Needing surgery is a frightening prospect that can trigger fears (both rationale and irrational) in any one of us. One of the most powerful of these fears is that of waking up during surgery, being able to hear and feel what is happening to you, but being unable to make anyone else in the room aware of your dilemma.

Fortunately, waking up during surgery, a condition referred to as surgical awareness, is a rare occurrence, affecting only 0.1% to 0.2% of all surgical patients. Patients who experience surgical awareness have memories of feeling paralyzed, of conversations, or of the actual surgical procedure. These perceptions are often accompanied by feelings of helplessness, fear, and even pain. The consequences of these experiences can range from immediate pain and suffering to long-term psychological symptoms, such as post-traumatic stress disorder .

During surgery, the anesthesiologist is responsible for administering the correct level of pain relief and sedation required for the surgery. This is traditionally done by monitoring the patient’s blood pressure and heart rate. However, these readings sometimes prove unreliable.

Additionally, certain types of surgery, such as trauma, cardiac, and cesarean sections are associated with a higher than average risk for awareness.

Recently, researchers developed the bispectral index (BIS) monitor, a machine that measures the level of electrical activity in the brain and rates it along a scale between 1 and 100 (with 0 being deep anesthesia and 100 being completely awake). Brain activity registering between 40-60 on this scale is generally considered appropriate for surgical procedures.

In past studies, use of BIS monitoring has been shown to shorten the recovery time of surgical patients. But, a group of researchers in Australia also wanted to know whether BIS monitoring could be used to predict the risk of awareness in surgical patients. The results of their study were published in the May 29, 2004 issue of The Lancet. The researchers found that BIS monitoring significantly reduced the risk of surgical awareness in adult at-risk surgical patients.

About the Study

The researchers enrolled 2463 adult participants, all of whom were at high risk of awareness during surgery because of the type of surgery they were receiving (cardiac, trauma, or cesarian section).

Each participant was given the usual preoperative care for their particular type of surgery and then were randomly assigned to receive either BIS monitoring (1225 patients) or routine anesthesia care (1238 patients).

A BIS sensor was attached to every participant’s forehead prior to their surgery. For those participants who were randomized to receive routine care, these sensors were simply never turned on. For those who were randomized to receive BIS monitoring, the sensor was turned on and adjusted to maintain the delivery of anesthesia at a level between 40 and 60.

Each participant’s level of surgical awareness was assessed using a questionnaire to determine their ability to recall events that occurred during their surgery. These interviews were conducted at 2-6 hours, 24-36 hours, and 30 days post-op.

The Findings

The researchers found that until at least 30 days post-op, the number of patients who reported awareness under anesthesia was significantly smaller in the BIS group than in the routine care group (1.8% (2) vs 2.2% (11) cases respectively). Overall, BIS monitoring reduced the risk of surgical awareness in one out of every 250 patients.

How Does This Affect You?

The researchers concluded that BIS monitoring during surgery significantly reduces the risk of surgical awareness in adult at-risk patients. This translates not only into greater peace of mind for patients, surgeons, and anesthesiologist alike, but also, according to the study, an estimated cost savings of approximately $2200 for every episode of surgical awareness prevented.

An editorial published in the same issue of The Lancet , considers the results of this study highly important and encourages anesthesiologists and surgeons alike to embrace BIS monitoring as a “great leap forward” for general surgery.

For those who have experienced surgical awareness, BIS monitoring offers hope of never having to experience it again. For those who have not, BIS monitoring offers the hope of never having to face one of our greatest fears.