Early Physiological Changes Before Rapid Response Team Activation Differentiate Patients Requiring ICU Transfer: A Retrospective Cohort Study.

Background/

Objectives

Failure to rescue deteriorating ward patients before irreversible organ injury remains a leading cause of preventable in-hospital mortality, yet current rapid response team (RRT) research relies predominantly on cross-sectional comparisons at the moment of activation, overlooking the short-horizon physiological changes that precede it.

Methods

This retrospective cohort study at a tertiary academic hospital in South Korea included 549 adults (191 ICU-transferred, 358 ward-remaining) with a first RRT activation between September 2023 and August 2025. Generalised estimating equations (GEE) with a time × group interaction modelled differential changes in 12 laboratory variables and the DeepCARS AI-derived risk score between 24 h before activation (T-24 h) and the moment of activation (T0). At T-24 h, physiological profiles were largely similar between groups, indicating that conventional static assessment failed to identify patients destined for ICU transfer.

Results

Over the ensuing 24 h, patients subsequently transferred to the ICU showed a steeper decline in SpO2/FiO2 (S/F) ratio (383.4 → 167.1 vs. 369.1 → 260.3; B = -0.547, p < 0.001) and steeper increases in lactate (2.91 → 4.02 vs. 2.05 → 2.98 mmol/L; B = 0.154, p = 0.045), creatinine (B = 0.076, p = 0.038), potassium (B = 0.019, p = 0.001), and DeepCARS score (B = 0.073, p = 0.028) compared with patients remaining on the ward. All five variables retained significance under Benjamini-Hochberg false discovery rate correction (q < 0.10). Seven inflammatory and haematological markers showed no differential change. Procalcitonin was excluded from the primary analysis because of very high missingness at the pre-activation time point (approximately 75%).

Conclusions

These findings demonstrate that short-horizon deterioration in oxygenation, perfusion, and renal function-rather than any single earlier measurement-distinguishes patients requiring ICU transfer, supporting the development of change-based early warning criteria to enable earlier clinical escalation.