Anesthesia awareness

Anesthesia awareness, or "intra-operative awareness" occurs during general anesthesia, when a patient is paralyzed with muscle relaxants but not enough general anesthetic or analgesic to prevent consciousness or, more importantly, the sensation of pain and the recall of events.

The experience may betraumatizing for the patient who is unable to communicate his or her distress due to the muscle relaxants.

Anesthesiologist have many approaches available to minimize the risk of awareness; however, it is not always possible to completely avoid it. Some patients, such as those undergoing cardiac or trauma surgery or emergency cesarean sections, have a somewhat higher risk. The anesthesiologist must weigh the need to keep the patient safe and stable with the goal of preventing awareness. Sometimes it is necessary to provide lighter anesthesia in order to preserve the life of the patient or the baby.

Possible causes of awareness include a predisposed drug tolerance or a tolerance induced by the interaction of other drugs. Inability to reliably measure consciousness with current technology is another important factor. Less frequently, causal human errors include inadequate drug dose, inadequate monitoring, and failure to refill the anesthetic machine's vaporisers with volatile anesthetic. The American Society of Anesthesiologist recently released a Practice Advisory outlining the steps that anesthesia professionals and hospitals should take to minimize these risks.

The prevalence of anesthesia awareness in the United States is believed to be 20,000 to 40,000 cases per year, which represents 0.1 percent and 0.2 percent of all patients undergoing general anesthesia (JCAHO 2004). However, these include cases in which the patient has only a hazy memory lasting a few seconds. Patients who experience lasting stress should be offered psychological counseling and support. Otherwise, in some cases, the effects can extend further than the event itself. Some victims experience posttraumatic stress disorder (PTSD), leading to long-lasting after-effects such as nightmares, flashbacks, and insomnia.

Anesthesiologists have been educated about this phenomenon for more than ten years, and most hospitals have had plans in place to prevent awareness as well as to respond to those cases that are not preventable.

References

Myles PS, Leslie K, McNeil J, Forbes A, Chan MTV, for the B-Aware trial group. Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomised controlled trial. Lancet 2004;363:1757-1763. Fulltext. PMID 15172773.
Joint Commission on Accreditation of Healthcare Organizations (JCAHO). Sentinel Event Alert 6 Oct 2004;32. Online version.

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References