Incidence of Anesthetic Awareness may be Higher in Low Flow Anesthesia

Abstract

Awareness is one of the most feared complications of general anesthesia. Incidence of anesthetic awareness is rare but it can be higher in haemodynamic unstable patients, trauma patients, obese patients, those with chronic pain, children and cardiac surgery. Scarce information is available on the incidence of awareness in low flow anesthesia. Literature search of databases yielded studies that refer to awareness during general anesthesia, and always referring to high flow anesthesia, but there are no references on awareness in low flow anesthesia. However, due to small amounts of inhaled anesthetics in low flow anesthesia there is a possibility of a higher incidence of awareness in this setting. The term “depth of anesthesia” must be distinguished from anesthetic awareness and it is necessary to take into account everything that is closely related to it, such as memory, consciousness or unconsciousness. Minimal alveolar concentration (MAC) and end-tidal anesthetic gas concentration (ETAG) can measure depth of anesthesia, but they are not enough regarding awareness and memory. MAC does not represent the effect of anesthesia on the brain, since movement in response to a surgical stimulus is mediated at the level of the spinal cord. Bispectral index (BIS) and entropy as objective techniques should be used to monitor awareness although there are confusing results even with their application. More studies are needed to investigate awareness during low flow anesthesia that will shed some light on the additional restrictions of its application.