Difference between type 1 and type 2 respiratory impairment
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type 1 type 2 respiratory failure hypoxemic hypercapnic definition official clinical reference
“Type 1” and “Type 2” usually refer to types of respiratory failure:
| Feature | Type 1 respiratory failure | Type 2 respiratory failure |
|---|---|---|
| Main problem | Failure of oxygenation | Failure of ventilation |
| ABG finding | PaO₂ < 60 mmHg on room air | PaCO₂ > 50 mmHg, usually with hypoxaemia |
| CO₂ level | Normal or low | Raised |
| Also called | Hypoxaemic respiratory failure | Hypercapnic respiratory failure |
| Typical mechanism | V/Q mismatch, shunt, diffusion impairment | Alveolar hypoventilation |
| Common causes | Pneumonia, pulmonary oedema, ARDS, pulmonary embolism, severe asthma | COPD exacerbation, severe asthma with fatigue, opioid/sedative effect, neuromuscular disease, obesity-hypoventilation, chest-wall disorders |
| Usual initial support | Oxygen and treatment of the lung cause | Controlled oxygen plus ventilatory support when needed, commonly NIV such as BiPAP |
Key distinction
- Type 1: low oxygen, but carbon dioxide removal is initially adequate.
- Type 2: carbon dioxide accumulates because ventilation is inadequate. It often causes drowsiness, headache, confusion, and CO₂ narcosis in severe cases.
They can coexist. For example, a person with a severe COPD exacerbation may have both low PaO₂ and high PaCO₂. The conventional thresholds are summarized in Current Surgical Therapy, 14e, which defines Type 1 as PaO₂ below 60 mmHg and Type 2 as PaCO₂ above 50 mmHg on room air. The Merck description of hypoxaemic failure gives the same Type 1 oxygenation threshold.
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