Freediving on 36-40% O2

[trux]

Yes, the urge to breath should be around the same with pure O2 or Nitrox as with normal air. Better told it should be even slightly higher, because of the Haldane effect that frees more CO2 from hemoglobin thanks to the higher PaO2, hence there is more CO2 (or HCO3 ions) increasing the respiratory acidosis. However, when breathing pure oxygen or enriched air, you rarely ventilate normally, so there is practically always some pre-dive hyperventilation reducing the initial CO2 level. And the increased Haldane effect (and the consequent CO2 release) due to the ventialtion with enriched air, is strongest during the breath-up, hence the hyperventilation is quicker than with air.

I am not sure whether the CO2 level in lungs increases significantly higher than at normal breath-hold. Very likely there is some difference (already due to the mentioned Haldane effect), but I do not think that the presence or non-presence of nitrogen plays any important role. It is more question of partial pressures of CO2 in alveoli, and in arterial blood, and those are not really influenced by the nitrogen. Well, in fact it is, but in the opposite way - without the N2, the partial pressure (not the volume) of CO2 in lungs would raise quicker with the consumption of O2 (the CO2 part becomes more important), so the diffusion from blood to the alveoli should become slightly slower. On the other hand, the PACO2 (arterial pressure) is also higher (due to the mentioned Haldane effect), so I am not sure what the final result really would be. I did not find any study specifically investigating levels of CO2 during O2 or Nitrox breath-holds, so all this is just a speculation.

Otherwise, high level of carbon dioxide is toxic to the heart and causes diminished contractile force, that's why it is difficult to revive someone under CO2 blackout. I am not sure what a normal person without advanced medical means can do. Artificial ventilating may help eliminating some excess CO2, but doing classical mouth-to-mouth may not be the best way for it. Probably better than nothing, though.

EDIT - Legal note: I am neither a physician, nor a diving expert, so do not use my opinions or advices for making your decisions if you are going to perform a CPR on someone under CO2 blackout, without verifying them with a real medicine expert!

 

[rnsaicic]

Hyperventilation may play an important role but, in my opinion, it is unlikely that the lowering of pCO2 by hyperventilation is the only (or dominant) reason for significantly prolonged apnea after breathing pure O2, or O2-enriched mixtures (with respect to normal static on air). Rare are freedivers who can perform >8 min static on air (hyperventilation does not help here); on the contrary, it seems that almost “anyone” can perform >10 min breath holds on O2, and trained individuals even much longer. In the case of “normal” apnea the limiting factor for the elite divers is hypoxia, and if blackout occurs, it is due to a low pO2. It is obvious that breathing pure O2 increases the reserve of O2 in the body, as here the hypoxic BO does not occur even after >10 min, although the diving reflex is less pronounced. The common wisdom says that the saturation of blood in O2 (when tidal breathing) is already 98%, so that hyperventilation does not improve the O2-reserve. However, this is related to the arterial saturation, not the venous one. It appears that breathing pure O2 increases venous pO2, which augments significantly total O2 reserve in the body. However, it still remains obscure why the urge to breath is diminished. Under normal conditions, most individuals are not capable to resist to the urge to breath at pCO2 levels which are well below one that causes CO2 BO; when submitted to pure O2, this tolerance increases and the break of the apnea comes much later. This fact makes me believe that some other mechanisms may also be involved.
Radomir

 

[trux]

Radomir, the venous saturation certainly helps at O2 breath-holds, but alone the oxygen in the lungs offers sufficient reserves for much longer breath-holds than we saw till now (I mean if we forget about the CO2 as limiting factor).

As for the CO2 - do not forget about the Haldane effect of O2, which means you cannot directly compare air and oxygen breath-holds, because there are different conditions - different levels of PaCO2, of HCO3-, of the hemoglobin affinity to CO2, and of pH. Also there is much less acid lactic production (if any at all), which has impact on the blood pH too. It is quite possible (and likely) that there are also other factors playing a role, but since breath-hold diving with enriched air is little studied, I would definitely discourage anyone making the test rabbit without qualified supervision with advanced CPR devices ready to use.

 

[TimoP]

What works to revive somebody after a CO2 blackout?

Though I've done an official life saver course with CPR training, this is a diffucult to answer for sure, because CO2 BO is something there shouldn't be at all... so it's not mentioned or trained in life saver courses.

CO2 is the problem in this case, so you must get rid of that extra CO2 as soon as possible. I think the only way is to get extra ventilation for lungs, if normal easier systems don't work as Kimmo wrote. In BO-situation the freediver (victim) him/herself don't breath effeciently enough to do that so well.

