The Barts Surgical Infection Risk (B-SIR) tool: external validation and comparison with existing tools to predict surgical site infection after cardiac surgery

Objective

Further to previous development and internal validation of the Barts Surgical Infection Risk (B-SIR) tool, this study sought to explore the external validity of the B-SIR tool and compare it with the Australian Clinical Risk Index (ACRI), and the Brompton and Harefield Infection Score (BHIS).

Study design and setting

This multi-centre retrospective analysis of prospectively collected local data included adult (age ≥18 years) patients undergoing cardiac surgery between January 2018 and December 2019. Pre-pandemic data were used as a reflection of standard practice. Area under the curve (AUC) was used to validate and compare the predictive power of the scores, and calibration was assessed using the Hosmer–Lemeshow test and calibration plots.

Results

In total, 6022 patients from three centres were included in the complete case analysis. The mean age was 66 years, 75% were men and 3.19% developed a surgical site infection (SSI). The B-SIR tool had an area under the curve (AUC) of 0.686 [95% confidence interval (CI) 0.649–0.723], similar to the developmental study (AUC=0.682, 95% CI 0.652–0.713). This was significantly higher than the BHIS AUC of 0.610 (95% CI 0.045–0.109; P<0.001) and the ACRI AUC of 0.614 (95% CI 0.041–0.103; P<0.001). After recalibration using a correction factor, the B-SIR tool gave accurate risk predictions (Hosmer–Lemeshow test P=0.423). The multiple imputation result (AUC=0.676, 95% CI 0.639–0.712) was similar to development data, and higher than the ACRI and BHIS.

Conclusion

External validation indicated that the B-SIR tool predicted SSI after cardiac surgery better than the ACRI and BHIS. This suggests that the B-SIR tool could be useful for use in routine practice.