How do you differentiate between septic and cardiogenic shock?

Differentiation Between Septic and Cardiogenic Shock

Septic shock and cardiogenic shock present with distinct hemodynamic patterns, clinical features, and laboratory findings that allow for accurate differentiation to guide appropriate management.

Key Hemodynamic Differences

Septic Shock

• Hemodynamic Profile: Characterized by distributive physiology with:
  • High cardiac output/cardiac index (>3.3 L/min/m²)
  • Low systemic vascular resistance (SVR)
  • Warm extremities (initially)
  • Normal or elevated mixed venous oxygen saturation (ScvO₂ >70%) 1
  • Hyperdynamic circulation in early stages

Cardiogenic Shock

• Hemodynamic Profile: Characterized by pump failure with:
  • Low cardiac output/cardiac index (<2.0 L/min/m²)
  • High systemic vascular resistance (compensatory)
  • Cold, clammy extremities
  • Low mixed venous oxygen saturation (ScvO₂ <70%) 2
  • High oxygen extraction ratio (average 48% vs. 24% in septic shock) 3

Clinical Features

Septic Shock

• Vital Signs:

  • Hypotension with wide pulse pressure
  • Tachycardia
  • Tachypnea
  • Fever (typically) or hypothermia

• Physical Examination:

  • Warm, flushed skin (early)
  • Bounding pulses (early)
  • Possible source of infection (pneumonia, urinary tract, abdominal, skin)
  • Normal heart sounds without murmurs or gallops

Cardiogenic Shock

• Vital Signs:

  • Hypotension with narrow pulse pressure
  • Tachycardia
  • Tachypnea

• Physical Examination:

  • Cold, clammy extremities
  • Weak, thready pulses
  • Jugular venous distention
  • Pulmonary crackles/rales
  • S3 gallop, murmurs, or other cardiac abnormalities
  • Hepatomegaly 2

Laboratory and Diagnostic Findings

Septic Shock

• Laboratory:

  • Leukocytosis or leukopenia
  • Elevated inflammatory markers (CRP, procalcitonin)
  • Positive blood cultures or other cultures
  • Elevated lactate (due to impaired oxygen utilization)
  • Metabolic acidosis

• Imaging/Diagnostics:

  • Evidence of infection source
  • Normal cardiac function on echocardiography (or sepsis-induced cardiomyopathy)

Cardiogenic Shock

• Laboratory:

  • Elevated cardiac biomarkers (troponin, BNP)
  • Elevated lactate (due to poor tissue perfusion)
  • Metabolic acidosis
  • Normal white blood cell count (unless concurrent infection)

• Imaging/Diagnostics:

  • Abnormal ECG (ST changes, arrhythmias)
  • Echocardiography showing reduced ejection fraction, wall motion abnormalities
  • Evidence of structural heart disease 2

Advanced Hemodynamic Monitoring

When clinical assessment is insufficient, advanced monitoring can help differentiate:

• Cardiac Output/Index: Low in cardiogenic shock, normal/high in septic shock
• SVR: High in cardiogenic shock, low in septic shock
• Pulmonary Artery Catheterization:
  • Cardiogenic shock: Elevated PCWP (>18 mmHg), low CO
  • Septic shock: Normal/low PCWP, normal/high CO 2

Response to Fluid Challenge

• Septic Shock: Often initially fluid responsive; requires large volume resuscitation (30+ mL/kg) 1
• Cardiogenic Shock: Minimal or negative response to fluid; may worsen with excessive fluid 2

Management Differences

Septic Shock

• Primary Interventions:
  • Early antibiotics within 1 hour
  • Source control
  • Aggressive fluid resuscitation
  • Vasopressors (norepinephrine first-line) 1

Cardiogenic Shock

• Primary Interventions:
  • Treat underlying cardiac cause
  • Cautious fluid management
  • Inotropic support
  • Afterload reduction when appropriate
  • Mechanical circulatory support if needed 2

Pitfalls to Avoid

1. Missing sepsis-induced cardiomyopathy: Septic shock can cause myocardial depression, creating a mixed shock picture 4

2. Overaggressive fluid resuscitation in cardiogenic shock can worsen pulmonary edema and hypoxemia

3. Inadequate fluid resuscitation in septic shock can lead to persistent hypoperfusion

4. Failure to recognize transition between shock states as patients may develop elements of both types during their clinical course

5. Relying solely on clinical appearance without advanced hemodynamic assessment in complex cases 2

Algorithm for Differentiation

1. Initial Assessment:

   • Evaluate vital signs, perfusion, and cardiac exam
   • Check for signs of infection vs. cardiac disease

2. Basic Investigations:

   • ECG, cardiac biomarkers, lactate, inflammatory markers
   • Cultures if infection suspected

3. Echocardiography:

   • Essential for evaluating cardiac function
   • Assess for wall motion abnormalities, valvular disease

4. Advanced Monitoring (if diagnosis remains unclear):

   • Measure cardiac output/index
   • Assess SVR
   • Evaluate ScvO₂

5. Therapeutic Trial:

   • Response to small fluid challenge (250-500 mL)
   • Response to vasopressors vs. inotropes

By systematically evaluating these parameters, clinicians can accurately differentiate between septic and cardiogenic shock to guide appropriate life-saving interventions.