Impact of body mass index on outcome in patients after coronary artery bypass grafting with and without valve surgery.

BACKGROUND: Among other preoperative parameters, extremely low or extremely high body mass index (BMI) has been discussed as a substantial risk factor for postoperative complications after cardiac surgery. However, the exact relationship between BMI and postoperative risk has not yet been defined.

METHODS: We retrospectively investigated consecutive patients (n=22666) who underwent coronary artery bypass grafting with or without concomitant valve surgery between 1990 and 2001 in our institution. A number of preoperative and intraoperative variables and BMI (as a quadratic term) were used in a logistic regression model as covariates. Further, the patients were divided into 20 groups each with an increase in BMI of 1kg/m(2)(BMI as a categorical variable). The calculations of odds ratios (ORs) for re-intubation, infection, re-exploration, prolonged stay (>1 day) on the intensive care unit (ICU) and 30-day mortality were adjusted for age, gender and type of surgery.

RESULTS: In the multivariate analysis only age (OR between 1.01 and 1.038, P<0.01), additional aortic valve (OR between 1.335 and 2.977, P<0.01) or mitral valve surgery (OR between 2.123 and 3.301, P<0.01) showed significant impact on all five end-points. Patients with BMI between 25 and 35kg/m(2)were not at elevated risk for any of the investigated end-points, except for infection. Patients with BMI between 21 and 27kg/m(2)were not at elevated risk for infection. The ORs for postoperative complications were significantly higher in underweight patients compared with obese or severely obese patients, except those for infection. Further, the underweight patients presented significantly more comorbidity.

CONCLUSION: Patients with low BMI are at higher risk after cardiac surgery than obese or severely obese patients. We hypothesize that a preoperative focus on avoiding and/or reversing cachexia may be more efficacious than reducing obesity in reducing the overall risk associated with heart surgery.