Diving and Hyperbaric Medicine Journal articles on Pubmed Central

[Dr Simon Mitchell]

Here is another one.

This is a little self indulgent (because I am an author), but this is an important paper being the consensus of an international panel of extremely experienced diving physicians on the optimal early management of decompression illness in the field. This is obviously an important issue for all divers, because early management is most often conducted by divers on the scene. This paper would form a valuable resource for all those teaching diving.

Mitchell SJ et al. Pre-hospital management of decompression illness: expert review of key principles and controversies. Diving Hyperb Med. 2018;48(1):45-55.
Available from: Pre-hospital management of decompression illness: expert review of key principles and controversies

Simon

 

[Dr Simon Mitchell]

Hello,

A paper that will likely interest all divers but technical divers in particular was published in Diving and Hyperbaric Medicine today. It describes the anaesthesia intervention in the Thailand cave rescue, and also testing of the full face mask they used on the boys, with particular reference to the positive pressure function that may have contributed significantly to the success of the rescue.

It can be accessed here:

DHM Journal, Immediate Release

Simon M

 

[wnissen]

Hello,

A paper that will likely interest all divers but technical divers in particular was published in Diving and Hyperbaric Medicine today. It describes the anaesthesia intervention in the Thailand cave rescue, and also testing of the full face mask they used on the boys, with particular reference to the positive pressure function that may have contributed significantly to the success of the rescue. View attachment 595159

It can be accessed here:

DHM Journal, Immediate Release

Simon M

Only partway through but this is fascinating. 80% O2 plus ketamine, sounds like quite a ride! Thanks for posting.

 

[Saniflush]

I'm fairly certain that it goes way over my head but have passed it along to Mrs Flush who will enjoy it. Thank you for posting

 

[Duke Dive Medicine]

Excellent write-up, thanks @Dr Simon Mitchell !

 

[Dr Simon Mitchell]

Hello,

Here are three more papers that have just become available on PubMedCentral, and that are likely to be of interest to divers.

A paper by Doug Ebersole's group evaluating the effectiveness of closure vs conservative diving on risk of DCS after discovery of a PFO. Available here:

The effectiveness of risk mitigation interventions in divers with persistent (patent) foramen ovale

A perspective on hypoxia experiences as a training intervention for rebreather divers (and aviators). More to come on that issue eventually as discussed. Available here:

The utility and safety of hypoxia experiences for rebreather divers

An evaluation of how accurate temp sticks are at predicting CO2 breakthrough in rebreather circuits. Available here:

The performance of ‘temperature stick’ carbon dioxide absorbent monitors in diving rebreathers

Simon M

 

[wnissen]

A perspective on hypoxia experiences as a training intervention for rebreather divers (and aviators). More to come on that issue eventually as discussed. Available here:

The utility and safety of hypoxia experiences for rebreather divers

I read the abstract and procedure section of this, and I'm not sure it entirely measures what it wants to measure. To summarize, they exposed 25 subjects to two tests while breathing 5.5% oxygen, separated by 5 weeks. The second time around, the subjects did no better or worse at their task: verbally identifying the number and suit of numberless cards displayed every 4 seconds. The test stopped when they got three wrong in a row. The subjects also didn't get better or worse at recognizing the total number of errors they made.

It does seem to categorically show that you can't condition the body with hypoxia and improve its performance. Is that really something people think is possible? There doesn't seem to be a response system that would cause that in the same way that you can train yourself to hold your breath longer or condition yourself aerobically. I'm purely (and permanently) an open-circuit diver, but the idea seems pretty out there.

But the thing is, the subjects knew they were about to go hypoxic because of a three-second countdown. Their previous experience didn't help them. But isn't the idea that you don't know when you're going to go hypoxic? It seems like what you want to know is whether you can improve the ability to recognize when it starts to happen.

Still, a very interesting experiment. I'm sure the research board had fun deciding if it was ethical to take their arterial oxygen saturation down to 50%!

 

[Dr Simon Mitchell]

I read the abstract and procedure section of this, and I'm not sure it entirely measures what it wants to measure.

Hello wnissen,

You are exactly right. If you had made it to the discussion section you would have seen that we discuss this issue in some detail. Here is a quote from the paper:

Our finding of very poor recall of errors during hypoxia is clear evidence of failure to accurately perceive the severity of impairment during hypoxia, or failure to form accurate memories of it, or both. Similarly, our subjects generally gave only mid-range severity ratings of those hypoxia symptoms related to cognitive function despite their invariably severe objective cognitive impairment. These findings raise the suspicion that prior knowledge of hypoxic symptoms might not help a task-loaded and significantly distracted aviator or diver to self-rescue during a subsequent hypoxic event as reliably as seems to be believed.

