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Body Mass Index Is Associated With Hospital Mortality in Critically Ill Patients: An Observational Cohort Study

Pickkers, Peter MD, PhD1,2; de Keizer, Nicolette PhD3,4; Dusseljee, Joost MSc3; Weerheijm, Daan MSc1; van der Hoeven, Johannes G. MD, PhD1,2; Peek, Niels PhD3

doi: 10.1097/CCM.0b013e31828a2aa1
Clinical Investigations

Objective: Obesity is associated with a variety of diseases, which results in a decreased overall life expectancy. Nevertheless, some studies suggest that being overweight may reduce hospital mortality of certain patient groups, referred to as obesity paradox. Conflicting results for critically ill patients are reported. Therefore, we wished to investigate the association of body mass index and hospital mortality in critically ill patients.

Design: Observational cohort study in Dutch critically ill patients.

Setting: A dataset from the Dutch National Intensive Care Evaluation registry that includes patients admitted to Dutch ICUs was used.

Patients: One hundred fifty-four thousand three hundred and eight ICU patients of teaching and nonteaching units in urban and nonurban hospitals.

Interventions: None.

Measurements and Main Results: We used logistic regression analysis, correcting for case mix (Simplified Acute Physiology Score II, age, gender, admission type, neoplasm, AIDS, hematologic malignancy, immunologic insufficiency, mechanical ventilation, and calendar year), to determine the relationship between body mass index and hospital mortality. Body mass index was included in the model as a continuous nonlinear covariate in a restricted regression spline transformation. To facilitate interpretation, adjusted odds ratios were calculated for the World Health Organization-based body mass index classes. Body mass index was found to be significantly associated with hospital mortality, with risks quickly increasing for underweight patients (body mass index < 18.5 kg/m2). Obese and seriously obese patients, with a body mass index of 30–39.9 kg/m2, had the lowest risk of death with an adjusted odds ratio of 0.86 (0.83–0.90).

Conclusions: This large observational database shows an inverse association between obesity and hospital mortality in critically ill patients that could not be explained by a variety of known confounders.

1Department of Intensive Care, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.

2Nijmegen Institute for Infection, Inflammation and Immunity (N4i), Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands.

3Department of Medical Informatics, Academic Medical Centre, Amsterdam, The Netherlands.

4National Intensive Care Evaluation, Amsterdam, The Netherlands.

Dr. Pickkers conceived the study and wrote the manuscript. Mr. Dusseljee, Mr. Weerheijm, and Dr. Peek were involved in the design and did the statistics and corrected the manuscript. Dr. de Keizer was responsible for data extraction and corrected the manuscript. Dr. van der Hoeven supervised the study and corrected the manuscript. All authors read and approved the final manuscript.

The authors have disclosed that they do not have any potential conflicts of interest.

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© 2013 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins