Blocking receptor contributing to memory deficits may prevent memory loss after anesthesia

Memory loss after anesthesia is a common adverse event upon awakening from surgery. Unfortunately the cause of such memory loss is unknown and there are no known treatments or prevention strategies. A study published in the November 2010 issue of Anesthesiology indicates that this memory loss could be prevented by blocking a receptor thought to contribute to memory deficits. Such a treatment may be able to solve the feeling of mental confusion that surgical patients so often feel shortly after coming out of anesthesia.

Memory impairment is an especially common occurrence in the elderly. Around 47 percent of elderly patients who underwent general anesthesia for minor surgical procedures exhibit memory deficits for at least 24 hours after surgery. Some of these deficits can linger: cognitive impairment, including memory loss, is present in 31-47 percent of patients at the time of hospital discharge.

Why memory loss happens, how severe it is, and how long it takes to recover remain poorly understood.

In the current study, Beverley A. Orser, M.D., Ph.D., F.R.C.P.C. and her research team at Sunnybrook Health Sciences Centre and Mount Sinai Hospital looked at two groups of anesthetized mice - one treated with a drug that inhibits a known memory-blocking receptor, and one treated with a control solution.

"When tested 30 minutes and at one day after anesthetic exposure, the mice in the control group exhibited a memory deficit that was not observed in the mice treated with the blocking compound," said Dr. Orser. "We found that the memory deficit in the post-anesthetic period could be completely prevented by treatment with a drug that inhibits the memory-blocking receptor."

Studies in patients involving anesthetics and their effects on memory are especially difficult, said Dr. Orser, because of the inability to disentangle the effects of anesthetics from other factors that can cause memory deficit. Therefore, animal models are important for helping to identify types of learning and memory susceptible to impairment and to identify certain molecular mechanisms.

Dr. Orser's study underscores the need for human clinical trials that will assess memory performance soon after surgery.

"In practical terms, our study suggests the need to re-evaluate and study the assumption that patients will remember important information given to them after surgery," said Dr. Orser. "Until such studies are performed, it seems prudent to use strategies such as written information or sharing information with family members to ensure that instructions are learned and remembered."