Association of early cumulative fluid balance with 28-day successful liberation from invasive mechanical ventilation in patients with severe pneumonia: a retrospective cohort study

Fluid accumulation may impair respiratory recovery in critically ill patients, but its association with successful liberation from invasive mechanical ventilation (IMV) in severe pneumonia remains uncertain when death before liberation is considered as a competing event. We evaluated the association between early cumulative fluid balance (CFB) and successful liberation from IMV by intensive care unit (ICU) day 28. This single-center retrospective cohort study included adults with severe pneumonia who received IMV between January 2020 and December 2025 and remained alive and invasively ventilated at 72 h after ICU admission. Early CFB was calculated as total fluid intake minus total output during the first 72 h. Patients were classified as having low or high CFB using the cohort median. Cumulative incidence functions and Fine–Gray models were used, with death before liberation treated as a competing event. The primary model adjusted for prespecified covariates available at ICU admission. Among 327 patients, the median 72-h CFB was 2.14 L; 203 patients achieved successful liberation and 82 died before liberation. By ICU day 28, the cumulative incidence of successful liberation was 74.6% in the low-CFB group and 52.3% in the high-CFB group, whereas the cumulative incidence of death before liberation was 15.6% and 35.8%, respectively (Gray’s test, both P < 0.001). In the primary baseline-adjusted model, each 1-L/72-h increase in CFB was associated with a lower subdistribution hazard of successful liberation (subdistribution hazard ratio [SHR], 0.95; 95% confidence interval [CI] 0.91–0.99). The adjusted SHR for high versus low CFB was 0.72 (95% CI 0.55–0.95). The overlap-weighted estimate was similar (SHR, 0.74; 95% CI 0.56–0.98). After additional exploratory adjustment for intermediate variables recorded during the exposure window, the estimate was attenuated (SHR, 0.77; 95% CI 0.57–1.03). Among adults with severe pneumonia who remained invasively ventilated at the 72-h landmark, higher early CFB was associated with a lower subdistribution hazard of successful liberation from IMV by ICU day 28. These findings identify early CFB as a prognostic marker and do not establish the benefit of a specific fluid-management strategy.