Summary

• Alveolar hypoventilation is defined as an elevation in PaCO2 to levels >45 mmHg.
• Disorders that have associated alveolar hypoventilation make up what is referred to as the hypoventilation syndrome. These include obesity-hypoventilation syndrome, restrictive thoracic disorders, central sleep apnoea syndromes, and COPD.
• Hypoxaemia is often present, especially during sleep, and is associated with hypercapnia.
• 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.