Beta-Blockers Could Increase Risk of Surgical Anemia Complications

A new study suggests that the cardioprotective effects of beta-blockers are compromised by acute surgical anemia, and even increase the risk of cardiac events.

Researchers at Toronto General Hospital (TGH; ON, Canada) conducted a retrospective review of 4,378 noncardiac surgery patient records at TGH from March 2005 to June 2006, to determine if there is a significant interaction between blood hemoglobin level and the beta-blocker effect. The primary outcome was a composite of major adverse cardiac events that included myocardial infarction (MI), nonfatal cardiac arrest, and in-hospital mortality. The lowest recorded hemoglobin in the first 3 days defined the nadir hemoglobin level. Propensity scores estimating the probability of receiving a perioperative beta-blocker were used to match patients who did or did not receive beta-blockers postoperatively. The relationship between nadir hemoglobin and major adverse cardiac event was then assessed.

The results showed that of those patients in whom nadir hemoglobin could be calculated, 1,153 (26%) patients were administered beta-blockers within the first 24 hours of surgery. Propensity scores created 827 matched pairs that were well balanced for all measured confounders. Major adverse cardiac events occurred in 54 (6.5%) beta-blocked patients and in 25 (3.0%) beta-blocker naive patients. Further analysis found that his difference was restricted to those patients in whom the hemoglobin decrease exceeded 35 percent of the baseline value; treatment with beta-blockers was not harmful to patients if blood loss remained in a range of 30% - 35%. The study was published in the January 2009 issue of the journal Anesthesiology.

"The natural response of the body to blood loss and the action beta blockers induce on the body create a paradox for treatment. Blocking the appropriate response of the body to anemia, as would happen with patients who are on or in need of beta blockers, may actually increase the risk of anemia-induced adverse cardiovascular events,” said lead author W. Scott Beattie, M.D., Ph.D. "This study should alert us to the fact that, potentially, there may be ways to mitigate and prepare for the demonstrated risks of beta blockade.”

Blood loss and anemia are very common in patients during and after surgery; more than 30 percent of patients undergoing moderate- to high-risk surgery experience a significant drop in blood levels. The normal response of a patient's body during significant blood loss is to increase cardiac output through increased heart rate to ensure sufficient delivery of oxygen to organs. Beta blockers, on the other hand, reduce blood pressure to treat a variety of conditions, including high blood pressure, heart attack, glaucoma, and migraines by reducing the heart rate. Beta-blockers are often prescribed for patients around the time of surgery to provide protection of the cardiovascular system.

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