Severity scoring systems and the prediction of outcome from intensive care

Severity scoring systems are tools that provide a predicted mortality for a group of intensive care unit patients on the basis of derangement of their physiology and some past medical history. This predicted mortality can then be compared with the actual mortality to give some indicator of the effectiveness of the package of care delivered by the intensive care unit, corrected for differences in case-mix. Thus, their primary use is in audit, and they are designed for use on large populations of patients and not on individuals. In spite of a large number of publications on the development, refinement and testing of scoring systems, papers describing their use in comparative audit are very rare. This may be partly due to limitations in their ability to predict mortality outside the population on which they were developed, and to the change in calibration of the system with time and advances in medical science. This review briefly addresses the limitations of severity scoring systems in light of recent publications.