The aims of this prospective observational cohort study are threefold: (1) to assess the prevalence of obesity hypoventilation syndrome (OHS) in individuals with obesity and obstructive sleep apnea (OSA) and identify associated risk factors, (2) to determine clinical predictors of OHS, and (3) to evaluate the therapeutic outcomes of combined airway and bariatric surgery (CABS) in this population.

This study was approved by the Institutional Review Board of Chang Gung Medical Foundation on August 8, 2022 (IRB No. 202201000A3). Written informed consent was obtained from all participants. All procedures adhered to the principles outlined in the Declaration of Helsinki and were reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROCSS) guidelines.

This was a two-year prospective observational cohort study conducted at the tertiary referral sleep center of Linkou Chang Gung Memorial Hospital from December 1, 2022, to November 30, 2024. Obesity hypoventilation syndrome (OHS) was diagnosed based on the presence of BMI ≥ 30 kg/m², PaCO₂ ≥ 45 mmHg on arterial blood gas (ABG) analysis, and sleep-disordered breathing, following the exclusion of other potential causes of alveolar hypoventilation using pulmonary function tests.

Adults aged 20 to 65 years were eligible if they met the following inclusion criteria: (1) BMI ≥ 30 kg/m², and (2) AHI ≥ 5 events/hour. Individuals were excluded if they had (1) persistent decompensated hypercapnic respiratory failure (arterial pH < 7.3), (2) acute respiratory failure requiring invasive mechanical ventilation, (3) significant neuromuscular disease, chest wall deformities, or pulmonary disease contributing to hypoventilation, (4) unstable coronary artery disease, or (5) cognitive impairment precluding informed consent or protocol adherence.

Following diagnosis, individuals with OHS were counseled on therapeutic options, including continuous positive airway pressure (CPAP) therapy, body weight reduction, or combined airway and bariatric surgery (CABS). The final decision was made through a shared decision-making process.

Outcome measures included (1) Polysomnography: All participants underwent attended level I polysomnography using the Nicolet UltraSom System (Nicolet, Madison, WI). AHI was the primary sleep parameter, defined as the total number of apneas (≥ 90% airflow reduction for ≥10 seconds) and hypopneas (> 50% airflow reduction with ≥ 3% oxygen desaturation or arousal) per hour of sleep. Scoring was performed by a single blinded sleep specialist. (2) Pulmonary function testing: Spirometry was performed using a handheld spirometer in accordance with international guidelines. Parameters included forced vital capacity (FVC), forced expiratory volume in 1 second (FEV₁), and FEV₁/FVC ratio. (3) Gas exchange: ABG analysis was conducted during daytime hours with the participant seated and breathing room air after resting for at least 60 minutes. (4) Epworth sleepiness scale: Daytime sleepiness was assessed using the Epworth Sleepiness Scale (ESS), a validated 8-item questionnaire with total scores ranging from 0 to 24; higher scores indicate greater daytime sleepiness.

The prevalence of OHS was calculated as the proportion of individuals diagnosed with OHS among those with concurrent obesity and obstructive sleep apnea (OSA). A multivariate logistic regression analysis with forward selection was conducted to identify independent predictors of OHS. Receiver operating characteristic (ROC) curve analysis was used to determine the optimal cut-off points for various predictors. To evaluate the effects of the CABS intervention, pre- and post-operative changes in clinical parameters were compared.

Inclusion Criteria:

(1) BMI ≥ 30 kg/m², and (2) AHI ≥ 5 events/hour.

Exclusion Criteria:

(1) persistent decompensated hypercapnic respiratory failure (arterial pH < 7.3), (2) acute respiratory failure requiring invasive mechanical ventilation, (3) significant neuromuscular disease, chest wall deformities, or pulmonary disease contributing to hypoventilation, (4) unstable coronary artery disease, or (5) cognitive impairment precluding informed consent or protocol adherence.

This study enrolled consecutive patients with obesity and OSA at the tertiary referral sleep center of Linkou Chang Gung Memorial Hospital from September 1, 2022, to August 31, 2024. OHS was diagnosed based on the presence of BMI ≥ 30 kg/m², PaCO₂ ≥ 45 mmHg on ABG analysis, and sleep-disordered breathing, following the exclusion of other potential causes of alveolar hypoventilation using pulmonary function tests.