The advent of movies and media reports have brought the fear of awareness under anesthesia into the forefront of patients’ anxiety going into surgery. Intraoperative awareness under general anesthesia rarely occurs, with a reported incidence of 0.1%-0.2%. While rare, significant psychological consequences may occur after such an occurrence and the patient may be affected for some time. Oftentimes intraoperative awareness may be unavoidable in hemodynamically unstable patients, such as patients in trauma or cardiac surgery.
Intraoperative awareness occurs when a patient becomes conscious during a procedure performed under general anesthesia, and subsequently has recall of these events. Recall can take the form of explicit memory (assessed by patient’s ability to recall specific events that took place during general anesthesia) and implicit memory (assessed by changes in performance or behavior without the ability to recall specific events that took place during general anesthesia that led to those changes).
Studies have suggested that certain procedures such as cesarean delivery, cardiac surgery, emergency surgery, trauma surgery as well as anesthetic techniques (rapid sequence inductions, reduced anesthetic doses with or without paralysis, difficult intubations, total intravenous anesthesia, use of nitrous oxide-opioid anesthetic technique) may be associated with an increased risk of intraoperative awareness. Furthermore, certain patient characteristics may place a patient at risk for intraoperative awareness including substance abuse (eg, opioids, benzodiazepines, cocaine), American Society of Anesthesiologists (ASA) physical status of IV or V, limited hemodynamic reserve, and history of awareness.
Preventive measures in the preinduction phase of anesthesia management may minimize the occurrence of intraoperative awareness. Such measures include checking the functioning of the anesthesia machine and the prophylactic administration of benzodiazepines. There have been reported cases of intraoperative awareness resulting from low inspired volatile anesthetic concentration or drug errors.
Double-blind randomized clinical trials have shown a lower frequency of intraoperative awareness, with the prophylactic administration of midazolam as an anesthetic adjuvant. Consultants from ASA agree that benzodiazepines or scopolamine should be used in patients requiring smaller dosages of anesthetics, cardiac surgery patients, and patients undergoing trauma surgery. Caution should be taken with benzodiazepines due to delayed emergence.
Intraoperative awareness cannot be measured during the intraoperative phase of general anesthesia because the recall component of awareness can only be determined postoperatively by speaking to the patient. Clinical techniques used to assess intraoperative consciousness include checking for patient movement, response to voice commands, eye opening, eyelash reflex, papillary response, perspiration, and tearing. Furthermore, conventional monitoring systems such as ECG, blood pressure, heart rate, end-tidal anesthetic analyzer, capnography are also valuable and help assess intraoperative depth of anesthesia.
There are a multitude of devices designed to monitor brain electrical activity for the purpose of assessing anesthetic effect. They record electroencephalographic activity from electrodes placed on the ...