This question is of high relevance to both rebreather diving and aviation but resolving it in an experimental setting would require a complex study. One would have to begin with subjects randomized into groups receiving initial hypoxic training (Group H – hypoxia) or not (Group N – no hypoxia). Then after some predetermined interval, both groups would then need to be randomized again to perform an objectively measurable and highly distracting task during either hypoxia or normoxia while blinded to their hypoxia/normoxia allocation, with an instruction to perform a secondary self-rescue task if they perceived impairment during the test. One would then compare the timing and execution of the self-rescue task in those Group H and Group N subjects randomized to hypoxia on the second exposure. The use of a valid task providing similar levels of motivation and distraction to flying a plane or operating a rebreather in the dynamic underwater environment would be a crucial component of such a study, as would blinding participants to their allocation (normoxia or hypoxia) in the second exposure. The difficulty in conducting such a study probably explains why it has not been done to date.

We are currently in the process of applying for a grant from the Office of Naval Research to perform this study.

In regard to your perceptive question about whether anyone really thinks that prior hypoxia might improve cognitive performance on a second later exposure, there was some weak support for that idea (which we cite in the paper), but I think our findings debunk that notion. I completely agree with you that it would seem implausible.

Still, a very interesting experiment. I'm sure the research board had fun deciding if it was ethical to take their arterial oxygen saturation down to 50%!

Yes, it was interesting! Such experiments in humans are rare. However, the level of impairment in our subjects was similar to that routinely induced during hypoxic training in hypobaric chambers and I suspect that the participants in those events all get down to the sort of oxygen saturations we measured in our subjects. The hypobaric training groups just don't measure saturations in their subjects. We were required to monitor our subjects with ECG, pulse oximetry and NIRS; and the presence of an anaesthesiologist (me) was required for all experiments.

One fascinating insight to come out of the work relates to the recent proposition that Covid-19 somehow renders hypoxic patients "happy" to sit in a bed profoundly hypoxic but reasonably undistressed. Having done this experiment and watched subjects with sats in the 50s and 60s diligently and enthusiastically persist with a card recognition test I am extremely skeptical that covid-19 is any different in that regard. The simple fact is that most people don't find hypoxia to be particularly distressing. The medical profession is only just discovering this. Prior to covid, any patient with oxygen saturations at those levels would have been intubated straight away and shoved on a ventilator. Thus, most doctors have never had the opportunity to observe very hypoxic subjects who are awake. Anyway - a bit of a digression but an interesting one.

Simon M

 

[wnissen]

If you had made it to the discussion section you would have seen that we discuss this issue in some detail.

Oops, see, I obviously have a problem with reading! I didn't notice you were first author on that paper, either...

One would have to begin with subjects randomized into groups receiving initial hypoxic training (Group H – hypoxia) or not (Group N – no hypoxia). Then after some predetermined interval, both groups would then need to be randomized again to perform an objectively measurable and highly distracting task during either hypoxia or normoxia while blinded to their hypoxia/normoxia allocation, with an instruction to perform a secondary self-rescue task if they perceived impairment during the test. One would then compare the timing and execution of the self-rescue task in those Group H and Group N subjects randomized to hypoxia on the second exposure.

Yes, that would have been a much more complicated experiment. It would also be interesting to see if people could ever get to the point where they could recognize imminent hypoxia while task loading. Certainly, it seemed like there was not much spread in terms of individual variation, either. I guess it is true that people seem to think that nitrogen narcosis can be resisted somewhat by conditioning, which to a certain extent seems almost equally unlikely.

I remember being really surprised when I read about an industrial multiple fatality accident where someone entered an enclosed space (a tank?) that was filled with nitrogen. Their co-workers were watching, saw them fall, and unfortunately elected to go right in after them. Yep, here it is: Confined Space - Multiple Fatalities. Three deaths, and almost a fourth! You would think after the third person saw the first two go in and pass out, they would reconsider, but that is momentum thinking for you. Obviously the victims were in no distress whatsoever when they lost consciousness, or otherwise they would have turned around once things started to go pear-shaped. And of course, nitrogen is used as a self-euthanasia method for the same reason.

Anyway, thanks for posting, and the science is quite interesting.

 

[Duke Dive Medicine]

Tagging @Dr. Doug Ebersole for this question: Doug, in your paper it seems that you considered ASD and PFO to be equivalent with respect to diving. Can you elaborate on this? I was under the impression that ASD was an absolute contraindication to diving and PFO was more relative. Thanks much in advance!