Background Anaemia is prognostically important and affects 30-40% of cardiac surgical patients. The objective of this study was to examine the association of pre- and postoperative anaemia with outcomes in cardiac surgical patients. Methods This was a single-institution retrospective cohort study including cardiac surgical patients from October 26, 2020 to December 3, 2021. Patients were classified as preoperatively non-anaemic (hemoglobin ≥ 130 g/L), anaemic, or treated with IV Iron. The main predictors of interest were nadir haemoglobin on postoperative days 1-2 and preoperative anaemia and receipt of IV iron therapy. The primary outcome was number of red blood cell units (RBC) transfused on postoperative days 1-7. Secondary outcomes included acute kidney injury, hospital length of stay, and 30 day in-hospital mortality. Regression models, adjusted for demographics, comorbidities, and surgical characteristics, examined the association between predictors and outcomes. Results A total of 844 patients were included [528 (63%) non-anaemic, 276 (33%) anaemic, and 40 (5%) anaemic, treated with IV iron]. There was no difference between groups in RBC transfusion or mortality, however anaemic patients had a higher adjusted risk for acute kidney injury [aOR 2.69 (95% CI, 1.37 to 5.30), p=0.004] and longer hospital length of stay [aRR 1.38 (95% CI, 1.24 to 1.54), p<0.0001] compared to non-anaemic patients. Patients treated with IV iron did not have the same increased risk. A lower postoperative haemoglobin nadir was significantly associated with increased risk for all outcomes. Conclusions Postoperative anaemia confers additional risk regardless of preoperative anaemia status. Further research is needed to better clarify these associations.

Justyna Bartoszko, MD, MSc: In part supported by a merit award from the Department of Anesthesiology and Pain Medicine, University of Toronto; has received honoraria from Octapharma Keyvan Karkouti, MD, MSc: In part supported by a merit award from the Department of Anesthesiology and Pain Medicine, University of Toronto; has received research support, honoraria, or consultancy for speaking engagements from Octapharma, Instrumentation Laboratory, and Bayer Jeannie Callum, MD: Has received research support from Canadian Blood Services and Octapharma Yulia Lin, MD: Has received research support from Canadian Blood Services; and is a consultant with Choosing Wisely Canada.

This study did not receive any funding

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