The most recent study on the long-term cognitive effects of anesthesia and surgery suggests that elderly people going under the knife have little reason to worry. According to a report in the November issue of the journal Anesthesiology, the rate of cognitive decline was the same in people who had surgery, were hospitalized for non-surgical illness, or in controls who avoided the hospital bed altogether. The work relied on long-term observational data from the Alzheimer’s Disease Research Center (ADRC) at Washington University in St. Louis, Missouri. However, the authors emphasize that their small study, with a heterogeneous group of subjects, must be repeated in a larger size before the field can form firm conclusions.
Short-term delirium or cognitive dysfunction following surgery is a well-known phenomenon, but beyond that, many patients, and anesthesiologists, are concerned that inhaled anesthetics might have long-term effects such as accelerating Alzheimer’s (see ARF related news story). Elderly people facing surgery, and their families, should find the data “reassuring,” said principal investigator Michael Avidan, an anesthesiologist at Washington University School of Medicine. Alex Evers, another anesthesiologist, co-designed the study. The authors discuss their work in a video on the university website.
Collecting solid data on the relationship between surgery and cognition can be tricky. “It is really hard to get appropriate controls for people who are about to undergo surgery,” Avidan noted. In addition, scientists generally have no data on a person’s rate of cognitive change before surgery. A patient might be in the process of gradual decline, but family members might not notice until after the surgery.
Avidan, Evers, and colleagues attempted to address these issues by joining forces with John Morris, director of WashU’s ADRC. Center scientists have been collecting cognitive data on volunteers aged 50 and older since 1985. Participants, some with and some without symptoms of Alzheimer’s, typically visit the center annually for a workup including a set of psychometric tests. During their relationship with the center, some people had surgery. People who remained healthy provided one control group. Those who were hospitalized for illness without surgery provided another control group—perhaps a better match for the surgical group because they had health problems. And because many people had two or more ADRC checkups before they needed surgery or hospitalizations, the study authors were able to track their rate of change in cognitive scores both before and after the event. The researchers also included in the analysis people with mild or moderate dementia, a population potentially at high risk for worsening cognition after surgery. “This important study has set new standards for the approach to peri-operative influence on cognition in the elderly,” wrote Roderic Eckenhoff, an anesthesiologist at the University of Pennsylvania in Philadelphia, in an e-mail to ARF (see full comment below).
The researchers examined data from 575 participants, calculating the slope of their cognitive scores over time before and after surgery or illness. For the control group, they calculated slopes before and after an imaginary “event,” occurring at approximately the same times as the events in the hospitalized populations. The slopes steepened after surgery or illness, indicating an increasing rate of cognitive decline. However, the same was true in the control group. The likely explanation is that, in general, elderly people in the study experienced a slightly increasing speed of cognitive decline. However, their decline after surgery or illness was probably no worse than it would have been without reason for hospitalization.
The authors acknowledged several limitations of their work. Participants had a variety of surgeries and illnesses, so it is possible that certain conditions that do affect cognition were present but went unnoticed in the heterogeneous data set. The researchers did not have data on the types of anesthetics used, so could not analyze the effect of different drugs. In addition, it remains possible that certain people are susceptible to cognitive decline after surgery. Although the researchers included those with mild dementia, they did not study people with more severe dementia, who might experience different effects after anesthesia. Genetics might also influence a person’s response to anesthesia.
A large, multicenter study is the next step, wrote Zhongcong Xie, of Massachusetts General Hospital in Boston, in an e-mail to ARF (see full comment below). Avidan and collaborators have begun to set up such a project, tapping Alzheimer’s research centers at several universities, but Eckenhoff estimates it will take at least five years to complete the work.—Amber Dance