Study of the role of different severity scores in respiratory ICU

Abstract

Background Scoring systems are increasingly used in the ICUs in an attempt to accurately predict the mortality outcome in critically ill patients. Objective The performance of the Acute Physiology and Chronic Health Evaluation II (APACHE II) score, the Sequential Organ Failure Assessment (SOFA) score, and the Simplified Acute Physiology Score (SAPS) II was compared in terms of calibration and discrimination in critically ill patients admitted to the respiratory ICU. Materials and methods Mean admission APACHE II, SAPS II, and SOFA scores were compared in 105 patients. The outcome measure was ICU mortality. The discriminatory ability of the scores was evaluated using the area under the receiver operating characteristic curve. Calibration was tested using the Hosmer-Lemeshow goodness-of-fit test. Results The mean admission APACHE II, SAPS II, and SOFA scores were higher in nonsurvivors compared with survivors; yet, only admission SOFA score differed significantly. There was highly significant positive correlation between the three scores. The cutoffs obtained by the receiver operating characteristic curve were 11 for APACHE II, 7.5 for SOFA, and 40 for SAPS II score. Discrimination power of the three scores was poor; yet, in the order of best discrimination, SOFA [area under the curve (AUC) = 0.63] was followed by APACHE II (AUC = 0.60) and then SAPS II (AUC = 0.59). In terms of calibration, SAPS II (χ 2 = 4.82; P = 0.78) had the best calibration and APACHE II (χ 2 = 7.34; P = 0.39) had the worst. Logistic regression analysis showed that, of the three scores, only the SOFA score was an independent predictor of mortality among the respiratory ICU patients; with a unit increase in the SOFA score, there was a 1.2 times higher risk for mortality. Conclusion The SOFA score performed well in terms of calibration, whereas the SAPS II score performed well in terms of discrimination. The APACHE II score did not perform well in terms of calibration and had poor discrimination power.