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Multicenter Study
. 2006 Mar;34(3):738-44.
doi: 10.1097/01.ccm.0000202207.87891.fc.

Body mass index is independently associated with hospital mortality in mechanically ventilated adults with acute lung injury

James M O'Brien Jr  1 , Gary S Phillips, Naeem A Ali, Maria Lucarelli, Clay B Marsh, Stanley Lemeshow
Affiliations
Multicenter Study

Body mass index is independently associated with hospital mortality in mechanically ventilated adults with acute lung injury

James M O'Brien Jr et al. Crit Care Med. 2006 Mar.

Abstract

Objective: To determine the association between body mass index (BMI) and hospital mortality for critically ill adults.

Design: Retrospective cohort study.

Setting: One-hundred six intensive care units (ICUs) in 84 hospitals.

Patients: Mechanically ventilated adults (n=1,488) with acute lung injury (ALI) included in the Project IMPACT database between December 1995 and September 2001.

Interventions: None.

Measurements and main results: Over half of the cohort had a BMI above the normal range. Unadjusted analyses showed that BMI was higher among subjects who survived to hospital discharge vs. those who did not (p<.0001). ICU and hospital mortality rates were lower in higher BMI categories. After risk-adjustment, BMI was independently associated with hospital mortality (p<.0001) when modeled as a continuous variable. The adjusted odds were highest at the lowest BMIs and then declined to a minimum between 35 and 40 kg/m2. Odds increased after the nadir but remained below those seen at low BMIs. With use of a categorical designation, BMI was also independently associated with hospital mortality (p=.0055). The adjusted odds were highest for the underweight BMI group (adjusted odds ratio [OR], 1.94; 95% confidence interval [CI], 1.05-3.60) relative to the normal BMI group. As in the analysis using the continuous BMI variable, the odds of hospital mortality were decreased for the groups with higher BMIs (overweight adjusted OR, 0.72; 95% CI, 0.51-1.02; obese adjusted OR, 0.67; 95% CI, 0.46-0.97; severely obese adjusted OR, 0.78; 95% CI, 0.44-1.38). Differences in the use of heparin prophylaxis mediated some of the protective effect of severe obesity.

Conclusions: BMI was associated with risk-adjusted hospital mortality among mechanically ventilated adults with ALI. Lower BMIs were associated with higher odds of death, whereas overweight and obese BMIs were associated with lower odds.

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Figures

Figure 1
Figure 1
Included and excluded subjects in study cohort (ALI, acute lung injury; ARDS, adult respiratory distress syndrome; BMI, body mass index).
Figure 2
Figure 2
Risk-adjusted odds ratio for continuous body mass index (BMI) model and hospital mortality. The solid line indicates the point estimates for the adjusted odds ratios for the BMI shown on the x-axis. The gray area represents the 95% confidence interval for the adjusted odds ratio at each BMI. The referent BMI is the rounded midpoint (BMI = 22 kg/m2) of the normal BMI category. Above the horizontal line indicates increased hospital mortality relative to those individuals with a BMI of 22 kg/m2 and below the line indicates decreased hospital mortality. The risk-adjusting model includes age, gender, race, Simplified Acute Physiology Score II probability of survival, diagnosis of renal or genitourinary disease, and an intensive care unit–acquired renal or genitourinary complication. Hosmer-Lemeshow goodness of fit test, p = .227.
See this image and copyright information in PMC

Comment in

  • Did the fat lady sing?
    Taegtmeyer H. Taegtmeyer H. Crit Care Med. 2006 Mar;34(3):915-6. doi: 10.1097/01.CCM.0000202444.39802.B0. Crit Care Med. 2006. PMID: 16505684 No abstract available.
  • Body mass index and mortality in patients with acute lung injury.
    Schultz MJ, Kuiper MA, Spronk PE. Schultz MJ, et al. Crit Care Med. 2007 Feb;35(2):674-5; author reply 675. doi: 10.1097/01.CCM.0000254968.36340.5C. Crit Care Med. 2007. PMID: 17251733 No abstract available.

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