Early mobilization is recommended in the intensive care unit (ICU), yet clinically meaningful early milestones remain unclear. We investigated whether achievement of sitting within 72 h of ICU admission was associated with post–intensive care outcomes among ICU survivors who underwent rehabilitation.

In this multicenter observational cohort study, we included mechanically ventilated adult ICU survivors who underwent rehabilitation. Early sitting was defined as achievement of sitting at the bedside within 72 h after ICU admission. The primary outcome was death or functional decline at 3 months after hospital discharge, assessed using the Kihon Checklist. Prespecified secondary and exploratory outcomes included domain-specific impairments (physical, cognitive, and depressive), hospital readmission, and a composite of readmission or death within 3 months. Overlap propensity score weighting was used to balance baseline covariates. Multiple prespecified sensitivity analyses (48-h alternative definition, landmark analysis, exclusion of never-sitters, adjustment for Day-3 clinical status and rehabilitation dose) and Benjamini–Hochberg (BH) multiplicity adjustment were performed.

Among 423 patients, 173 achieved early sitting (≤72 h) and 250 did not. After overlap weighting, baseline characteristics were balanced. Early sitting was not associated with the primary outcome (adjusted risk ratio [aRR] 0.94, 95% confidence interval [CI] 0.80–1.09; p = 0.401). In exploratory analyses, early sitting was associated with a lower risk of cognitive domain impairment or death (aRR 0.80, 95% CI 0.67–0.97; p = 0.024; BH-adjusted p = 0.096) and of readmission or death (aRR 0.53, 95% CI 0.32–0.88; p = 0.014; BH-adjusted p = 0.027). No individual KCL item showed a clear association after weighting, and the cognitive association was not observed under a stricter definition. Associations with readmission-related outcomes were attenuated after adjustment for Day-3 clinical status.

Achieving sitting within 72 h of ICU admission was not associated with death or functional decline at 3 months. The exploratory associations with cognitive-functional impairment and readmission-related outcomes may reflect the selection of clinically stable patients for early sitting rather than an effect of sitting itself. These findings support the feasibility of early sitting in clinically stable patients but do not establish early sitting as a therapeutic target; randomized trials are needed.