The Use of Sevoflurane to Test the Concept of Intra-individual Variability in Bispectral Index Monitor and Cognitive Reserve by Examining Time to Emergence and Recovery

Cognitive reserve (CR) refers to an individual's ability to resist damage to the brain and is thought to be associated with an individual's education, cognitive stimulation, and physical activity. Those with greater CR have protection against degenerative brain changes such as dementia. Currently, CR is evaluated through a host of proxy tests such as questionnaires aimed to assess various aspects of cognitive function. These ways of measuring CR test directly only on an individual's ability to perform certain tasks when the brain is in its "unchallenged" state. However, this approach poses significant limitations since CR is developed as a concept representing the physiological brain reserve that helps counter the clinical manifestation of a diseased or "challenged" brain. A method that simulates a state of "challenged" brain during CR measurement may provide a more precise assessment of CR.

Anesthetic agents are known to reversibly alter brain function resulting in a state of sedation or amnesia. Whether this way of brain "challenge" can provide information on CR is unknown.

A previous study showed preliminary evidence that patients with higher CR correlates with less variability in bispectral index (BIS) during steady state of anesthesia with inhaled anesthetic sevoflurane (1). While the result of this study is encouraging, further study is needed to develop the concept of using anesthetic agents to evaluate CR. Specifically, a study investigating the correlation between intraoperative BIS variability and timing of clinical recovery from anesthesia will be necessary. This will further elucidate how to use anesthetic agent for the evaluation of CR.

Building on the previous study result and the concept that higher CR means higher resilience against brain function in a "challenged" state, we hypothesize that less intraoperative BIS variability correlates with shorter recovery time from anesthesia.