Reducing Perioperative Neurocognitive Disorders (PND) Through Depth of Anesthesia Monitoring: A Critical Review

Abstract

General anesthesia has been administered for over 150 years, and in that time, has become progressively safer. Improvements in outcomes have been driven by multiple advances, including the use of non-invasive monitors to assess cardiovascular and respiratory status. More recent advances have included the development and use of monitors to measure neurologic status by means of "processed" electroencephalography (pEEG), wherein the frontal EEG signal is analyzed by proprietary algorithms to produce a dimensionless number (scaled from 0 to 100), wherein low values are associated with deepening levels of sedation that progresses to loss of consciousness. Such monitors have been shown to enable anesthetic titration so as to expedite emergence and early recovery, and their use is advocated for the prevention of intraoperative awareness in the setting of administration of total intravenous anesthesia and neuromuscular blockade. Whether their use can minimize, or prevent, longer term adverse events is a matter of debate. In this narrative review of the most recent literature, we provide an assessment on the use of pEEG monitors in the prevention of a notable, and important, postoperative adverse outcome -delirium -in elderly patients. As we will discuss, the existing data do not support its routine use for the prevention of postoperative delirium in this, or any other, patient population.

Comment on: Variation in propofol induction doses administered to surgical patients over age 65

“…Some may prefer to avoid the need for vasopressors and give smaller, incremental doses of propofol, others are more concerned about hypertension, tachycardia, and awareness and will administer larger doses of propofol although some may be worried about the long-term effects of deep anesthesia. [4][5][6] In sum, this is a fascinating report, and it provides excellent insight into the range of total propofol doses used during induction in actual patients. Nevertheless, it does not tell us which bolus dose we should start with when inducing a patient with propofol.…”

“…Finally, clinicians may vary subjectively in what they want propofol to accomplish. Some may prefer to avoid the need for vasopressors and give smaller, incremental doses of propofol, others are more concerned about hypertension, tachycardia, and awareness and will administer larger doses of propofol although some may be worried about the long‐term effects of deep anesthesia 4–6 …”

The use of dexmedetomidine to prevent delirium after major cardiac and non‐cardiac surgery

“…Examples of peri‐operative care bundles have included: the Hospital Elder Life Program (orientation, nutritional support, early mobilisation) after abdominal surgery [4]; and a multidisciplinary approach to hip fracture surgery (fascia iliaca blocks, rationalising prescribing practices and avoidance of triggers) [5]. Investigations of single interventions have included: benzodiazepine restriction [6]; intra‐operative use of the inhalational anaesthetic agent, xenon [7]; depth of anaesthesia monitoring [8]; and dexmedetomidine given at various time‐points in the peri‐operative period [9].…”

Neurological Aging and Pharmacological Management of Geriatric Patients

“…Though some retrospective studies have demonstrated correlation between increased depth of anesthesia and delirium, recent randomized control trials have been more circumspect about that association [27,28]. Titration of anesthetics, using depth of anesthesia monitors in elderly patients, has not been able to show conclusively a decrease in the incidence of delirium or postoperative neurocognitive dysfunction [28].…”

“…Though some retrospective studies have demonstrated correlation between increased depth of anesthesia and delirium, recent randomized control trials have been more circumspect about that association [27,28]. Titration of anesthetics, using depth of anesthesia monitors in elderly patients, has not been able to show conclusively a decrease in the incidence of delirium or postoperative neurocognitive dysfunction [28]. However, using well-established decreased dosing regimens of anesthetics in elderly would be prudent practice, as it may avoid other complications such as hypotension, respiratory depression, or delayed recovery.…”