In the primary analysis, pooled results from 3 trials with 2364 participants showed that a restrictive hemoglobin transfusion trigger of less than 7 g/dL resulted in reduced in-hospital mortality (risk ratio [RR], 0.74; confidence interval [CI], 0.60-0.92), total mortality (RR, 0.80; CI, 0.65-0.98), rebleeding (RR, 0.64; CI, 0.45-0.90), acute coronary syndrome (RR, 0.44; CI, 0.22-0.89), pulmonary edema (RR, 0.48; CI, 0.33-0.72), and bacterial infections (RR, 0.86; CI, 0.73-1.00), compared with a more liberal strategy. The number needed to treat with a restrictive strategy to prevent 1 death was 33. Pooled data from randomized trials with less restrictive transfusion strategies showed no significant effect on outcomes.
In patients with critical illness or bleed, restricting blood transfusions by using a hemoglobin trigger of less than 7 g/dL significantly reduces cardiac events, rebleeding, bacterial infections, and total mortality. A less restrictive transfusion strategy was not effective.
Observational studies on patients with very low hemoglobin concentrations (5 or 6) who are normovolemic show that they tolerate it well. Compensatory mechanisms for the anemia are cited:
A systematic review found consistent evidence that normovolemic anemia is associated with a reduction in systemic vascular resistance and an increase in cardiac output, coronary and cerebral blood flow, and synthesis of 2,3-diphosphoglycerate in red blood cells, resulting in maintenance of oxygen delivery and extraction.
Increased red cell 2,3 DPG levels shifts the oxy-hemoglobin dissociation curve to the right, making hemoglobin less stingy. Transfused red cells on the other hand may have decreased 2,3 DPG levels as a result of storage.
Improved outcomes with a restrictive strategy were seen across the board, including two groups of particular interest: acute bleeding and coronary artery disease.
Here is a recent study showing improved outcomes with a restrictive strategy in patients with GI bleeding.
Related editorial here.
My institution has adopted a restrictive transfusion strategy, leveraged by the EMR. It has worked, as evidenced by the number of frantic calls I get from nursing personnel, triggered by very low H&H levels on morning labs.