Acute normovolemic hemodilution and cardiac surgery-associated acute kidney injury: a retrospective cohort study

Allogeneic blood transfusions are associated with increased postoperative morbidity and mortality, highlighting transfusion-sparing strategies. Acute normovolemic hemodilution (ANH) is one strategy; nevertheless, its adoption in cardiac surgery remains limited due to concerns about organ perfusion-particularly renal oxygenation. Because allogeneic transfusions are linked to the risk of cardiac surgery-associated acute kidney injury (CSA-AKI), ANH may lower this risk. We sought to evaluate the association between ANH and CSA-AKI, defined as postoperative renal replacement therapy (RRT) after elective cardiac surgery.

We conducted a retrospective cohort study using the JMDC (JMDC Inc., Tokyo, Japan) Hospital database, focusing on patients undergoing elective cardiac surgery between 1 April 2016 and 31 May 2023. Patients were classified according to whether they underwent ANH, into ANH and non-ANH groups. The primary outcome was initiation of RRT within seven days postoperatively. Secondary outcomes were in-hospital mortality, length of hospital stay, and units of allogeneic blood transfusion on the day of surgery. To address confounding, we used marginal structural models with standardized mortality ratio weighting based on the propensity score.

Among 19,387 patients, 1,644 (8%) received ANH. After standardized mortality ratio weighting, the ANH group had a lower incidence of postoperative RRT than the non-ANH group (28/1,644 [2%] vs 45/1,639 [3%]; risk ratio, 0.63; 95% confidence interval, 0.43 to 0.92; P = 0.02). The ANH group also required fewer allogeneic blood transfusion units on the day of surgery. In-hospital mortality did not differ significantly between groups.

In elective cardiac surgery, ANH was associated with reduced postoperative RRT and allogeneic transfusion requirements; however, residual confounding may persist, requiring confirmation in future studies.