Acute normovolaemic haemodilution after cardiac surgery: a meta-analysis of randomised controlled trials

Background: Acute normovolaemic haemodilution (ANH) is a widely adopted packed red blood cells (pRBC) transfusion sparing strategy after cardiac surgery. While the intraoperative effect is plausible and likely enhanced by the lack of blinding, the effect on the overall in-hospital transfusion rate is unknown. We conducted a meta-analysis of randomised controlled trials to assess whether ANH reduced the proportion of cardiac surgery patients who received allogeneic pRBC transfusions during the postoperative hospital stay. Methods: We searched for trials on ANH in adults undergoing elective cardiac surgery. The primary outcome was the number of patients receiving allogenic pRBC transfusions during the in-hospital postoperative period (excluding trials which solely reported observation period ≤48 h). Secondary outcomes included the number of patients transfused within 48 h after surgery, surgical revision, and all-cause mortality. Results: The proportion of patients who received allogeneic pRBC transfusions was similar in the ANH and standard groups (755/1899 [40%] vs 831/1914 [43%]; risk ratio [RR] 0.94, 95% confidence interval, CI 0.85–1.02]; P=0.15; I2=80%), while they received fewer transfusions in the first 48 postoperative hours (RR 0.64, 95% CI [0.48–0.84]; P=0.001; I2=73%). There was no difference in surgical revision rate (RR 1.22, 95% CI [0.91–1.65]; P=0.18; I2=0%;), all-cause mortality (RR 0.73, 95% CI [0.43–1.24]; P=0.25; I2=0%), or other secondary outcomes. Most included trials had intermediate risk of bias because of lack of outcomes reporting and blinding. Conclusions: Acute normovolaemic haemodilution did not reduce the proportion of cardiac surgery patients who received allogeneic packed red blood cell transfusions during the postoperative hospital stay. This result should be interpreted considering the risk of bias of the included trials. Systematic review protocol. PROSPERO (CRD420251054530).