Awareness Under Anesthesia

Dear Patient,

RE: Anesthesia “Awareness”


With the release of the Hollywood movie “Awake”, Ontario’s Anesthesiologists would like to educate the public about the phenomenon known as “Anesthesia Awareness”. The movie tells the story of a man who, while undergoing open-heart surgery, experiences an episode of awareness.

What is “Awareness”?

This is a rare condition that occurs while patients are undergoing a General Anesthetic, when the patient can recall their surroundings, an event and sometimes even pain. It can range from brief, hazy recollections to some specific awareness of your surroundings. Patients may dream during surgery and may think that they have experienced some awareness. Such a sensation or memory does not necessarily represent awareness during surgery.

What is not “Awareness”?

When using other types of Anesthesia (spinal, epidural, deep sedation, or local techniques), it is expected that patients will have some awareness or recall after the procedure.

What is the incidence of anesthesia awareness?

The reported incidence has been 1 or 2 per 1000 general anesthetics (0.1-0.2%). This includes all patients undergoing general anesthesia, including those in the well know high-risk groups. (See below). A recent prospective study suggests that the actual incidence for non high-risk patients is indeed much lower in the order of 1:15,000 to 1:40,000.1

Are certain surgical procedures associated with an increased incidence of awareness?

Awareness is more common with caesarean sections (GA), cardiac surgery, trauma surgery, seriously ill patients with hemodynamic instability, and other emergency procedures. In most of these cases the anesthetic depth needs to be reduced to prevent the patient from dying.

How do patients describe the awareness?

Patients may recall elements of conversation, knowledge of the fact that a surgical procedure is taking place, and pressure and discomfort at the operative site. Pain is reported infrequently.

Are there other conditions that predispose patients to awareness?

Patients who are opioid-tolerant, or consume benzodiazepines, alcohol, and cocaine have a greater risk of awareness.

Can the Anesthesiologist detect awareness during the surgical procedure?

There is no reliable way for an Anesthesiologist to detect awareness during general anesthesia. Awareness has been reported in the absence of tachycardia or hypertension. Patients are often given muscle relaxants (paralytic agents) during these procedures so purposeful movements cannot take place.

What are the consequences of anesthesia awareness?

Some patients may experience psychological symptoms after an episode of awareness. These may include post-traumatic stress disorder that is characterized by nightmares, flashbacks, and insomnia. Although these patients generally improve over time, they tend to fear operating rooms, hospitals, and the thought of general anesthesia. If you encounter a patient with a history of recall or awareness, please refer them for an Anesthesia consultation. There may be alternatives to general anesthesia for some patients (depending on the surgery being contemplated).

Is there technology to monitor the patient’s level of consciousness?

There is no known definitive strategy to prevent awareness and NO monitoring system has been shown to conclusively prevent awareness. There is extensive research into a type of EEG monitor, which converts brain waves into a signal index (Bi-spectral Index or BIS) with values of 0-100. Fully conscious patents would register a “100” and no brain activity would be a “0″. A value of 40-60 on the BIS during general anesthesia is desirable, however recall has been reported even at this reading. The BIS monitor is no guarantee against awareness.

If you feel that you have experienced an episode of awareness, we would encourage you to contact the Anesthesiologist or the surgeon involved in your care for follow up.

If you would like additional information please contact Ontario Anesthesiologist’s central office 416-642-6336 or your colleagues in the Anesthesia department of your hospital. If your patients have any concerns about awareness, please refer them for a pre-op Anesthesia Consultation.


Stephen Brown MD, FRCPCChair – OMA Section on Anesthesiology


1.    Pollard RJ, Coyle JP, Gilbert RL, Beck JE: Intraoperative Awareness in a Regional Medical System, A Review of 3 Year’s Data. Anesthesiology 2007; 106:269-74