Introduction CPAP treatment for symptomatic OSA improves sleepiness, and reduces vascular risk by reducing blood pressure (BP) and cholesterol. Minimally symptomatic OSA is far more prevalent than symptomatic disease, and treatment of this group is contentious. This trial describes the effect of CPAP on sleepiness and calculated vascular risk in minimally symptomatic OSA.
Methods 391 patients from 10 centres, with proven OSA (sleep study ODI>7.5 h), but insufficient sleepiness for CPAP (based on established evidence), were randomised (minimisation by ODI, recruiting centre, and cardiovascular risk score (Pocock)), to either 6 months CPAP (ResMed Autoset S8 Spirit), or standard care. CPAP training and fitting was according to local clinical practice. Co-primary outcomes were the mean changes in Epworth Sleepiness Score (ESS) and the vascular risk score (comprising age, sex, systolic BP, smoking, diabetes, total cholesterol, height, creatinine, LVH on ECG, previous MI or stroke) from baseline to 6 months (intention to treat analysis). Home BP was measured in triplicate three times daily over 7 days at baseline and after 6 months, and the weekly average was used for further analysis.
Results Of 391 randomised, 14 withdrew or were lost to follow-up and have been excluded from the primary analysis. 347 patients attended for their 6 month visit within the predefined time window. The study groups were well matched at baseline. Median CPAP use was 3.25 h/night. Full data on ESS and the cardiovascular risk score components were available from 341 and 310 patients respectively.
Sleepiness outcome CPAP reduced daytime sleepiness (mean (SE) ESS change with CPAP −1.68 (0.24); control +0.32 (0.22), mean difference −2.00, 95% CI −1.37 to −2.64, p<0.0001), a cost effective outcome (UK NICE criteria).
Cardiovascular risk outcome CPAP did not reduce cardiovascular risk score (mean (SE) cardiovascular risk score change with CPAP +0.08 (0.17); control −0.37 (0.17), mean difference +0.45, 95% CI −0.03 to +0.93, p=0.064); the small increase with CPAP is not clinically significant.
Conclusions 6 months of CPAP in minimally symptomatic OSA is associated with a cost effective reduction in daytime sleepiness, but does not reduce calculated cardiovascular risk.