Blood transfusions in cardiac surgery patients often are performed inappropriately, and transfusion rates would improve if more restrictive strategies for performing them were employed, according to the results of two separate studies reported in the Oct. 13 issue of JAMA.
In one large observational study, investigators showed that, despite the availability of clinical practice guidelines for blood transfusion, rates of transfusion among cardiac surgery patients vary dramatically among hospitals in the United States. Transfusion rates in the multicenter study of 102,470 patients who underwent primary isolated coronary artery bypass graft surgery with cardiopulmonary bypass during 2008 varied from 8% to 93% for red blood cell transfusions, from 0% to 98% for fresh-frozen plasma, and from less than 1% to more than 90% for platelets at hospitals performing at least 100 eligible on-pump coronary artery bypass graft operations, Dr. Elliott Bennett-Guerrero of Duke University, Durham, N.C., and his colleagues found.
After adjusting for patient-level risk factors, some significant variation in transfusion rates was seen based on geography, hospital academic status, and hospital volume, but these factors accounted for only 11% of the variation and case mix accounted for about 20%. Furthermore, no significant association between hospital-specific transfusion rates and all-cause mortality was seen on either adjusted or unadjusted analysis (JAMA 2010;304:1568-75).
Given that cardiac surgery patients receive a large proportion of the 14 million units of red blood cell transfusions performed each year in the United States, and that such transfusions are costly and have been shown to increase the risk of adverse outcomes, the variability in transfusion rates should be seen as a potential quality improvement opportunity, the investigators said.
Studies have shown that the use of blood conservation programs can be effective for improving transfusion rates, and since this study demonstrated that the availability of practice guidelines does not appear to improve transfusion rates, such programs might be a more effective approach, Dr. Bennett-Guerrero and his associates noted.
Indeed, the findings from the second study – a randomized controlled noninferiority trial showing that a perioperative red blood cell (RBC) transfusion strategy restricting transfusions to patients with hematocrit values less than 24% resulted in 30-day mortality and severe morbidity rates that were similar to those with a more liberal strategy that allowed transfusions in patients with hematocrit values less than 30% – appear to support a more conservative approach. In this study, it was the receipt of any red blood cell transfusion, not the treatment strategy, that was associated with higher complication and mortality rates after surgery, Dr. Ludhmila A. Hajjar of the University of Sao Paulo (Brazil) and colleagues found (JAMA 2010;304:1559-67).
Although the Brazilian investigation, known as the TRACS (Transfusion Requirements After Cardiac Surgery) study, was designed to explore optimal transfusion practices rather than to evaluate a blood conservation strategy, the finding that RBC transfusion was independently associated with a 1.2-fold increased risk of death at 30 days for each unit transfused nonetheless “supports a restrictive therapy in cardiac surgery,” the investigators wrote.
They studied 502 consecutive patients undergoing cardiac surgery with cardiopulmonary bypass at a university hospital in Brazil between February 2009 and February 2010. The restrictive and liberal transfusion strategies resulted in transfusion rates of 47% and 78%, respectively, yet the rate of the composite outcome of 30-day all-cause mortality and severe morbidity was similar, at 11% and 10%, respectively.
Severe morbidity included cardiogenic shock, acute respiratory distress syndrome, or acute renal injury requiring dialysis or hemofiltration during the patient’s hospital stay.
“As expected, the restrictive-strategy patients received fewer RBC units than the liberal-strategy patients and, consequently, had lower mean hemoglobin levels during the study [mean of 9.1 g/dL and 10.5 g/dL, respectively]. Interestingly, this did not result in a higher incidence of clinical complications,” the investigators wrote, adding that this was presumably because the restrictive strategy did not lead to reduced oxygen availability to the cells.
The finding that the number of transfused RBC units predicted 30-day mortality in a dose-dependent fashion not only supports a more restrictive strategy for transfusion in cardiac surgery, but also suggests that clinicians should administer only 1 unit at a time, as this may provide similar benefits with less risk, Dr. Hajjar and associates said.
Taken together, the findings suggest that there is a great need for improvement of transfusion rates and that a primary strategy in patients undergoing cardiac surgery should be to avoid giving red blood cell transfusion solely to correct low hemoglobin levels.
Dr. Bennett-Guerrero is principal investigator for a multicenter, National Institutes of Health–funded study assessing the impact of blood transfusion on peripheral and cerebral oxygenation and the microcirculation. He is also a named inventor on a patent application related to methods of washing red blood cells. His study was supported by the Society of Thoracic Surgeons through the National Adult Cardiac Surgery Database and the Duke Clinical Research Institute. Dr. Hajjar and coauthors had no disclosures to report.