# How does mouth-to-mouth work since you're exhaling mostly carbon dioxide? **URL:** \ **Category:** Factual Questions\ **Created:** [December 20, 2002, 4:38pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046 "2002-12-20T16:38:05Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [December 20, 2002, 4:38pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/1 "2002-12-20T16:38:05Z")
How is the nonbreathing person benefited by inhaling a nonoxygenated gas? ---
**Author:** ![Waverly](https://avatars.discourse-cdn.com/v4/letter/w/57b2e6/32.png) [@Waverly](https://boards.straightdope.com/u/Waverly)\ **Post date:** [December 20, 2002, 4:39pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/2 "2002-12-20T16:39:50Z")
You only use a fraction of the oxygen. Plenty is left for the recipient. ---
**Author:** ![dylan\_73](https://avatars.discourse-cdn.com/v4/letter/d/ecccb3/32.png) [@dylan\_73](https://boards.straightdope.com/u/dylan_73)\ **Post date:** [December 20, 2002, 4:40pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/3 "2002-12-20T16:40:14Z")
There’s still enough oxygen in the exhaled breath to help. It’s not ideal but it is after all an emergency procedure. ---
**Author:** ![Captain\_Amazing](https://avatars.discourse-cdn.com/v4/letter/c/6de8d8/32.png) [@Captain\_Amazing](https://boards.straightdope.com/u/Captain_Amazing)\ **Post date:** [December 20, 2002, 4:40pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/4 "2002-12-20T16:40:29Z")
Well, your lungs don’t take all the oxygen out of the air you inhale, so, when you’re doing mouth-to-mouth, there’s still enough oxygen in your exhaled breath to help the person. ---
**Author:** ![dylan\_73](https://avatars.discourse-cdn.com/v4/letter/d/ecccb3/32.png) [@dylan\_73](https://boards.straightdope.com/u/dylan_73)\ **Post date:** [December 20, 2002, 4:44pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/5 "2002-12-20T16:44:29Z")
[http://www.patrol.org/instructor/oec/o2/tsld030.htm](http://www.patrol.org/instructor/oec/o2/tsld030.htm) has some details on relative percentages. ---
**Author:** ![CrazyCatLady](https://avatars.discourse-cdn.com/v4/letter/c/dfb087/32.png) [@CrazyCatLady](https://boards.straightdope.com/u/CrazyCatLady)\ **Post date:** [December 20, 2002, 4:51pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/6 "2002-12-20T16:51:19Z")
As our CPR instructor pointed out, any oxygen is better than no oxygen, so even if our lungs removed 90% of the oxygen from the air we breathe (which they don’t, by a long shot) mouth to mouth would still be an improvement over no breathin at all. ---
**Author:** ![Liberal](https://avatars.discourse-cdn.com/v4/letter/l/848f3c/32.png) [@Liberal](https://boards.straightdope.com/u/Liberal)\ **Post date:** [December 20, 2002, 4:56pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/7 "2002-12-20T16:56:27Z")
Thanks for the prompt replies! 🙂 ---
**Author:** ![coffeecat](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/coffeecat/32/3405_2.png) [@coffeecat](https://boards.straightdope.com/u/coffeecat)\ **Post date:** [December 20, 2002, 5:11pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/8 "2002-12-20T17:11:21Z")
I think the extra CO[sub]2[/sub] can stimulate the victim to start breathing on his own, too. ---
**Author:** ![bcullman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bcullman/32/8207_2.png) [@bcullman](https://boards.straightdope.com/u/bcullman)\ **Post date:** [December 20, 2002, 6:10pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/9 "2002-12-20T18:10:56Z")
I always thought that the physical movement caused by the intake of a large quanity of air by the non breathing party was also advantageious. ---
**Author:** ![BaldTaco](https://avatars.discourse-cdn.com/v4/letter/b/47e85d/32.png) [@BaldTaco](https://boards.straightdope.com/u/BaldTaco)\ **Post date:** [December 20, 2002, 7:35pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/10 "2002-12-20T19:35:16Z")
The air we breathe in contains about 21% oxygen, and as the site referenced by dylan\_73 mentions, we breathe out about 16%. I’ve never heard anything about the volume of air having positive effects on it’s own. Contrary to popular belief, the main purpose of AR (artificial respiration) is not to restart breathing, but to continue supplying oxygen to the victim’s bloodstream in order to prevent brain death. This goes for CPR as well. Some victims can be revived through these techniques (particularly children), but this is not common. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [December 20, 2002, 7:54pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/11 "2002-12-20T19:54:05Z")
Do an experiment. Hold your breath until you feel like you’re going to explode. Then exhale into a paper bag. Breath in from the bag. Repeat. One (impressively strong) component of the drive to breath is simply the need to “unload” or relax the lungs periodically. ---
**Author:** ![BMalion](https://avatars.discourse-cdn.com/v4/letter/b/e274bd/32.png) [@BMalion](https://boards.straightdope.com/u/BMalion)\ **Post date:** [December 20, 2002, 8:11pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/12 "2002-12-20T20:11:25Z")
> [@](#): > > \*Originally posted by KarlGauss \* > \*\*Do an experiment. > > Hold your breath until you feel like you’re going to explode. Then exhale into a paper bag. Breath in from the bag. Repeat. > > One (impressively strong) component of the drive to breath is simply the need to “unload” or relax the lungs periodically. \*\* Um… can I … take…my…head… out… 😕of… the bag …now…please?.. ---
**Author:** ![Muad\_Dib](https://avatars.discourse-cdn.com/v4/letter/m/35a633/32.png) [@Muad\_Dib](https://boards.straightdope.com/u/Muad_Dib)\ **Post date:** [December 20, 2002, 8:36pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/13 "2002-12-20T20:36:17Z")
Try breathing into a bag. Notice how it takes several breaths for the air to become very stale? Even then, the air is only stale. If you were really breathing out mostly CO2 you would immediately choke on the air from the bag. ---
