Association between perioperative changes in complement levels and postoperative delirium in elderly patients undergoing hip or knee arthroplasty: a prospective cohort study

Postoperative delirium (POD) is a common postoperative complication in elderly patients undergoing major surgery, characterized by an acute disturbance of consciousness and cognition occurring within a short period after surgery. POD has substantial adverse effects on patient health, and early perioperative identification of high-risk individuals is crucial for timely intervention and improved clinical outcomes. A prospective cohort of 153 elderly patients scheduled for hip or knee arthroplasty was enrolled. Peripheral blood samples were collected to measure plasma concentrations of complement components C1q, C3, and C4. POD was assessed from postoperative days 1 to 7 using standardized diagnostic criteria. POD was observed in 17 (11%) out of 153 participants. After adjustment for age, preoperative Mini-Mental State Examination (MMSE) score, and duration of anesthesia, the postoperative increase in plasma C3 (ΔC3) was significantly associated with POD (adjusted OR = 1.069, 95% CI 1.021–1.120, P = 0.005). A sensitivity analysis using Firth’s penalized logistic regression yielded consistent results, supporting the stability of this association. Receiver operating characteristic (ROC) analysis showed moderate discriminative ability (AUC = 0.729, 95% CI 0.587–0.872, P = 0.002), with a sensitivity of 64.7% and specificity of 84.6% at a cutoff of 24.0 mg/dL. ΔC3 showed a weak positive correlation with POD symptom burden (ρ = 0.199, P = 0.014) and remained significantly associated with greater symptom burden after adjustment (OR = 1.032, 95% CI 1.008–1.057, P = 0.010). A greater postoperative increase in plasma C3 was significantly associated with the occurrence of POD and greater POD symptom burden in elderly patients undergoing hip or knee arthroplasty. The trial was retrospectively registered at Chinese Clinical Trial Registry (ChiCTR2400090451) on September 30, 2024.