Anesthesia awareness, or unintended intra-operative awareness is something most people think of as a horrible urban legend meant to scare little children or give your parents nightmares.  The only problem is, it’s not a legend.  In fact, it happens a lot more often than most people think.

Now first, I want to make a disclaimer here.  Almost all surgeries have few, if no complications.  On a percentage basis, waking up during surgery is a rare occurrence.  And you should never put of a needed operation because of fear of waking while under anesthesia. 

So what is Anesthesia Awareness?  In layman’s terms, in rare cases of surgery when an anesthetic is necessary, the anesthesiologist makes a miscalculation and under administers the amount of anesthetic needed to put their patient completely to sleep and rendering them clinically unconscious.

So how rare are cases of Anesthesia awareness?  According to information pulled from Pubmed (http://www.ncbi.nlm.nih.gov/pubmed), it is estimated that the number of cases exceeds 26,000 per year.  A much larger number than was previously believed before this first case study was completed.

Here is an excerpt from their findings…

“Awareness with recall after general anesthesia is an infrequent, but well described, phenomenon that may result in posttraumatic stress disorder. There are no recent data on the incidence of this complication in the United States. We, therefore, undertook a prospective study to determine the incidence of awareness with recall during general anesthesia in the United States…

…data from 19,575 patients are presented. A total of 25 awareness cases were identified (0.13% incidence). These occurred at a rate of 1-2 cases per 1000 patients at each site. Awareness was associated with increased ASA physical status (odds ratio, 2.41; 95% confidence interval, 1.04-5.60 for ASA status III-V compared with ASA status I-II). Age and sex did not influence the incidence of awareness.

There were 46 additional cases (0.24%) of possible awareness and 1183 cases (6.04%) of possible intraoperative dreaming. The incidence of awareness during general anesthesia with recall in the United States is comparable to that described in other countries. Assuming that approximately 20 million anesthetics are administered in the United States annually, we can expect approximately 26,000 cases to occur each year.”

Who is at Risk?

There is a much higher risk for patients that must be treated differently than the norm.  Patients who are hemodynamically unstable are often given smaller doses of anesthesia in order to not cause additional injury to the patient. 

This becomes a fine balancing act as enough anesthetic must be administered to cause total sedation, yet not enough to cause the patient additional injury due to complications and/or side effects.  This is usually where most cases of  Anesthesia awareness are documented.

There are many such “special” circumstances that can cause an anesthesiologist to need to administer smaller doses of an anesthetic.  Such special circumstances include, but are not limited to cardiac cases: know heart problems that exist whether related to the surgery or not; obstetric cases: pregnancy in any stage; major trauma victims: accident victims, etc…

What are the challenges?

The biggest challenge for an anesthesiologist to determine if their patient is indeed feeling pain or is aware of what is happening to them stems from the actual anesthetic that is being administered.

Most anesthetics are meant to immobilize a patient and deaden pain as well as making them unconscious.  Typically, communication is sent through motor responses made by the patient such as movement.  Or through easily monitored increases in heart rate or increased blood pressure.

But again, the anesthetics used are often mixed with necessary paralytic agents used to relax muscles during an operation so that a patient remains completely still.  This also has the effect of lowering blood pressure and preventing heart rate spikes.

So if a patient does become conscious, it is almost impossible for them to communicate, whether through voice, physiologic or simple motor movement to the anesthesiologist what is happening to them. So even the most qualified doctors could easily be unaware that there is a problem.


Anesthesiologists are looking for better and more predictable methods of monitoring patients during their operations.  One method of monitoring that holds a lot of promise is the use of  electroencephalography (EEG) devices that are used to scan a patient’s brain activity during surgery.  Thus the limitation of using the physical body’s means of communication are no longer are a barrier.

Rather, the physician can monitor the patient’s brain waves and look for spikes in activity that can show alertness or realization of pain or other factors of Anesthesia awareness.  The use of scanning equipment, in theory at least as there has not been any clinical trails or studies conducted as of yet, should be a much safer indicator to an anesthesiologist that complications have arisen.

A body of evidence has not yet accumulated to definitely define the role of these devices in detecting and preventing anesthesia awareness; the Joint Commission expects additional studies on these subjects to emerge. In its review of the Bispectral Index (BIS)® monitor, the Food and Drug Administration determined that “Use of BIS monitoring to help guide anesthetic administration may be associated with the reduction of the incidence of awareness with recall in adults during general anesthesia and sedation.”

In Summary

Although Anesthetic Awareness cases are highly infrequent, they do occur.  And depending on which statistics you are using, they occur at a frequency of between 25,000 to 40,000 cases per year worldwide.  Now while that number may seem large, it is actually quite small when compared to the number of surgeries being conducted while anesthesia is being used per year in just the United States alone; “40 million and rising” according to the Anesthesia Quality Institute.