Routinely used to treat patients for heart attack or high blood pressure, beta blockers are known for their role in helping to protect the heart. A new study in the January issue of the journal Anesthesiology looks at the effects of beta blockers on surgical outcomes, revealing that the cardioprotective effects of the medication could be compromised by acute surgical anemia.
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 are used to treat a variety of conditions, including high blood pressure, heart attack, glaucoma and migraines. The medication works to reduce the heart rate, reducing blood pressure as a result. Beta blockers are often prescribed for patients around the time of surgery to provide protection of the cardiovascular system.
"Beta blockers are known to reduce death from cardiac complications after noncardiac surgery and have been recommended for patients with clinical risk factors. However, previous studies such as the POISE (Perioperative Ishemic Evaluation) trial published in the May 31, 2008 Lancet have revealed that increased stroke rates and mortality were associated with blood loss in patients treated with high doses of beta blockers," said W. Scott Beattie, M.D., Ph.D., F.R.C.P.C., Fraser Elliot Chair in Cardiac Anesthesia, University Health Network, Toronto General Hospital in Toronto, Ontario, Canada.
Dr. Beattie further explained, "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. "
About the Study
To determine if there is a significant interaction between the hemoglobin level and beta blocker effect, Dr. Beattie and colleagues performed a retrospective review of 4,378 noncardiac surgery patients at Toronto General Hospital from March 2005 to June 2006. Researchers compared the effect of acute anemia on adverse cardiovascular outcomes in two propensity score-matched cohorts; one containing patients treated with beta blockers and the other containing patients matched for cardiac, respiratory and hematologic risk factors that were not treated with beta blockers.
The review revealed that major cardiac complications and death rates were increased for patients treated with beta blockers who experienced more than a 35 percent drop in blood count (or hemoglobin). Researchers discovered that treatment with beta blockers was not harmful to patients if blood loss remained in a range of 30 to 35 percent.
Dr. Beattie concluded, "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. To validate these findings and to take the next steps in patient treatment and surgical safety, prospective studies are required to further investigate the importance of the interaction between hemoglobin blood levels and beta blocker effects."
New for 2010 in Anesthesiology
As part of a mission to promote new discoveries and influence clinical practice, the January issue of Anesthesiology
marks the debut of a newly designated "Education" section. This section is designed to highlight clinical material, making it more accessible and relevant for implementation in everyday clinical practice.