Comparison of Acute Physiology and Chronic Health Evaluations II and III and Simplified Acute Physiology Score II: A prospective cohort study evaluating these methods to predict outcome in a German interdisciplinary intensive care unit

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Abstract
To evaluate the ability of three scoring systems to predict hospital mortality in adult patients of an interdisciplinary intensive care unit in Germany. A prospective cohort study. A mixed medical and surgical intensive care unit at a teaching hospital in Germany. From a total of 3,108 patients, 2,795 patients (89.9%) for Acute Physiology and Chronic Health Evaluation (APACHE) II and 2,661 patients (85.6%) for APACHE III and Simplified Acute Physiology Score (SAPS) II could be enrolled to the study because of defined exclusion criteria. None. Probabilities of hospital death for patients were estimated by applying APACHE II and III and SAPS II and compared with observed outcomes. The overall goodness-of-fit of the three models was assessed. Hospital death rates were equivalent to those predicted by APACHE II but higher than those predicted by APACHE III and SAPS II. Calibration was good for APACHE II. For the other systems, it was insufficient, but better for SAPS II than for APACHE III. The overall correct classification rate, applying a decision criterion of 50%, was 84% for APACHE II and 85% for APACHE III and SAPS II. The areas under the receiver operating characteristic curve were 0.832 for APACHE II and 0.846 for APACHE III and SAPS II. Risk estimates for surgical and medical admissions differed between the three systems. For all systems, risk predictions for diagnostic categories did not fit uniformly across the spectrum of disease categories. Our data more closely resemble those of the APACHE II database, demonstrating a higher degree of overall goodness-of-fit of APACHE II than APACHE III and SAPS II. Although discrimination was slightly better for the two new systems, calibration was good with a close fit for APACHE II only. Hospital mortality was higher than predicted for both new models but was underestimated to a greater degree by APACHE III. Both score systems demonstrated a considerable variation across the spectrum of diagnostic categories, which also differed between the two models.
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