SAN DIEGO – Though blood products have unique, lifesaving qualities, they are often in limited supply, and fresh red blood cells have a short shelf life. Frozen red blood cells can stabilize and extend the supply provided by fresh products, and were found safe and effective when used in trauma patients.
“Frozen red blood cells can be stored in massive quantities and represent a flexible blood supply that can be used interchangeably with fresh blood,” Dr. Martin Schreiber, professor of surgery at Oregon Health & Science University, Portland, said at the American Surgical Association’s annual meeting. Frozen red blood cells have a favorable biochemical profile when compared to fresh red blood cells, added Dr. Schreiber.
Of the 14 million units of blood transfused annually, 10%-15% are used for trauma patients. Fresh refrigerated red blood cells must be used within 42 days, meaning that $80 million worth of red blood cells (RBCs) are wasted every year because they can’t be used before expiration. Further, there are seasonally increased needs for red blood cells and seasonal troughs in donation patterns. Particularly for those with rare blood types or in case of natural disasters or civil emergencies, blood supply issues can create a critical missing link in the chain of trauma and surgery care, he said.
Cryopreserved red blood cells (CRBCs) offer the potential for a more predictable and secure blood supply. However, concerns about the safety and efficacy of routine use of CRBCs have persisted, although cryopreservation has been in use since the 1950s, when it was pioneered by the U.S. military. Military use of frozen blood red blood cells occurred through the Vietnam War and continues into the present day in conflict arenas. The American Red Cross also maintains frozen red blood cells as part of its rare donor registry program, as does the New York Blood Center for its rare phenotype program.
Red blood cells are frozen to –80 degrees Celsius within 6 days after donation, and may be kept frozen for up to 10 years. Glycerol is used to protect the cells during freezing and must be washed from the cells on thawing. The thawing process takes about 90 minutes; the blood may then be refrigerated and must be used within 14 days of thawing.
In a multisite prospective, randomized, double blind study conducted at five level-I trauma centers in the United States, Dr. Schreiber and his colleagues compared the safety and efficacy of new RBCs (14 days old or younger) and old RBCs (older than 14 days) to CRBCs for stable adult trauma patients requiring transfusion. Patients were included if they had an injury severity score of greater than 4, were considered stable, and if transfusion was an anticipated component of their care. Excluded were pregnant trauma patients and those requiring emergent or massive transfusion.
Patients, whose demographics and hospital length of stay were similar among groups, were randomized by the blood bank to receive young RBCs (n = 82), old RBCs (n = 86), or CRBCs (n = 86). The researchers used near infrared spectroscopy (NIRS) to measure tissue oxygenation as one of two primary outcome measures; the second primary outcome measure was clinical outcomes, including acute renal failure, infection, pulmonary complications, pulmonary embolus or deep venous clots, and death.
Secondary outcome measures assessed how the three types of blood products affected blood biochemistry. Among the measures included were measurement of blood proteins, including hemoglobin and C-reactive protein; inflammatory cytokines, including interleukins, tumor necrosis factor–alpha, and granulocyte-macrophage colony stimulating factor (GM-CSF); and coagulation measures, including PT, PTT, D-dimer, and fibrinogen. There were no significant differences among the three treatment groups in tissue oxygenation from baseline to 3 hours after transfusion, and all clinical outcomes were similar among groups as well.
Overall, CRBCs exhibited “a superior biochemical profile,” according to Dr. Schreiber: Those receiving CRBCs had significantly lower levels of interleukins 2 and 4, as well as lower levels of GM-CSF, another cytokine associated with systemic inflammation. Coagulation and hemoglobin measures were similar among groups.
This study had a relatively small sample size and was not powered for equivalence, noted Dr. Schreiber, nor did it assess the long-term effects of receiving CRBCs. Also, the study examined only stable trauma patients who received an average of two units of RBCs, though trauma patients have received massive amounts of CRBCs in battlefront situations and further studies will include massively transfused patients.
Even so, the “quality of this study and the completeness of the biochemistry are truly noteworthy,” said discussant Dr. Ronald Maier of the University of Washington, Seattle.