Hemodynamic Parameters in Septic Shock
The correct answer is A: High cardiac output is the characteristic hemodynamic parameter in septic shock, which typically presents as a hyperdynamic state with elevated cardiac output, low systemic vascular resistance, and low pulmonary capillary wedge pressure despite adequate fluid resuscitation. 1
Understanding Septic Shock Hemodynamics
Septic shock represents a distributive shock state with distinct hemodynamic characteristics that differ fundamentally from other shock types:
Classic Hemodynamic Profile
Cardiac output is typically elevated (hyperdynamic state) with cardiac index often >4.5-6.0 L/min/m² in adequately resuscitated patients, representing the body's compensatory response to profound vasodilation 1, 2
Systemic vascular resistance (SVR) is markedly decreased, not elevated, due to inflammatory mediator-induced vasodilation—this is the hallmark of distributive shock 1, 3
Pulmonary capillary wedge pressure (PCWP) remains low to normal (target 8-12 mmHg) after adequate fluid resuscitation, not elevated, as septic shock does not involve primary cardiac pump failure 1, 4
Central venous pressure (CVP) should be normalized to 8-12 mmHg with fluid resuscitation, not low, as adequate preload is essential for maintaining the hyperdynamic state 1
Why the Other Options Are Incorrect
Option B: High Systemic Vascular Resistance
This is fundamentally wrong—septic shock is characterized by low SVR, not high SVR, which distinguishes it from cardiogenic or hypovolemic shock 1, 3
High SVR would indicate a hypodynamic state (phenotype 3), which represents only a minority of septic shock patients and typically indicates inadequate resuscitation or late-stage decompensation 5
Option C: High Pulmonary Capillary Wedge Pressure
Elevated PCWP suggests cardiogenic shock or fluid overload, not septic shock 4
The Surviving Sepsis Campaign targets PCWP of 12-15 mmHg maximum during resuscitation, not elevated values 1, 4
Option D: Low Central Venous Pressure
Low CVP indicates inadequate fluid resuscitation, not a characteristic of properly managed septic shock 1
Initial resuscitation targets CVP of 8-12 mmHg to ensure adequate preload for the hyperdynamic circulation 1, 4
Hemodynamic Subphenotypes in Septic Shock
Recent evidence identifies four distinct hemodynamic patterns, with the hyperdynamic state being most common 5:
Hyperdynamic subphenotype (most common): Highest cardiac output with lowest SVR—this is the classic presentation 5
High preload subphenotype: Characterized by elevated filling pressures 5
Hypodynamic subphenotype: Lowest cardiac output with highest SVR, indicating inadequate resuscitation or myocardial depression 5
Preserved subphenotype: Relatively normal parameters but still requiring vasopressor support 5
Clinical Implications for Management
The hyperdynamic state with high cardiac output requires vasopressor support (norepinephrine first-line) to increase SVR and restore adequate perfusion pressure, targeting MAP ≥65 mmHg 1, 6
Aggressive fluid resuscitation (minimum 30 mL/kg crystalloid within 3 hours) is essential to achieve and maintain the hyperdynamic state 1
Inotropic support (dobutamine) is reserved for the minority of patients with true myocardial dysfunction and low cardiac output despite adequate preload 1
Common Pitfall to Avoid
Do not assume all septic shock patients are hyperdynamic—approximately 20-40% may present with or develop a hypodynamic state (low cardiac output, high SVR), particularly early in resuscitation or with concurrent myocardial depression, requiring different therapeutic approaches including inotropic support 4, 5. However, the question asks about characteristic parameters, and high cardiac output remains the defining hemodynamic feature of adequately resuscitated septic shock 1, 2.