The Association of Postoperative Anaemia with Outcomes in Cardiac Surgical Patients Eligible for Patient Blood Management: A Single Institution Retrospective Cohort Study

Abstract

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.