Canadian Anesthesiologists' Society

What is Anesthesia Awareness?

One of the more common concerns expressed by patients is that they will wake up or experience pain in the middle of surgery. This fear is likely heightened by pop culture references such as the 2007 movie Awake and an episode of Grey’s Anatomy where a patient wakes up during surgery.

What is awareness during general anesthesia?
Awareness under general anesthesia (i.e. where the patient is not meant to be aware) is rare, and occurs when a patient describes their being aware of conversation, movement, pressure or discomfort. While awareness of any sort is rare, awareness that includes pain is very rare.

How common is awareness during general anesthesia?
It is thought to occur in approximately 1 per 1,000 general anesthetics overall. This includes all patients undergoing general anesthesia including those in well-known high-risk groups. (see below). A recent 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

Do all patients who experience awareness also experience pain?
No. Pain is reported in a small minority of patients who experience awareness – roughly 1/3 of patients with awareness report discomfort.

What are the long-term effects of awareness during general anesthesia?
The experience of awareness can be very distressing and a small percentage of patients who experience awareness may go on to develop long-term psychological consequences such as post traumatic stress disorder. There may be alternatives to general anesthesia for some patients (depending on the surgery being contemplated). It is important to discuss a previous episode of awareness with your anesthetist.

When is some “Awareness” (see above for definition) normal or expected ?
Some surgeries are preformed under regional anesthesia (such as spinal or epidural anesthesia or under a nerve block ) instead of general anesthesia. In these cases, patients are often given intravenous medication to help them relax and make them sleepy. This technique is called conscious sedation or the older term ‘neurolept’ anesthetic. In lay terms it is sometimes called ‘twilight’ sleep.
When above is used, it is normal to have a degree of awareness and a sense of pressure at the site of the surgery. This is not considered ‘awareness under general anesthesia’ as it is expected and the regional anesthesia techniques as described above prevents any pain.

Secondly. as patients fall asleep or wake up from general anesthesia, they may briefly be aware of their surroundings as the anesthetic medications take effect or wear off.

Why does awareness occur?
The anesthetist simply administers ‘too little’ anesthesia - either deliberately (see paragraph below) to save the patient or by error.

Anesthesia may have significant effects on blood pressure and heart function. These effects can be much more in cases of patients with severe underlying medical conditions - especially those affecting the heart, circulation and lungs. These effects can also be much more in cases of patients that suffered severe injuries or severe bleeding. In these patients the anesthesiology focus is save the life during the surgery. In these cases the ‘amount of anesthesia’ may needs to be reduced. This increases the risk of awareness under general anesthesia.
Medications errors (wrong drug or wrong dose) or equipment malfunction can lead to awareness.

Another explanation is that the patient does not respond in the normal way and seems more resistant (called ‘tolerance’ in medical terms) to anesthetic medications. This can be due to other medications used (like benzodiazepines) or alcohol and cocaine abuse. A small group of patients may have an inborn resistance. Research on this patient subset is currently underway. At present there is no way or detecting these patients.

However, even amongst patients at higher risk, awareness is still very rare.
Are there some surgeries that have a higher risk of awareness under general anesthesia ?

Yes - these would be caesarean section (done under general anesthesia), cardiac surgery and trauma surgery.

How can my anesthesiologist prevent me being aware?
Always being with you in the operating room is the most important step.
Secondly we are highly trained and always aware of the risk of awareness. We also continuously monitor your vital signs.

Can the anesthesiologist always detect awareness during the surgical procedure?
There is no absolute guarantee of being able to detect awareness - hence the issue. No monitors exist that rule awareness out in 100% of cases.

Are there certain medications that can be administered that will reduce the likelihood of awareness during general anesthesia?
Yes, but again these do not guarantee an absence of awareness. Choosing a regional anesthesia may reduce your fear of being aware and not being able to communicate your pain or anxiety.

Written by:
Dr. J Koval, MD (Resident Physician)

Reviewed by:
Dr. Martin van der Vyver, MBChB, FRCPC (Specialist Anesthetist) and Dr. B. Orser, MD, FRCPC (Specialist Anesthetist)

Date created:
November 1, 2010


American Society of Anaesthesiologists. Practice Advisory of Intraoperative Awareness and Brain Function Monitoring. Anesthesiology 2006; 104:847-64

Orser B, Mazer D, Baker A. Awareness during anesthesia. CMAJ 2008; 178:185-9

Domino K, et al. Awareness during Anesthesia: A Closed Claims Analysis. Anesthesiology 1999; 90:1053-61 


Intraoperative Awareness
article from the Canadian Medical Association Journal

Key points of the article
Intraoperative awareness, which is the unexpected recall of events that occur during anesthesia by patients who receive general anesthesia, occurs in up to 1 to 2 per 1000 patients. Most patients do not experience pain but, rather, have vague recall of auditory events or dreaming. However, approximately 36% of patients who experience recall report some degree of pain, which is occasionally severe.

Risk factors for awareness include patient age, cardiac reserve and substance abuse. Procedures associated with increased risk include cardiac and trauma surgery and cesarean section.

Preventative strategies include monitoring by a skilled anesthesiologist and possibly the use of benzodiazepines. Current neurophysiologic monitors aimed at estimating the depth of anesthesia are not recommended for routine use.

To view this article in its entirety, click here:;178/2/185

Please note: this notice is geared to specialist physicians.




Anesthesia Awareness

Side effects

Allergic reactions and surgery