Sleep apnoea in patients following stroke

Introduction: Sleep apnoea is commonly found in patients following stroke, with some studies reporting a prevalence >70% shortly after the event. We have recently shown a lower prevalence of 43%, in good outcome stroke patients at 3 months, a value not significantly different from controls. We have investigated whether the discrepancy may be related to improvement in sleep apnoea paralleling functional improvement, or to survival bias with sleep apnoea being associated with poorer outcome. Methods: Inpatients with acute stroke underwent sleep studies (ResMed Autoset II) at week 2 and 6 post onset. Change in Apnoea-Hypopnoea Index (AHI) was determined for patients with paired studies. The initial AHIs of survivors and those who died within 3 months were compared. Results: Of 32 patients undergoing a first study, repeat studies were unobtainable on four patients, three died and two suffered a second stroke prior to the second study. Three further patients, including both patients with recurrent stroke, died subsequent to the second study but still within 3 months of onset. The median AHI of the 32 patients studied at week 2 was 23. Nineteen of the 23 (72%) patients who underwent two valid studies showed an reduction in AHI, p<0.05 (Wilcoxon Signed Rank). However the magnitude of the improvement was small (Week 2: median AHI 23, mean 29) vs (Week 6: median 21, mean 23). The AHI at week 2 of patients who subsequently died (n=6) was significantly greater than that of survivors (median 49.5 vs. 22, p<0.001). Conclusions: These results suggest that the apparent reduction in severity of sleep apnoea during the first weeks after stroke is due mainly to survivor bias, together with a small improvement in AHI in those who survive.