Sleep and Breathing Disorders: OSA, Hypoventilation, and Positive Pressure
Sleep and breathing disorders test the diagnosis and management of obstructive sleep apnoea, central sleep apnoea, obesity hypoventilation, and sleep-related hypoventilation. Expect questions on sleep studies, positive airway pressure, and driving safety.
Core rules
- OSA diagnosis combines symptoms (snoring, witnessed apnoeas, daytime sleepiness) with an apnoea–hypopnoea index (AHI) ≥5; severity is mild 5–14.9, moderate 15–29.9, severe ≥30 events per hour.
- Home sleep apnoea testing is useful in high-probability OSA without major comorbidity; in-hospital polysomnography is preferred when other sleep disorders or significant cardiorespiratory disease are suspected.
- CPAP is first-line for symptomatic moderate-to-severe OSA; weight loss, positional therapy, and mandibular advancement devices are alternatives in selected patients.
- Obesity hypoventilation syndrome requires awake PaCO2 >45 mmHg plus obesity and exclusion of other causes.
Worked example
A 52-year-old with BMI 36, loud snoring, witnessed apnoeas, and Epworth score 16 has an AHI of 22 on home testing. This is moderate OSA. Discuss CPAP, weight loss, and driving advice; screen for hypertension and diabetes. If daytime hypercapnia is present, check awake PaCO2 to exclude OHS.
Traps
Diagnosing OSA on symptoms alone; ignoring central apnoeas or Cheyne–Stokes respiration; missing OHS in a sleepy obese patient; and failing to advise about driving.