Level 1: Likely reliable evidence
Continuous positive airway pressure (CPAP) has been found to be effective in reducing sleepiness and improving quality of life in moderate-to-severe obstructive sleep apnea (OSA), based on a systematic review of 36 randomized trials that evaluated nocturnal CPAP (for at least two weeks) in 1,718 adults with OSA (Cochrane Database Syst Rev. 2006:CD001106). Compared with inactive control, CPAP improved objective and subjective sleepiness and several quality-of-life, cognitive-function, and depression measures; the Epworth Sleepiness Scale improved by 3.83 units (95% confidence interval [CI] 3.09-4.57, possible score range 0-24). Compared with oral appliances, CPAP significantly reduced the apnea-hypopnea index (AHI) by about eight events per hour in crossover trials, improved sleep efficiency by 2.31%, and improved minimum oxygen saturation by 4.14%. Patients strongly preferred oral appliances over CPAP when both were effective but were more likely to withdraw from a study when on an oral appliance than when on CPAP.
A subsequent systematic review and meta-analysis of seven randomized trials evaluated CPAP for at least one week in 418 adults with mild-to-moderate OSA (AHI 5-30 events per hour) (Thorax. 2006;61:430-434). CPAP reduced subjective daytime sleepiness by 1.2 points on the Epworth Sleepiness Scale (95% CI 0.5-1.9) but had no effect on objective daytime sleepiness. CPAP improved objective daytime wakefulness by 2.1 minutes (95% CI 0.5-3.7 minutes). These small effects may be of limited clinical significance.