Which monitoring modality is used in ALS Step 3 to assess perfusion during CPR?

• A. To assess forward movement of blood
• B. To monitor oxygen saturation
• C. To measure blood pressure
• D. To guide defibrillation energy

Answer: (A)

The key idea here is that perfusion during CPR is about whether blood is actually being pushed forward to the tissues. The most direct way to judge that in ALS Step 3 is to check for forward movement of blood by feeling for a pulse in a major artery (such as the carotid or femoral). If a pulse is present, there is some forward blood flow, indicating perfusion; if not, you continue chest compressions to generate it.

Oxygen saturation reflects oxygen delivery to the tissues, but during ongoing CPR it can be unreliable due to poor peripheral perfusion and movement artifacts. Blood pressure measurement can be difficult and not dependable during active chest compressions. Guiding defibrillation energy depends on the rhythm and likelihood of shockable patterns, not on current perfusion. So the direct, most informative sign of perfusion during CPR is the forward movement of blood, i.e., the presence of a palpable pulse.