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

Background and objective The 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 [ HCO 3 − v ] can be used to detect OHS . Methods In this prospective multicentric study, we measured [ HCO 3 − v ] in consenting obese patients attending pathology analysis laboratories. Patients with [ HCO 3 − v ] ≥ 27 mmol/L were referred to a pulmonologist for comprehensive sleep and respiratory evaluations. Those with [ HCO 3 − v ] < 27 mmol/L were randomized to either referral to a pulmonologist or ended the study. Results For the 1004 screened patients, the [ HCO 3 − v ] 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, PaCO 2 , forced expiratory volume in 1 s ( FEV 1 ), apnoea–hypopnoea index ( AHI ), BMI , use of ≥3 anti‐hypertensive drugs, anti‐diabetics, proton pump inhibitors and/or paracetamol were related to raised [ HCO 3 − v ]. Conclusion The 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 [ HCO 3 − v ] may also reflect multimorbidity and polypharmacy, which should be taken into account when using [ HCO 3 − v ] to screen for OHS .