Previous studies of lower risk cardiac surgical patients found a link between age of transfused blood and adverse outcomes, but no risk of increased mortality, Bennett-Guerrero said.
"We hypothesized that the effects of storage duration would be more pronounced in patients who are more likely to receive multiple blood transfusions, such as those undergoing a repeat open-heart procedure," he said.
Lower-risk heart patients use an average of two units of blood, compared to the current study's high-risk population that received an average of five units of blood. The more units of blood a patient receives increased the probability of receiving an older unit of blood, Bennett-Guerrero said.
For their study, the researchers retrospectively analyzed the medical files of 321 patients who underwent a repeat open-heart procedure for coronary artery bypass or valve replacement between 1995 and 2001 and who received donated blood during surgery or recovery.
The team correlated the clinical findings for each patient with the number and age of the units of blood the patient received, statistically adjusting for a host of patient characteristics such as age, obesity, other diseases, number of units received and hypertension. For comparison purposes, the researchers assigned patients into four groups, based on the age of the oldest unit of blood they received: 1-19 days, 20-26 days, 27-30 days, 31-42 days.
The researchers found that increasing age of the blood corresponded significantly with an increased risk of death. "In terms of mortality, kidney damage and length of stay in the intensive care unit and hospital, we saw the rate of risk increase with each successive quartile," Bennett-Guerrero said.