General Anesthesia Does Not Increase Delirium in the Elderly
October 17, 2011 (Chicago, Illinois) — Inhaled anesthetic agents do not increase the incidence of delirium in the early postoperative period, according to a study presented here at American Society of Anesthesiologists (ASA) 2011 Annual Meeting.
The prospective study compared elderly patients receiving general anesthesia plus isoflurane with those receiving total intravenous anesthesia (TIVA). Only the patient's medical condition and cognitive status prior to surgery had an effect on the occurrence of delirium, reported Terri G. Monk, MD, from the Duke University Health System in Durham, North Carolina.
Preoperative cognitive status, but not the type of general anesthesia, is a significant predictor of postoperative delirium. These findings support the use of preoperative cognitive testing to identify patients at risk for delirium, Dr. Monk said.
"This study should reassure elderly patients that the type of general anesthesia does not affect early cognitive outcomes after surgery and that they should not avoid necessary surgery or general anesthesia if it is required," Dr. Monk added.
Why the Concern?
Volatile anesthetics have been considered to be nontoxic to the brain for decades. Recent cellular and animal studies, however, have demonstrated that the commonly used inhaled anesthetic isoflurane enhances amyloid beta generation and aggregation, which are hallmarks of Alzheimer's disease pathogenesis, she noted.
It is possible, therefore, that isoflurane-induced neuronal changes predispose high-risk populations, such as the elderly, to postoperative cognitive problems. An alternative is TIVA, usually with propofol, which does not appear to change amyloid beta protein generation in standard doses.
Investigators randomly assigned 200 adults 65 years or older (mean age, 73 years) to either inhaled isoflurane or TIVA with propofol for anesthetic maintenance during major orthopedic surgery.
All patients completed the Geriatric Depression Score and underwent cognitive testing using standardized cognitive measures prior to surgery. Composite scores for executive function and memory were computed.
Dr. Monk's team premedicated patients with midazolam, and anesthesia was induced with propofol. Anesthesia was maintained with either isoflurane or TIVA at the recommended depth of anesthesia (bispectral index [BIS] of 40 to 60). They received fentanyl for analgesia, had ventilation with a 50% air/oxygen mixture, and received neuromuscular blocking agents.
During the preoperative interview and the first 3 postoperative days, the presence of delirium was assessed using the Confusion Assessment Method for the Intensive Care Unit, along with multiple other tests of neuropspychologic function, and predictors of delirium were determined. Because age and Geriatric Depression Score have been associated with delirium in previous studies, they were included in the models, as were variables that were significantly associated with delirium in the current analyses.
No Significant Differences by Anesthesia Type
Postoperative delirium occurred in 12.6% of patients in the isoflurane group and 13.6% in the TIVA group (P = .84), suggesting that general anesthesia does not increase risk, Dr. Monk reported.
There were no associations between delirium and age (P = .19), educational level (P = .30), or depression (P = .34).
There was a trend for higher rates of delirium in white patients, in patients with higher ASA scores, in women, and in patients with lower scores on preoperative cognitive testing (in particular, the executive and memory composites).
In the multivariate analysis, only baseline cognition, especially the executive composite (P = .02), remained an independent predictor of delirium.
Scott Kelley, MD, who has a clinical practice at Brigham and Women's Hospital, Boston, Massachusetts, and is chief medical officer of Covidien, which manufactures the BIS monitor, noted that Dr. Monk and colleagues kept the depth of anesthesia between 40 and 60, which he feels was important in preventing delirium in the inhaled anesthesia group.
"There has been concern over possible harm from volatile anesthetics to the developing brains of children. Elderly patients potentially have vulnerable brain tissue as well, and we have evidence that as patients get older they need less anesthetic. Using the BIS to guide and adjust the amount of anesthesia to the elderly patient's individual requirement makes a lot of sense," Dr. Kelley said.
"My approach is to always adjust the medication to what the brain needs, which is the advantage of brain-monitoring technology. I think this could have an impact on delirium."
John Dombrowski, MD, head of communications for the ASA and director of the Washington Pain Center, in Washington, DC, noted that the study is particularly relevant, considering the growing population of elderly patients. "The message is that anesthesiologists need not be afraid of exposing their older patients to general anesthesia" if that is the best approach for the procedure, he told Medscape Medical News.
Medscape by Caroline Helwick
Dr. Monk and Dr. Dombrowski have disclosed no relevant financial relationships.
American Society of Anesthesiologists (ASA) 2011 Annual Meeting. Abstract 613. Presented October 16, 2011.