End-tidal CO2

Quantitative End-tidal CO2 has quickly become the standard of care for monitoring the efficiency of CPR. By monitoring the CO2 coming from the lungs, we can not only confirm placement of an endotracheal tube after intubation, but using new technology with real-time electronic monitoring we can determine the levels of CO2 with each breath.


With each chest compression, some volume of air will also be expelled from the lungs. Initially this air contains residual CO2 from the lungs, but those levels will disappear to zero quickly. In an arrest patient, the end-tidal CO2 will remain at zero.  However, if blood is moving through the lungs (no matter how slow), gas exchange from the capillaries to the alveoli will still occur. Good chest compressions WILL move enough blood that oxygen will still be delivered to the tissues, and CO2 will be brought to the lungs to be exhaled and measured.

Using this knowledge, the quality of CPR can now be monitored – if adequate chest compressions are circulating blood it will be reflected by end-tidal CO2.  If the person performing CPR gets tired, or someone is doing bad compressions, ETCO2 will decrease.

ETCO2 has also eliminated the need to stop chest compressions in order to check a pulse.  ETCO2 is lower with CPR than in patients with spontaneous circulation. Now, instead of stopping CPR to feel the carotids for a subjective pulse, monitoring ETCO2 will show a significant jump when spontaneous circulation returns (illustrated in the image below), and a pulse has likely returned. If ETCO2 is being monitored during CPR and a sustained increase in CO2 by 15 mmHg is noted, return of spontaneous circulation has likely occurred.

Even after a jump in ETCO2 is noted, compressions should be continued for a full minute before halting chest compressions to check for a pulse.

This image illustrates ETCO2 monitoring during CPR, with a sharp, sustained increase with ROSC.

By the numbers:
Bad CPR = ETCO2 <15
Good CPR = ETCO2 >15
ROSC = ETCO2 increases suddenly by 15