Purpose of review: Outcome prediction models measuring severity of illness of patients admitted to the intensive care unit should predict hospital mortality. This review describes the state-of-the-art of Simplified Acute Physiology Score models from the clinical and managerial perspectives. Methodological issues concerning the effects of differences between new samples and original databases in which the models were developed are considered.
Recent findings: The progressive lack of fit of the Simplified Acute Physiology Score II in independent intensive care unit populations induced investigators to propose customizations and expansions as potential evolutions for Simplified Acute Physiology Score II. We do not know whether those solutions did solve the issue because there are no demonstrations of consistent good fit in new databases. The recently developed Simplified Acute Physiology Score 3 Admission Score with customization for geographical areas is discussed. The points shared by the Simplified Acute Physiology Score models and the pros and cons for each of them are introduced.
Summary: Comparisons of intensive care unit performance should take into account not only the patient severity of illness, but also the effect of the 'intensive care unit variable', that is, differences in human resources, structure, equipment, management and organization of the intensive care unit. In the future, moving from patient and geographical area adjustment to resource use could allow the user to adjust for differences in healthcare provision.