Can we afford to do cardiac operations in 1996? A risk-reward curve for cardiac surgery

Parsonnet risk estimates and postoperative lengths of stay were studied for two cohorts of cardiac surgical patients. The first cohort consisted of 287 patients and was taken from 1984, the first full year of this cardiac surgical program. The second cohort consisted of all 1,167 patients operated on in the calendar years 1989 to 1991. We found that the mean risk for the patients had nearly doubled in this interval and that the risk distribution changed significantly from one skewed toward good-risk patients to a nearly uniform distribution through all risk categories. A high correlation was identified (0.9761) between the postoperative length of stay and the mean risk estimates for the 1989 to 1991 cohort of patients. This permits a regression equation to be calculated showing that the length of stay could be estimated at 7.06 days + 0.21 times the mean risk for a patient or cohort of patients. This relationship is then used to develop a relationship between the net income for a given case or cohort of patients and the length of stay or risk. These data suggest that, in most hospitals, hospital fixed costs are a major determinant, even more so than daily charges, of the relationship between the hospital's finances and the mean risks of patients undertaken in the cardiac surgical program. The consequences of this are discussed.