Preoperative Anemia Linked to Postoperative Delirium in New Study

A recent retrospective analysis study indicated a correlation between preoperative anemia and likelihood of postoperative delirium (POD) in elderly patients after non-cardiac surgery.1

POD is a serious complication that affects up to 5% of general surgery patients, depending on type of surgery and patient population. POD is also increased with longer hospital or ICU stays, higher morbidity, and higher risk of mortality.2 However, despite various identified risk factors, very few have been modifiable in any meaningful way.

“Therefore, this retrospective study aimed to investigate the relationship between preoperative anemia and POD in elderly patients undergoing non-cardiac surgery,” wrote Ah Ran Oh, MD, PhD, Samsung Medical Center, Sungkyunkwan University School of Medicine, and colleagues. “We hypothesized that preoperative anemia would be associated with increased risk of delirium after non-cardiac surgery.”1

The team analyzed 62,600 patients >60 years undergoing non-cardiac surgery between January 2011 and June 2019. Participants were divided into 2 groups depending on presence of preoperative anemia, which was defined as hemoglobin <13 g/L for men and <12 g/dl for women.1

The primary outcome was POD within 7 days after surgery. The secondary outcome was mortality, which was investigated during a one- and a three-year follow-up after surgery.1

Based on preoperative hemoglobin levels, the team sorted 45,199 (72.2%) patients into the normal group and 17,401 (27.8%) into the anemia group. Mean preoperative hemoglobin level was 13.9+/- 1.1 g/dl in the normal group and 11.1 +/- 1.2 g/dl in the anemia group.1

Patients in the anemia group tended to be older and had a higher incidence of comorbidities than the normal group. Patients with anemia also underwent high-risk and emergency surgery more often than patients without anemia.1

Oh and colleagues indicated that the overall incidence of POD within a week after surgery was 3.9% (n = 2447); it was higher in the anemia group (7.2%) than the control group (2.6%). A significant association was discovered between preoperative anemia and POD through adjusted analysis (adjusted odds ratio [aOR], 1.42 [95% CI, 1.30-1.55]; P <.001).1

The anemia group also experienced more 1- and 3-year mortalities (aHR, 2.68 [95% CI, 2.45-2.93]; P <.001 for 1-year mortality; aHR, 2.19 [95% CI, 2.07-2.33]; P <.001 for 3-year mortality).1

Patients were then divided into mild anemia (n = 10,664) and moderate-to-severe anemia (n = 6,737): POD incidence was 6.1% in the mild group and 9.0% in the moderate-to-severe group. The risk of POD increased with anemia severity in both groups (adjusted OR, 1.32 [95% CI, 1.18-1.47]; P <.001 in the mild group and adjusted OR 1.70 [95% CI, 1.50-1.93]; P <.001 in the moderate-to-severe group).1

Further analysis showed 1-year (aHR, 2.24 [95% CI, 2.02-2.49]; P <.001 in mild anemia and aHR, 4.13 [95% CI, 3.67-4.65]; P <.001 in moderate-to-severe anemia) and 3-year (aHR, 1.96 [95% CI, 1.83-2.10]; P <.001 in mild and aHR, 3.03 [95% CI, 2.79-3.30]; P <.001 in moderate-to-severe anemia) mortality exhibited a similar association.1

Oh and colleagues suggested that one possible explanation for the association between anemia and delirium was the diminished oxygen-carrying capacity of blood, which can potentially lead to cerebral hypoxia.1

Previous studies have corroborated this by indicating that poor cerebral oxygenation is correlated to delirium. However, the team noted no direct relationship between anemia and low cerebral oxygenation was made in this study.1

Subgroup analysis highlighted a 70% or higher increased risk in the moderate-to-severe anemia group than control, compared to a 32% increased risk in the mild anemia group. The association between anemia and POD was more significant among men than women, as well as those with a low Charlson Comorbidity Index.1

Oh and colleagues do, however, mention the study’s potential limitations as well, such as the fact that POD is notoriously difficult to detect medically. Similarly, perioperative anemia correction through iron, tranexamic acid, or erythropoietin could not be accounted for given the study’s format.1

“Further prospective studies should be conducted to demonstrate whether mediating preoperative anemia can effectively reduce POD,” Oh and colleagues wrote.1

References

1. Oh A R, Park J, Kim CS, Lee SM, Yoo SY. Association between preoperative anemia and postoperative delirium in elderly patients undergoing non-cardiac surgery: A retrospective observational study. Korean Journal of Anesthesiology. Published online April 7, 2025. doi:10.4097/kja.24701

2. Deiner S, Silverstein JH. Postoperative delirium and cognitive dysfunction. Br J Anaesth. 2009;103 Suppl 1(Suppl 1):i41-i46. doi:10.1093/bja/aep291