Body mass index is associated with the development of acute respiratory distress syndrome

Abstract

Background: The relationship between body mass index (BMI) and development of acute respiratory distress syndrome (ARDS) is unknown.

Methods: A cohort study of critically ill patients at risk for ARDS was carried out. BMI was calculated from admission height and weight. Patients were screened daily for AECC (American European Consensus Committee)-defined ARDS and 60-day ARDS mortality.

Results: Of 1795 patients, 83 (5%) patients were underweight (BMI <18.5 kg/m(2)), 627 (35%) normal (BMI 18.5-24.9), 605 (34%) overweight (BMI 25-29.9), 364 (20%) obese (BMI 30-39.9) and 116 (6%) severely obese (BMI > or =40). Increasing weight was associated with younger age (p<0.001), diabetes (p<0.0001), higher blood glucose (p<0.0001), lower prevalence of direct pulmonary injury (p<0.0001) and later development of ARDS (p = 0.01). BMI was associated with ARDS on multivariate analysis (OR(adj) 1.24 per SD increase; 95% CI 1.11 to 1.39). Similarly, obesity was associated with ARDS compared with normal weight (OR(adj) 1.66; 95% CI 1.21 to 2.28 for obese; OR(adj) 1.78; 95% CI 1.12 to 2.92 for severely obese). Exploratory analysis in a subgroup of intubated patients without ARDS on admission (n = 1045) found that obese patients received higher peak (p<0.0001) and positive end-expiratory pressures (p<0.0001) than non-obese patients. Among patients with ARDS, increasing BMI was associated with increased length of stay (p = 0.007) but not with mortality (OR(adj) 0.89 per SD increase; 95% CI 0.71 to 1.12).

Conclusion: BMI was associated with increased risk of ARDS in a weight-dependent manner and with increased length of stay, but not with mortality. Additional studies are needed to determine whether differences in initial ventilator settings may contribute to ARDS development in the obese.

Figure 1

Breakdown of patients by weight in the Molecular Epidemiology of ARDS cohort

Figure 2

Development of ARDS (Figure 2a) and 60-mortality after developing ARDS (Figure 2b) by BMI category. P-values is for Cochran-Armitage trend test.

Figure 3

Odds ratio for development of ARDS (Figure 3a) and 60-mortality after developing ARDS (Figure 3b) by BMI category. Reference group is patients in the normal weight category. Odds ratio for development of ARDS are stratified by calendar year of study and adjusted for age, gender, Apache III score (without the Pa0₂/FiO₂ score), diabetes, clinical risk for ARDS such as septic shock and direct pulmonary injury, hematologic failure, transfusion of packed red blood cells, peak glucose in the first 24 hours of ICU admission and acute respiratory failure on ICU admission. Odds ratio for ARDS mortality are stratified by calendar year of study and adjusted for age, gender, Apache III score, etiology for ARDS (septic shock, or direct pulmonary injury), comorbidities such as diabetes and chronic liver disease, hematologic failure, number of packed red cells transfused, peak glucose in the first 24 hours of ICU admission, and high tidal volume ventilation (> 8 cc/kg IBW) on day ARDS criteria were fulfilled.