The predictive performance of SAPS 2 and SAPS 3 in an intermediate care unit for internal medicine at a German university transplant center; A retrospective analysis

OBJECTIVE: To analyze and compare the performance of the Simplified-Acute-Physiology-Score (SAPS) 2 and SAPS 3 among intermediate care patients with internal disorders. MATERIALS AND METHODS: We conducted a retrospective single-center analysis in patients (n = 305) admitted to an intermediate-care-unit (ImCU) for internal medicine at the University Hospital Essen, Germany. We employed and compared the SAPS 2 vs. the SAPS 3 scoring system for the assessment of disease severity and prediction of mortality rates among patients admitted to the ImCU within an 18-month period. Both scores, which utilize parameters recorded at admission to the intensive-care-unit (ICU), represent the most widely applied scoring systems in European intensive care medicine. The area-under-the-receiver-operating-characteristic-curve (AUROC) was used to evaluate the SAPS 2 and SAPS 3 discrimination performance. Ultimately, standardized-mortality-ratios (SMRs) were calculated alongside their respective 95%-confidence-intervals (95% CI) in order to determine the observed-to-expected death ratio and calibration belt plots were generated to evaluate the SAPS 2 and SAPS 3 calibration performance. RESULTS: Both scores provided acceptable discrimination performance, i.e., the AUROC was 0.71 (95% CI, 0.65–0.77) for SAPS 2 and 0.77 (95% CI, 0.72–0.82) for SAPS 3. Against the observed in-hospital mortality of 30.2%, SAPS 2 showed a weak performance with a predicted mortality of 17.4% and a SMR of 1.74 (95% CI, 1.38–2.09), especially in association with liver diseases and/or sepsis. SAPS 3 performed accurately, resulting in a predicted mortality of 29.9% and a SMR of 1.01 (95% CI, 0.8–1.21). Based on Calibration belt plots, SAPS 2 showed a poor calibration-performance especially in patients with low mortality risk (P<0.001), while SAPS 3 exhibited a highly accurate calibration performance (P = 0.906) across all risk levels. CONCLUSIONS: In our study, the SAPS 3 exhibited high accuracy in prediction of mortality in ImCU patients with internal disorders. In contrast, the SAPS 2 underestimated mortality particularly in patients with liver diseases and sepsis.