Factors associated with the diagnosis of hypoventilation syndrome among patients qualified for bariatric surgery.

<bold>Introduction:</bold> Obesity is associated with increased risk of obstructive sleep apnoea (OSA). However, there is scarcity of studies describing the incidence of hypoventilation in patients scheduled for bariatric surgery. <bold>Aims:</bold> We aimed to describe the incidence of hypoventilation in patients qualified for bariatric surgery and to determine clinical, polysomnographic and laboratory factors related to this disorder. <bold>Methods:</bold> In this retrospective study we analyzed medical records of patients qualified for bariatric surgery who were included in the nationwide pilot programme KOS-BAR. Patients were hospitalized from January 2022 to December 2023 in the Department of Pulmonology in Jagiellonian University Medical College, Kraków, Poland. We gathered data on patients` medical history and performed anthropometric measurements, arterial blood gas analysis and polysomnography with capnometry. <bold>Results:</bold> We enrolled 134 patients at the median age of 44 (IQR 38.0-51.0) years, 59.7% of whom were female. Hypoventilation was confirmed in 30 patients (22.4%). Patients with hypoventilation were more likely to be diagnosed with severe OSA (80.0% vs. 52.9%, p=0.008), had lower mean SpO2 (90% vs. 93%, p=0.001), higher ODI (65.1/h vs. 34.1/h, p=0.006), higher pCO2 (41.5 vs. 39.3, p<0.001), lower pO2 (74.0 vs. 79.0, p=0.024) and higher HCO3- (26.5 vs. 25.2, p=0.002). Increased HCO3- levels were found more commonly in patients with hypoventilation (37.9% vs. 4.1%, p<0.001). <bold>Conclusion:</bold> Hypoventilation is common in patients qualified for bariatric surgery and should be actively sought for. Importatnly, increased bicarbonates do not exclude the presence of hypoventilation.