The Devils Advocate - End Tidal CO2

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Nurses Edition Commentary

Mizuho Morrison, DO, Lisa Chavez, RN, and Kathy Garvin, RN

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Mike J., M.D. -


As a new attending this argument was a monthly event at our staff meeting. At the time we didn't have end tidal and i was firmly in the camp of no O2 and watch the pt like a hawk. I was a vocal minority. Fortunately this discussion brought about the institution of end tdal for all sedations. Sadly it took several years to get end tidal for post intubation. Go figure.


EMCrit -

Hey brother, glad to hear the good guys won eventually.

David G., M.D. -

I agree with both Rob and Scott that in the setting of procedural sedation, the value of the ETCO2 detector is that the wave form indicates whether the patient is breathing or not. The value is not the actual numerical reading. I disagree with Anand that watching this number is a reliable measure of PaCO2.

The ETCO2 reading is determined by two variables: 1. The level of CO2 in the blod (PaCO2), and 2. Dead space in the lungs. The more dead space, the lower your ETCO2 reading. Imagine if you were to just move trace amounts of air in and out of your trachea, (say due to sedation, you are now hypoventilating with very low tidal volumes), your ETCO2 reading would drop to near zero (ambient air), while your PaCO2 would be markedly rising. All you can say from the ETCO2 reading, is that the PaCO2 level has to be higher, but how much higher is impossible to say without a blood gas.

daniel m. -

Hey there, I enjoyed the segment, but the Chemistry major in me can't help but point out that your graphic is erroneous in 2 ways:
1- CO2 is a linear molecule.
2- Oxygen is a more massive element than Carbon, but your graphic has it the other way around.

Your graphic actually shows the ball & stick representation of water, not carbon dioxide. Is this clinically relevant? No, and it's terribly nerdy of me to point this out, but I suspect the good Dr. Weingart appreciates correctness for correctness' sake.

EMCrit -

Totally Agree! I Have nothing to do with the graphics; if I did I would want them to be chemically correct. Thanks Brother!

EMCrit -

Took the words out of my mouth.

Geoffrey M. -

Scott, thanks for putting things right - that november review just seemed to say 'just wing it'- the more safety built into sedation the better.
Also you mentioned " the triple point in anaesthesia" - and said it blunts laryngospasm.
Could you please point me in the direction of the evidence for this? I mentioned it to an experienced anaesthetist and he had not heard of this.

EMCrit -

Anesthesiology Issue: Volume 89(5), November 1998, p 1293–1294
Laryngospasm-The Best Treatment

Geoffrey M. -

Thanks for that

Donald Z. -

Scott as usual i love to hear your hard hitting analysis but... i wonder when you say that if patient not on 02 you see immediatelty if it is plumetting but doesnt this forget the lag time. So the 02 may not plummet for a minute after the patient stops breathing which is a bit long.

Donald Z. -

i have use the "triple point" and even pointed it out to one of our anesthesiologists who thanked me later.

EMCrit -

Don Z. definitely a good point, though lag is rarely the issue it is in sick pts. Should be < 30 secs in these healthy pts getting ed proc sed

Bill Hinckley, MD -

Thanks for setting things straight, Scott. This has been bugging the crap out of me as well. And I'm with you regarding that annoying NIBP cuff being more harm than benefit during procedural sedation! If you've got to dump one vital sign during sedation, that would be the one, not the capnograph.

William F., DO -

When I was young and dumb, I used to put a pulse ox on my finger and hold my breath to see how long it took to drop. In general, on room air, it took over a minute and a half to start dropping, and then it dropped precipitously. I was an avid skin diver when I was young, so my breath holding skills were much better than they are now, that being said, maybe young people have a longer oxygen reserve on room air. I guess it just depends on how apneic is too apneic. As my SaO2 approached 90, I could no longer resist the urge to breath, and the SaO2 would fall to 88 before bouncing back up. Not recommended for all, but just my experience.

Colin K. -

I'll take the opposing view...
I have been using propofol for procedural sedation since 1996 and I never used EtCO2 until 2007. I tried it on all of my ED sedations. After a year of using it, I realized that the reading (number) or presence or absence of a wave form never changed anything I did! When I realized that I had stopped looking at the monitor, I stopped using it...never went back to it. I can estimate 1 sedation every other shift so about 8 a month--times 12 months, times 19 years = 1824 estimated sedations. Let's say that seems like a generous number so if we cut it down and say, maybe 1000 sedations...I can count on one hand the number of times I have had to bag someone. Even then, the BVM was used for only a few breaths. I can confidently say I have never had someone not wake up from my sedations. Although I did not to neuropsychometric testing on them before and after, nobody seemed any worse for wear. I do a very highly technical procedure during sedation. I use high-flow oxygen, I go slow when I push propofol (or ketafol or ketamine) and I watch my patient! I think in this setting, EtCO2 has never changed anything about my I vote no on data I seem to not need to act on. Just my opinion.


Josh G. -

Whatever happened to watching the patient for apnea? It's old fashioned but our eyes are pretty good. This presumes you are not the physician doing the procedure. If there is no one assigned to watch the airway, then definitely much easier to look up at the monitor.

Sulaiman A. -

Off the main topic ... Captain Morgan for Hip reduction ? can we have a demo of that ?

Rob O -

Here's a vid of Al Sacchetti doing the Capt Morgan

Adrien S. -

Do you have the link on how to set up a nasal cannula with an ETCO2? I can't seem to find it on EMCRIT.

EMCrit -

here you go Adrien:

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