Institutional volume and postoperative efficiency as determinants of in-hospital mortality after coronary artery bypass grafting: a multilevel analysis in São Paulo, Brazil.

OBJECTIVE

To evaluate the association between hospital procedural volume, postoperative efficiency, and in-hospital mortality and costs among patients undergoing coronary artery bypass grafting in the public health system of the State of São Paulo, Brazil.

METHODS

This retrospective ecological study analyzed isolated coronary artery bypass grafting procedures recorded in the Brazilian Hospital Information System in São Paulo between 2008 and 2024. Outcomes included in-hospital mortality, postoperative length of stay, and inflation-adjusted hospitalization costs. We assessed mortality using Poisson regression models, while we analyzed costs and length of stay using linear mixed-effects models with hospital-level random intercepts. We performed sensitivity analyses using alternative inclusion criteria.

RESULTS

We included 82,398 procedures from 45 hospitals. Median annual hospital volume was 71 procedures. Overall in-hospital mortality was 6.75%, and mean length of stay was 12.2 days. High-performing centers showed substantially lower mortality (4.82% versus 9.94%), shorter length of stay (12.3 versus 16.5 days), and lower adjusted costs (R$24,246 versus R$28,633) compared with low-performing institutions. At the institutional level, longer mean postoperative stay was positively associated with higher hospital-level mortality rates (incidence rate ratios: 1.015 per day; 95%CI 1.006 - 1.024), though reverse causation cannot be excluded given the ecological study design. Higher annual procedural volume was independently associated with lower costs, whereas prolonged hospitalization significantly increased expenditures. Between 2008 and 2024, total surgical volume declined, while mortality decreased, suggesting progressive improvements in care quality.

CONCLUSION

Higher institutional volume and greater postoperative efficiency are associated with lower mortality and reduced costs after coronary artery bypass grafting in the public health system of the State of São Paulo, Brazil. Postoperative length of stay emerged as a key marker of institutional performance and clinical course.