Nocturnal hypoxaemia in severe scoliosis

The relationship between spirometry and daytime blood gases on the one hand and hypoxaemia during sleep on the other was studied in 13 patients with severe thoracic scoliosis. Eight patients had hypoxaemia (mean Sao₂<90%) during sleep. They were characterized by a lower vital capacity (30 versus 50% of predicted, P<0.01) and by a greater fall in vital capacity from sitting to supine (26 versus 7% of sitting VC, P<0.05). All patients with hypoxaemia during sleep were hypercapnic during the daytime. The fall in Sao₂ with sleep was related to the increase in transcutaneous Pco₂, indicating hypoventilation as the main mechanism behind hypoxaemia during sleep in scoliosis patients.