Continuous Positive Airway Pressure

Continuous positive airway pressure (CPAP) is the primary treatment modality in patients with severe obstructive sleep apnoea syndrome, a condition in which the throat narrows or collapses repeatedly during sleep. ^[1] CPAP is the first-line treatment for patients with moderate to severe obstructive sleep apnea and works by ameliorating respiratory disturbances. ^[2] In an American Academy of Sleep Medicine clinical practice guideline, clinicians are recommended to use positive airway pressure, compared to no therapy, to treat obstructive sleep apnea in adults with excessive sleepiness. ^[3]

In obstructive sleep apnea, repeated upper-airway collapse causes intermittent hypoxia and hypercapnia, recurrent arousals, and increased respiratory effort, leading to secondary sympathetic activation, oxidative stress, and systemic inflammation. ^[1] During a titration study, CPAP pressure is increased until obstructive respiratory events such as apneas, hypopneas, respiratory effort-related arousals, and snoring are eliminated, maintaining upper airway patency. ^[4] CPAP remains the approved therapy capable of reversing most of the known molecular alterations driven by the intermittent hypoxia and oxidative stress of obstructive sleep apnea. ^[5]

CPAP ameliorates respiratory disturbances, leading to improvements in daytime sleepiness, quality of life, blood pressure, and cognition. ^[2] In a worldwide individual patient data meta-analysis of 36 randomised studies including 9434 patients, CPAP treatment was associated with blood pressure reduction mainly in patients with uncontrolled office blood pressure at baseline. ^[6] Clinical trials have not provided consistent evidence that CPAP improves cardiovascular outcomes, findings that might be explained by limitations in trial design and low levels of adherence to CPAP. ^[7] In a meta-analysis of 4186 participants with cardiovascular disease and obstructive sleep apnea, the first major adverse cardiac and cerebrovascular event was similar between CPAP and no-CPAP groups, but an on-treatment analysis showed that good adherence to CPAP (at least 4 hours per day) was associated with a reduced risk of such events (hazard ratio 0.69). ^[8]

Obstructive sleep apnea is associated with cardiovascular comorbidities including hypertension, arrhythmias, stroke, coronary heart disease, atherosclerosis, and overall increased cardiovascular mortality, as well as metabolic dysfunction. ^[1] Despite the high efficacy of CPAP to reverse upper airway obstruction, treatment effectiveness is limited by variable adherence, and when adherence is defined as more than 4 hours of nightly use, 46 to 83% of patients with obstructive sleep apnea have been reported to be nonadherent. ^[9] Whether treating sleep apnoea can fully reverse its chronic consequences remains to be established in adequately designed studies. ^[1]