Hypoventilation syndromes

Hypoventilation syndrome comprises disorders associated with alveolar hypoventilation (an elevation in PaCO₂ to levels >45 mmHg). Hypoxaemia is also present in most cases, especially during sleep (PaO₂ <60 mmHg).

Alveolar hypoventilation can occur with obesity hypoventilation syndrome, restrictive thoracic disorders, central sleep apnoea syndromes, and COPD.

Symptoms are often non-specific, but almost always include disturbed sleep and impaired daytime function.

Physical examination often reveals signs of cor pulmonale in addition to those associated with the primary disorder.

Diagnosis is usually made by the clinician's awareness that alveolar hypoventilation is often associated with certain medical disorders. Investigations include arterial blood gas analysis, pulmonary function tests, measurement of respiratory muscle strength, and an overnight polysomnogram.

Treatment involves nocturnal ventilation, including the use of invasive ventilation.

Alveolar hypoventilation, defined as an elevation in PaCO₂ to levels >45 mmHg, can occur with several disorders: obesity hypoventilation syndrome, restrictive thoracic disorders, central sleep apnoea syndromes, and COPD.[1]American Academy of Sleep Medicine. International classification of sleep disorders. 3rd ed, text revision. Darien, IL: American Academy of Sleep Medicine; 2023.​ These are referred to as the hypoventilation syndromes. Associated with hypercapnia is the development of hypoxaemia, which adds to the clinical manifestations and morbidity. In addition, during sleep, hypoventilation becomes more profound and can worsen pre-existing hypercapnia and hypoxaemia. In some cases, hypercapnia and hypoxaemia may develop only during sleep, which may be unsuspected based on awake values.​