Inhaled anesthetics commonly used for general anesthesia (GA), such as isoflurane, do not increase the incidence of postoperative delirium, according to a new study.

Researchers at the Duke University Health System (Durham, NC, USA) conducted a prospective randomized study involving 188 adult patients (age 65 years or older), that were randomized to either isoflurane or total intravenous anesthesia (TIVA) via propofol during major orthopedic surgery, maintaining the recommended depth of anesthesia. All patients completed the Geriatric Depression Score (GDS) and underwent cognitive testing prior to surgery, and composite scores for executive function and memory were computed. During the preoperative interview and the first three postoperative days, the differences between groups were analyzed to determine predictors of delirium.

The results showed that postoperative delirium occurred in 12.6% of the patients receiving inhaled anesthesia, and 13.6% of the patients receiving intravenous anesthesia. Importantly, it was found that only the patient's medical condition and cognitive status before surgery had an effect on whether he or she would experience delirium. Significantly, patients who developed postoperative delirium experienced a 40% orthopedic failure rate, compared to a low 5% failure rate for those patients who did not experience delirium. The study was presented at the American Society of Anesthesiologists (ASA) annual meeting, held during October 2011 in Chicago (IL, USA).

“The type of general anesthesia does not affect early cognitive outcomes after surgery,” said study presenter and lead author Terri Monk, MD, of the department of anesthesiology. “A patient's preoperative medical problems and the ability to process information and concentrate and learn and remember are independent predictors of postoperative delirium.”

Volatile anesthetics, which are commonly used for GA, 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, hallmarks of Alzheimer’s disease (AD) pathogenesis. It is therefore possible that these isoflurane-induced neuronal changes may predispose elders to postoperative cognitive problems.

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