External validation of the sepsis severity score

Abstract

Introduction: Sepsis is defined as a life-threatening organ dysfunction caused by a dysregulated host response to infection. Mortality rates are high, exceeding 50% in patients with septic shock. The sepsis severity score (SSS) was developed to determine the severity of sepsis and as a prognostic model. The aim of this study was to externally validate the SSS model. Methods: Calibration and discrimination of the SSS were retrospectively evaluated using data from a single-center sepsis registry. Results: Data from 156 septic patients were recorded; 56% of them had septic shock, 94% of patients required mechanical ventilation. The observed hospital mortality was 60.3%. The mean SSS value was 94.4 (95% CI 90.5–98.3). The SSS presented excellent discrimination with an area under the receiver operating characteristic curve (AUC) of 0.806 (95% CI 0.734–0.866). The pairwise comparison of APACHE II (AUC = 0.789; 95% CI 0.715–0.851) with SSS and 1st day SOFA (AUC = 0.75; 95% CI 0.673–0.817) with SSS revealed no significant differences in discrimination between the models. The calibration of the SSS was good with the Hosmer-Lemeshow goodness-of-fit H test 9.59, P > 0.05. Analyses of calibration curve show absence of accurate predictions in lower deciles of lower risk (2nd and 4th). Conclusion: The SSS demonstrated excellent discrimination. The calibration evaluation gave conflicting results; the H-L test result indicated a good calibration, while the visual analysis of the calibration curve suggested the opposite. The SSS requires further evaluation before it can be safely recommended as an outcome prediction model.