An association between red blood cell (RBC) transfusion and increased incidence of perioperative complications has been highlighted in a large number of prospective and restrospective studies. In the study published in JAMA Surgery by Ruchika Goel and her group, the authors looked at a potential association between perioperative RBC transfusion and the incidence of postoperative venous thromboembolism (VTE).

The authors performed a retrospective analysis of a national database, the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP), a multicentre prospective registry of patients undergoing surgery in 525 institutions across North America. A total of 750 937 patients who underwent surgical procedures and were included in the 2014 ACS-NSQIP database were analysed.

After adjustment for several potential confounders (e.g. age, sex, race, body mass index, functional health status before surgery, American Society of Anesthesiology severity class, hospital length of stay, occurrence of sepsis, mechanical ventilation dependence, disseminated cancer, and work-related relative value units as a surrogate for complexity of surgery), perioperative RBC transfusion was associated with higher odds of VTE (adjusted odds ratio [aOR], 2.1; 95% CI, 2.0-2.3), deep vein thrombosis (aOR, 2.2; 95% CI, 2.1-2.4), and pulmonary embolism (aOR, 1.9; 95% CI, 1.7-2.1). The authors also reported a significant dose-response effect with increased odds of VTE as the number of intraoperative and/or postoperative RBC transfusions increased.

The study by Goel et al. is very interesting and highlights new important aspects of transfusion medicine. The authors nicely review and introduce the concept of allogeneic RBCs affecting inflammation and coagulation, and thereby promoting increased incidence of VTE. Even though the study was not designed to look at the aetiology of RBC transfusion-associated thrombotic complications, the authors describe an interesting concept that will need to be studied in vivo.

In their study, the authors were only allowed to report an association between RBC transfusion and an increase risk of VTE. Despite their efforts to adjust for confounding factors and to perform multiple sensitivity analyses, they were not able to take every parameters into consideration. As an example, one could argue that patients exposed to RBC transfusion were also exposed to non-RBC transfusions or coagulation factors. Indeed, the ACS-NSQIP does not record transfusion of platelets, plasma, cryoprecipitate or any other coagulation factor concentrates that could have been administered as part of the bleeding management strategy. In addition, the chronic thrombotic profile of the patients was not taken into account (e.g. history of thrombosis, antiplatelet therapy, anticoagulation).

In summary, the paper published Goel et al. in JAMA Surgery is an important piece, highlighting a new concept, namely that RBC transfusion could increase the risk of thrombotic complications in the surgical population. Further studies are needed to confirm that this is more than an association, i.e. that allogeneic RBCs actually promote clot formation and thrombosis in the surgical population.

David Faraoni, MD, PhD, FCCP, FAHA
Associate Professor of Anesthesia
Department of Anesthesia
University of Toronto
Staff Anesthesiologist
Division of Cardiac Anesthesia
Department of Anesthesia and Pain Medicine
The Hospital for Sick Children
Toronto, ON, Canada