Abstract 1772: Transfusion of Stored Red Blood Cells Results in Distinct Hemodynamic Alterations with Increases in Systemic and Pulmonary Vascular Resistance
Anemia is a common symptom in critically ill patients. As a consequence these patients receive a large number of red blood cell (RBC) transfusions with the intention to augment oxygen supply to peripheral tissues. This view has been challenged by recent findings which implicate RBC transfusion in a deterioration of peripheral oxygen consumption. These deleterious effects have been attributed to a decreased deformability of stored RBC and to an increased concentration of cell free hemoglobin in stored blood. It has been demonstrated that free hemoglobin rapidly scavenges nitric oxide (NO) yielding nitrate and methemoglobin and thereby decreases the regional bioavailability of vasodilating NO. Since hemolysis in stored RBC depends in part on storage duration we looked in detail on hemodynamic parameters after application of fresh (not older than 15 days, mean age 6.8 ± 2.5 days) or stored RBC (older than 15 days, mean age 27.5 ± 7.3 days). A total of 40 patients were included in the study and monitored with a pulmonary artery catheter. All variables were determined before and after one RBC transfusion in each group. During transfusion dosage of administered vasoactive substances was not changed. Patients (n = 20) who received stored RBC showed a significant increase in pulmonary vascular resistance index (247 ± 56 vs. 418 ± 83 dyn*sec*cm-5*m-2, P < 0.005) as well as a rise in the transpulmonary gradient (10.4 ± 2.8 vs. 15.8 ± 3.4 mmHg, P < 0.005). Additionally, a pronounced increase in systemic vascular resistance index (1051 ± 76 vs. 1367 ± 123 dyn*sec*cm-5*m-2, P < 0.005) was evident. Concomitantly, a significant rise in serum nitrate levels together with a marked decrease in serum haptoglobin levels were measured. The described hemodynamic alterations were absent in patients who were given fresh RBC (n = 20). In this group the pulmonary vascular resistance index and transpulmonary gradient did not change during transfusion of RBC. Likewise no increase in systemic vascular resistance index was noticed. Collectively, these findings demonstrate profound hemodynamic effects of stored RBC in critically ill patients which favours a more restrictive transfusion practice. We speculate that NO scavenging by cell free hemoglobin accounts at least in part for these effects.