Background OSA is a significant public health problem which can be treated effectively with CPAP. Compliance of 4 h/night is required to achieve clinical effectiveness. Sleep clinics regularly monitor CPAP compliance subjectively, for example, patient questionnaires, but such estimates may differ from actual compliance.
Aim The aim of the study was to measure errors in estimating compliance and to look for regional variations in degrees of error.
Methods This is a prospective, two-centre study, carried out in 2009–2010. Centre 1 is a Tertiary centre with a local population including large numbers of South Asian people and those with lower socio-economic status. Centre 2 is a District General Hospital with a predominantly Caucasian local population. Both centres have similar sleep clinic setups and routinely download CPAP machine hours. Subjective compliance was assessed by patient questionnaires and objective evidence of compliance was obtained from machine usage data simultaneously.
Results 107 patients were included from each centre. In centre 1, 80% patients over-estimated their compliance, the mean objective usage of CPAP was 5.0 h/night and the mean error in estimating compliance was +2.2 h/night. In centre 2, 52% of patients over-estimated their compliance, the mean objective usage of CPAP was 5.67 h/night and the mean error in estimating compliance was +1.03 h/night. Patients in Centre 2 had significantly higher CPAP usage (5.67 vs. 5 h/night, p=0.02) and a lower percentage of people over-estimating their compliance (52% vs 80%, p<0.00001). Overall, there was still a significant error in estimating compliance, although this was lower in Centre 2 (1.03 vs 2.2 h/night, p<0.00001).
Discussion This study highlights the fact that patients tend to be significantly inaccurate about their compliance. Reasons for this are uncertain but may include aiming to please the health professional, poor cognitive insight into their usage and fear of relinquishing their machine. Electronic assessment of CPAP usage data should therefore be routine in all sleep clinics. Furthermore, there seem to be regional variations both in usage and in degrees of error. This may be attributed to differences in education levels and socio-economic status. Ethnicity may also contribute because of different cultural beliefs and lifestyles.
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