In 2016, the Journal of the American Medical Association published the AABB guidelines for packed red blood cell (pRBC) transfusion and storage. They summarized data across multiple subgroups using data published between 1950 and May of 2016. Five trials were used to justify a transfusion threshold of 8 g/dL hemoglobin (Hgb) for patients hospitalized following nonemergent cardiac surgery. The guideline authors noted that postcardiac surgery patients may tolerate a lower threshold, but most relevant trials used 8 g/dL Hgb in the restrictive arm. They noted that an ongoing randomized controlled trial (RCT) of nonemergent postcardiac surgery patients using a lower threshold (7.5 g/dL Hgb), with results due in 2017, might determine whether "lower is better."
The 30-day results from the RCT (known as the TRICS trial) were released in 2017, and the New England Journal of Medicine recently published a 6-month follow-up. TRICS enrolled postcardiac surgery patients at moderate-to-high risk for death, according to EuroSCORE (European System for Cardiac Operative Risk Evaluation) criteria. Patients in the restrictive group received pRBCs at a Hgb of 7.5 g/dL, regardless of location within the hospital. In the liberal group, the Hgb target was 9.5 g/dL in the operating room or intensive care unit, but 8.5 g/dL on the hospital wards. At 30 days, the restrictive strategy was noninferior for the composite outcome of death from any cause, myocardial infarction, stroke, or new-onset renal failure with dialysis. A significantly smaller percentage of patients in the restrictive group received pRBCs, compared with the liberal group. Notably, patients older than 75 years were significantly less likely to experience the composite outcome if they were in the restrictive group.
The randomized Transfusion Indication Threshold Reduction (TITRe2) trial, which also enrolled nonemergent cardiac surgery patients, found higher mortality in a restrictive transfusion group (Hgb < 7.5 g/dL) at 90 days. These results raised concern that following patients past 30 days might prove that perioperative restrictive transfusion strategies are harmful. To address this concern, the TRICS trial followed all patients to 6 months. They also added a second composite outcome to their analysis, which included all components of the primary composite, with the addition of emergency department visits, hospital readmission, and coronary revascularization within 6 months after surgery. At 6 months, the restrictive strategy was noninferior to the liberal strategy for the primary composite outcome. There were no significant differences in the secondary composite outcome or mortality at 6 months either.
I am not sure you can get more certainty than we now have. The TRICS trial included more than 5000 patients, tracked clinically meaningful outcomes, and followed patients for 6 months. It is safe, and probably preferable, to target an Hgb of 7.5 g/dL in patients recovering from nonemergent cardiac surgery. Because the study was designed to prove noninferiority for the primary composite outcome measure, it is unclear whether a restrictive strategy is better. However, given that it reduces transfusion needs, I am ready to adopt it. I would be willing to generalize this data to patients with stable coronary artery disease (CAD) as well. The subgroup analysis from the TRICC trial said these patients do fine with a restrictive strategy (7.0 g/dL Hgb target). Since the majority, if not all, of the patients in the TRICS trial had stable CAD following revascularization, TRICS implies that a 7.5 g/dL target is safe.
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Cite this: Aaron B. Holley. RBC Transfusion and Cardiac Surgery: Be Strict and Restrict? - Medscape - Feb 07, 2019.