The good thing is - logically! - that there is a bottle of pure O2 or enriched air nearby, if C02 BO has happend. So giving it to victim MIGHT be a good thing (edit: see trux's posts below). Not for O2 itself (because in this case there shouln't be a lack of O2), but to do easy and effective ventilation of lungs. But don't use too much pressure or gas volume, it's pressurized gas and the victim can't say in time "Stop it!". You may blow up the lungs! If there is not a bottle near enough, then do normal mouth-to-mouth rescutation. If there are severe heart problems a defibrillation eguipment or manual heart massage may be needed. Call a ambulance immediatly, if there are heart problems or any other problems with rescue or after that.

So, I really don't want to arrange on purpose a situation, where I must TRY to rescue a CO2 BO case. Do somebody else want to?

In fact I have a bottle of pure O2 for rescue purposes. We train freediving several times every week, and I'm interest in testing things. But we haven't combined using pure O2 or enriched air with freediving. Mainly for safety reasons, but also because it is not useful if you want to train your freediving abilities.

CO2 Black Out is only one example of risks of using pure O2 or enriched air in freediving. Especially if going deeper that 10 m with pure O2 there come more very serious risks (in a really bad case could be fatal), as e.g. technical divers know.

 

[trux]

Yes, as I already mentioned, getting rid of the excess CO2 by artificial ventilation is necessary. I also wrote that CO2 indeed does influence the function of the heart (diminishes its contractile force), so heart massage (or electro-stimulation) may be also needed.

One thing that I am not sure of at all, is the immediate administration of oxygen - in fact, due to the Haldane effect, it can lead to a sudden increase of free CO2 in blood, and possibly aggravate the situation. Please note that I am not sure about it, because I do not know which part of the CO2 causes the heart dysfunctionality (whether it is the free CO2, the HCO3, or the CO2 bound to hemoglobin), and I also do not know if other advantages of the O2 ventilation do not overweight the disadvantage of immediate CO2 release.

 

[TimoP]

Yes I agree. We don't know much for sure what then really happens. And that's why CO2 BO is a scary thing. So a traditional mouth-to mouth-system has less risks. If there is a bottle of comperessed air, that might be safer to use than pure O2 or enriched air in a CO2 BO rescue case, so better to use it. Thanx again trux for more exact information!

 

[trux]

So a traditional mouth-to mouth-system has less risks. If there is a bottle of comperessed air, that is safer to use than pure O2 or enriched air in a CO2 BO rescue case.

Well, mouth-to-mouth pushes quite a bit of CO2 into the victims lungs, so it is probably also not optimal. Normally, the high CO2 at mouth-to-mouth has advantage because it stimulates breathing reflex at the victim, but that's not what we are looking for in this case. Ventilation device using plain air may be a better option. But as I told, I am not necessarily correct here at all. It is quite possible that pure O2 or Nitrox may be finally better. Definitely an opinion of an expert who has experience with handling CO2 intoxications would be preferable.

 

[TimoP]

Yes that CO2 in mouth-to-mouth system was the reason I didn't mentioned it in the first place. Of course it's better to ventilite lungs somehow in a real situation, than just think about risks of different ventilation systems and do nothing :head
I appreciate very much (like you do trux), that we think about risks before we are in the real situation, and even better, think how to avoid to get there in to a bad situation at all.

I find some symptoms, related in volume percent of CO2 in the inhaled air (if you inhale in minimum a few minutes this kind of air):
At 2% it is mildly narcotic and causes increased blood pressure and pulse rate, and causes reduced hearing.[39]
At about 5% it causes stimulation of the respiratory centre, dizziness, confusion and difficulty in breathing accompanied by headache and shortness of breath.[39]
At about 8% it causes headache, sweating, dim vision, tremor and loss of consciousness after exposure for between five and ten minutes.[39]

[39]Davidson, Clive. 7 February 2003. "Marine Notice: Carbon Dioxide: Health Hazard". Australian Maritime Safety Authority

Also in these cases precents of CO2 are higher in lungs than in the inhaled air. In the lungs of CO2 BO victim percent of CO2 is much higher than in those of who is giving mouth-to-mouth resuscitation...I suppose...but trux you have something to say to this I guess

BTW. our freediving testman EricF probably has been near limits, if you read his decription and this:
At about 8% it causes headache, sweating, dim vision, tremor, and loss of consciousness after exposure for between five and ten minutes.[39]

Edit:
More about symptoms of too high CO2:
Wiki (CO2 retention, diving): CO2 retention with its attendant dangers of death from convulsions and hypoxia (low oxygen level) is primarily of concern to the scuba diver due to "skip breathing". Other mechanisms of CO2 retention are breath-hold diving, breathing in a sealed environment, faulty regulator, exercise at extreme depth and using contaminated air.
Symptoms include rapid respiration in 4-6%, rapid pulse rate, shortness of breath in 7-10% and convulsions and unconsciousness in 11-20%.
These percents are different, bacause these must be in the air in the lungs, I think.
.

