Cardiac surgical mortality: comparison among different additive risk-scoring models in a multicenter sample

OBJECTIVE: To compare the performance of several risk-scoring models to predict surgical mortality following open heart surgery. DESIGN: A prospective observational study. SETTING: Seven tertiary cardiac centers (3 private and 4 public and teaching hospitals) in Catalonia (Spain). PATIENTS: A consecutive sample of 1287 patients submitted to open heart surgery during a 6 1/2-month period (February 14, 1994, to August 31, 1994). INTERVENTION: None. MAIN OUTCOME MEASURE: Model discrimination capability was assessed with the c-statistic. A chi(2) test to compare observed and predicted mortality rates was used as a measure of model calibration. Performance of centers was evaluated through the standardized mortality ratio and using the center as an indicator variable in a logistic regression model. The agreement among models for individual predictions was tested using weighted K statistics. RESULTS: Models developed in other health care contexts showed, as expected, lower c-statistics and an inappropriate calibration. There were no statistically significant differences among hospitals after adjusting for baseline patients' risk factors with the use of any of the different models. Models also agree in the standardized rank of centers. Weighted K statistics indicated poor agreement among models for individual patient risk prediction. CONCLUSIONS: Models can be a useful tool to compare providers' performance and to give a more in-depth look at the process of care when appropriately customized to the context. Severity-adjusted models can also play a role in supporting the informed and subjective surgeon's assessment, but it is inappropriate to use them for individual predictions.