I S S U E S   F A C T   S H E E T

For Information Contact:
Jill Freeman-Stack, Communicore
714/721-8081
jstack@communicore.com


PATIENT AWARENESS DURING GENERAL ANESTHESIA


Anesthesia and the Problem of Patient Awareness

During general anesthesia, patients usually receive several types of medications to 
achieve satisfactory surgical anesthesia, including:

* An anesthetic to induce unconsciousness and amnesia;
* A neuromuscular blocking agent to paralyze muscles, causing immobility and full 
relaxation during surgery;
* A narcotic to block pain sensation.

The goals of general anesthesia are to achieve unconsciousness and to prevent pain 
during surgery.  Episodes of awareness may occur when inadequate anesthesia is 
administered.  This problem can be difficult to detect visually because patients are 
often given muscle relaxants to prevent movement during surgery.  As a result, 
patients may be awake and aware of events and may experience pain during surgical 
anesthesia but may be unable to communicate this to the surgeon or anesthesiologist.

What Patients Experience During Episodes of Awareness

Patients who become aware during surgery report experiencing fear, anxiety, panic 
due to the inability to communicate, a feeling of suffocation, and sometimes feeling 
unbearable pain.

These patients may also report experiencing muscle paralysis due to the 
neuromuscular blocking agents often given to prevent movement during surgery.  
Because of their inability to move or communicate with the surgical team, 
inadequately anesthetized patients often report feeling intense helplessness and an 
overwhelming fear of dying.  Awareness victims also have reported memories of 
sounds, including conversations among members of the surgical team.

Post-traumatic stress disorder is a common long-term problem for patients 
experiencing awareness.  Patients report experiencing symptoms such as fear of 
falling asleep, aversion to darkness, nocturnal awakening, recurrent nightmares, 
irrational fears, and difficulty performing routine tasks.  These symptoms may 
persist for many months or years following the event and are often alleviated only 
through counseling.

Incidence of Awareness

Estimates of the scope of awareness during general anesthesia vary widely, but 
researchers estimate that 0.2-1 percent of surgery patients--40,000-200,000 of the 
approximately 20 million patients who undergo surgery with general anesthesia in 
the United States each year--may experience this trauma.  Ten percent of these 
patients report actually feeling pain.  Cases of awareness and fright that went 
undetected during surgery represent an estimated 4 percent of closed malpractice 
claims against anesthesiologists.  

This problem often goes unreported for a number of reasons.  People often are 
embarrassed to discuss their symptoms, and victims may question their own mental 
stability or are convinced that awareness could not possibly occur.

Why People Experience Awareness

Recommended dosages of anesthesia are usually based on an average determined by 
clinical studies of middle-aged men.  The actual dose required for individual 
patients can vary greatly from that average dose.  The amount of a particular drug 
that is sufficient for some people may be either excessive or insufficient for others, 
potentially resulting in relative overdoses or underdoses and resultant awareness 
during surgery.

The current practice of monitoring the effects of anesthesia relies heavily upon 
hemodynamic responses--changes in blood pressure and pulse.  Hemodynamic 
responses, however, are not reliable for predicting patient awareness as pulse and 
blood pressure are not directly indicative of consciousness, and modern anesthetics 
have varying and sometimes offsetting effects on hemodynamic variables.  

Certain patients may be at a higher risk of being awake and aware during surgery 
because their medical conditions may not allow them to tolerate high levels of 
anesthetic drugs.  For example, patients who require surgery following major 
trauma may be at higher risk because their weakened conditions dictate the use of 
lower-than-normal doses of anesthetic drugs.  Women undergoing Cesarean 
deliveries may be given relatively low doses to prevent over-sedation of their babies.  
Elderly patients also may receive less-than-optimal doses because larger amounts 
could harm their already fragile systems.

In addition, clinicians and hospitals face mounting pressure to increase efficiency by 
reducing the time for patients to awaken from anesthesia.  To accomplish this, 
efforts are being made to avoid excessive anesthesia doses.  Many hospitals are 
implementing "fast-track" cardiac anesthesia programs designed to facilitate earlier 
recovery after open-heart procedures.  One goal of these protocols is to allow 
patients to begin breathing on their own earlier so that they can be extubated 
(breathing tube removal) more rapidly.  In some cases, extubation can be performed 
as soon as four hours following open-heart surgery, allowing patients to be moved 
more quickly from expensive critical care areas to less costly areas of the hospital.  
The effort to avoid deep anesthesia can increase the risk of underdosing, and in 
addition increase the risk of patient awareness.

A Solution

Clinical studies indicate that analysis of brain waves using an electroencephalograph 
(EEG) monitor may provide the critical measurement of a patient's level of 
consciousness during anesthesia.  The EEG is known to be affected by such events as 
anesthetic and neuroactive drug administration, as well as other physiologic changes 
that occur during surgery such as cerebral ischemia and hypothermia.  Therefore, 
the development of an EEG monitor that provides an objective measure of the 
effects of anesthetics and other pharmacologic agents on patients' level of 
consciousness will allow anesthesiologists to immediately determine when patients 
are regaining consciousness.

Bispectral analysis is capable of detecting more subtle changes in the EEG wave form 
than has been possible with any other signal processing technology.  A new monitor 
has combined the power of bispectral analysis with statistical algorithms to generate a 
numerical index--the Bispectral Indexª (BIS)--that describes the complex EEG 
pattern as a single number that correlates closely with the patient's level of sedation 
and consciousness and assists in the detection of awareness.  

The BIS values range from 100, indicating that the patient is awake, to zero, 
indicating lack of brain activity in the patient.  Clinical studies have shown that a BIS 
value of greater than 70 is associated with a high probability that the patient was 
awake, while a value of less than 60 indicates unconsciousness.  

The BIS can be used to monitor the brain activity of anesthetized patients, especially 
in the presence of neuromuscular blocking agents.  A recent study found the BIS to 
be useful as an indication of return of consciousness during general anesthesia, 
demonstrating the potential application of the BIS--the ability to intraoperatively 
track patient arousals due to inadequate anesthesia as a result of drug delivery 
problems or changes in the patient's drug requirement due to altered levels of 
stimulation or metabolism.

In addition to monitoring for inadequate anesthesia, the BIS helps anesthesiologists 
avoid the administration of too much anesthesia which can result in long recovery 
times.  A major, multicenter, clinical utility trial validated the specific use of the BIS 
as a monitor of anesthesia.  The findings from this trial demonstrate improved 
outcomes associated with the use of the BIS, including a reduction in anesthetic 
drug use, faster wake-up times, and improved recovery for patients undergoing 
general anesthesia.  The findings were presented at the 1996 Annual Meeting of the 
American Society of Anesthesiologists (ASA).  

The U.S. Food and Drug Administration recently cleared the BIS as a monitor of 
the effects of anesthesia.  


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