What are the types of respiratory failure?

Types of Respiratory Failure

Respiratory failure is classified into two main types: Type 1 (hypoxemic) and Type 2 (hypercapnic), with additional categories including acute, chronic, and acute-on-chronic respiratory failure based on their presentation and pathophysiology. 1

Type 1: Hypoxemic Respiratory Failure

• Definition: PaO₂ < 60 mmHg (8 kPa) or SaO₂ < 88% with normal or low PaCO₂ 1, 2
• Pathophysiology: Results from:
  • Ventilation/perfusion (V/Q) mismatch
  • Shunt
  • Diffusion limitation
  • Low inspired oxygen tension 2
• Common causes:
  • Pneumonia
  • Pulmonary edema
  • Acute respiratory distress syndrome (ARDS)
  • Pulmonary embolism
  • Severe asthma
• Management approach:
  • Target SpO₂ 94-98% for most patients 1, 3
  • Oxygen therapy via appropriate device based on severity:
    • Nasal cannula (1-6 L/min) for mild hypoxemia
    • Simple face mask (5-10 L/min) for moderate hypoxemia
    • Reservoir mask (15 L/min) for severe hypoxemia 3

Type 2: Hypercapnic Respiratory Failure

• Definition: PaCO₂ ≥ 45 mmHg (6 kPa) with pH < 7.35 4, 2
• Pathophysiology: Results from:
  • Alveolar hypoventilation
  • Increased dead space ventilation
  • Increased CO₂ production 2
• Common causes:
  • COPD exacerbation
  • Severe asthma
  • Neuromuscular disorders
  • Chest wall deformities (e.g., kyphoscoliosis)
  • Obesity hypoventilation syndrome
  • Drug overdose 1, 5
• Management approach:
  • Target SpO₂ 88-92% to avoid worsening hypercapnia 1, 3
  • Controlled oxygen therapy (24-28% Venturi mask) 1, 3
  • Non-invasive ventilation (NIV) for respiratory acidosis (pH 7.25-7.35) 1, 4
  • Consider respiratory stimulants if pH < 7.25 (H⁺ > 55 nmol/L) 6
  • Invasive ventilation if NIV fails or severe acidosis persists 3

Acute vs. Chronic Respiratory Failure

Acute Respiratory Failure

• Sudden onset (minutes to hours)
• Minimal compensatory mechanisms
• Often life-threatening
• Requires immediate intervention

Chronic Respiratory Failure

• Develops over time (days to months)
• Compensatory mechanisms present:
  • Renal bicarbonate retention in chronic hypercapnia
  • Polycythemia in chronic hypoxemia
• Often managed with long-term oxygen therapy and/or NIV

Acute-on-Chronic Respiratory Failure

• Acute worsening of pre-existing chronic respiratory failure
• Common in COPD exacerbations
• Requires careful oxygen titration to avoid worsening hypercapnia
• Higher risk of requiring ventilatory support 1

Special Considerations in Management

For Type 1 (Hypoxemic) Respiratory Failure:

• Treat underlying cause (antibiotics for pneumonia, diuretics for pulmonary edema)
• Consider prone positioning for severe ARDS 7
• Consider inhaled vasodilators as rescue therapy for refractory hypoxemia 7
• Extracorporeal life support for severe cases unresponsive to conventional therapy 7

For Type 2 (Hypercapnic) Respiratory Failure:

• NIV is first-line therapy for COPD exacerbation with respiratory acidosis 1, 5
• Avoid excessive oxygen (can worsen hypercapnia in COPD) 1
• Monitor arterial blood gases to assess response to therapy 1
• Consider extracorporeal CO₂ removal for refractory hypercapnia 5

Risk Factors for Poor Outcomes in Respiratory Failure

• Older age
• Severe acidosis (pH < 7.25)
• Hypotension
• Renal failure
• Multiple organ dysfunction
• Failure to improve within 24 hours of appropriate therapy 6

Monitoring Requirements

• Continuous pulse oximetry
• Regular vital sign checks (every 15-30 minutes until stable)
• Serial arterial blood gas measurements to assess:
  • Oxygenation
  • Ventilation
  • Acid-base status
• Use of physiological 'track and trigger' systems (e.g., NEWS) 1, 3

Understanding the type of respiratory failure is crucial for appropriate management, as treatment strategies differ significantly between hypoxemic and hypercapnic respiratory failure, with oxygen therapy targets and ventilation approaches tailored to the specific pathophysiology.