Monitoring for Intraoperative Awareness

AORN Journal,  Dec, 1998  by Sandra M. Ouellette,  Chrysanne Simpson

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Other causes of awareness are patient-related. In general, anesthetic requirements decrease with age. Obesity creates another risk factor because of altered uptake and distribution of anesthetic agents, difficulty with intubation, and prolonged intervals between anesthetic induction and maintenance. Substance abusers develop a tolerance to anesthetic agents, which can increase the risk of IOA.

CONSEQUENCES OF AWARENESS

Awareness during a surgical procedure can lead to a number of immediate or delayed psychological problems. Victims of IOA often complain of anxiety, anger, depression, irritability, and mental anguish. Some patients develop postoperative traumatic neurosis, in which the event is persistently reexperienced through distressing dreams and psychological trauma when exposed to events that resemble the trauma. Other signs and symptoms include

* recurrent nightmares,

* difficulty falling or staying asleep,

* difficulty concentrating,

* exaggerated startle response, and

* an unnatural preoccupation with death.

Patients often are silent about the complication. One study reported that only 35% of patients had informed their anesthesia care provider about their awareness and recall.(10)

The American Society of Anesthesiologists' committee on professional liability has conducted studies on closed malpractice claims related to anesthesia. These studies indicate that 4% of anesthesia-related claims were the result of IOA. The median malpractice payment for IOA was $18,000, with a range of $390 to $9 million.(11)

EVALUATING DEPTH OF ANESTHESIA

Many methods have been introduced into clinical practice to monitor anesthetic depth to prevent IOA (Table 2).

Table 2

MONITORING ANESTHETIC DEPTH

Clinical signs

Isolated forearm technique

Electroencephalogram

Electromyogrom

Lower esophageal contractility

Evoked potentials

Bispectral index

Indirect measures. The most basic assessment of depth encompasses indicators that are gleaned from patients: automatic reflexes (ie, heart rate, blood pressure, diaphoresis, pupillary dilation, tearing) and somatic reflexes (ie, movement). These indicators, however, are far from perfect because of the variability in surgical stimulation and the inconsistent relationship between hemodynamic response and consciousness. Also, the indicators often are masked by adjunct medications such as neuromuscular blocking medications, narcotics, and beta blockers.(12)

Other indirect methods for monitoring anesthetic depth include temperature changes in the skin surfaces, respiratory sinus arrhythmia (RSA), lower esophageal contraction, and frontalis electromyogram (EMG). Lower esophageal contraction, however, cannot be used as a monitor of awareness because it has been shown to be unreliable in discriminating between consciousness and unconsciousness.(13)

The most promising of these methods is RSA, which reflects parasympathetic inhibition of the heart via the vagus nerve and diminishes with induction of anesthesia. This method is able to demonstrate fluctuations in patients' response to changing propofol infusion. Moreover, the primary advantage of RSA is its simplicity.(14)