Intraoperative allogeneic packed red blood cell transfusions and postoperative delirium: a retrospective cohort study in the USA

Background: Delirium is a frequent and often detrimental postoperative complication that may be precipitated by perioperative inflammation. Packed red blood cell (PRBC) transfusions are important to maintain adequate oxygen delivery to ensure cerebral oxygenation, but can trigger inflammatory responses. This study aimed to evaluate the association between intraoperative PRBC transfusions, dependent on transfusion threshold and postoperative delirium. Methods: This was a retrospective cohort study analyzing registry data from an academic tertiary-care center in Massachusetts, United States of America. Adult hospitalized patients who underwent general anesthesia for surgery between January 1, 2008 and January 15, 2024 with intraoperative hemoglobin measurements were included. Exclusion criteria included preoperative delirium or cognitive impairment, postoperative ventilation >72 h, an American Society of Anesthesiologists physical status >IV, and missing confounder data. The primary exposure was intraoperative allogeneic PRBC transfusions. The primary outcome was delirium diagnosed within seven days after surgery, identified through diagnostic codes, Confusion Assessment Method, and manual chart review. Findings: Among 42,313 included patients, 6970 (16.5%) received intraoperative PRBC transfusions, and 2871 (6.8%) developed postoperative delirium. Patients receiving intraoperative PRBC transfusions had a higher risk of postoperative delirium (adjusted odds ratio 1.15, 95% confidence interval 1.03-1.29, P = 0.016) in a dose-dependent manner. The PRBC transfusion-associated risk of delirium was higher when intraoperative hemoglobin was at higher nadirs (P-for-interaction = 0.002). At nadirs below 7.3 g/dL, PRBC transfusions were not associated with delirium. Interpretation: Intraoperative PRBC transfusions administered at higher hemoglobin nadirs, around 7.3 g/dL, were associated with an increased risk of postoperative delirium, suggesting that greater attention to delirium risk may be warranted among transfused patients and that transfusion triggers during surgery merit careful consideration. Funding: Department of Anesthesia, Critical Care, and Pain Medicine, Beth Israel Deaconess Medical Center.