Watch for intraoperative awareness
and notify the Department of Anesthesia

	A recently published study by the Royal Children’s Hospital in Melbourne, Australia, determined the incidence of awareness of 0.8 percent during anesthesia in children ages 5 to 12 years.

By Dean B. Andropoulos, M.D., and Stephen A. Stayer, M.D.

We would like to educate physicians about intraoperative awareness.

Awareness is the postoperative recall of events that occur during general anesthesia, and is a complication that commonly goes unrecognized. Patients may not report the recall of intraoperative events for more than a week after surgery, and since anesthesiologists usually do not have contact with patients by then, awareness is rarely reported to the anesthesiologist.

Intraoperative awareness is a well-described complication of anesthesia in the adult surgical population, with an incidence of 0.1 percent to 0.2 percent.^(1–5) In adults, awareness can be distressing and may have significant psychological ramifications.⁽⁶⁾ The Department of Anesthesiology is interested in learning about these events to determine the frequency of occurrence, try to reduce the incidence, and to provide counseling to the patients who need it.

A recently published study by the Royal Children’s Hospital in Melbourne, Australia, determined the incidence of awareness of 0.8 percent during anesthesia in children ages 5 to 12 years. In this study, some features of awareness were similar to those found in studies of adult awareness. Children described auditory and tactile sensations in proportions similar to those described in adults.⁽⁷⁾ In adult anesthesia, awareness is more common when muscle relaxation is used.⁽⁷⁾ However, awareness occurred in this study despite the infrequent use of muscle relaxants. Also, in contrast to adult studies, none of the children who were aware described severe pain and none of the children who were aware reported being upset by their memories.

Prevention is a priority
The prevention of awareness continues to be a priority for anesthesiologists. A recent randomized, controlled trial demonstrated that processed electroencephalogram (EEG) monitoring reduced the incidence of awareness in a particular high-risk adult population.⁽⁸⁾ The Bispectral Index (BIS) monitor (Aspect Medical Systems, Newton, Mass.) is one Food and Drug Administration (FDA) approved device currently used to assess the depth of anesthesia. BIS sensor electrodes are applied to the forehead and temple, producing a frontal-temporal montage that connects to a processing unit. Via a proprietary algorithm of Aspect Corporation based on the normal adult EEG, BIS utilizes Fourier transformation and bispectral analysis of a one-channel processed EEG pattern to compute a single number, the BIS.⁽⁹⁾ This index ranges from 0 (isoelectric EEG) to 100 (awake) with mean awake values in the 90 to 100 range in adults, infants and children.⁽¹⁰⁾

Before routine EEG monitoring can be advocated for reduction of awareness in children, the nature, causes, implications and incidence of awareness in children need to be known. Once this information is available, the potential role for EEG monitoring in children will be clearer, and relevant randomized controlled trials can be planned.

The Department of Anesthesia would like to know about any case of intraoperative awareness. If your patient, or your patient’s family ever shares with you they have experienced anesthesia awareness, please notify Dr. Dean Andropoulos or Dr. Stephen Stayer immediately at 832-826-5831 or 832-824-5809.

1. Sandin RH, Enlund G, Samuelsson P, Lennmarken C. Awareness during anaesthesia: a prospective case study. Lancet 2000; 355:707–11.

2. Myles PS, Williams DL, Hendrata M, et al. Patient satisfaction after anaesthesia and surgery: results of a prospective survey of 10,811 patients. Br J Anaesth 2000;84:6 –10.

3. Liu WH, Thorp TA, Graham SG, Aitkenhead AR. Incidence of awareness with recall during general anaesthesia. Anaesthesia 1991;46:435–7.

4. Wennervirta J, Ranta SO, Hynynen M. Awareness and recall in outpatient anesthesia. Anesth Analg 2002;95:72–7.

5. Sebel PS, Bowdle TA, Ghoneim MM, et al. The incidence of awareness during anesthesia: a multicenter United States study. Anesth Analg 2004;99:833–9.

6. Lennmarken C, Bildfors K, Enlund G, et al. Victims of awareness. Acta Anaesthesiol Scand 2002;46:229 –31.

7. Davidson AJ, Huang GH, Czarnecki C, Gibson MA, Stewart SA, Jamsen K, Stargatt R. Awareness during anesthesia in children: a prospective cohort study. Anesth Analg. 2005;100:653-61.

8. Myles PS, Leslie K, McNeil J, et al. Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomized controlled trial. Lancet 2004;363:1757– 63.

9. Sigl JC, Chamoun NG. An introduction to bispectral analysis for the electroencephalogram. J Clin Monit 1994;10:392-404.

10. Denman WT, Swanson EL, Rosow D, et al. Pediatric evaluation of the bispectral index (BIS) monitor and correlation of BIS with end-tidal sevoflurane concentration in infants and children. Anesth Analg 2000;90:872-7.

Dean B. Andropoulos, M.D., is chief of Anesthesiology, and director of Pediatric Cardiovascular Anesthesiology for Texas Children’s Hospital, and associate professor of Anesthesiology and Pediatrics, Baylor College of Medicine. Stephen A. Stayer, M.D., is the associate chief for the Department of Anesthesiology and the medical director of Perioperative Services at Texas Children’s Hospital, as well as professor of Pediatrics and Anesthesiology, Baylor College of Medicine.

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