Fatal dive accident - Lake Werbellin, Germany

[JohnN]

Sounds like a time for @Duke Dive Medicine

Back of the envelope says at 3 ATM 100% O2 in a hyperbaric chamber would give about 3% disolved O2 in the blood plasma. Doesn't seem like much, if DDM doesnt
chime in I know a retired gas-passer that might know

 

[DandyDon]

Right, the theory is that at sufficient PP of dissolved O2 our metabolism will use it and leave hemogolobin with its CO alone, and the question is how little (or much) of dissolved O2 there needs to be for that to happen.

All well and good but test every tank and avoid CO.

 

[scubaozy]

It looks like this accident is not related to CO poisoning. It has been written somewhere, that both had empty tanks.

This is also what I read, not sure whether it is confirmed though. As far as I understood, CO poisoning was a speculation due deceased divers being a couple and could have potentially filled their tanks at home with their own compressors.

 

[Duke Dive Medicine]

Sounds like a time for @Duke Dive Medicine

Back of the envelope says at 3 ATM 100% O2 in a hyperbaric chamber would give about 3% disolved O2 in the blood plasma. Doesn't seem like much, if DDM doesnt
chime in I know a retired gas-passer that might know

That's a part of arterial oxygen content and it sounds a bit low to me. We typically treat CO poisoning patients at 2.82 ata. Using the alveolar gas equation and assuming healthy lungs, that's an arterial oxygen partial pressure (PaO2) of roughly 2000 mmHg (normal on normobaric air is 80-100 mmHg). For actual content, multiply that by 0.003 ml O2 per mmHg of arterial O2 partial pressure, and that gives you 6 ml of O2 per 100 ml of blood, or 6.0 volume percent from dissolved O2.

From a medical standpoint, dissolved O2 is not measured in percentages, it's measured in mmHg as above. With a PaO2 of 2000 mmHg there's no need to deoxygenate hemoglobin. At 60 feet in the chamber on 100% O2 we could spin all of your red blood cells out and you'd do just fine. In theory. It's been done in pigs, but not in humans.

Best regards,
DDM

 

[dmaziuk]

From a medical standpoint, dissolved O2 is not measured in percentages, it's measured in mmHg as above. With a PaO2 of 2000 mmHg there's no need to deoxygenate hemoglobin.

This IMO is one of the most annoying things about nitrox and "O2 metabolizes" argument in the deco formulae where oxygen just doesn't count. You have to figure out how to convert these absolute amounts into something resembling ratios and partial pressures used in deco model, to see if it is plausible.

 

[cathal]

Apologies in advance for my ignorance, but can I ask what are the precise circumstances about the incident that are leading to the hypothesis of Co2 poisoning?

 

[Duke Dive Medicine]

Apologies in advance for my ignorance, but can I ask what are the precise circumstances about the incident that are leading to the hypothesis of Co2 poisoning?

It's sheer speculation. Also, a minor point, but CO, or carbon monoxide, is the gas being discussed. CO2, carbon dioxide, can also be problematic while diving but it's a different animal than CO poisoning.

Best regards,
DDM

 

[Duke Dive Medicine]

This IMO is one of the most annoying things about nitrox and "O2 metabolizes" argument in the deco formulae where oxygen just doesn't count. You have to figure out how to convert these absolute amounts into something resembling ratios and partial pressures used in deco model, to see if it is plausible.

You might consider that at an inspired pO2 of 1.4 ATA, or 1064 mmHg, the arterial partial pressure of O2 will be somewhere in the neighborhood of 960 mmHg. Duplicating the math from above, 960 * 0.003 = 2.88 ml of dissolved O2 per 100 ml of blood, or 2.88 volume %. O2 content related to hemoglobin would be somewhere in the neighborhood of 16-20 ml O2 / 100 ml blood, or 16-20 volume %. At rest, the body extracts 4-5 ml O2 / 100 ml of blood during metabolism, or 4-5 volume %. O2 dissolved in plasma is more readily available since it doesn't have to dissociate from hemglobin. So, it's reasonable to assume that most, if not all, of the dissolved arterial O2 when breathing a gas with an O2 partial pressure of 1.4 ata will be metabolized as it passes through the body tissues. Its effect on tissue loading at at that partial pressure would be negligible.

Best regards,
DDM

 

[cathal]

"Apologies in advance for my ignorance, but can I ask what are the precise circumstances about the incident that are leading to the hypothesis of Co2 poisoning?"

It's sheer speculation.

Then is there any chance the Admin could split this thread off, as we are learning nothing about the actual incident, its specific trigger factors and the COD?

 

[DandyDon]

is there any chance the Admin could split this thread off, as we are learning nothing about the actual incident, its specific trigger factors and the COD?

I would hope not. Yes, there is a lot of speculation here, but that's how we learn to minimize risks when the facts are not forthcoming. We do not know if the fill station monitored its gases for CO, if the divers tested their tanks, or if the investigation thoroughly looked at that risk but then those risks are usually not examined. Until we do know, CO is certainly a possible risk here as it does fit the incident.