What is the marginal cost for marginal risk in cardiac surgery?

Background. It has been shown that postoperative length of stay (LOS) correlates highly with mortality risk for cardiac surgical procedures. Similar correlations have been found for charges with LOS and costs with risk. Methods. Postoperative LOS and risk scores were obtained, tabulated, and compiled into the five original Parsonnet risk groups for 2,589 patients who underwent cardiac operations from 1992 through 1996 at one hospital. The correlation of the group mean LOS with the group mean risk was tested. Results. The correlation coefficient was 0.9827; 96.58% of the variance was removed using risk to predict LOS. A calculation of the difference in cost for difference in risk for cohorts of patients is developed. Conclusions. The high correlation of mean LOS with mean risk permits calculation of marginal cost for marginal risk based on clinical data. The marginal cost is equal to the difference in variable costs for cohorts.