Association of body mass index with short-term outcomes after cardiac surgery: retrospective study and meta-analysis

The relationship between higher body mass index (BMI), decreased morbidity and mortality is known as the "obesity paradox", and has been described in cohorts of patients with hypertension, diabetes, heart failure, coronary and peripheral artery diseases, non-cardiac surgery, and end-stage renal disease. Here we investigated the relationship between BMI and short-term outcomes after adult cardiac surgery to explore the existence of an obesity paradoxical effect. A secondary objective was to perform an updated systematic review to further analyze the association between BMI and 30-day in-hospital mortality after cardiac surgery. A retrospective analysis was performed from a consecutive series of 1823 adult patients who underwent cardiac surgery, that were assigned to five BMI groups: normal weight (18.5-24.9 kg/m2), overweight (25-29.9 kg/m2), class I obese (30-34.9 kg/m2), class II obese (35-39.9 kg/m2), and class III obese or morbidly obese (40-49.9 kg/m2). A systematic review search was performed including controlled trials and observational studies identified in MEDLINE, Embase, SCOPUS, and the Cochrane library (to the end of June 2017). In the present series, overweight and obese patients had similar or slightly lower in-hospital mortality rates after cardiac surgery compared with normal-weight individuals. Conversely, postoperative complication rates increased with higher BMI levels. Most studies included in the review showed that overweight and obese patients had at least the same mortality rate as normal-weight patients, or even a lower death risk. Pooled-data of the meta-analysis provided evidence on the association between higher BMI levels and a lower all-cause in-hospital mortality rate after cardiac surgery.