Factors influencing severity of obesity hypoventilation syndrome: a proposal for classification based on functional parameters
| Mild | Moderate | Severe | |
| Pa,CO2 mmHg | 46–60 | 60–80 | ≥80 |
| Pa,O2 mmHg | ≥70 | 60–70 | ≤60 |
| BMI kg·m−2 | 30–40 | 40–50 | ≥50 |
| AHI events·h−1 | <5 | 5–15 | >15 |
| Complications or comorbidities | No | No | Yes |
Pa,CO2: arterial carbon dioxide tension; Pa,O2: arterial oxygen tension; BMI: body mass index; AHI: apnoea/hypopnoea index. 1 mmHg = 0.133 kPa.