Femoral artery collapse ratio as a real-time physiologic marker of cardiopulmonary resuscitation quality: A case series.

High-quality cardiopulmonary resuscitation (CPR) requires effective chest compressions, yet real-time physiologic assessment during ongoing resuscitation in the emergency department (ED) remains limited. End-tidal carbon dioxide (ETCO₂) is a guideline-endorsed surrogate of CPR quality, but its measurement is influenced by ventilation and pulmonary factors. We report a prospective case series of 20 adult cardiac arrest patients evaluating the feasibility of femoral artery collapse ratio (FACR) measurement using M-mode point-of-care ultrasound during uninterrupted CPR and its relationship with ETCO₂ and return of spontaneous circulation (ROSC). FACR was successfully obtained in all patients without interrupting chest compressions. Higher FACR values were observed in patients with a mean ETCO₂ ≥20 mmHg and among those achieving ROSC. FACR demonstrated physiologic concordance with ETCO₂ across the cohort. FACR may represent a practical, ultrasound-based adjunct for real-time physiologic assessment of chest compression effectiveness in the emergency department, particularly when interpretation of end-tidal carbon dioxide is limited. Further prospective studies are needed to define clinically meaningful thresholds and outcome impact.