The guillotine: Not a bad way to go?

[brossa]

@Napier

In fact, I think our defenses against suffocation are driven by our ability to sense high CO2 in the air we breathe, and am surprised they would mix CO2 into nitrogen for euthanasia. Wouldn’t that feel like suffocation and produce agonized struggling and panic?

Not so much in the air you breathe as in the bloodstream, but high CO2 in inspired air quickly leads to high CO2 in blood, which drops the blood pH and trips the sensor in the brain. My impression of animal euthanasia with CO2 is that it is not so much mixing CO2 and N2 as it is adding a lot of CO2 to the air already in the chamber. Here is a review of CO2 in lab animal euthanasia; high enough carbon dioxide levels result in death even if there is more than adequate oxygen present, and the carbon dioxide appears to induce unconsciousness and death in a way that is different from simple hypoxia. The review notes that CO2 levels greater than 40% are acutely unpleasant to breathe because of the formation of carbonic acid in the mucous membranes of the airway, but if you keep the levels in the 30% range you will render your mouse unconscious and then dead without the muscular spasms or seizure that can be seen with inert gas like argon or nitrogen. So, maybe it does feel like suffocation, but it acts quickly and maybe looks more peaceful than hypoxia?

Expediency may also be a driving force here: a quick’n’easy method to kill masses of birds in factory farms is to drown them with foam. I don’t think anyone claims that it is particularly peaceful, in fact it’s called depopulation rather than euthanasia. Instead it’s just cheap and easy to clean up and not dangerous to the humans doing it and quick in a we-can-do-a-whole-barnfull-in-ten-minutes kinda way.

[Machine_Elf]

@brossa

Not so much in the air you breathe as in the bloodstream, but high CO2 in inspired air quickly leads to high CO2 in blood, which drops the blood pH and trips the sensor in the brain. My impression of animal euthanasia with CO2 is that it is not so much mixing CO2 and N2 as it is adding a lot of CO2 to the air already in the chamber. Here is a review of CO2 in lab animal euthanasia; high enough carbon dioxide levels result in death even if there is more than adequate oxygen present, and the carbon dioxide appears to induce unconsciousness and death in a way that is different from simple hypoxia. The review notes that CO2 levels greater than 40% are acutely unpleasant to breathe because of the formation of carbonic acid in the mucous membranes of the airway, but if you keep the levels in the 30% range you will render your mouse unconscious and then dead without the muscular spasms or seizure that can be seen with inert gas like argon or nitrogen. So, maybe it does feel like suffocation, but it acts quickly and maybe looks more peaceful than hypoxia?

Yes, CO2 is toxic, not just an asphyxiant (as opposed to N2, which is simply an asphyxiant). This was a major issue during Apollo 13: there was enough O2 on board to get the crew home, but they had to rig up a CO2 scrubber to keep CO2 concentrations below the lethal limit.

And yes, CO2 is irritating to the lungs. Inhale a lungful from a mostly-empty 2-liter soda bottle, and you’ll instantly feel exactly like you’ve been holding your breath for two minutes.

@Napier

I’ve had too much nitrogen and too little oxygen, working with liquid nitrogen in an enclosed space. Turns out this is a very dangerous situation. I would have been much less at risk if I understood it better at the time. I noticed I was feeling intoxicated, but also that I felt extremely pleasant and relaxed and at ease with the situation. We don’t raise our defenses when what we feel is the opposite of frightening or painful or worrisome. Anybody at risk of being in too much nitrogen should know ahead of time that when the hazard starts they will not object at all.

Illustrated nicely by this incident, in which party organizers dumped liquid nitrogen into an occupied swimming pool. The intent was to create a fun fog effect (mission accomplished) - but they didn’t realize this also created an oxygen-poor layer of nitrogen gas on the surface of the pool, asphyxiating the swimmers. nine people ended up in the hospital.