Study designs of evaluations included in the review
Prospective studies were eligible for inclusion, whereas case reports were excluded. Most of the included studies were before-and-after studies; other designs included randomised controlled trials (RCTs) and parallel cohort studies.
Specific interventions included in the review
Studies of CPAP were eligible for inclusion if they reported titration of CPAP level until the Apnea-Hypopnea Index (AHI) was less than 5; studies of bilevel positive airway pressure were excluded. The review defined CPAP treatment as positive airway pressure delivered through a nasal mask, nasal prongs, or a full-face mask. The duration of CPAP in the included studies ranged from one night to one year (mean 4.9 months). The comparison groups involved no CPAP, subtherapeutic CPAP, ranitidine, placebo tablet, nasal strips, and sleep hygiene plus weight loss.
Participants included in the review
Studies of adults (older than 18 years) with OSAHS (defined as an AHI of more than 5 events per hour) were eligible for inclusion. Studies of patients with central sleep apnoea, Cheyne Stokes respiration, upper airways resistance syndrome, or obstructive sleep apnoea due to neuromuscular, cardiac or renal disease, were excluded. Most of the participants (85%) in the included studies were male. One study used people without OSAHS as the comparison group.
Outcomes assessed in the review
Studies that assessed standardised neurobehavioural outcomes appropriate for assessing sleep apnoea, which were consistent with the classification described by the American Thoracic Society (ATS) and American Sleep Disorders Association (ASDA), were eligible for inclusion. The review assessed performance (encompassing psychomotor and cognitive measures such as measures of learning and integrative functions), neurophysiological outcomes renamed as psychological outcomes, sleepiness and quality of life. The review excluded assessments of physiological measures of sleepiness, e.g. the multiple sleep latency test and the maintenance of wakefulness test.
The included studies used fourteen different parameters of performance (measured using 36 different instruments), eleven different instruments (plus numerous subscales) to assess psychological outcomes, four instruments to measure sleepiness, and four instruments to measure quality of life.
How were decisions on the relevance of primary studies made?
Three reviewers independently retrieved potentially relevant studies for inclusion. Any disagreements were resolved through consensus.