Early detection of obesity hypoventilation syndrome: prevalence and physiological differences within a cohort of obese patients

<bold>Introduction:</bold> Some of severe obese subjects develops hypoventilation defining the obesity-hypoventilation syndrome (OHS), due to altered ventilatory demand and drive, often associated with sleep apnea (OSA). Compared to eucapnic counterparts, OHS patients are characterized by increased morbidity and diagnosis is often made only after an episode of acute respiratory failure. Earlier identification and better understanding of the pathophysiology behind OHS will permit optimal interventions improving prognosis. Despite tolerance challenges, positive airway pressure is the only available treatment, as alternative therapies are under evaluation. We aimed to identify different OHS subclasses and the related pathophysiology within patients screened for a pharmacological trial. <bold>Methods:</bold> In the framework of a proof of concept randomized, double blind trial testing a pharmacotherapy for OHS in adults with a body mass index (BMI) ≥ 35 kg/m2 (ATOHS), we performed polysomnography with transcutaneous overnight CO2 measurement for the early OHS diagnosis. We also performed morning blood gas analyses, chemosensitivity tests and clinical evaluation. <bold>Results:</bold> Over 25 patients (9 males, median [IQR] BMI 44 [40-50] kg/m2, age 55 [38-59] years), 7 presented nocturnal hypercapnia with increased diurnal bicarbonates (stage 2 OHS), 5 presented diurnal hypercapnia (stage 3 OHS). All of them had OSA. Stage 3 OHS showed increased max PetCO2 and lower chemosensitivity measured as P0.1/PetCO2 slope. <bold>Conclusion:</bold> Fifty percent of the severely obese patients recruited had OHS or pre-OHS according to ERS criteria, suggesting the need for a more careful evaluation of severely obese patients