The impact of low preoperative fat-free body mass on infections and length of stay after cardiac surgery: a prospective cohort study

Several studies have shown low fat-free mass index to be a stronger predictor for mortality than low body mass index. The main aim of this study was to assess the still unknown association between preoperative low fat-free mass index and adverse cardiac surgical outcomes. In a prospective observational study, fat-free mass index was determined by bioelectric impedance spectroscopy on hospital admission. Associations between low fat-free mass index and postoperative infections and mortality, as well as prolonged intensive care unit and hospital stays, were analyzed with logistic and Cox regression techniques. Between February 2008 and December 2009, 325 adult patients admitted for elective heart surgery were included. Analyses showed that low fat-free mass index, present in 8.3% of patients, was independently associated with occurrence of infections after cardiac surgery (18.5% vs 4.7%; adjusted odds ratio, 6.9; 95% confidence interval, 1.8-27.7; P = .01). Low fat-free mass index also tended to be associated with higher risk of longer postoperative intensive care unit stay (adjusted hazard ratio, 0.7; 95% confidence interval, 0.4-1.1; P = .09). When classifying patients as undernourished by traditional methods (body mass index ≤21.0 kg/m(2) or ≥10% weight loss in preceding 6 months), half of patients with low fat-free mass index were misclassified as well nourished. Low fat-free mass index is associated with increased occurrence of adverse outcomes after cardiac surgery. We advocate fat-free mass index as the leading parameter in classifying and treating undernourished cardiac surgical patients, which might improve recovery rates after cardiac surgery