**Author:** ![bcullman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bcullman/32/8207_2.png) [@bcullman](https://boards.straightdope.com/u/bcullman)\ **Post date:** [December 20, 2002, 8:50pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/14 "2002-12-20T20:50:45Z")
> [@](#): > > \*Originally posted by KarlGauss \* > \*\*Do an experiment. > > Hold your breath until you feel like you’re going to explode. Then exhale into a paper bag. Breath in from the bag. Repeat. > > One (impressively strong) component of the drive to breath is simply the need to “unload” or relax the lungs periodically. \*\* Doesnt this support what i posted earlier about this? [QUOTE] I always thought that the physical movement caused by the intake of a large quanity of air by the non breathing party was also advantageious. [QUOTE] ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [December 20, 2002, 9:33pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/15 "2002-12-20T21:33:39Z")
I understand that carbon dioxide, while technically slightly poisonous (according to Isaac Asimov), also triggers the breathing reflex. It’s a surprise obstetricians have not caught on to this as a means of starting a newborn baby breathing, rather than slapping the poor soul on his/her rear end to do it. :rolleyes: ---
**Author:** ![E72521](https://avatars.discourse-cdn.com/v4/letter/e/dbc845/32.png) [@E72521](https://boards.straightdope.com/u/E72521)\ **Post date:** [December 20, 2002, 10:54pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/16 "2002-12-20T22:54:17Z")
It is true that the lungs contain _baroreceptors_–nerves that tell the brain whether or not the lungs are being stretched, as in breathing. This is considered to be only a secondary drive to breathe. The main drive to ventilate your lungs is your arterial blood’s pH, which is inversely related to the arterial blood’s carbon dioxide content. If you stop breathing but your heart continues to beat, your CO2 content will skyrocket. If your condition allows, this will eventually stimulate you to breathe. Oxygen, OTOH is not a primary drive to ventilate. As long as you are able to exhale, or get rid of CO2, you should not feel any shortness of breath in lowered oxygen atmospheres. You would feel drunk-like euphoria, increased heart rate and blood pressure, chest pain and eventually death. Most folks can live just fine breathing 16-18% oxygen. ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [December 20, 2002, 11:01pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/17 "2002-12-20T23:01:39Z")
Dougie, they DON’T typically slap babies on the butt to start them breathing. Almost all babies start breathing and crying on their own. And if they don’t, they’ll give them oxygen or some other intervention. My daughter was born 5 weeks ago and they certainly didn’t slap her! ---
**Author:** ![Lemur866](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lemur866/32/434_2.png) [@Lemur866](https://boards.straightdope.com/u/Lemur866)\ **Post date:** [December 20, 2002, 11:04pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/18 "2002-12-20T23:04:56Z")
E72521 is right, which is why hypoxia is so sneaky. You can pass out from oxygen deprivation without even noticing that you are short on oxygen. ---
**Author:** ![artemis](https://avatars.discourse-cdn.com/v4/letter/a/91b2a8/32.png) [@artemis](https://boards.straightdope.com/u/artemis)\ **Post date:** [December 20, 2002, 11:10pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/19 "2002-12-20T23:10:26Z")
> [@](#): > > \*Originally posted by dougie\_monty \* > \*\*I understand that carbon dioxide, while technically slightly poisonous (according to Isaac Asimov), also triggers the breathing reflex. It’s a surprise obstetricians have not caught on to this as a means of starting a newborn baby breathing, rather than slapping the poor soul on his/her rear end to do it. :rolleyes: \*\* Obstetricians don’t generally slap the baby on the rear to induce breathing - you’ve been watching too many TV medical dramas. They merely suction the secretions out of the infant’s nose and mouth (so that when the child takes that first breath, he/she doesn’t aspirate them), and stimulate the child by rubbing it (necessary in any case to remove the birth fluids from the infant’s body). A healthy newborn doesn’t really need much if any external stimulation to start breathing. And administering carbon dioxide would be unnesessary in any case - since your tissues produce it as a byproduct of metabolism, once you stop breathing and are no longer blowing off that CO2 from your lungs, the blood levels of CO2 rise very rapidly. If your breathing centers are not responding to that rapid natural rise, then they’re not going to respond any better to exogenously administered CO2. Better to intubate the patient and concentrate on getting oxygen into the bloodstream in time to keep the patient’s brain from being permanently damaged by anoxia (which will generally happen in less than 4 minutes), and worry about getting him/her breathing spontaneously later. ---
**Author:** ![dougie\_monty](https://avatars.discourse-cdn.com/v4/letter/d/439d5e/32.png) [@dougie\_monty](https://boards.straightdope.com/u/dougie_monty)\ **Post date:** [December 20, 2002, 11:40pm UTC](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046/20 "2002-12-20T23:40:55Z")
_Originally posted by Artemis_ > [@](#): > > Obstetricians don’t generally slap the baby on the rear to induce breathing - you’ve been watching too many TV medical dramas. That’s not where I heard about it. In fact it was in the book _The Human Body_ by Asimov. I took a course in Contemporary Health at El Camino College in 1984, in which we saw a movie (a documentary) of a delivery. Not for the squeamish! All of us, male and female alike, winced and screamed slightly when seeing the baby pop out of its mother. I don’t remember what the obstetrician did to the baby just after the delivery, because of my (quite normal) reaction to seeing the birth that was recorded on film. For the record, I haven’t watched a TV drama since _Emergency!_ went off the air in 1978. [Next page](https://boards.straightdope.com/t/how-does-mouth-to-mouth-work-since-youre-exhaling-mostly-carbon-dioxide/144046.md?page=2)