For patients undergoing cardiac surgery that involves cardiopulmonary bypass who are at high risk for perioperative mortality, a restrictive red blood cell transfusion strategy lowers the need for transfusion without increasing the incidence of acute kidney injury, new research shows.

The issue is more nuanced than it first appears because a lower hemoglobin level causes tissue hypoxia, which has the potential to injure the kidney, said Amit Garg, MD, from the London Health Sciences Centre in Ontario, Canada, during a news briefing here at Kidney Week 2018.

"However, RBC transfusions are not benign," he noted. In addition to liberating free hemoglobin, "RBC products from transfusions have been shown to be associated with kidney injury in and of themselves."

There is "equipoise regarding when you should jump in and give a transfusion," said Garg, which is why a randomized controlled trial "is very helpful regarding trying to tease out what the right trigger is for initiating blood transfusions."

TRICS3 Kidney Substudy

Overall results from the Transfusion Requirements in Cardiac Surgery (TRICS) 3 trial were recently presented at the European Society of Cardiology Congress, as reported by Medscape Medical News.

In the main study, a restrictive approach to blood transfusions was shown to be noninferior to a liberal approach concerning the primary composite outcome of death from any cause, myocardial infarction, stroke, and new-onset renal failure with dialysis six months after surgery.

Patients treated with the restrictive approach received a transfusion when the hemoglobin levels fell below 7.5 gm/dL. Patients treated with the liberal approach received a transfusion when hemoglobin levels fell below 9.5 g/dL in the operating room or intensive care unit or fell below 8.5 g/dL in a nonintensive care ward.

In a kidney substudy of TRICS 3, Garg and his colleagues compared acute kidney injury and related kidney outcomes in 2257 patients randomized to the restrictive strategy and 2280 patients randomized to the liberal strategy.

The mean age of the study cohort was 72 years, two-thirds of the patients were men, three-quarters had been treated for hypertension, and one-quarter had diabetes.

Also, approximately one-third of the patients had preoperative chronic kidney disease, defined as an estimated glomerular filtration rate (eGFR) of less than 60 mg/min per 1.73 m2.

For patients with preoperative chronic kidney disease, the risk for acute kidney injury was not appreciably different between the restrictive and liberal strategies (33.6% vs. 32.5%).

"We found no higher risk of AKI when we looked at it from multiple different ways, so that was reassuring," Garg noted. Also, there were 38% fewer blood transfusions in the restrictive group than in the liberal group (1.8 vs. 2.9).