting somewhere that's called a whole lot of things that aren't ever going to be used for food. And they're not species of fish. Sometimes it's bird. Sometimes it's marine mammals that, you know, no one wants to catch. Anyway. I mean, nets are a very unselective way of catching fish. But getting rid of those ghost nets. There's a couple of groups. Well, there's one group here in New Zealand that is very active in that regard. And I, you know, I really admire them because they put a huge amount of time and effort into it. And it's, you know, such a cool thing to do. It's not, it's not going to solve the world's fishing problems, but AI as a focused project. I think it's a super cool thing.

 

Matt Waters  

Yeah, yeah. I got on. Yeah. Yeah, we've got a few ghost nets over here in Australia as well funded by the government. I think they call them shark nets. Excuse me, has your passion for diving or the industry itself changed over time? And if so, how?

 

Simon Mitchell  

Well, a passion has never changed, really, but certainly the nature of the activities I've done and like I said earlier, so one of the super cool things about diving is you can reinvent yourself as a diver multiple times throughout a long career and did you kind of need to otherwise things just get a bit routine, but I've like I said, you know, I've cycled through. Snorkelling, spearfishing This is an approximate chronological order Scuba diving, instruction, military diving rebreathers mix guest diving photography, you know, it just it's been a fantastic evolution. In the end, sometimes I've ducked in and out of those different things over the course of the year. So it's it is an activity where you can do lots of different stuff. The passion levels might stay the same throughout the whole time, but you can certainly change what you do. And the emphasis on your activities. The industry Well, I guess the emergence of technical diving as something that non military non occupational people can do has been a real revolution. And some of the achievements of you know, my technical diving colleagues are just extraordinary. I mean, it has its risks. But I think it's, I think that that is a very important evolution in the industry.

 

Matt Waters  

Yeah, I can't imagine what its gonna be like in a couple of 100 years.

 

Simon Mitchell  

Well, who would know? You know, one atmosphere diving suits that you can go to 1000 feet and not have any decompression? You know, who knows? We're not that far away that now.

 

Matt Waters  

Yeah, I agree. I agree. Now, here's a difficult question for her probably the most difficult question you've ever answered. What are your top five bucket list? diving destinations?

 

Simon Mitchell  

Ah, well, of course, some of them I've already ticked off. If you'd asked me what my bucket list was, you know, years ago. I, you know, I would have included places like bikini and track that and there are two places that I've been to multiple times now, and, and never get tired of them. But if you're talking about places, I've never dived, you know, because there are some extraordinary places here in Australia, and, and sorry, here in New Zealand and Australia that I've died. But no, you're talking about hosts, I've yet to dive. There's a few. I'd really like to go to the Galapagos. I've never done that. And, yeah, I just, I think that that's definitely a bucket list location. And I would like to I'd like to dive the caves in Florida. That would be another bucket list. In Mexico. Now I actually have done a little bit of Kevin diving in Mexico, but I've never done the you know, the big time cave. So this three. I'd also really like to, you'll notice the pattern here is that they're all places that are quite weird in their own way. I quite like to go into the northern, I've dived Antarctica, but I'd really like to go and dive, do some cold water diving, perhaps ice diving up in Norway, or, you know, the polar, the north polar ice cap somewhere. That would be an amazing thing. You get different creatures up there. Yeah. And I mean, that's probably five. You know. As a passionate diver, I don't I'm, I'm actually pretty cool with just diving anywhere, this fascination to find where to jump in the water. But yeah, those there's some ideas about places I'd love to go.

 

Matt Waters  

So it's creatures as well. And it's, you know, you mentioned the Galapagos, and you've got to go get on one of beach trips, or whatever. I'm going at the end of July. Yeah, July, I've got an expedition going. And it's just, it's sensational. And if you're in it, the big critters are boy, they get big and plentiful down there, that's for sure.

 

Simon Mitchell  

Yeah. Yeah, no, I'll certainly take that advice.

 

Matt Waters  

And take a take a lot of SD cards with you. Okay, um, how would you describe the dive community to a non diver?

