Venous dimension of shock: Integrating arterial inflow and venous back-pressure in hemodynamic assessment

Table 1 Hemodynamic phenotypes based on disturbances in arterial inflow and venous pressure

Phenotype	Arterial inflow	Venous pressure	AVPG	Typical clinical settings	Key bedside features
Normal perfusion	Adequate	Normal	Preserved	No clinically relevant mismatch between arterial inflow and venous outflow	Normal perfusion markers, preserved urine output, stable mentation, and no evolving organ dysfunction
Reduced arterial inflow	Decreased	Normal or low	Decreased mainly from the arterial side	Hypovolemia, cardiogenic shock, and distributive shock with impaired effective flow	Hypotension, low cardiac output, elevated or rising lactate, prolonged capillary refill time, oliguria
Predominant venous congestion	Preserved or relatively preserved	Increased	Decreased mainly from the venous side	Right ventricular failure, pulmonary hypertension, obstructive shock, fluid overload, and over-resuscitated septic shock	Elevated or rising CVP, systemic venous congestion, abnormal venous Doppler or VExUS, oliguria, renal or hepatic dysfunction
Combined inflow-congestion failure	Decreased	Increased	Markedly decreased from both sides	Advanced heart failure, late septic shock after fluid loading, RV failure with impaired LV filling, and complex cardiopulmonary failure	Hypotension or low forward flow with systemic venous congestion, elevated CVP, organ dysfunction, and persistent hypoperfusion

Representative evidence supporting these phenotypes is drawn from studies and guidelines on shock classification, venous congestion, right ventricular failure, fluid responsiveness, and septic/cardiogenic shock phenotyping[1-4,9,10,13,17,27-30,34]. These phenotypes represent dominant patterns rather than mutually exclusive categories. Microcirculatory dysfunction may complicate any phenotype and should be suspected when tissue hypoperfusion persists despite apparent correction of arterial pressure, forward flow, and venous congestion. AVPG: Arterial-venous perfusion gradient; CVP: Central venous pressure; RV: Right ventricle; VExUS: Venous excess ultrasound.