Association between preoperative anemia and postoperative delirium in elderly patients undergoing non-cardiac 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.