Background Mortality in acute respiratory failure remains high despite the use of lung-protective ventilation. Recent studies have shown an association between baseline ventilation parameters (driving pressure or mechanical power) and outcomes for patients with acute respiratory distress syndrome. Strategies focused on limiting these parameters have been proposed to further improve outcomes. However, it remains unknown whether driving pressure and mechanical power should be limited over the entire duration of mechanical ventilation and in all patients with acute respiratory failure. We aimed to estimate the association between exposure to different intensities of mechanical ventilation over time and intensive care unit (ICU) mortality in patients with acute respiratory failure.In this registry-based, prospective cohort study, we obtained data from the Toronto Intensive Care Observational Registry, which includes all patients receiving mechanical ventilation for 4 h or more in nine ICUs that are affiliated with the University of Toronto (Toronto, ON, Canada). We included all adult (≥18 years) patients who received invasive mechanical ventilation between April 11, 2014, and June 5, 2019. Patients were excluded if they received treatment with extracorporeal life support. The primary outcome was ICU mortality. Bayesian joint models were used to estimate the strength of associations, accounting for informative censoring due to death during follow-up.Of 13 939 patients recorded in the registry, 13 408 (96·2%) were eligible for descriptive analysis. The primary analysis comprised 7876 (58·7%) patients with complete baseline characteristics, and a secondary analysis included all 13 408 patients after multiple imputation in the joint model analysis. 2409 (18·0%) of 13 408 patients died in the ICU. After adjustment for baseline characteristics, including age and severity of illness, a significant increase in the hazard of death was found to be associated with each daily increment in driving pressure (hazard ratio 1·064, 95% credible interval 1·057-1·071) or mechanical power (hazard ratio 1·060, 95% credible interval 1·053-1·066). These associations persisted over the duration of mechanical ventilation.Cumulative exposure to higher intensities of mechanical ventilation was harmful, even for short durations. Limiting exposure to driving pressure or mechanical power should be evaluated in further studies as promising ventilation strategies to reduce mortality in patients with acute respiratory failure.Canadian Institutes of Health Research.