Hypoxia episodes during sleep in high tetraplegia

To determine whether oxygen desaturation occurs during sleep in high tetraplegics, 10 neurologically stable male patients (aged 17 to 55 years) with complete motor lesions (C4 to C6) had continuous pulse oximetry recordings and sleep observations on two nights. The patients were studied during admissions for nonrespiratory problems (eg, pressure sores, urinary infection, respite). Lung function tests and daytime arterial blood gases were also measured. Mean forced vital capacity was 46% of predicted, but mean awake PaO2 and PaCO2 were normal (95.0 mmHg and 42.8 mmHg, respectively). Three subjects showed severe nocturnal oxygen desaturation spending greater than 10% of the time overnight with arterial oxyhaemoglobin saturation (SaO2) levels of less than 90%. For the group as a whole, the percentage of time spent under 90% SaO2 correlated with body mass index. Mean overnight SaO2 correlated inversely with body mass index and directly with maximal expiratory pressure, a measure of respiratory muscle strength. Low overnight SaO2 was also associated with higher levels of injury. The pattern of nocturnal oxygen desaturation observed was episodic and was suggestive of obstructive sleep apnoea during rapid eye movement (REM) sleep. Levels of nocturnal oxygen desaturation similar to those observed in the three most severely affected patients have been shown, in other disorders, to be associated with cognitive impairment, cardiovascular disease and increased mortality. Our results suggest up to a third of high tetraplegics may be at risk of potentially serious nocturnal hypoxic episodes.