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.