PHILADELPHIA – Blood transfusions can kill surgery patients, a finding that puts the onus on surgeons to administer transfusions only when absolutely necessary, according to Dr. Gaetano Paone.
An analysis of more than 31,000 patients who underwent isolated coronary artery bypass grafting (CABG) surgery in Michigan during January 2006–June 2010 showed that receiving one or more blood transfusions conferred a nearly threefold increased risk of operative mortality, compared with not receiving a transfusion, Dr. Paone reported at the annual meeting of the American Association for Thoracic Surgery.*
The propensity analysis, which controlled for 17 significant clinical and demographic variables, confirms that "patients who get transfusions don’t do as well as those who don’t. I can’t say unequivocably that it’s the blood transfusions that cause these worse outcomes, but this is a reason to – whenever possible – avoid giving blood transfusions," Dr. Paone said in an interview.
"There is great variability in the rates of transfusions across institutions," noted Dr. Paone, a cardiac surgeon at Henry Ford Hospital in Detroit. In some places, the transfusion rates of isolated CABG patients are 15%, and other places have rates of more than 90%. "That suggests it’s quite discretionary."
Surgeons "have different opinions on the necessary blood level, and the appropriate hematocrit level. It’s hard to see an almost fivefold range of differences in transfusion rates and not have that somehow based on individual preferences rather than on science," he added.
Dr. Paone suggested that surgeons who believe that it is often necessary to give transfusions should strive to make it less necessary. "It’s not just on the basis of this study," he noted. "This study looked at the situation from a somewhat different perspective, but it reached the same conclusion as many others."
Dr. Paone and his associates examined data on 31,818 patients who underwent isolated CABG during the study period at any one of the 33 Michigan hospitals that perform cardiac surgery. The data came from records maintained by the Michigan Society of Thoracic and Cardiovascular Surgeons Quality Collaborative.
The researchers calculated the mortality risk faced by each patient using the STS-PROM (Society of Thoracic Surgeons Predicted Risk of Mortality) model, which takes into account 30 preoperative patient variables. They stratified the patients into four risk groups based on their scores, which represent the percent risk for 30-day perioperative mortality (less than 2%, 2%-5%, 6%-10%, and more than 10%). The percentage of study patients in each ascending risk stratum were 69%, 21%, 7%, and 3%, respectively. The analysis also divided patients into the 55% who received transfusions and the 45% who did not receive any blood. Overall operative mortality among the patients studied was 2%.
As expected, operative mortality was higher among patients who received a transfusion (3.3%), compared with those who did not get blood (0.6%) – a statistically significant sixfold difference in death rates.
The analysis also showed that the significant link between increased mortality and transfusion remained fairly constant across all four risk strata in the study, ranging from a twofold increased risk among patients with an STS-PROM score of 2%-5%, to a fourfold increased risk among patients with a score of more than 10%. The researchers found no statistically significant differences in the increased rate of death among the transfusion recipients across the four preoperative risk strata, Dr. Paone said.
In a further analysis aimed at teasing apart the mortality risk from transfusion and the patients’ background mortality risk based on their disease severity, the researchers performed a propensity score analysis that controlled for 17 significant preoperative risk determinants, including age, sex, weight, race, hypertension, smoking status, need for dialysis, and chronic obstructive pulmonary disease. This analysis showed that patients who received a transfusion had a 2.88-fold increased risk for operative death, compared with patients who did not receive a transfusion, Dr. Paone said.
Dr. Paone said that he had no disclosures.
* Correction, 5/26/2011: An earlier version of this story incorrectly identified the name of the American Association for Thoracic Surgery.