BackgroundThe main aim of this study was to evaluate the effect of oxygen saturation on mortality in critically ill patients with mechanical ventilation according to obesity status. MethodsWe conducted an observational study in mechanically ventilated patients admitted to the ICU retrospectively. Demographic, arterial blood gas, ventilator setting, interventions, and peripheral oxygen saturation (Spo(2)) during the first 24 h were recorded and analyzed between non-obese and obese patients. The main exposure included Spo(2), time-weighted mean Spo(2) (TWM-Spo(2)), and proportion of time spent in different Spo(2) (PTS-Spo(2)) levels. The primary outcome was hospital mortality. We used multivariable logistic regression models to assess the relationship between Spo(2) and mortality, as well as the interaction between PTS-Spo(2) and obesity status. ResultsA total of 25,100 patients were included, of which 10,564 (42%) were obese patients. After adjusting for confounders, compared with TWM-Spo(2) of 94-98%, TWM-Spo(2) of < =88% (OR 3.572; CI [2.343, 5.455]; p < 0.001) and of 89-93% (OR 1.514; CI [1.343, 1.706]; p < 0.001) were both associated with higher risk of mortality. PTS-Spo(2) of 99-100% was associated with increased risk of mortality for obese patients (OR 1.028; 95% CI 1.010-1.046; p = 0.002; P-interaction = 0.001), while PTS-Spo(2) of 89-93% was associated with increased risk of mortality (OR 1.089; 95% CI 1.051-1.128; p < 0.001; P-interaction = 0.001) for non-obese patients. ConclusionsFor obese and non-obese critically ill patients with mechanical ventilation, the impact of oxygen saturation on hospital mortality is different.