Synopsis
Detect obesity-related awake ventilatory failure, separate it from uncomplicated sleep apnoea and other causes, and select CPAP, NIV, oxygen and weight care safely.
- OHS is obesity with awake alveolar hypoventilation after excluding another primary cause; it is not synonymous with obesity plus snoring.
- Most people with OHS also have OSAHS, but some have predominantly non-obstructive sleep hypoventilation and need a different positive-pressure strategy.
- Clues include morning headache, hypersomnolence, dyspnoea, oedema, hypoxaemia, raised serum bicarbonate and unexplained secondary polycythaemia or pulmonary hypertension.
Key red flags
Infection, fluid overload, sedatives or uncontrolled oxygen can precipitate drowsiness, worsening hypercapnia and acidaemia; absence of dramatic wheeze does not make this less urgent.
Investigation priorities
Confirm daytime hypercapnia and quantify acute or chronic compensation.
Management branches
Obesity coexists with low saturation, raised bicarbonate, sleepiness or morning headache.
- Assess symptoms, respiratory rate, oedema, OSAHS features, medicines, alcohol and prior gases, treating acute decompensation before elective work-up.
- Measure awake arterial or arterialised capillary gas and document oxygen exposure; use bicarbonate only as a screening bridge, not the final diagnosis.
OHS is confirmed outside acute ventilatory failure.
Key medicines
CPAP for OHS with severe OSAHSUse the sleep-service-titrated fixed or auto-adjusting pressure throughout sleep as first-line stable treatment when severe obstructive events predominate.
Bilevel non-invasive ventilationUse the specialist-selected interface, inspiratory and expiratory pressures and backup rate nightly, with daytime support added only when clinically prescribed.