Positive airway pressure for obstructive sleep apnoea : systematic evaluation versus clinical and technological drift : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Public Health at Massey University, Wellington Campus, New Zealand
The practice of sleep medicine is expanding and evolving rapidly, often ahead of the evidence base to support clinical practice. Obstructive Sleep Disordered Breathing (SDB) is a condition characterised by repetitive airway collapse causing harmful intermittent blood oxygen desaturations and fragmented sleep. When combined with daytime sleepiness it is known as Obstructive Sleep Apnoea Syndrome (OSAS). Continuous Positive Airway Pressure (CPAP) eliminates SDB by pneumatically splinting open the airway with positive air pressure applied through the nose and/or mouth. CPAP effectively reduces daytime sleepiness in patients with severe OSAS. However, doubt remains as to the effectiveness of CPAP in the majority of patients with mild-moderate OSAS. The effects of CPAP were compared to a placebo CPAP during a three week crossover Randomised Controlled Trial (RCT) that included 31 mild-moderate OSAS patients. CPAP effectively eliminated SDB (when worn) and moderately improved subjective sleepiness. But. it did not improve objective wakefulness, mood, psychomotor function, or quality of life. Patients who were extremely sleepy at baseline tended to gain the most placebo adjusted benefit from treatment. A systematic review and meta-analysis aimed to gather and objectively combine all relevant RCT studies to find our whether CPAP reduced sleepiness in patients with mild-moderate OSAS. Seven trials were combined and showed that both subjective sleepiness and objective wakefulness were slightly improved by CPAP therapy. Objective sleepiness was not improved by CPAP. It is not clear from these two studies that treating mild-moderate OSAS with CPAP is an effective use of resources. CPAP effectiveness might be limited by sub-optimal compliance. C-Flex aims to improve compliance by modulating pressure during exhalation. C-Flex was compared to CPAP during a pilot RCT that included 19 patients with severe OSAS. C-Flex was associated with a non-significant increase in compliance of 1.7 hours/night compared to CPAP. However, this increase in compliance was not associated with better daytime patient outcomes. Further experiments are proposed as a result of our pilot RCT. This thesis helps expand evidence-based sleep medicine. Practitioners need to be vigilant, ensuring that treatments are effective in the patients groups in which they are being used (clinical drift), and that new treatments are not adopted without superiority over existing treatments (technological drift).
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