EMCrit Podcast 2 – ETCO2


I did a spot on ETCO2 for Amal Mattu’s podcast a couple of weeks ago. I try to clear up some of the myths on the use of ETCO2.

Of course the most pervasive and potentially dangerous myth is that ETCO2=PaCO2.
Long story short, in our patients, it doesn’t.

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  1. SamG says

    Hey Scott-
    Quick question for ya:

    What is it pathophysiologically that causes End-Tidal to drop as CPR progresses, despite continuing adequate compressions? If compressions are constant, and arterial CO2 is probably rising if anything, why does End-Tidal ever diminish (<10 after 20 mins, etc) ?

    • says

      In cardiac arrest and shock states, ETCO2 is almost entirely a reflection of cardiac output and the amount of blood pumped to the lungs not the level of CO2 in the blood

      • SamG says

        Hey Scott,
        I totally understand that point- but so then as long as we are performing excellent chest compressions, why should the End-Tidal ever get to less than 10-20 mm/Hg?

        (The amount of blood circulating should generally theoretically stay the same, and the minor variable (CO2 in the blood) should only increase if anything)

        • Ronnie says

          During cardiac arrest the partial pressure of end-tidal carbon dioxide (PetCO2) falls to very low levels, reflecting the very low cardiac output achieved with cardiopulmonary resuscitation (CPR). Little part of lungs gets perfused thus lesser gas exchange area causing decreased PetCo2 though PaCO2 may be higher than normal as you said. ROSC achieves full perfusion in all lung zones( normal state) and larger gas exchange area causing increase in level of PetCO2.Higher levels of the PetCO2 in CPR indicate better cardiac output and thus quality of CPR.

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