The association between obesity and outcomes in critically ill patients

background: Obesity rates are increasing worldwide, particularly in North America. The impact of obesity on the outcome of critically ill patients is unclear. Methods: A prospective observational cohort study of consecutive patients admitted to a tertiary critical care unit in Canada between January 10, 2008 and March 31, 2009 was conducted. Exclusion criteria were age < 18 years, admission < 24 h, planned cardiac surgery, pregnancy, significant ascites, unclosed surgical abdomen and brain death on admission. Height, weight and abdominal circumference were measured at the time of intensive care unit ( ICU) admission. Coprimary end points were ICU mortality and a composite of ICU mortality, reintubation, ventilator- associated pneumonia, line sepsis and ICU readmission. Subjects were stratified as obese or nonobese, using two separate metrics: body mass index ( BMI) >= 30 kg/ m(2) and a novel measurement of 75th percentile for waist- to-height ratio ( WHR). Results : Among 449 subjects with a BMI = 18.5 kg/ m2, both BMI and WHR were available for comparative analysis in 348 ( 77.5%). Neither measure of obesity was associated with the primary end points. BMI = 30 kg/ m2 was associated with a lower odds of six- month mortality than the BMI < 30 kg/ m2 group ( adjusted OR 0.59 [ 95% CI 0.36 to 0.97]; P= 0.04) but longer intubation times ( adjusted RR 1.56 [ 95% CI 1.17 to 2.07]; P= 0.003) and longer ICU length of stay ( adjusted RR 1.67 [ 95% CI 1.21 to 2.31]; P= 0.002). Conversely, measurement of 75th percentile for WHR was associated only with decreased ICU readmission ( OR 0.23 [ 95% CI 0.07 to 0.79]; P= 0.02).