Severity of Illness Scoring Systems in Critical Care

Critical care consumes about 4% of national health expenditure and 0.65% of United States gross domestic product. There are approximately 94,000 critical care beds in the United States, and provision of critical care services costs approximately $80 billion per year. The enormous costs and the heterogeneity of critical care have led to scrutiny of patient outcomes and cost-effectiveness by a variety of governmental and nongovernmental organizations; furthermore, individual critical care practitioners and their hospitals should evaluate the care delivered. This review discusses scoring systems in medicine, critical care systems, development, validation, performance, and customization of the models, adult intensive care unit (ICU) prognostic models, model use, limitations, prognostic models in trauma care, perioperative scoring systems, assessment of organ failure, severity of illness and organ dysfunction scoring in children, and future directions. Figures show the distribution of predicted risk of death using two different prediction models among a population of patients who ultimately are observed to either live or die, a comparison of  “expected” deaths (based on the expectation