 

[trux]

Yes, of course, you are right - any type of ventilation is better than nothing. I just mentioned the other options for the case you have a choice. If the first revival attempts fail, professional rescuer would probably use intubation and mechanical respiratory support at most types of gaseous intoxication. Usually oxygen enriched mix is used in such cases, because in case of gaseous intoxications hypoxia and asphyxia are common. That would not be the case, though at a CO2 intoxication at a diver breathing O2 or Nitrox. That's why I voiced my doubts about the possible sudden increase of free CO2 due to the Haldane effect. However, if ventilated, the free CO2 would be removed sooner or later anyway, so perhaps the concern is void. I just read some articles about possible respiratory problems at patients treated with pure oxygen, but am not sure if it would apply here or not.

Anyway, at CO2 poisoning victim you should definitely first check the victim's pulse, and if there is none, applying heart massage.

 

[TimoP]

I just read some articles about possible respiratory problems at patients treated with pure oxygen, but am not sure if it would apply here or not.

This was discussed when we were in the life saver course. We were told that it's a problem if giving pure O2 big amounts for a longer time, meaning about over a hour. We were also told, that it shouldn't be a problem in normal rescue situation and it's no reason to avoid to give pure O2 in rescue cases (the discuss didn't include CO2 BO cases then). It's more a concern in hospitals.

O2 can be given for a very long time to patients by nasal cannula, but the result is a kind of an enriched air. The oxygen fraction provided to the patient ranges roughly from 24% to 35% (precents are from wiki).

 

[trux]

Yes, I know, and that's exactly the reason I mentioned it here - because we speak about the rescue of someone who was already breathing oxygen (or Nitrox) for possibly prolonged time. Hence applying O2 during the rescue may fall in the same category. Additionally, in common rescue situations, the initial critically increased CO2 level is usually not a problem as it is here.

 

[TimoP]

Something that I found about giving pure O2 too long from
All about Oxygen
(Critical care medicin):

"The extent of injury appears to depend on 1. The FiO2, 2. The duration of exposure, 3. The barometric pressure under which exposure occurred. It appears that the critical FiO2 for toxicity is around 50%
"
and

"How much oxygen is safe is a moot point. It is more important that you do not withhold life saving oxygen therapy than to be concerned about oxygen toxicity. It is, nonetheless, important that FiO2 is minimized to normalization of blood gas in intensive care patients: i.e. there is little to be gained in having a PaO2 of greater than 100mmHg."

PaO2 means here PaO2 in arteria blood gas. Normal medical reference ranges (but not maybe in freediving) for that:
At a PaO2 of less than 60 mm Hg, supplemental oxygen should be administered.
At a PaO2 of less than 26 mm Hg, the patient is at risk of death and must be oxygenated immediately.

 

[trux]

As far as I remember, it was not only the toxicity that was of a concern at uncontrolled oxygen administration to patients. It was also the CO2 level that somehow related to it. I remember reading a study examining objects with respiratory obstructions due to injury or disease (i.e. asthma), who were not only hypoxic, but also hypercapnic because of it. If I remember well, the pure O2 administration had paradoxically negative effect on the gas exchange.

 

[TimoP]

Yes there was mentioned several times in medical documents, that CO2 must be checked for hypercapnia in many different types of patients when using O2 (enriched air). But there was also some critic for some "traditions" in O2 limits concerning COPD-patients having CO2 retentio(=>hypercapnia): All about Oxygen
(Maybe it interests those freedivers too who do too often huge packing (or who smoke), and therefor MAY have a bigger risk to get COPD lung disease when old...you never know...I neither. And damn yes, I use to pack in trainings, but not so huge so often...)

More about oxygen (clear, short and "relatively easy" texts to understand even though it's medicin tutorials in University level):
All about Oxygen

Anyway:
-It seems to be, that very rich or pure (50-100 %) oxygen is more dangerous in many ways than enriched air including up to 50% of O2.
(-So if somebody still want to test something, it's not SO dangerous do it with Nitrox that it is with pure oxygen.)
-As said, if used in freediving, also enriched air/Nitrox is dangerous and it can has fatal consequences with or without warning signs, no question about that.
.