Does body mass index (BMI) affect cost in cardiac surgery? 'A pound (pound) for pound (lb) analysis'.

The effect of BMI on cost of intensive care unit (ICU) stay and ward stay in cardiac surgery is currently unknown. To assess these data on BMI, ICU stay and EuroSCORE were prospectively collected for 6100 patients undergoing cardiac surgery between 2000 and 2004. Patients were categorised according to BMI and comparisons were conducted, using non-parametric tests (Kruskal-Wallis and Mann-Whitney U-tests). One day in ICU was costed at pound1,300 and one ward-day pound300/day by this hospital's finance department. Despite similar median (due to a distribution skewed to a short ICU stay), a significant difference is observed between all 6 groups (Kruskal-Wallis; P<0.001) for ICU stay and ward stay. Underweight and morbidly obese patients had longer ICU stays compared with the ideal weight patients (P=0.010 and P=0.004, respectively); while overweight and obese patients had shorter ICU stays (P<0.001 and P=0.007, respectively). Underweight patients had a longer ward stay than ideal weight patients (P=0.005) but there was no difference between ideal and morbidly obese patients (P=0.789). These results demonstrate that BMI has a significant impact on ICU and ward stay with 'ideal weight' not always being ideal for patients undergoing cardiac surgery. This cost appears to be independent of EuroSCORE.