Lower short- and long-term mortality associated with overweight and obesity in a large cohort study of adult intensive care unit patients

Abstract

Introduction: Two thirds of United States adults are overweight or obese, which puts them at higher risk of developing chronic diseases and of death compared with normal-weight individuals. However, recent studies have found that overweight and obesity by themselves may be protective in some contexts, such as hospitalization in an intensive care unit (ICU). Our objective was to determine the relation between body mass index (BMI) and mortality at 30 days and 1 year after ICU admission.

Methods: We performed a cohort analysis of 16,812 adult patients from MIMIC-II, a large database of ICU patients at a tertiary care hospital in Boston, Massachusetts. The data were originally collected during the course of clinical care, and we subsequently extracted our dataset independent of the study outcome.

Results: Compared with normal-weight patients, obese patients had 26% and 43% lower mortality risk at 30 days and 1 year after ICU admission, respectively (odds ratio (OR), 0.74; 95% confidence interval (CI), 0.64 to 0.86) and 0.57 (95% CI, 0.49 to 0.67)); overweight patients had nearly 20% and 30% lower mortality risk (OR, 0.81; 95% CI, 0.70 to 0.93) and OR, 0.68 (95% CI, 0.59 to 0.79)). Severely obese patients (BMI ≥ 40 kg/m2) did not have a significant survival advantage at 30 days (OR, 0.94; 95% CI, 0.74 to 1.20), but did have 30% lower mortality risk at 1 year (OR, 0.70 (95% CI, 0.54 to 0.90)). No significant difference in admission acuity or ICU and hospital length of stay was found across BMI categories.

Conclusion: Our study supports the hypothesis that patients who are overweight or obese have improved survival both 30 days and 1 year after ICU admission.

Figure 1

Study cohort selection. Cohort selection and criteria for exclusion. *The primary analyses did not include the patients without weight data; a subsequent sensitivity analysis included those patients based on imputed values for BMI.

Figure 2

The 30-day mortality by SAPS category and BMI. Graph illustrating the differences in 30-day mortality based on the admission SAPS score and BMI category.

Figure 3

Kaplan-Meier curve for 30-day survival by BMI category. Kaplan-Meier curve for survival by BMI category over the first 30-day period. The numbers represent the number of patients still surviving in each BMI category at the start of each time period. Note: the survival probability is truncated at 0.6 for display purposes.