Aim: It has been suggested that obese patients with obstructive sleep apnoea syndrome (OSAS) have an overall greater adherence with continuous positive airway pressure (CPAP) than their non-obese counterparts. We wanted to evaluate this hypothesis further.

Methods: Consecutive patients diagnosed with OSAS (apnoea-hypopnea index [AHI]> 15) and initiated on treatment with CPAP over a period of 1 year were included in this study. Adherence to treatment, documented by usage on the inbuilt clock on the CPAP machines (in average hours per night), was evaluated at 1 week and at 1 year. Patient demographics, BMI (obesity defined as BMI ?30), AHI and CPAP usage (average hours per night) data was collected.

Results: 285 patients (obese 241; mean age 57 years; and 73% males) were included in this study. AHI was significantly higher in the obese group (38.5 vs. 28.2, p=.004). One-week CPAP adherence in obese and non-obese groups were 6.05 and 5.87 respectively (p=0.55); at one-year this was 5.48 vs. 4.68 (p=.038). 38 patients (31 in the obese and 7 in the non-obese; p=ns) had adherence of <4hrs/night at 1 week; adherence at 1 year in this group continued to be lower (3.49 vs. 5.98 in the obese group, p <0.001; and 4.68 vs. 5.87 in the non-obese group, p < 0.001), compared to those with ?4hours / night.

Conclusion: Our data demonstrates that non-obese OSAS patients have a poorer long-term CPAP compliance than obese OSAS patients. We also observed that <4hrs/night usage of CPAP short-term was a predictor of sub-optimal adherence longer-term as well, irrespective of BMI. These groups of patients may benefit from further interventions to improve outcomes.