Predictive Performance of the Acute Physiology and Chronic Health Evaluation II, Simplified Acute Physiology Score II and Sequential Organ Failure Assessment score in Critically ill Patients in Intensive Care Unit

Abstract

Background: Severity scoring systems are widely used in intensive care units to assess illness severity, predict mortality, and support clinical decision-making. However, most systems, including the Acute Physiology and Chronic Health Evaluation II, Simplified Acute Physiology Score II, and Sequential Organ Failure Assessment, were developed in high-income countries, and their validity in low- and middle-income settings such as Nepal remains uncertain. This study evaluated and compared the predictive performance of Acute Physiology and Chronic Health Evaluation II, Simplified Acute Physiology Score II, and Sequential Organ Failure Assessment among critically ill patients admitted to a tertiary hospital intensive care units in Nepal.
Methods: A prospective observational study was conducted among 501 adult intensive care units’ patients over one year. Acute Physiology and Chronic Health Evaluation II, Simplified Acute Physiology Score II, and Sequential Organ Failure Assessment scores were calculated using the worst physiological values within the first 24 hours of intensive care units’ admission. Patients were followed until intensive care units discharge and categorized as survivors or non-survivors. Discrimination was assessed using the area under the receiver operating characteristic curve, and calibration was evaluated using the Hosmer–Lemeshow test and standardized mortality ratio. The Mann–Whitney U test compared median scores between outcome groups.
Results: The intensive care units mortality rate was 36.9%. Sequential Organ Failure Assessment demonstrated excellent discrimination (Area under receiver operating characteristics curve 0.895), outperforming Simplified Acute Physiology Score II (0.748) and Acute Physiology and Chronic Health Evaluation II (0.722). Sequential Organ Failure Assessment showed good model fit (p=0.129), while Acute Physiology and Chronic Health Evaluation II and Simplified Acute Physiology Score II had poor calibration by Hosmer–Lemeshow testing. Although Acute Physiology and Chronic Health Evaluation II and Simplified Acute Physiology Score II showed moderate standardized mortality ratio calibration, SOFA significantly overestimated mortality (Standardized mortality ratio 0.38, p<0.001). All three scores were significantly higher among non-survivors (p<0.001).
Conclusions: All three scoring systems effectively differentiated survivors from non-survivors. Sequential Organ Failure Assessment demonstrated superior discriminative ability and overall predictive performance, making it the most reliable mortality predictor in this intensive care units setting, although recalibration may be required for accurate absolute mortality estimation in resource-limited contexts.
Keywords: APACHE II score; critical illness; intensive care units; SAPS II score; SOFA.