Sex-Specific Differences in Tidal Volumes and Mortality of Mechanically Ventilated Patients

OBJECTIVES: Previous work reported that critically ill female patients received higher tidal volumes per predicted body weight (PBW) than male patients during the first 24 hours of mechanical ventilation, which might be associated with higher mortality. We investigated if sex inequity in daily tidal volumes during mechanical ventilation persisted beyond the first 24 hours and remained associated with mortality. Also, we examined if the association was mainly explained by baseline factors that differed between female and male patients. DESIGN: In this registry-based cohort study, Bayesian joint models were used to estimate indirect (through tidal volumes) and direct effects of sex on mortality using data recorded in the Toronto Intensive Care Observational Registry between April 2014 and December 2022. PATIENTS: Adult patients (18 yr old or older), mechanically ventilated for greater than or equal to 24 hours. SETTING: Nine ICUs from six University of Toronto-affiliated hospitals. INTERVENTION: None. MEASUREMENTS AND MAIN RESULTS: Of 20,351 eligible patients, 7,635 (38%) were female. Unadjusted mortality was 18% for female (1,384/7,635) and 17% for male (2,113/12,716) patients. We noticed that 2820 female (37%) and 4335 male patients (34%) underwent mechanical ventilation without recordings for body height. Every increase in daily tidal volumes (1 mL/kg PBW) was associated with higher mortality (hazard ratio: 1.10, 95% credible intervals [CrIs], 1.07-1.13), adjusted for severity of illness changing over time. Female patients had on average a lower height and consistently received higher daily tidal volumes (+0.6 mL/kg PBW, 95% CrI, +0.6 to +0.7 mL/kg PBW) and driving pressures (+1 cm H2O; 95% CI, 1-1 cm H2O) compared with male patients, suggesting an indirect effect of sex on mortality mediated by ventilator management. No direct effect of sex on mortality was observed. CONCLUSIONS: Measurement of height and daily adjustments of tidal volumes and driving pressures may reduce mortality, particularly for female patients with lower height.