Campus Life

The Medical Minute: Anesthesia awareness

By Jansie Prosesky and
Berend Mets

Anesthesia awareness is the phenomenon of a patient having general awareness so they can recall events that occurred during his/her surgery. Occasionally patients remember voices, machines beeping or, very rarely, may feel pain at the surgery site. Some patients try to signal that they are awake, but if muscle paralysis is required for the surgery, movement is not possible. This was the premise of the movie, "Awake," which was released last fall.

Awareness under anesthesia for surgery is uncommon, with an incidence in the United States of roughly one patient per 700. Yet every case is a cause for concern. This is especially so when an exaggerated fear of the risk of awareness under anesthesia results in a patient not choosing surgery when it may be the best medical option.

To understand this phenomenon, it is helpful to know a few key concepts.

What anesthesia is and isn't

During general anesthesia, a loss of consciousness is induced by the administration of anesthetic drugs, which results in the patient not responding to painful stimulation. As part of the general anesthetic, an intravenous muscle paralyzer often is administered to allow placement of a breathing tube, which protects the airway and assists breathing. This ensures the airway remains open, because breathing can become depressed as a result of general anesthesia. The resulting muscle relaxation makes surgery safer around the heart, bowels and other areas, because there is less muscle movement and risk of injuring important organs.

General anesthesia is different from conscious sedation, which may be used for some diagnostic procedures, such as radiology examinations, when the patient can easily be awakened by a mild stimulation like calling his or her name.

Analgesia is often confused with anesthesia. Analgesia is pain relief. Many anesthesia professionals also administer analgesic agents, such as morphine, to decrease pain from surgery. Analgesics often are administered with the anesthetic and may work long after surgery.

How anesthesia awareness can happen

Awareness during general anesthesia may occur at the start of anesthesia, when anesthetics have not taken full effect, or at the end of surgery when the patient is waking up after anesthesia has been stopped. It is only very rarely that this occurs during surgery itself. However affected individuals may suffer significant psychological trauma from such an event.

A number of reasons exist why awareness under anesthesia for surgery can happen. Deep anesthesia can be dangerous in some high-risk surgery patients. This could be the case for people undergoing heart surgery, trauma surgery or in critically ill patients requiring any surgical procedure. This is because anesthesia may significantly impair blood circulation to the heart, brain and other vital organs, which can lead to organ malfunction. To minimize these effects, anesthesiologists attempt to maintain light anesthesia in such critically ill patients. But because there is still no single, fool-proof, clinical sign or monitor to verify that a patient is fully unaware, this can occasionally lead to awareness when not enough anesthetic is given to maintain unconsciousness.

Furthermore the dosage requirements for anesthetic drugs to keep a patient unconscious differ from person to person, and each person reacts differently to anesthesia.

Another reason for awareness under anesthesia may be from human error, such as giving the wrong medication or a technical failure in the equipment used to deliver anesthesia. Modern anesthesia machines measure the concentration of each anesthetic delivered and make this increasingly less likely.

Minimizing anesthesia awareness

Anesthesia providers are critically aware of this potential problem. There is no substitute for experience, expertise and training as the best way to minimize awareness during the procedure requiring general anesthesia. Since there is no single, reliable monitor of this phenomenon, judgment needs to be used in the administration of anesthetics to minimize unwanted effects.

Over the years, a variety of depth of anesthesia monitors have been developed to attempt to gauge the depth of anesthesia and levels of awareness. These include monitors to measure esophageal pressures or eye pupil size, and more recently, to evaluate electrical brain waves. Varying factors influence the utility and reliability of these monitors, such as patient positioning, other medications given and surgical equipment used in the operating room. Not all anesthesia medications can be interpreted reliably. Monitor values can lead anesthesia providers to use too little or too much anesthesia in some instances.

There is developing evidence that, in some categories of patients at high risk of awareness, a certain type of brainwave monitoring may help decrease the incidence of awareness. Such monitors can be used as an additional way of assessing anesthetic depth, but they are not a solution in themselves.

What patients can do

It is crucial for patients to discuss concerns about awareness and any other issue related to anesthesia during the preoperative visit or interview with an anesthesiologist. The best choice of anesthesia for the particular surgery can then be discussed.

In the unlikely situation that a patient thinks he or she was awake during surgery, it is very important to talk to the anesthesia provider about the experience. Doing so will help establish when awareness may have occurred and allow the anesthesia provider to explain events in the operating room that could have led to awareness. It also may be important to provide psychological counseling to some patients who have experienced awareness under anesthesia.

The American Society of Anesthesiologists and the American Society of Nurse Anesthetists understand patients fear the possibility of awareness and provide an information booklet on this subject listing 10 points that surgical patients should know. This is readily accessible at and Both Web sites provide further valuable information that patients may access to learn more about the phenomenon of anesthetic awareness.

Jansie Prosesky is assistant professor of anesthesiology, and Berend Mets is Eric A. Walker professor and chair, Anesthesiology at Penn State College of Medicine.

Last Updated March 19, 2009