Objectives: Acute hypoxemic respiratory failure (AHRF) is a leading cause of ICU admission and is associated with significant morbidity and mortality. Yet, epidemiological data on AHRF remain limited, and current management strategies largely derive from studies on acute respiratory distress syndrome (ARDS). We examined the prevalence of AHRF among ICU patients receiving supplemental oxygen or respiratory support for at least 4 hours, as well as initial respiratory support strategies and associated outcomes.

Design: Multicenter registry-based cohort study, 2014-2023.

Setting: Nine university of Toronto affiliated ICUs.

Patients: Adult ICU patients receiving supplemental oxygen or respiratory support who met AHRF criteria, defined as Pao2/Fio2 less than or equal to 300 mm Hg or, if Pao2 was not available, peripheral oxygen saturation (SpO2)/Fio2 less than or equal to 315, within the first 24 hours of ICU admission.

Interventions: None.

Measurements and main results: The primary outcome was AHRF prevalence. Secondary outcomes included ICU length of stay, invasive mechanical ventilation (IMV) duration, ventilator-free days, and ICU mortality, stratified by AHRF severity. Of 21,714 patients recorded in the registry, 10,832 (50%) met AHRF criteria, of whom 76% required IMV. Most received lung-protective ventilation. With increasing AHRF severity, ICU length of stay and IMV duration increased, while ventilator-free days and probability of ICU discharge at 30 days decreased. ICU mortality was 23% overall and 47% among patients on IMV with severe AHRF.

Conclusions: AHRF is common early after ICU admission among patients requiring supplemental oxygen or respiratory support and is frequently managed using ARDS-based strategies. A pragmatic, standardized, and operationally feasible definition of AHRF may improve patient recognition, enable comparisons across studies, and guide future research.