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

OBJECTIVE: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.