Redefining Vasoplegia: A New Hemodynamic Model for Differentiating Cardiac vs. Vascular Dysfunction using the Resistance Flow Ratio

ABSTRACT Background Conventional definitions of vasoplegia and cardiogenic shock rely on fixed thresholds for mean arterial pressure (MAP), cardiac index (CI), and systemic vascular resistance (SVR), failing to account for the physiologic interdependence between cardiac output and vascular tone. We propose the Resistance:Flow Ratio (RFR = SVRI/CI) as a continuous, physiologically anchored measure to differentiate vascular versus cardiac dysfunction and to unify compensated, decompensated, and mixed shock states. Methods Single-center retrospective study of adult cardiac surgery cases, 2014-2024. Hemodynamic data for the first 72h post-operatively were analyzed. RFR thresholds were derived by modeling the relative efficiency of an increase in CI versus SVRI in improving perfusion pressure (PP: calculated as MAP minus central venous pressure) by 25%, identifying inflection points corresponding to vasoplegic, mixed, and cardiac-dominant physiology. Patients were categorized into six states by combining RFR-defined etiology with perfusion status (PP ≥50 vs