Blood Storage Impacts Survival Rate
By DAVID ARMSTRONG
March 20, 2008;
A new study suggests that the amount of time donated blood is stored can substantially affect patients getting blood transfusions during heart surgery.
Patients who received red blood cells stored more than two weeks died at a higher rate, experienced more incidents of kidney failure and suffered more potentially dangerous infections than those who received newer blood, Cleveland Clinic researchers reported.
The findings aren't expected to prompt immediate changes in procedures at blood banks, including the American Red Cross, which handles about 40% of the country's blood supply. Officials say the issue needs to be studied more rigorously. Whether older blood is harmful has been the subject of several studies in the past decade, with some results showing harm and others indicating no negative effects.
"This paper addresses an ongoing debate in the field, and although provocative in findings and conclusions, it does not provide a definitive answer," said Richard Benjamin, the chief medical officer for the national office of the Red Cross. "I would tell patients facing cardiac surgery that, of the many risks they face from their underlying health issues caused by their disease, this is not the one they should be preoccupied about."
The Food and Drug Administration allows blood to be stored for as long as 42 days. The median storage time of red blood cells nationally is 15 days, which means about half of the country's supply falls into the older range of stored blood.
"Blood banks need to explore changing their inventory-management practices," says Colleen Koch, a cardiac-surgery anesthesiologist at the Cleveland Clinic and lead author of the study in this week's edition of the New England Journal of Medicine.
The Cleveland researchers say their study is the largest to date and did a better job than prior efforts to control for variables that could influence the results. In the study, the death rate in the hospital after the surgery was 2.8% for the older blood group, compared with 1.7% for those getting new blood. A year after the surgery, the survival rate in the old-blood group was 89%, compared with 92.6% in the newer blood group.
Restricting the storage time of blood to two weeks or less would prevent one death a year for every 28 patients undergoing heart surgery, the researchers estimated. Patients receiving older blood were also more likely to need prolonged ventilator support to help them breathe -- 9.7%, compared with 5.6% -- and suffered multiple organ failures at about three times the number of those receiving new blood.
The standard inventory practice among blood banks is known as first in, first out. This means older blood is used first. Dr. Koch says one alternative is to distribute the newer blood first. But other experts say there may not be enough blood in supply banks for that inventory strategy to work.
James AuBuchon, chairman of pathology at Dartmouth-Hitchcock Medical Center in Hanover, N.H., says the Cleveland Clinic study didn't randomly assign patients to receive older or newer blood, a research strategy that medicine regards as more authoritative, partly because it allows researchers to control for other variables that may affect complications or survival rates. Instead, the researchers went back and reviewed the records of 6,002 patients who received blood transfusions while undergoing bypass and heart-valve surgery between 1998 and 2006.
Dr. Koch says the clinic is in the early stages of a 2,000-patient randomized clinical trial comparing outcomes with transfusions using older and newer blood.
Researchers aren't sure why older blood may be bad for patients, but they do know that the red cells undergo physical and chemical changes during storage that may affect their function and viability after surgery.
The study findings should urge doctors to be "more conservative with how they approach blood transfusion," says Dr. Koch. For instance, many patients who are anemic can take iron supplements before surgery to minimize the need for red-blood-cell transfusions.
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