obesity hypoventilation syndrome (OHS)

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Obesity hypoventilation syndrome (OHS)

  • is defined as the combination of obesity (body mass index [BMI] of 30 kg/m2 or more), raised arterial or arterialised capillary carbon dioxide (CO2) level when awake, and breathing abnormalities during sleep, which may consist of obstructive apnoeas and hypopnoeas, or hypoventilation, or a combination of both. OHS is a specific formInitial assessment for OHS

When to suspect OHS

  • take a sleep history and assess people for OHS if they have a BMI of 30 kg/m2 or more with:
    • features of obstructive sleep apnoea/hypopnoea syndrome of chronic ventilatory failure
      • take a sleep history and assess people for OSAHS if they have 2 or more of the following features:
        • snoring
        • witnessed apnoeas
        • unrefreshing sleep
        • waking headaches
        • unexplained excessive sleepiness, tiredness or fatigue
        • nocturia (waking from sleep to urinate)
        • choking during sleep
        • sleep fragmentation or insomnia
        • cognitive dysfunction or memory impairment
    • features of nocturnal hypoventilation such as:
      • waking headaches
      • peripheral oedema
      • hypoxaemia (arterial oxygen saturation less than 94% on air)
      • unexplained polycythaemia

Assessment scales for suspected OSAHS

  • when assessing people with suspected OSAHS:
    • use the Epworth Sleepiness Scale in the preliminary assessment of sleepiness
    • consider using the STOP-Bang Questionnaire as well as the Epworth Sleepiness Scale
    • do not use the Epworth Sleepiness Scale alone to determine if referral is needed, because not all people with OSAHS have excessive sleepiness


Last edited 09/2021 and last reviewed 10/2021