 

Simon Mitchell  

It's a very community. It's like, I think lots of different people want to want to work different types of people. One of the things I often say to prospective divers is that it's a great activity for families. And it's a great activity for women, which sounds a bit kind of like off in this modern day and age. But, you know, sometimes these things need to be said, and partly the reason I say that is that women actually, you know, objectively make better divers than men, probably because they're more sensible and not driven by, you know, the desire to strip as much biomass from the marine environment as possible every time they jump in the water. So, I mean, I think I think it's a great gender balanced activity, although there are more men than women in the sport. And I think the community consists of lots of individuals doing their own thing, but it also consists of focus groups who identify as groups and actually if what you're looking for is a sense of belonging or camaraderie, there's lots of that and diving if you want it, you know, so especially in tech diving, there's lots of groups and various places that identify as sort of projects or communities that do a lot of diving together and organise things together. So I think it's generally is populated by nice people. There are some big ego, there are some big egos, of course, rebury the forum for I mean, that was like 300 of the biggest egos in the world all crammed. But actually, you know, they all played nicely. And I think, I think it's Jin Jin, really, you know, go to a meeting like oz tech or something like that. And the vibe you get is pretty warm and collegial? You know, I think I actually think it's involved in that way. When I first got into diving, there was a lot of, you know, clique Enos to it. And people who consider themselves sort of above everybody else, but I think that's all sort of worn off. And basically, it's a nice community. Yeah, sorry, a bit of a long winded answer. But,

 

Matt Waters  

ya know, I'd say of course, brilliant answered this. This is why I asked these questions, these 10 questions to every guest that comes on because albeit, you know, some answers are very long, some are very short, but they're all coming to the same thing, especially that one. You know, it's I think, for me, it's, it's a, it's the closest thing when it comes to camaraderie that I've ever experienced outside of the military. Quite frankly, I fucking love it. It's great. Yeah. Last one, and I think I know the answer to this one of the many safety procedures we have in the industry, if you had to choose one as the most important, what would it be?

 

Simon Mitchell  

Well, you know, we've had this discussion. It in terms of bang for your buck, in terms of objective evidence that would result in less deaths? Without question, it would be pre jump checklists for rebreather divers. There's no no, it's, it's easy. That's an easy question to answer. And we know this from parallel fields. And in fact, some research and diving to the dam Group published a really big study looking at the efficacy of pre dive checklists, not pre jump checklist, specifically, but it did reduce critical events in the water. It's a very underrated study, in fact, but we know from aviation and medicine that, you know, short killer item checklists will prevent bad things from happening. And there's no question. We know that these bad things happen and rebreather divers and checklists can prevent them if people did them. So yeah, that's it easy outside.

 

Matt Waters  

You get them done. Happy days. Simon. Let's wrap this bad boy up and get get on with the weekend ahead. Thank you so much for your time and coming on the show. Ladies and gents. Thanks for listening in. And all of the details that we've been talking about will be in the show notes, and see you all soon. Bye for now.

Introductions
How did you first get into diving?
Simon’s Career & diving
Explanation of Decompression Illness comprising of Decompression Sickness & Arterial Gas Embolism
Patent Foramen Ovale
RSTC Medical questionnaire
The abuse & misinformation of hyperbaric oxygen therapy in the high street
Non-specific signs and symptoms of DCS
WHAT TO DO WHEN SYMPTOMS OCCUR AFTER DIVING
subcutaneous emphysema
Arterial Gas Embolism
How the dive profile helps the medical practitioners evaluate signs and symptoms
US Navy table 6 - recompression for patients
Are we complying with recommendations commendably?
The Future of hyperbaric medicine
Simon's most rewarding moments - Hospital Ship (AHS) Centaur
How do you describe your position as a diver to people who are not familiar with the activity?
Is there an increase in issues due to a lack of preparation?
If someone wanted to pursue a career similar to yours, what advice would you give them?
If you could change anything about the diving industry or scuba diving in general, what would it be?
What are your thoughts on ways to minimize human impact on the oceans?
Is there a particular conservation effort that you are particularly passionate about? If so, which one and why?
Has your passion for (diving or your industry) changed over time, and if so, how?
What are your top five bucket list destinations?
How would you describe the dive community to a non-diver?
Of the many safety procedures, we have in the industry, if you had to choose one as the most important, what would it be?