Sleep disorders - sleep apnoea
Description
Definitions
- Apnoea - >=90% airflow reduction for >=10 s
- Hypopnoea - >=30% airflow reduction for >=10 s + >=3% desaturation or arousal
- AHI = apnoeas + hypopnoeas per hour of sleep
- RDI = AHI + respiratory effort-related arousals
- ODI = >=3% or 4% desaturation dips per hour (the 4% ODI correlates best with cardiovascular outcome)
- T90 - % of sleep time with SpO2 <90% (hypoxic burden predicts cardiovascular risk better than AHI)
Types
| Effort | Mechanism | |
|---|---|---|
| Obstructive (OSA) | Present (paradoxical thoraco-abdominal movement) | Pharyngeal collapse despite drive |
| Central (CSA) | Absent | Absent or unstable respiratory output |
| Mixed | Central onset, obstructive end | Both |
| Obesity hypoventilation (OHS) | - | BMI >30 + awake PaCO2 >45 + no other cause |
Severity by AHI
| Normal | Mild | Moderate | Severe |
|---|---|---|---|
| <5 | 5-15 | 15-30 | >30 |
- *AHI correlates poorly with symptoms.* Treat the patient, not the number
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