Prevalence of obesity hypoventilation syndrome in ambulatory obese patients attending pathology laboratories

Background and objectiveThe prevalence of obesity hypoventilation syndrome (OHS) in the unselected obese is unknown. Our objectives were: (i) to determine the prevalence of OHS in ambulatory obese patients not previously referred to a pulmonologist for suspicion of sleep breathing disorders and (ii) to assess whether venous bicarbonate concentration [HCO3v-] can be used to detect OHS. MethodsIn this prospective multicentric study, we measured [HCO3v-] in consenting obese patients attending pathology analysis laboratories. Patients with [HCO3v-] <27mmol/L were referred to a pulmonologist for comprehensive sleep and respiratory evaluations. Those with [HCO3v-]<27mmol/L were randomized to either referral to a pulmonologist or ended the study. ResultsFor the 1004 screened patients, the [HCO3v-] was 27 mmol/L in 24.6% and <27 mmol/L in 45.9%. A total of 29.5% who had previously consulted a pulmonologist were excluded. A population of 241 obese patients underwent sleep and respiratory assessments. The prevalence of OHS in this population was 1.10 (95% CI=0.51; 2.27). In multivariate analysis, PaCO2, forced expiratory volume in 1s (FEV1), apnoea-hypopnoea index (AHI), BMI, use of 3 anti-hypertensive drugs, anti-diabetics, proton pump inhibitors and/or paracetamol were related to raised [HCO3v-]. ConclusionThe prevalence of OHS in our obese population was lower than previous estimations based on hospitalized patients or clinical cohorts with sleep breathing disorders. Apart from hypercapnia, increased [HCO3v-] may also reflect multimorbidity and polypharmacy, which should be taken into account when using [HCO3v-] to screen for OHS. The prevalence of undiagnosed obesity hypoventilation syndrome (OHS) in ambulatory obese patients who have not previously consulted a pulmonologist ranges from 0.5% to 2.3%, much lower than previous estimations based on cohorts of patients with sleep-disordered breathing.