Dose–response relationship of early out-of-bed mobilization with functional decline and adverse events in patients after cardiovascular surgery requiring prolonged intensive care: a retrospective cohort study

BACKGROUND: Patients requiring prolonged ICU care after cardiovascular surgery are at high risk of functional decline, yet the optimal mobilization dose remains unclear. This study examined the associations between mobilization dose, functional decline at discharge, and adverse events during ICU rehabilitation. METHODS: This retrospective cohort study was conducted in a cardiovascular ICU and included 610 patients who underwent cardiovascular surgery and required ≥ 3 days of postoperative ICU care. The cumulative duration of out-of-bed activities at or above standing level (ICU Mobility Scale ≥ 4) was quantified, with 20 min defined as one unit. Patients were categorized into low-dose (< 2 units/day) and high-dose (≥ 2 units/day) groups. The primary outcome was postoperative functional decline, defined as a ≥ 5-point decrease in the Barthel Index at discharge compared with baseline. Adverse events during mobilization were also assessed. Propensity score matching was performed to adjust for baseline differences. RESULTS: After 1:1 propensity score matching, 196 patients were included in each group. Functional decline was more frequent in the low-dose group than in the high-dose group (31.6% vs. 19.9%; odds ratio 2.03; 95% confidence interval [CI] 1.19-3.45; p = 0.009). Adverse events were infrequent (1.2%) and did not differ significantly between groups (incidence rate ratio 0.88; 95% CI 0.43-1.74; p = 0.70). Restricted cubic spline analysis demonstrated a nonlinear dose-response relationship between mobilization dose and functional outcomes. CONCLUSIONS: Lower mobilization doses were associated with functional decline, while higher doses were not associated with increased adverse events. Ensuring an adequate mobilization dose may be associated with better preservation of physical function without compromising safety.