Which of the following is a clinical indicator of return of spontaneous circulation (ROSC)?

• A. A Palpable Pulse
• B. A Sudden and Sustained Increase in ETCO2
• C. A Decrease in Blood Pressure
• D. Absence of Arterial Line Waveform

Answer: (B)

End-tidal CO2 monitoring reflects how well blood is flowing through the lungs and, by extension, how effectively the heart is pumping. During CPR, the amount of CO2 reaching the lungs is limited by reduced perfusion, so ETCO2 stays relatively low. When spontaneous circulation returns, blood flow to the lungs improves markedly, delivering more CO2 to the lungs and causing a sudden, sustained rise in ETCO2. This change is a reliable, continuous sign that circulation has resumed and often appears before other signs become clearly positive.

A palpable pulse can be helpful, but it can be unreliable or delayed during resuscitation, and a sudden drop in blood pressure points to perfusion issues rather than recovery. Absence of an arterial line waveform only tells you there’s no arterial pressure monitoring, not that ROSC has occurred. So the rapid, lasting increase in ETCO2 best signals that circulation has been restored.