A gradient-boosted model analysis of the impact of body mass index on the short-term outcomes of critically ill medical patients

OBJECTIVE To evaluate the impact of body mass index on the short-term prognosis of non-surgical critically ill patients while controlling for performance status and comorbidities. METHODS We performed a retrospective analysis on a two-year single-center database including 1943 patients. We evaluated the impact of body mass index on hospital mortality using a gradient-boosted model that also included comorbidities and was assessed by Charlson's comorbidity index, performance status and illness severity, which was measured by the SAPS3 score. The SAPS3 score was adjusted to avoid including the same variable twice in the model. We also assessed the impact of body mass index on the length of stay in the hospital after intensive care unit admission using multiple linear regressions. RESULTS A low value (< 20kg/m2) was associated with a sharp increase in hospital mortality. Mortality tended to subsequently decrease as body mass index increased, but the impact of a high body mass index in defining mortality was low. Mortality increased as the burden of comorbidities increased and as the performance status decreased. Body mass index interacted with the impact of SAPS3 on patient outcome, but there was no significant interaction between body mass index, performance status and comorbidities. There was no apparent association between body mass index and the length of stay at the hospital after intensive care unit admission. CONCLUSION Body mass index does appear to influence the shortterm outcomes of critically ill medical patients, who are generally underweight. This association was independent of comorbidities and performance status.