Absence of a relationship between surgical volume and mortality in cardiac surgery units in Spain

Introduction and objectives. The relationship between the annual number of cardiac procedures at a particular center (i.e., volume) and surgical outcome is controversial. Several studies in western countries indicate that there is an inverse relationship between surgical volume and mortality. We studied the number of procedures carried out at several cardiac surgery units in Spain and their relationship to overall and risk-adjusted mortality. Methods. This prospective observational study carried out in 6054 patients undergoing cardiac surgery at 16 hospitals represents 34% of all cardiac surgery performed in Spain during 2004. Data on risk factors and outcomes for each patient treated at participating institutions were analyzed. Data from each center were checked by an external referee. Surgical risk was evaluated for each patient using the Parsonnet and EuroSCORE methods, with the aim of determining risk-adjusted mortality. Results. Overall mortality was 7.7% (95% confidence interval, 7.0%-8.4%). The risk-adjusted mortality index was calculated to be 0.81 using the Parsonnet method, and 1,12 using EuroSCORE. The Pearson correlation coefficient for the relationship between the number of procedures carried out at a center and mortality was 0.065 for overall mortality, 0.092 for risk-adjusted mortality (Parsonnet method), and 0.111 for risk-adjusted mortality (EuroSCORE method). After discarding data from the two centers with highest and lowest mortality rates, respectively, the correlations were -0.464, -0.420 and -0.267, respectively. Conclusions. No statistically significant relationship was found between the number of cardiac procedures carried out at a particular center in Spain and inhospital mortality.