Safety of a Restrictive versus Liberal Approach to Red Blood Cell Transfusion on the Outcome of AKI in Patients Undergoing Cardiac Surgery: A Randomized Clinical Trial

Abstract

Background: Safely reducing red blood cell transfusions can prevent transfusion-related adverse effects, conserve the blood supply, and reduce health care costs. Both anemia and red blood cell transfusion are independently associated with AKI, but observational data are insufficient to determine whether a restrictive approach to transfusion can be used without increasing AKI risk.

Methods: In a prespecified kidney substudy of a randomized noninferiority trial, we compared a restrictive threshold for red blood cell transfusion (transfuse if hemoglobin<7.5 g/dl, intraoperatively and postoperatively) with a liberal threshold (transfuse if hemoglobin<9.5 g/dl in the operating room or intensive care unit, or if hemoglobin<8.5 g/dl on the nonintensive care ward). We studied 4531 patients undergoing cardiac surgery with cardiopulmonary bypass who had a moderate-to-high risk of perioperative death. The substudy's primary outcome was AKI, defined as a postoperative increase in serum creatinine of ≥0.3 mg/dl within 48 hours of surgery, or ≥50% within 7 days of surgery.

Results: Patients in the restrictive-threshold group received significantly fewer transfusions than patients in the liberal-threshold group (1.8 versus 2.9 on average, or 38% fewer transfusions in the restricted-threshold group compared with the liberal-threshold group; P<0.001). AKI occurred in 27.7% of patients in the restrictive-threshold group (624 of 2251) and in 27.9% of patients in the liberal-threshold group (636 of 2280). Similarly, among patients with preoperative CKD, AKI occurred in 33.6% of patients in the restrictive-threshold group (258 of 767) and in 32.5% of patients in the liberal-threshold group (252 of 775).

Conclusions: Among patients undergoing cardiac surgery, a restrictive transfusion approach resulted in fewer red blood cell transfusions without increasing the risk of AKI.

Keywords: Cardiac surgery; acute kidney injury; red blood cell transfusion.

Graphical abstract

Figure 1.

A total of 4723 patients were included in this substudy, and 4531 were included in the per-protocol analysis. ^aNonadherence to the assigned treatment was considered to have occurred if (1) a transfusion was given without a protocol-defined hemoglobin threshold being met, (2) a transfusion was not initiated after a threshold was met, or (3) a repeat hemoglobin value above the threshold was not documented within the protocol-defined time period. All other aspects of care were left to the discretion of attending clinicians.

Figure 2.

During the 7-day post-operative period, the mean hemoglobin concentration in patients with CKD was approximately 1 g/dl lower in the restrictive-threshold group than the liberal-threshold group. ICU, intensive care unit.

Figure 3.

A restrictive approach to red blood cell transfusion was noninferior to a liberal approach on the risk of AKI in patients with and without CKD.