– If humans breathe in oxygen and exhale CO2, then why does mouth-to-mouth resuscitation work?
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Because we don’t exhale one element only. It’s a mixture. And I’m that mixture of an exhale, we also exhale oxygen. The percentage of oxygen in the air when we inhale drops when we exhale it, but alas, it’s still there.
We don’t JUST breathe in oxygen and breathe out CO2. It’s a mix of gases. The air we are used to breathing in only contains 21% oxygen. We breathe out about 16% oxygen. That’s still enough to keep someone oxygenated for awhile.
We convert oxygen to CO2. But not all of the oxygen in the air.
Normal air has 21% oxygen.
Exhaled air has 16% oxygen.
So it still works because we’re breathing out plenty of oxygen still.
It doesn’t really which is reflected in newer guidelines. There’s more oxygen in air so you’re better off having someone hold the airway open and do chest compressions.
Unless it’s drowning. Mouth to mouth stimulates the patient to breathe and cough.
You don’t exhale pure CO2. There is just a little bit more of it in the air you breathe out. A tiny bit more, just a few percent more.
We also do not inhale pure oxygen.
Adding to this: this is also how and why an rebreather works: you inhale one last time and exhale into a bag/container. After that you use that air mixture to breathe, giving you some crucial extra breathing time in case of submersion (a.i. helicopter crash)
Basically, the “breathe in oxygen breath out CO2” line is an over simplification
Your lungs turn Oxygen into CO2. That doesn’t mean they’re 100% efficient at it.
The air you breathe in is 21% oxygen
The air you breathe out is still 16% oxygen
This is why you can hold your breath for a minute or two; you still have oxygen in your lungs, just less than is comfortable.
In the case of CPR life breaths, comfort isn’t really your first perrogative. You possibly even broke some ribs during the chest compressions anyway.
The other answers are correct- there’s still a lot of oxygen left in the air we breathe out. But I’ll add two things:
Tidal volume: a fair amount of the air we breathe never reaches the inside of our lungs (alveoli) at all. When we inhale, the last air we take in only makes it as far as our airway, mouth, or nose. And when we exhale, the air deep in our lungs doesn’t make it all the way out, either. That works to our benefit during CPR.
But the other thing is that, really, it doesn’t “work” anyway. It’s worth trying, but CPR might extend someone’s life by a minute or so if done properly- giving about a 15% chance that medical help arrives in time. In the event of a cardiac problem, there’s often enough oxygen in a person’s lungs to sustain them for a while: but without blood flow it can’t get to cells, which is why they (especially brain cells) die. Many first-aid classes now teach compression-only CPR – compressing someone’s chest to pump their blood also squeezes their lungs, giving some of the benefits of full CPR without the risk of transmitting disease.
An Automated External Defibrillator (AED) is much, much more effective in V-fib cases. If an AED is available for a cardiac patient the survival rate is around 80%.
We don’t “breathe in oxygen and exhale CO2”, we “breath in air that’s relatively rich in oxygen and breath out air that has slightly less oxygen and little more CO2.”
As others have said, we breathe out about 16% Oxygenated air. Enough to keep someone alive.
On a related note: Many authorities no longer recommend mouth to mouth resuscitation. A lot of people are afraid of performing mouth to mouth because of special boundaries, and it’s not absolutely necessary. Oxygenated blood has enough reserves to keep an (unconscious, calm) person going for a good 5 minutes before any permanent damage begins to set in, provided the blood is still pumped. Hence why many authorities nowadays only recommend doing Chest Compressions to keep the blood pumping
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