The Glories of End Tidal CO2

If you were to choose one vital sign for your critically ill patient, what would you choose?  Blood pressure?  Pulse?  Respiratory rate?  O2 sat? Temperature? Certainly it’s nice to know if a patient’s BP is super low or sky high, but if you are evaluating someone for the presence of shock, and you are waiting on the BP cuff to cycle one more time, you are already behind in recognizing and correcting the patient’s physiologic derangements.

Tachycardia presents earlier in shock but what about the elderly patient on beta-blockers?  What about the trauma victim with a belly full of blood (vagal nerve stimulation leading to an attenuation of their tachycardia)?  Too easy to be misled with that one, I say.

What about respiratory rate?  …  How many times have you seen a respiratory rate documented correctly? Lovett, et al (2005) found that neither the clinical measurement of respiratory rate by nursing staff or electronic monitors at triage accurately measured respiratory rate.  For a critically ill patient, you can imagine how much more difficult this can be?  You can probably look at the patient for 5-10 sec and get a sense of too-fast or too-slow, but subtle changes in respiratory rate are tricky to pick up.

What about O2 sat?  Even if you can keep it on your patient’s finger/strapped to their ear or forehead, you are going to be late in the game at detecting complications peri-intubation and during sedations.  You may have experienced this lag time after intubating a patient and having a brief drop in the O2 sat into the 70’s.  Everyone in the resus bay turns and stares at the monitor for 20 sec while someone bags (furiously and unnecessarily fast) as the O2 sat slowly rise into the 90’s.  And, have you ever seen an oxygen-dissociation curve? That thing looks dangerous.  I've seen cliff's that have shapes similar to it...


Temperature?  Really?  Temperature?

Nope, for me the vital sign of choice is undoubtedly EtCO2 (End tidal CO2).  Why?  A single, non-invasive, set up that can give you a glimpse into the ventilation, perfusion, and metabolism of the patient?  Yes please, I’ll have some of that.


I think it’s well documented that waveform capnography can help lead to better prevention of hypoxic events in procedural sedation (Deitch, et al, 2009) and can help in the detection of esophageal intubation (though probably shouldn’t be relied on as a sole indicator ET tube location). (Grmec, S. 2002) In the accompanying podcast to this post, Dr. Jason McMullan, the EMS Fellowship Director here at UC, talks about the use of EtCO2 in the prehospital environment.  Whether it is detecting tube dislodgment in an intubated patient, avoiding hypercapnia in a patient with TBI, or even monitoring your resuscitation in a patient with hemorrhagic shock, waveform capnography is a powerful piece of monitoring equipment in the prehospital environment.

For a rundown on interpreting waveform capnography check out these excellent FOAMed resources:

  • Lovett, P., Buchwald, J., Sturmann, K., & Bijur, P. (2005) The vexatious vital: Neither clinical measurements by nurses nor an electronic monitor provides accurate measurements of respiratory rate in triage. Annals of Emergency Medicine. 45(1) 68-76. doi:
  • Deitch, K., Miner, J., Chudnofsky, C., Dominici, P., & Latta, D. (2009) Does End Tidal CO2 Monitoring During Emergency Department Procedural Sedation and Analgesia with Propofol Decrease the Incidence of Hypoxic Events? A Randomized, Controlled Trial. Annals of Emergency Medicine. 55(3). 258-264. DOI:
  • Grmec, S. (2002) Comparison of three different methods to confirm tracheal tube placement in emergency intubation. Intensive Care Medicine. 28(6) 701-704.
  • Donald, M. & Paterson, B. (2006) End tidal carbon dioxide monitoring in prehospital and retrieval medicine: a review. Emergency Medicine Journal. 23. 728-730. doi: 10.1136/emj.2006.037184