Difference Between Type 1 and Type 2 Respiratory Failure
Type 1 respiratory failure is defined by a PaO2 of <8 kPa with a normal or low PaCO2, while type 2 respiratory failure is defined by a PaO2 of <8 kPa and a PaCO2 of >6 kPa. 1
Pathophysiological Differences
Type 1 Respiratory Failure (Hypoxemic)
- Definition: PaO2 < 60 mmHg or SaO2 < 88% with normal or low PaCO2 2
- Mechanisms:
- Ventilation/perfusion (V/Q) mismatch
- Anatomical shunt
- Diffusion limitation
- Low inspired oxygen tension
- Common causes:
- Pneumonia
- Pulmonary edema
- Acute respiratory distress syndrome (ARDS)
- Pulmonary embolism
- Asthma (early stages)
Type 2 Respiratory Failure (Hypercapnic)
- Definition: PaCO2 ≥ 45 mmHg and pH < 7.35, with or without hypoxemia 2
- Mechanisms:
- Alveolar hypoventilation
- Increased dead space ventilation
- Increased CO2 production
- Common causes:
- COPD exacerbation
- Severe asthma
- Neuromuscular disorders
- Central nervous system depression
- Chest wall deformities
- Obesity hypoventilation syndrome
Clinical Presentation Differences
Type 1 Respiratory Failure
- Tachypnea
- Increased work of breathing
- Hypoxemia-related symptoms (confusion, restlessness)
- Usually normal or low PaCO2 due to compensatory hyperventilation
Type 2 Respiratory Failure
- Signs of hypercapnia:
- Headache
- Confusion
- Somnolence
- Asterixis (flapping tremor)
- Papilledema (in severe cases)
- May have concurrent hypoxemia
- Respiratory acidosis on arterial blood gas
Management Approaches
Type 1 Respiratory Failure
- Oxygen therapy targeting SpO2 94-98% in most patients 3
- For moderate hypoxemia: simple face mask at 5-6 L/min
- For severe hypoxemia: reservoir mask at 15 L/min
Type 2 Respiratory Failure
- Cautious oxygen therapy targeting SpO2 88-92% to avoid worsening hypercapnia 3
- Recommended devices:
- 24% Venturi mask at 2-3 L/min
- Nasal cannulae at 1-2 L/min
- Non-invasive ventilation (NIV) for respiratory acidosis (pH 7.25-7.35) 3
- Invasive mechanical ventilation when NIV fails, in severe acidosis (pH < 7.25), altered mental status, or hemodynamic instability 3
Monitoring Considerations
Type 1 Respiratory Failure
- Regular monitoring of oxygen saturation
- Arterial blood gases to assess oxygenation
- Close observation for signs of deterioration
Type 2 Respiratory Failure
- Continuous monitoring of oxygen saturation
- Regular arterial blood gas measurements to monitor pH and PaCO2
- Vigilance for signs of increasing CO2 retention (drowsiness, confusion)
- Serum bicarbonate levels (cutoff of 27 mmol/L) can help detect hypercapnia 3
Potential Complications
Type 1 Respiratory Failure
- Progression to multi-organ dysfunction
- Development of ARDS
- Secondary infections
Type 2 Respiratory Failure
- Respiratory acidosis
- Respiratory arrest
- Cor pulmonale (in chronic cases)
- CO2 narcosis
Common Pitfalls to Avoid
Excessive oxygen in Type 2 respiratory failure: High-flow oxygen can suppress respiratory drive in patients with chronic CO2 retention, worsening hypercapnia.
Delayed recognition of Type 2 respiratory failure: Patients may not appear severely distressed despite significant hypercapnia.
Failure to recognize mixed respiratory failure: Many patients have elements of both types, especially as disease progresses.
Overlooking Type 2 respiratory failure in patients without obvious respiratory symptoms: Patients with neuromuscular diseases, chest wall deformity, obesity, or acute confusional states may have respiratory failure without significant breathlessness 1.
Relying solely on pulse oximetry: This can miss hypercapnia, making arterial blood gas analysis essential for complete assessment.