Body mass index and hospital mortality in mechanically ventilated patients with acute hypoxaemic respiratory failure: A retrospective cohort study.

Background: An obesity paradox has been described in general and selected intensive care populations, whereby obese patients experience lower mortality than healthy-weight patients despite physiological disadvantages. Whether this paradox exists among a selected group of patients with acute hypoxaemic respiratory failure (AHRF) requiring mechanical ventilation remains uncertain. We examined the association between body mass index (BMI) and in-hospital mortality in a large, contemporary cohort of mechanically ventilated intensive care unit (ICU) patients with AHRF. Methods: This retrospective cohort study used the ANZICS Adult Patient Database (2020-2024). We included unplanned adult ICU admissions requiring invasive mechanical ventilation with AHRF, defined as admission PaO Results: Among 40 352 eligible patients, overall unadjusted in-hospital mortality was 21% (22.7% in healthy-weight patients). After adjustment, mortality was lower in preobese patients (BMI 25-29.9 kg/m Conclusion: Among patients ventilated for AHRF, overweight and moderately obese BMI categories were associated with modestly lower in-hospital mortality. This association is conditional on the decision to intubate and is compatible with a modest degree of selection bias. The conclusions should be interpreted as a prognostic association within ventilated patients rather than the presence of obesity improving survival.