The public is keenly aware of anesthesia awareness. It's a horrifying concept that makes for sensational headlines, nightly news features and even movie plots. But true intraoperative awareness is actually quite rare, occurring in 1 out of every 1,000 surgical procedures performed under general anesthesia. Despite its rarity, and based on the number of surgeries performed in the United States each day, intraoperative awareness is still an issue that anesthesia providers are concerned with during every case, no matter how long or short. Level-of-consciousness monitors reduce the likelihood that your patients will experience intraoperative awareness, but they're not a standard of care or a fail-safe guarantee. So should they be used during most procedures? In my opinion: yes.

Awareness risk factors
The American Society of Anesthesiologists hasn't made using a consciousness monitor a standard of care, and probably won't for some time because of a lack of sufficient properly controlled studies on the available systems. As the ASA has pointed out, there's no gold standard for comparing monitoring devices. In a practice advisory published in 2006, the ASA says that the use of consciousness monitors should be weighed on a case-by-case basis.

However, there are risk factors for intraoperative awareness that may make using a consciousness monitor worthwhile:

• Alcohol or drug abuse. Because the bodies of heavy drinkers or drug abusers are accustomed to metabolizing drugs, more medication may be required to create the desired state of anesthesia in these patients. Make a strong effort to find out if patients abuse alcohol or use recreational drugs such as marijuana, cocaine or benzodiazepines.
• Anxiety or hyperactivity. Anxious patients may require a higher dose of drugs just to go to sleep, and may metabolize drugs faster, requiring higher maintenance doses.
• High sensitivity to drugs. The opposite of drug abusers, patients with a known high sensitivity to drugs may need much less medication for general anesthesia. That puts them at risk for underdosage because the anesthesia provider could underestimate the minimal amount of anesthetic needed.
• Weakness or debilitation. Patients with a weak heart, low blood pressure or congestive heart problems usually can't tolerate a normal dose of many anesthetic drugs. As a result, the anesthesia provider may need to decrease the dosage. In these cases, a consciousness monitor helps the anesthesia provider titrate to the lightest effective dose without putting them at risk of awareness.
• Genetic predisposition. Patients who have an immediate relative who has experienced intraoperative awareness have a higher risk of experiencing awareness themselves. Also, there's more than anecdotal evidence that redheaded women need more anesthetic than the general population. A University of Louisville study published in the August 2004 issue of the journal Anesthesi-ology found that redheads needed 20% more desflurane than brunettes did.
• Airway surgery. When anesthetic gases are used during these cases there's more risk that the gas won't reach its target because the airway is compromised and ventilation is not as effective.
• Difficult to intubate. Patients with a history of difficult intubation and those likely to be difficult to intubate — such as obese patients and those with high Mallampati scores (used to predict the ease of intubation), a history of obstructive sleep apnea or a small, short mandible — have a higher likelihood of experiencing awareness because intubation may take longer. This increases the risk that the induction dose of anesthetic may wear off before intubation is completed and an additional anesthetic is given.

Limitations and drawbacks
Consciousness monitors have several limiting factors. The devices are most accurate in the middle of the course of anesthesia and are least useful at the upper end of unconsciousness, such as during induction and just before emergence. Also, the machines have a lag time of 20 to 90 seconds. For short outpatient procedures, this makes a consciousness monitor less effective — by the time the device is most useful, the case is almost finished.

I've found that procedures of 30 minutes or more are best suited for consciousness monitor use. The device's value is its ability to show a trend in a patient's level of consciousness rather than just a single real-time measure of the patient's level of consciousness.

Consciousness monitoring also has physical limitations. Sometimes the procedure or surgical site doesn't lend itself to monitoring. This is true in cosmetic procedures such as facelifts and other types of surgeries performed on the face or head, when placing electrodes on the forehead is not suitable.

A consciousness monitor is designed to filter artifacts from the EEG signal. However, small EEG signals or higher electrode impedances can create artifacts that obscure the signal and create a higher reading, leading the anesthesia provider to believe that the patient needs more anesthetic. In these instances the chance of overmedicating the patient increases.

Consciousness monitors give a measure of the apparent quality of the incoming signal and rely on several sophisticated automated features to reduce artifacts. However, you should routinely look at the raw EEG signal, since the human eye is better at detecting artifacts than most automated processes. If the level of consciousness index differs significantly from the clinical picture, first retest the electrode impedances and look for signs of electromyogram (EMG) contamination from facial muscles. Then examine raw EEG signals for evidence of either a very low amplitude EEG or excessive noise. If no obvious reason is found for the unexpectedly high reading, which indicates that the patient is regaining consciousness, a small dose of additional sedative should be given to see if the monitor's index responds appropriately, indicating that the patient indeed needs more anesthetic.

Is it worth the cost?
Consciousness monitors run between $4,000 and $8,500. Assuming that the cost per use is about $15 to $20, the monitor is 80% effective and the incidence of awareness is 0.18%, the cost of preventing a single case of intraoperative awareness can be estimated at $12,000. For patients in high-risk categories, however, the cost of prevention is approximately $2,400.

Is the expense worth it? Facilities and anesthesia providers need to make their own decisions based on the cost of the devices, the risk factors among the patient populations they serve and the current evidence related to how often awareness occurs when a monitoring device is used.

The monitors let providers improve the basic care that patients receive because patients are less likely to become over-sedated. In many cases, that translates to shorter post-op stays, which can save facilities money on staffing expenses and improve patient satisfaction scores. Those factors may be difficult to quantify, but in my opinion they make the use of consciousness monitors a no-brainer.