Impact of Oxygen Saturation on Mortality in Obese and Non-obese Critically Ill Patients With Mechanical Ventilation: A Retrospective Observational Study

BACKGROUND: The 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. METHODS: We 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. RESULTS: A 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. CONCLUSIONS: For obese and non-obese critically ill patients with mechanical ventilation, the impact of oxygen saturation on hospital mortality is different.