Any reported cases of Ox Tox between 1.4 and 1.6?

[AeroSpartacus]

Some of these will start oxygen flushing at 30ft / 9m because "it's easier to hit 1.6" when in reality they will be off-gassing better at 10 ft / 3 metres at a ppO2 of ~1.3

Not your point, but I will start flushing at ~30 ft if I remember for verifying cells but I don't hang out there for deco

 

[Nick_Radov]

uints should be abolished from all „control“ software tbh, not like memory is such a bottleneck nowadays (or a really specific usecase)

Wait this is _still_ out there? Such an overflow surely must have been fixed already

Unfortunately it's only partially fixed. The FIT file format defines the various message types for CNS% as uint8 which would be difficult to change at this point. Garmin did change the CNS% calculation algorithm in 2022 so that if you exceed 1.6atm for a few seconds it no longer goes totally wacky and instead now basically copies Shearwater's algorithm, which although still arbitrary at least seems more reasonable. So in practice the risk of an overflow is greatly reduced. But since the CNS% algorithm is worthless anyway I just ignore the computer warnings about exceeding 100% and stick within the commonly accepted tech diving oxygen exposure guidelines. Garmin makes excellent hardware but some of their software design decisions leave me scratching my head and wondering if their employees do any real diving?

Shearwater does have a good article "Oxygen Seizures at PO2 ≤ 1.6 Bar: How Rare?" which is relevant to the original question on this thread and summarizes the available research as of 2017.

 

[Kendall Raine]

Curiosity pulled the cats tail, and I found myself here: https://cumbria-hyperbaric.org/wp-content/uploads/2019/09/repex0.pdf
I will dig in now that I realize repex is an algorithm

See also this article (it gets the exponent sign correct...)

 

[Kendall Raine]

See also this article (it gets the exponent sign correct...)

Here is a link to the original 1988 Hamilton, et. al. source document. Too big to upload.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://repository.library.noaa.gov/view/noaa/60673/noaa_60673_DS1.pdf&ved=2ahUKEwiznvaelM2JAxUIIUQIHfZ-E3kQFnoECCAQAQ&usg=AOvVaw0ZXdlbqc1iXg7FtAJDE7qR

 

[JMarc]

Unfortunately it's only partially fixed. The FIT file format defines the various message types for CNS% as uint8 which would be difficult to change at this point.

It should still be possible to compute a "correct" value and use a saturated one when protocols and files formats mandate the use of a field unable to represent it.

 

[Seaweed Doc]

Hard to say given that this is secondhand information. Did you mean elbows plural? Bilateral pain could be indicative of a spinal/nerve hit, so if that's the case, then possibly. Was she treated in the chamber, and did the symptoms resolve? What about the tingling in the feet?

Best regards,
DDM

Thanks for the response!

Initial pain was severe and in her left elbow. At that point, DCS seemed like a low probability so we all walked up the beach, doffed gear, and I asked her about the elbow which still hurt. Then I asked if the other elbow hurt, or just the one and she said it did, but not as badly. So bilateral, but a big difference in severity and a time delay between the two.

On oxygen, the pain in her right elbow resolved and it was reduced in the left elbow. We sent her to the local hospital ER (a mistake, in hindsight) which dithered for several hours. During this time, the tingling began.

When they finally transported her by ambulance to the chamber, they chose to use an ambulance. They'd dithered long enough that they were concerned about the symptoms progressing; initially they were going to have a friend drive her to the chamber. (I'd note it's only about 20 minutes by car from the initial ER to the chamber, and would have only been about half an hour from the dive site to the chamber.) They gave her one treatment in the chamber which resolved all symptoms, and then sent her home to dive again.

Later evaluation showed the PFO. The wonders of the insurance industry are such that they wouldn't pay to have the PFO fixed unless it happened again. Since then, she's resumed diving including doing dives to 100' (the depth which triggered the first event).

I'm learning locally we have a disconnect between diver training, where the mantra is "take them to the nearest ER, not the chamber" and our local hospitals who say "why'd you bring them here, and not straight to the hospital with the chamber?"

 

[Duke Dive Medicine]

Thanks for the response!

Initial pain was severe and in her left elbow. At that point, DCS seemed like a low probability so we all walked up the beach, doffed gear, and I asked her about the elbow which still hurt. Then I asked if the other elbow hurt, or just the one and she said it did, but not as badly. So bilateral, but a big difference in severity and a time delay between the two.

On oxygen, the pain in her right elbow resolved and it was reduced in the left elbow. We sent her to the local hospital ER (a mistake, in hindsight) which dithered for several hours. During this time, the tingling began.

When they finally transported her by ambulance to the chamber, they chose to use an ambulance. They'd dithered long enough that they were concerned about the symptoms progressing; initially they were going to have a friend drive her to the chamber. (I'd note it's only about 20 minutes by car from the initial ER to the chamber, and would have only been about half an hour from the dive site to the chamber.) They gave her one treatment in the chamber which resolved all symptoms, and then sent her home to dive again.

Later evaluation showed the PFO. The wonders of the insurance industry are such that they wouldn't pay to have the PFO fixed unless it happened again. Since then, she's resumed diving including doing dives to 100' (the depth which triggered the first event).

