Association between Obesity Severity and Nocturnal Hypoxemia in Obstructive Sleep Apnea

Aim: To evaluate the association between obesity severity and nocturnal hypoxemia in patients with obstructive sleep apnoea (OSA), and to compare the ability of body mass index (BMI) and the apnea–hypopnea index (AHI) to identify nocturnal hypoxemia. Methods: This retrospective cross-sectional study included 70 adult patients diagnosed with OSA who underwent full-night attended polysomnography. Anthropometric data, including BMI and obesity class, and polysomnographic parameters were collected. Nocturnal hypoxemia was defined as peripheral oxygen saturation (SpO₂) < 90%. Associations between nutritional status, nocturnal oxygenation, snoring parameters, and AHI were analysed. Receiver operating characteristic (ROC) analysis was used to assess the discriminatory ability of BMI and AHI for nocturnal hypoxemia. Results: The median age was 58 years (IQR 47–64), and 76% of patients were male. Obesity was present in 74.3% of patients, including 42.3% with class I, 32.7% with class II, and 25.0% with class III obesity. Mean nocturnal oxygen saturation and oxygen saturation nadir declined progressively with increasing obesity class (p = 0.008 and p = 0.02, respectively), whereas AHI showed only a non-significant increasing trend (p = 0.09). Nocturnal hypoxemia was observed predominantly in obese patients and was most frequent in class III obesity (47%, p = 0.04). Both BMI (AUC 0.742) and AHI (AUC 0.805) were significantly associated with nocturnal hypoxemia, with no significant difference between ROC curves (p = 0.41). Conclusion: Obesity severity is strongly associated with nocturnal hypoxemia in OSA, independent of AHI. BMI provides clinically meaningful information comparable to AHI in identifying patients at risk of nocturnal hypoxemia, supporting a complementary approach to OSA severity assessment. Keywords: obstructive sleep apnea; obesity; nocturnal hypoxemia