what is the maximum amount of nitrogen you can give a patient without suffocating them?

It would depend, as most medical things do, on the person, their weight, age, fitness level, any predisposition to a hypersensitivity to nitrogen. Contact a doctor directly with these details in mind and they may be able to give you a ballpark figure. Good luck with the novel.

I'm not sure about the amount, but this may be helpful.

I've seen suggestions that nitrogen should be used in gas chambers for

a much more humane execution than happens with stinky and chokey

hydrogen cyanide. Nitrogen's odorless, and there's very little feeling

of hypoxia when you breathe it. You just pass out, which is what makes

it so dangerous. And with nitrogen you could use the old equipment,

but dispense with most of the time and effort associated with handling

cyanide gas and keeping it away from everybody but the condemed.

Unfortunately, cyanide is historically what we started with, and it's

hard to change habit.

its not the nitrogen that kill a person, its the displacement of oxygen.

at altitude 43,000ft where oxygen concentration drop from 21% to 3.6%, the pilot needs oxygen. because when oxygen concentration is 4-6%, a person loss consciousness in 40 sec and died within a few minutes.

in the pass there is a talk about capital punishment by nitrogen asphyration. again this kill a person because of lack of oxygen, CO2 is being recirculate to the body.

You need to remember that air is about 80% nitrogen and we arent suffocating yet. If you give too much nitrogen the patient wont suffocate they will continue to breathe as normally and then die because the brain would be starved of oxugen

You scared me for a minute, then I saw the 2nd paragraph of your answer. I was ready to report you to the police!!! lol