I'm learning locally we have a disconnect between diver training, where the mantra is "take them to the nearest ER, not the chamber" and our local hospitals who say "why'd you bring them here, and not straight to the hospital with the chamber?"

That's really interesting. Thanks for those details. Neurological involvement probably couldn't be ruled out in this case but I don't know that you'd find many cardiologists who would close a PFO based just on those symptoms. @Dr. Doug Ebersole ?

Re where to transport a diver: if someone becomes ill after diving, diving just widens the differential diagnosis. Example: myocardial infarction can look an awful lot like pulmonary DCS. If you transport a diver who's having a heart attack post-dive two hours to a hospital with a chamber vs. 15 minutes to a hospital with a cardiac cath lab, you've done them a disservice and possibly harmed them. Best practice is to take them to the nearest ED for assessment and stabilization if needed unless the difference in transport time is small.

Best regards,
DDM

 

[Seaweed Doc]

That's really interesting. Thanks for those details. Neurological involvement probably couldn't be ruled out in this case but I don't know that you'd find many cardiologists who would close a PFO based just on those symptoms. @Dr. Doug Ebersole ?

Re where to transport a diver: if someone becomes ill after diving, diving just widens the differential diagnosis. Example: myocardial infarction can look an awful lot like pulmonary DCS. If you transport a diver who's having a heart attack post-dive two hours to a hospital with a chamber vs. 15 minutes to a hospital with a cardiac cath lab, you've done them a disservice and possibly harmed them. Best practice is to take them to the nearest ED for assessment and stabilization if needed unless the difference in transport time is small.

Best regards,
DDM

I think that's the issue: Our transport time difference is pretty small where I do most of my diving. Where the DCS hit happened, it might have been 10 minutes longer to the chamber and while 10 minutes may be the difference between life and death with an MI, the hospital with the chamber is, to be frank, a lot better than the closer one. I'm not sure which would end up treating the patient sooner, even with the added drive time. There are other hospitals en route from that dive site to the chamber as well, if things went south en route. And with anything that involves shortness of breath, I'd be calling emergency services and letting them decide and transport.

At the site I most often have students, the transport time is the same to any ER, including the chamber. (We have "pill hill" in Seattle with multiple hospitals in a small area.) Emergency services, however, has SOP to take the patient to the county hospital/level 1 trauma center, not the one with the chamber. We're also at an advantage in that the chamber can accommodate multiple patients (more than a dozen, I think) and, if pressed, have 3 separate treatment protocols going simultaneously. That's a far cry from the remote location where maybe the chamber operator is awake and sober, or maybe not. Maybe somebody is already in the chamber, or maybe not.

Ultimately, this seems kind of like a situational thing. For most dives in most parts of the world, the closest ER seems like the best bet. I may just live in a weird (blessed?) corner of the world.

 

[tursiops]

I think that's the issue: Our transport time difference is pretty small where I do most of my diving. Where the DCS hit happened, it might have been 10 minutes longer to the chamber and while 10 minutes may be the difference between life and death with an MI, the hospital with the chamber is, to be frank, a lot better than the closer one. I'm not sure which would end up treating the patient sooner, even with the added drive time. There are other hospitals en route from that dive site to the chamber as well, if things went south en route. And with anything that involves shortness of breath, I'd be calling emergency services and letting them decide and transport.

At the site I most often have students, the transport time is the same to any ER, including the chamber. (We have "pill hill" in Seattle with multiple hospitals in a small area.) Emergency services, however, has SOP to take the patient to the county hospital/level 1 trauma center, not the one with the chamber. We're also at an advantage in that the chamber can accommodate multiple patients (more than a dozen, I think) and, if pressed, have 3 separate treatment protocols going simultaneously. That's a far cry from the remote location where maybe the chamber operator is awake and sober, or maybe not. Maybe somebody is already in the chamber, or maybe not.

Ultimately, this seems kind of like a situational thing. For most dives in most parts of the world, the closest ER seems like the best bet. I may just live in a weird (blessed?) corner of the world.

There is a reason that DAN's protocol is to go to an ER, not a chamber, because the chamber you go to may not be available to you.

 

[justinthedeeps]

So for extended deco divers,

Is there a specific study showing that ppO2 1.6 (100%) + 'air' (trimix) breaks is better/safer than incorporating lower ppO2's, setpoints or oxygen deco blends (e.g. 80%, 50%) into the final stops?

Did I miss that in other threads?
That long list of NEDU studies in the other thread aren't available thru Rubicon anymore.

100% alternating with 18/45 breaks is suggested in other threads/agencies as more convenient than deploying/breathing down a 50% stage for some of the time to manage oxygen toxicity. Might have to manually program these into a planner to check...

Anyone disagree that for O2/CNS/gradient matters, 3 metres / 10ft is a safer final stop depth than 6 metres / 20 ft?

Anyone modifying their air break protocols based on whether they are forced to stay on oxygen at 6m/20ft (1.6) vs at 3m/10ft (1.3?)

Anyone on long CCR deco doing in-loop 'air breaks' (low setpoint/deco dil flushes?) Vs. periodic 'air break' bailouts?