Researchers at the University of Toronto's Faculty of Medicine have shown why anesthetics can cause long-term memory loss, a discovery that can have serious implications for post-operative patients.
Until now, scientists haven't understood why about a third of patients who undergo anesthesia and surgery experience some kind of cognitive impairment - such as memory loss - at hospital discharge.
One-tenth of patients still suffer cognitive impairments three months later.
Anesthetics activate memory-loss receptors in the brain, ensuring that patients don't remember traumatic events during surgery. Professor Beverley Orser and her team found that the activity of memory loss receptors remains high long after the drugs have left the patient's system, sometimes for days on end.
Animal studies showed this chain reaction has long-term effects on the performance of memory-related tasks.
"Patients - and even many doctors - think anesthetics don't have long-term consequences. Our research shows that our fundamental assumption about how these drugs work is wrong," says Orser, a Professor in the Departments of Anesthesia and Physiology, and anesthesiologist at Sunnybrook Health Sciences Center.
In the study - led by PhD candidate Agnes Zurek - the team gave healthy male mice a low dose of anesthetic for just 20 minutes and found that receptor activity was increased for a week afterwards. These results suggest the same effect can impact a patient's learning and memory during a time when they are receiving critical information about their care.
"There's a lot going on after surgery, which can alter our ability to think clearly. Loss of sleep, new environments and medications can all impact a patient's mental function. Anesthetics likely compound these issues," says Orser.
She recommends physicians and family members carefully monitor patients after surgery for any signs of memory loss. "Patients should write everything down or have a second pair of ears with them after surgery. For high-risk groups, physicians need to inform patients about these possible side effects and help manage the impact on recovery and overall health," says Orser.
The likelihood of a patient experiencing cognitive impairment depends on their age, health, type of surgery and the anesthetic, with chances increasing for more intricate procedures. The incidence is highest in the elderly or those undergoing major surgery such as cardiopulmonary bypass.
"Anesthetics don't put you to sleep - they induce a pharmacological coma. We shouldn't take these drugs lightly," Prof. Orser cautions.
Orser and her team are looking at drugs that can stop the receptors and restore memory loss. While they are still in the early stages of research, they say some of the drugs show very promising results in animal studies.
The study was published in the Journal of Clinical Investigation.
Press Release by Wiley Dated 22-Feb-2018
Findings from a new Anaesthesia study suggest that patients may score slightly lower on certain memory tests after having surgery and anaesthesia.
In the study of 312 participants who had surgery and 652 participants who had not (with an average age in the 50s), surgery between tests was associated with a decline in immediate memory by one point out of a possible maximum test score of 30 points. Memory became abnormal in 77 out of 670 participants with initially normal memory comprising 18% of those who had had surgery compared with 10% of those who had not. No differences in other measures of memory and executive function were observed between participants having and not having surgery. Reduced immediate memory scores at the second visit were significantly associated with the number of operations in the preceding nine years. Working memory decline was associated with longer cumulative operations.
"The cognitive changes we report are highly statistically significant in view of the internal normative standards we employ, and the large sample size of the control, or non-surgery, population. But the cognitive changes after surgery are small-most probably asymptomatic and beneath a person's awareness," said senior author Dr. Kirk Hogan, of the University of Wisconsin-Madison School of Medicine and Public Health. "The results await confirmation both in follow-up investigations in our own population sample after more surgeries in aging participants, and by other investigators with other population samples."
Dr. Hogan noted that it is too early to recommend any changes in clinical practice regarding prevention, diagnosis, management, and prognosis of cognitive changes after surgery.