Systemic immune-inflammation index predicts postoperative delirium in elderly patients after surgery: A retrospective cohort study

Background: Postoperative delirium (POD) is a common complication among elderly patients after surgery. It is unclear whether the systemic immune-inflammation index (SII) can be a predictor of POD. We explored the prognostic value of the SII in predicting POD in elderly patients undergoing nonneurosurgery and noncardiac surgery in a large retrospective cohort. Methods: We enrolled elderly patients undergoing nonneurosurgery and noncardiac surgery between January 2014 and August 2019. Univariate and multivariate logistic regression analyses were performed to explore the correlation between POD and the SII value as both a continuous and categorical variable. Then, propensity score matching (PSM) analysis was applied to eliminate the confounding effect of covariates and prove our results. Subgroup analyses were then performed to discover the association between the SII and POD in different subgroups. Results: A total of 29608 patients with a median age of 70 years (IQR: 67-74) were enrolled in the retrospective cohort. The cut-off value of the SII was 650, which was determined by the receiver operating characteristic (ROC) curve. The ORs of an SII value>650 was 2.709 (95% CI:2.373-3.092, P< 0.001), 1.615 (95% CI:1.384-1.882, P< 0.001), 1.855 (95% CI:1.602-2.146, P650 was 1.301 (95% CI: 1.062-1.598, P=0.011). The subgroup analysis indicated that the SII indicates a significantly increased risk of POD in patients with Hb<130 g/L, 4*10 9 /L<WBC≤10*10 9 /L, albumin <39 g/L, or a duration of MAP<60 mmHg ≥5 min. The SII was found to be a useful prognostic predictor of POD for patients with different ages, sexes, and ASA classifications. Conclusions: The SII had a predictive value for POD in patients undergoing nonneurosurgery and noncardiac surgery. As an index generated from routine blood tests, the SII has advantages regarding cost and time. After further validation, the SII may provide a new option for POD prediction.