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

BackgroundConventional 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. MethodsSingle-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 [&ge;]50 vs <50 mmHg). Transition dynamics were analyzed using Markov chain modeling. Agreement with conventional definitions of vasoplegia and cardiogenic shock was assessed using sensitivity, specificity, predictive values, and accuracy relative to RFR-PP defined states. ResultsOut of 10,338 cases, 3,378 met inclusion criteria. RFR thresholds of <400, 400-900, and >900 corresponded to vasoplegic, mixed, and cardiogenic shock, respectively. Conventional (decompensated) vasoplegia occurred in 19.4% of patients, versus 22.8% by RFR-PP criteria, while 39.9% met criteria for compensated vasoplegia. Decompensations occurred within the same RFR category in 65% of cases, validating physiologic separation of etiology from compensation. Markov chain modeling revealed a postoperative drift from pump-failure to vasoplegic states during the postoperative course. RFR-PP definitions showed greater sensitivity than conventional criteria while maintaining high specificity. ConclusionsThe RFR-PP framework quantitatively separates cardiac from vascular dysfunction, captures compensated precursor states, and links directly to therapeutic logic. RFR-PP could provide a scalable platform for real-time, physiology-based hemodynamic assessment and shock management.