Withholding angiotensin receptor blockers after surgery increases risk of postoperative death

Withholding angiotensin receptor blockers (ARBs) for longer than two days after surgery is associated with a significantly increased risk of postoperative death, according to a study of more than 30,000 patients in the VA health care system by researchers at UC San Francisco and the San Francisco VA Medical Center (SFVAMC).

ARBs are prescribed for high blood pressure, heart disease and kidney disease, explained lead author Susan M. Lee, MD, an SFVAMC anesthesiologist and UCSF clinical instructor.

"For non-cardiac surgery, ARBs are commonly stopped on the day of surgery because that makes it much easier to control blood pressure for a patient under general anesthesia," said Lee. "In many patients, they are often not restarted right away because of continued concerns about low blood pressure or kidney function. It turns out that this may be contributing to higher postoperative mortality."

The researchers found that patients who were not put back on ARBs within two days after surgery were up to one and a half times more likely to die within 30 days than patients whose ARBs were resumed.

The study was published today in the Online First edition of Anesthesiology, the official medical journal of the American Society of Anesthesiologists.

The authors analyzed the medical records of 30,173 VA patients nationwide who underwent inpatient non-cardiac surgery between 1999 and 2011 and who were regularly prescribed an ARB. Almost 34 percent were not put back on ARBs within two days after surgery. After adjusting for other variables, the researchers found that those patients had one and a half times the risk of dying within 30 days after surgery compared with patients whose ARB prescriptions were resumed within two days.

What are angiotensin receptor blockers, and how do they work?

Angiotensin II is a very potent chemical formed in the blood that causes muscles surrounding blood vessels to contract, thereby narrowing the vessels. This narrowing increases the pressure within the vessels and can cause high blood pressure (hypertension). Angiotensin II receptor blockers (ARBs) are medications that block the action of angiotensin II by preventing angiotensin II from binding to angiotensin II receptors on the muscles surrounding blood vessels. As a result, blood vessels enlarge (dilate) and blood pressure is reduced. Reduced blood pressure makes it easier for the heart to pump blood and can improve heart failure. In addition, the progression of kidney disease caused by the high blood pressure or diabetes is slowed. ARBs have effects that are similar to angiotensin converting enzyme (ACE) inhibitors, but ACE inhibitors act by preventing the formation of angiotensin II rather than by blocking the binding of angiotensin II to muscles on blood vessels.

The researchers did not look at possible reasons for the increased risk, but they did find that the patients whose ARBs were restarted sooner had reduced rates of infections, pneumonia, heart failure and kidney failure.