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 classifications based on onset and underlying pathophysiology. 1

Type 1 Respiratory Failure (Hypoxemic)

• Defined by PaO2 < 8 kPa (60 mmHg) with normal or low PaCO2 1
• Results from failure to maintain adequate oxygenation despite normal or increased ventilatory effort 1
• Caused primarily by ventilation-perfusion (V/Q) mismatch, right-to-left shunts, diffusion impairment, or alveolar hypoventilation 1
• Common clinical scenarios include:
  • Acute respiratory distress syndrome (ARDS) 1
  • Pneumonia 1
  • Pulmonary edema 1
  • Pulmonary embolism 2

Type 2 Respiratory Failure (Hypercapnic)

• Defined by PaCO2 > 6.1 kPa (45 mmHg), often with concurrent hypoxemia 1
• Represents failure of ventilatory pump function 3
• Normal range for PaCO2 is 4.6-6.1 kPa (34-46 mmHg) 1
• Common causes include:
  • COPD exacerbations 1
  • Neuromuscular disorders 1
  • Chest wall deformities (scoliosis, thoracoplasty) 1
  • Obesity hypoventilation syndrome 4
  • Central nervous system depression 3

Acute vs. Chronic Respiratory Failure

• Acute respiratory failure:

  • Sudden onset with rapid deterioration of arterial blood gases 1
  • Often requires immediate intervention 5
  • May present as acute lung injury or severe asthma attack 5

• Chronic respiratory failure:

  • Develops gradually over time 3
  • Often involves compensatory mechanisms (e.g., renal bicarbonate retention) 1
  • May present with fewer symptoms despite significant blood gas abnormalities 3

• Acute-on-chronic respiratory failure:

  • Acute deterioration in patients with pre-existing chronic respiratory failure 5
  • Common in COPD exacerbations 1
  • Presents unique challenges due to altered baseline physiology 1

Pathophysiological Classifications

Hypercapnic Respiratory Failure

• Results from reduced alveolar ventilation for a given CO2 production 3
• Mechanisms include:
  • Mechanical defects of the respiratory system 4
  • Central nervous system depression 3
  • Imbalance between energy demands and supplies 3
  • Respiratory muscle fatigue 4
  • Increased work of breathing (e.g., in COPD with PEEPi) 1

Hypoxemic Respiratory Failure

• Can be further classified based on severity (e.g., mild, moderate, severe ARDS) 1
• May be refractory and life-threatening despite high FiO2 6
• Pathophysiological mechanisms include:
  • V/Q mismatch 1
  • Intrapulmonary shunting 1
  • Diffusion limitation 1
  • Alveolar hypoventilation 1

Clinical Implications and Management Considerations

• Type 1 (hypoxemic) failure:

  • Typically responds to oxygen therapy 1
  • May require high-flow oxygen or CPAP in severe cases 1
  • Refractory cases may need prone positioning or extracorporeal support 6

• Type 2 (hypercapnic) failure:

  • Requires cautious oxygen therapy (target SpO2 88-92%) 1
  • Non-invasive ventilation is first-line treatment when pH < 7.35 1, 4
  • Ventilator settings must accommodate for underlying pathophysiology (e.g., longer expiratory time in COPD) 4

• Monitoring requirements:

  • Regular assessment of arterial blood gases 1
  • Continuous pulse oximetry 1
  • Use of early warning scores like NEWS 1
  • Close monitoring for deterioration requiring escalation of care 1