The safe lower limit of hematocrit or hemoglobin that should trigger a red blood cell (RBC) transfusion has not been defined. The objective of this study was to examine the physiological effects of anemia and compare the acute responses to transfusion in preterm infants who were transfused at higher or lower hematocrit thresholds.
We studied 41 preterm infants with birth weights 500-1300 g, who were enrolled in a clinical trial comparing high (“liberal”) and low (“restrictive”) hematocrit thresholds for transfusion. Measurements were performed before and after a packed RBC transfusion of 15 ml/kg, which was administered because the infant's hematocrit had fallen below the threshold defined by study protocol. Hemoglobin, hematocrit, red blood cell count, reticulocyte count, lactic acid, and erythropoietin were measured before and after transfusion using standard methods. Cardiac output was measured by echocardiography. Oxygen consumption was determined using indirect calorimetry. Systemic oxygen transport and fractional oxygen extraction were calculated.
Systemic oxygen transport rose in both groups following transfusion. Lactic acid was lower after transfusion in both groups. Oxygen consumption did not change significantly in either group. Cardiac output and fractional oxygen extraction fell after transfusion in the low hematocrit group only.
Our results demonstrate no acute physiological benefit of transfusion in the high hematocrit group. The fall in cardiac output with transfusion in the low hematocrit group shows that these infants had increased their cardiac output to maintain adequate tissue oxygen delivery in response to anemia and, therefore, may have benefitted from transfusion.