BACKGROUND: The impact of obesity on postoperative mortality and morbidity in coronary artery bypass grafting (CABG) operations is a widely studied but poorly defined topic. OBJECTIVE: To investigate the effect of body mass index (BMI) on in-hospital mortality and morbidity after isolated CABG surgery. METHODS: Prospectively collected data of a series of 1057 consecutive patients who underwent on-pump isolated CABG surgery were retrospectively analyzed. Patients were divided into five groups according to WHO BMI categorization (defined as underweight [BMI = 20 kg/m(2) to = 25 kg/m(2) to = 30 kg/m(2) to = 35 kg/m(2)]). RESULTS: Of 1057 patients, 13 patients (1.2%) were underweight, 298 (28.2%) were normal weight, 462 (43.7%) were overweight, 218 (20.6%) were obese and 66 (6.2%) were morbidly obese. The mean age was significantly lower in underweight patients, who were also more likely to be male. In contrast, obese and morbidly obese patients were older, and more likely to have comorbidities such as diabetes and hypertension. The incidence of postoperative bronchodilator use (P<0.001), leg wound infection (P=0.038), sternal dehiscence (P=0.039) and development of new-onset atrial fibrillation (P<0.001) was significantly higher in obese and morbidly obese groups. In contrast, postoperative prolonged ventilation (P<0.001), need for blood transfusions (P<0.001) and revision for bleeding (P=0.041), as well as gastrointestinal complications (P<0.001), were significantly higher in underweight patients. Multivariate logistic regression analysis showed that not BMI but female sex, older age and diabetes mellitis were independent risk factors for early mortality after CABG surgery. CONCLUSION: No effect of BMI on early postoperative mortality after CABG surgery could be demonstrated. However, in terms of morbidity, postoperative bleeding and revision for bleeding were increased in underweight patients while sternal dehiscence, wound infections and occurrence of atrial fibrillation were increased in obese and morbidly obese patients
