A probably dumb question.

[Mike Boswell]

Somewhere in a discussion of rebreathers I read that when a person exhales, that exhalation contains about 4% CO2 and since only 3% CO2 is toxic, we cannot rebreathe our own exhalation.

If this is true, how can we perform rescue breathing without poisoning our patient?

 

[DocVikingo]

Hi Mike,

CO2 makes up ~.04% of normal ambient air. Exhalations in the normal individual contain between ~3.5-4.0% CO2. CO2 can be "toxic" (e.g., cause drowsiness) at as little as 1% if breathed for an extended period. At ~5% it can result in shortness of breath, dizziness, confusion, anxiety and headache. By 8% loss of consciousness can occur after exposure for 5-10 mins. CO2 levels >4% usually can be tolerated for quite some time, but the individual clearly will be symptomatic and exposure to such levels is not wise.

The primary reason we don't cause CO2 "poisoning" in our patients when performing rescue breathing is that along with the CO2 we also are providing ~16-18% O2. This oxygenation is sufficient to sustain life until professional assistance with 100% O2 arrives. It certainly is more O2 than the person who is not breathing would otherwise obtain.

Regards,

DocVikingo

 

[TSandM]

As Doc Vikingo says, rescue breathing is based on the lesser of two evils. Yes, it is better to provide fresh air than exhaled air, but some oxygen is a lot better than none, where the central nervous system is concerned. We tolerate the elevated CO2 levels, which can cause anxiety, shortness of breath, decreased level of consciousness, and pH disturbances in the blood, because the lack of oxygen causes irreversible brain injury. And exhaled gas is what you have with you, that you can easily provide to the patient.

And it's not a dumb question. It's actually quite a good one.