Is obstructive sleep apnoea a rapid eye movement-predominant phenomenon?

Obstructive sleep apnoea (OSA) is thought to be worse during rapid eye movement (REM) sleep. REM rebound in the late postoperative period can follow the REM suppression shown to occur after some types of surgery. This is thought to worsen nocturnal episodic hypoxaemia, leading to greater cardio-respiratory risk. We set out to determine if OSA was a REM-predominant phenomenon. We reviewed the sleep clinic records of 64 consecutive patients with a diagnosis of OSA on full overnight polysomnography and sufficient data to determine the presence of a sleep stage predominance. OSA was diagnosed if the number of apnoeas/hypopnoeas per hour of sleep, the respiratory disturbance index (RDI), was greater than 10. The variables recorded for the purposes of this study were the RDI and the minimum blood oxygen saturation using pulse oximetry (Sp(O2min)) for both REM and non-rapid eye movement (NREM) sleep. All values are presented as mean (SD). The Wilcoxon signed rank test was used for statistical analysis. The means for NREM and REM RDI were, respectively, 36 (26) and 38 (27) per hour (P=0.96). In 32 of the 64 patients (50%) the RDI in NREM was greater than in REM. Thirty-one (48%) had a larger number during REM. One patient had identical RDIs for both REM and NREM. Sixty-two patients had satisfactory pulse oximetry recordings for both NREM and REM, and the mean Sp(O2min) values were, respectively, 84 (7) and 82 (13)% (P=0.15). Twenty-nine patients (47%) had a lower Sp(O2min) in REM (seven by more than 10% and two by more than 40%), while 24 (39%) were lower in NREM (two by more than 10%). Nine patients (14%) had identical values in REM and NREM. In contrast to suggestions that OSA is a REM-predominant phenomenon, this study suggests that respiratory disturbance is not greatly affected by sleep stage, in most patients. While a small number clearly desaturate much more during REM, the majority do not. Thus, postoperative REM rebound may worsen OSA in some patients, but in many it may do otherwise. The implications of postoperative sleep disturbance are therefore likely to be more complex than previously suggested.