If ROSC occurs, which of the following ETCO2 findings would you expect to encounter?

• A. A sudden drop to zero
• B. An abrupt and sustained increase in ETCO2
• C. No change in ETCO2
• D. A gradual decline over time

Answer: (B)

End-tidal CO2 reflects how much CO2 is being delivered to the lungs, which depends on pulmonary blood flow and circulation. During CPR, cardiac output is limited, so ETCO2 stays relatively low. When spontaneous circulation returns, blood flow to the lungs surges suddenly, carrying CO2 from the tissues to the lungs. This causes an abrupt and sustained increase in ETCO2, and it usually stays elevated as long as circulation remains good.

So, the expected finding after ROSC is a sharp rise in ETCO2 that then remains higher. A sudden drop to zero would suggest loss of ventilation or a severed circuit, while no change or a gradual decline wouldn’t reflect the abrupt restoration of circulation.