Using ETCO2 to Determine ROSC

This is our first featured post on how to use ETCO2 in determining return of spontaneous circulation (ROSC) in your post cardiac arrest patients!

Have you ever wondered why your patient’s ETCO2 (End Tidal Carbon Dioxide) rises when you achieve ROSC (Return of Spontaneous Circulation)? Why do we see that sudden increase in CO2 on the monitor when before it was reading at 15mmHg?

First let’s go back and touch base on what ETCO2 is. ETCO2 is the partial pressure of carbon dioxide in the exhaled air measured at the end of expiration. CO2 is produced in perfused tissues by aerobic metabolism (where oxygen is used to make energy) as well as anaerobic metabolism (no oxygen is used to make energy). It diffuses from the cells into the blood and is transported by the venous circulation to the lungs, where it is removed by ventilation. So what should a provider look at when monitoring CO2? In a non-cardiac arrest patient, your readings should aim at 35-45 mmHg. If your patient is breathing too fast, your ETCO2 readings will drop. The reason is because the patient is blowing off their CO2; which is noticed in patients experiencing anxiety attacks because they are hyperventilating. You might notice patients experiencing diabetic ketoacidosis have CO2 readings less than 35mmHg readings as well. When your patient’s readings are higher than 45mmHg, this means the patient is not breathing adequately and the CO2 is building up in their system. This can be seen with patients with low respiratory rates (hypoventilation) from narcotic overdoses.

Overdose scene from the movie “Pulp Fiction”

So now that we have a basic understanding of what CO2 is, let’s go back to our cardiac arrest patient. You have your patient intubated and you see a reading of 15 mmHg. Should you be worried about this then as it’s below 35mmHg? The answer is no, remember those readings of 35-45 mmHg were for non-cardiac arrest patients. So what does a reading of 15 mmHg mean for a cardiac arrest patient? It means you and your crew members are performing excellent compressions! ACLS guidelines state that having high quality chest compressions on your patient should produce a reading between 10 to 20 mmHg, this reading is from the heart’s cardiac output from the compressions. So now you know your crew members are performing excellent CPR. Suddenly you notice your CO2 readings go from 15 to 45 mmHg. So now what does this mean? This means there is a high possibility your patient has achieved ROSC. The sudden increase in CO2  represents your patient having an increase in blood flow circulation. With your patient now having this increase in blood flow, this will make more CO2 unload into the lungs. With more CO2 unloading into the lungs, the number will climb higher and higher. This is where post-arrest guidelines and protocols come into consideration.

Post Credit: JD

Scopeducation admin insert:

Remember, us performing CPR is not as effective as the heart pumping normally. So the rapid increase in ETCO2 is a high indicator that the heart has started beating spontaneously! Because our CPR is not as effective as the heart pumping, CO2 will build up in the body. So when ROSC is obtained, all of that built up CO2 will flood into the lungs.

This site is meant to be used for educational use only. We strive to push evidence based medicine with no bias to help you obtain all the important information. You should always follow your protocols that have been set in place.

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Kodali, Bhavani, and Richard Urman. “Capnography during Cardiopulmonary Resuscitation: Current Evidence and Future Directions.” Journal of Emergencies, Trauma, and Shock, Medknow Publications & Media Pvt Ltd, Oct. 2014,

Says, Angelo, et al. “Waveform Capnography.” Learn & Master ACLS/PALS, 9 Apr. 2020,

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