Effect of obesity on 12-month survival following admission to intensive car

Abstract and Introduction

Abstract

Objective: Evaluate the effect of intensive care (ICU) admission body mass index (BMI) on 30-day and 12-month survival in critically ill patients and determine the impact of obesity on outcome.
Design: Prospective, observational cohort study.
Setting: Fourteen-bed medical and surgical ICU of a university-affiliated hospital.
Patients: Four hundred and ninety-three adult patients.
Interventions: None.
Measurements and Main Results: BMI (kg/m) was calculated from height (m) and measured weight (kg) within 4 hrs of ICU admission, using the PROMED weighing device, or premorbid weight (documented in the previous month) (BMI_measured). Follow-up was for ≥12 months post-ICU admission. Time to mortality outcome, censored at 30 and 365 days (12-months), was analyzed using a log-normal accelerated failure time regression model. Predictor variables were parameterized as time ratios (TR), where TR <1 is associated with decreased survival time and TR >1 is associated with prolonged survival time. Mean (sd) age and Acute Physiology and Chronic Health Evaluation II score were 62.3 (17.5) years and 20.7(8.4), respectively; 56.0% (285 of 493) of patients were male and 60.6% (299 of 493) medical. ICU admission weight and BMI_measured (available in 433 patients) were 79.1 (22.1) kg and 27.8 (7.0) kg/m, respectively. In 16.9% (73 of 433) of patients, weight was ≥100 kg, and in 29.8% (129 of 433), BMI_measured was ≥30 kg/m. Raw intensive care, 30-day, and 12-month mortality rates were 15.2% (66 of 433), 22.3% (95 of 433), and 37.3% (159 of 433), respectively. BMI_measured was a significant determinant of mortality at 30 days (TR 1.853, 95% confidence interval 1.053-3.260, p = .032) and 12 months (TR 1.034, 95% confidence interval 1.005-1.063, p = .019). The effect of BMI on 12-month mortality was linear, such that increasing BMI was associated with decreasing mortality.
Conclusions: ICU admission BMI was a determinant of short- to medium-term survival. Obesity was not associated with adverse outcomes and may be protective.

Introduction

The prevalence of obesity is progressively increasing in developed countries such as the United States, Canada, and Australia. More important, population-based longitudinal studies demonstrate that obesity increases both morbidity and the relative risk of dying over time, even after controlling for confounding variables such as comorbid disease, age, smoking, and alcohol consumption.

In the critically ill population, obesity is also presumed to be associated with a poor outcome; factors such as impaired lung function, airway difficulties, increased cardiac stroke work, and an increased incidence of thromboembolic events contribute (mechanistically) to the commonly held belief that obese patients have an increased risk of death following admission to the intensive care unit (ICU). However, whether the same negative effect on outcome observed in the general population can be extrapolated to critically ill patients is unclear, as the available literature is both limited and conflicting.

In a recent prospective, case-matched cohort study of mechanically ventilated obese patients, ICU mortality was increased in patients with a body mass index (BMI) >30 kg/m compared with ideal weight patients (BMI 18.5-24.9 kg/m (odds ratio [OR] 2.1; 95% confidence intervals [CI] 1.2-3.6). Similarly, obesity was also shown to have been an independent predictor of ICU mortality in a prospective study comparing medical ICU patients with a BMI >27 kg/m or <27 kg/m (75th percentile of the study population). Hospital and beyond-hospital mortality were not examined in either study.

In contrast, a negative relationship between obesity and 28-day mortality was not observed in a retrospective analysis of acute lung injury patients from the Acute Respiratory Distress Syndrome Network low tidal volume ventilation study. Moreover, there was the suggestion that obesity (BMI >40 kg/m) may be protective in the critically ill. Likewise, in a recent French study, hospital mortality was decreased in patients with a BMI >30 kg/m (OR 0.60; 95% CI 0.40-0.88).

The significance (if any) of obesity in determining morbidity and in-hospital mortality in the critically ill population is, thus, not resolved. Moreover, until now, there have been no studies examining the relationship between obesity and medium- to long-term survival post-ICU admission. The purpose of the present study was to evaluate the effect of BMI on 30-day and 12-month mortality in patients admitted to a tertiary-level, multidisciplinary ICU and, more specifically, to determine the impact of obesity on outcome.