Association between preoperative anemia and postoperative delirium in elderly patients undergoing noncardiac surgery: a retrospective observational study

Background: The association between preoperative anemia and postoperative delirium (POD) is unclear. We sought to evaluate the effect of preoperative anemia on the risk of POD in elderly patients after non-cardiac surgery. Methods: We retrospectively analyzed 62 600 patients aged over 60 years undergoing non-cardiac surgery between January 2011 and June 2019. The patients were divided into two groups according to the presence of preoperative anemia defined as hemoglobin < 13 g/dl for men and < 12 g/dl for women. Anemia was further categorized into mild or moderate-to-severe anemia based on a cutoff of 11 g/dl. The primary outcome was POD within 7 days after surgery. The secondary outcomes included one-and three-year mortality after surgery. The inverse probability of treatment weighting (IPTW) method was used to adjust for confounders between the two groups. Results: The overall incidence of POD was 3.9% (2447/62 600) within 7 days after surgery. After IPTW, preoperative anemia was significantly associated with increased risk of POD (odds ratio [OR]: 1.42, 95% CI [1.30−1.55], P < 0.001). Also, the risk of POD increased with the severity of anemia (OR: 1.32, 95% CI [1.18−1.47], P < 0.001 for mild anemia; and OR: 1.70, 95% CI [1.50−1.93], P < 0.001 for moderate-to-severe anemia). This association was similar for one-and three-year mortality. Conclusions: Preoperative anemia was associated with an increased risk of POD in elderly patients after non-cardiac surgery. Further investigations are required to verify whether preoperative anemia is a modifiable risk factor for POD.