What are the differences between acute respiratory distress syndrome (ARDS) and heart failure?

Distinguishing ARDS from Heart Failure

ARDS and heart failure both present with bilateral pulmonary infiltrates and respiratory distress, but ARDS is defined by the explicit exclusion of cardiac failure as the primary cause of pulmonary edema, whereas heart failure produces cardiogenic pulmonary edema from elevated left atrial pressures. 1, 2

Key Diagnostic Differences

Mechanism of Pulmonary Edema

• ARDS: Non-cardiogenic pulmonary edema caused by inflammatory injury to the alveolar-capillary membrane, resulting in increased vascular permeability 2, 3

  • Leukocyte infiltration and local immune activation damage both vascular endothelium and alveolar epithelium
  • Leads to protein-rich fluid accumulation in alveoli

• Heart Failure: Cardiogenic pulmonary edema from elevated left atrial and pulmonary capillary wedge pressures 1

  • Hydrostatic pressure forces fluid into alveoli
  • Typically shows signs of fluid overload systemically

Clinical Presentation Patterns

ARDS characteristics:

• Acute onset within 1 week of known clinical insult (sepsis, pneumonia, trauma, aspiration) 1, 2
• Profound hypoxemia (PaO2/FiO2 ≤ 300 mmHg with minimum 5 cmH2O PEEP)
• Bilateral opacities on chest imaging
• Absence of clinical signs suggesting left atrial hypertension as primary cause 1
• Mortality 30-45% 1, 2

Heart Failure characteristics:

• Clinical signs of volume overload (elevated jugular venous pressure, peripheral edema, S3 gallop) 4, 5
• May have chronic progressive course or acute decompensation
• Responds to diuresis and afterload reduction
• Elevated BNP/NT-proBNP levels

Critical Diagnostic Pitfall

The two conditions can coexist 6. Approximately 6.3% of ARDS patients have comorbid congestive heart failure, and congestive heart failure can aggravate the non-cardiogenic pulmonary edema of ARDS 6. The Berlin definition explicitly states that bilateral opacities must be "not entirely explained by cardiac failure or fluid overload" 1—meaning some cardiac contribution may be present, but it cannot fully account for the clinical picture.

Practical Differentiation Algorithm

When bilateral infiltrates and hypoxemia are present:

1. Assess for known ARDS risk factors (within past week):

   • Pneumonia or sepsis (most common) 5, 3
   • Aspiration, trauma, pancreatitis, blood transfusion
   • If absent, heart failure becomes more likely

2. Evaluate cardiac function and volume status:

   • Echocardiography: Assess left ventricular function and filling pressures
   • Clinical examination: Look for jugular venous distension, peripheral edema, hepatomegaly
   • BNP/NT-proBNP: Elevated in heart failure
   • If these suggest primary cardiac etiology with adequate explanation for pulmonary edema, diagnosis is heart failure

3. Assess response to diuresis:

   • Heart failure typically improves with diuretics
   • ARDS shows minimal response to diuretics alone and may worsen with aggressive fluid removal 7

4. Timing and progression:

   • ARDS: Rapid onset (hours to days) after identifiable insult
   • Heart failure: May be more gradual or have chronic baseline dysfunction

Management Implications

The distinction matters critically for treatment:

• ARDS management 1, 8, 3:

  • Lung-protective ventilation (low tidal volume 6 mL/kg predicted body weight)
  • Higher PEEP strategies
  • Prone positioning for severe cases
  • Conservative fluid management (avoid overload but maintain perfusion)
  • Corticosteroids for PaO2/FiO2 < 300

• Heart Failure management 4:

  • Diuresis for volume overload
  • Afterload reduction
  • Guideline-directed medical therapy
  • Address underlying cardiac dysfunction

When both conditions coexist, management becomes more complex and requires balancing lung-protective strategies with appropriate cardiac support, avoiding both fluid overload and inadequate perfusion 7, 6.