EEG Signal Analysis in Anesthesia - Quantitative EEG Analysis Methods and Clinical Applications - page 251

appears to work in all but infants ( 12 months of age). This is due to the develop-

ment changes in the EEG of children. It has been demonstrated that close titration of
anesthetic effect using BIS improves some measures of patient outcome or operating
suite efficiency [72, 73]. Finally, and most significant to patients is that anesthetic
titration using BIS has been demonstrated in two large clinical trials to reduce the
incidence of unintended recall of intraoperative events [74, 75].

=

9.6 Conclusions

Divining the anesthetic effect message within the EEG has long been sought. Gen-
eral anesthetic vapors, propofol, barbiturates, and benzodiazepines induce synchro-
nization and eventual slowing of cortical electrical activity. EEG itself is not the end
point clinicians desire, but it may serve as a surrogate for the behaviors which are
important. The recent availability of devices including Aspect's BIS and GE Medi-
cal's Entropy monitors, which claim to link the behaviors of awareness and recall to
the EEG, is a significant step forward in this endeavor. Although there is currently
no theoretical or mechanistic link proposed between neural network pharmacology
in the cerebral cortex and the intrafrequency coupling notion of the BIS, or the
channel complexity implicit in entropy analysis, the empirical correlations have
been confirmed. The exact role and limitations of this new technology will be deter-
mined through additional clinical experience. With the attainment of this present
benchmark level of clinical correlation, further refinements in signal processing can
now be reasonably expected to create increasingly useful tools for a wide range of
clinical settings.

References

[1] Guyton, A. C., and J. E. Hall, Textbook of Medical Physiology , 10th ed., Philadelphia, PA:

W.B. Saunders, 2000.

[2] Fukuda, S., and D. S. Warner, “Cerebral Protection,” British Journal of Anaesthesia,

Vol. 99, No. 1, July 2007, pp. 10-17.

[3] Rampil, I. J., et al., “Prognostic Value of Computerized EEG Analysis During Carotid

Endarterectomy,” Anesthesia and Analgesia, Vol. 62, No. 2, February 1983, pp. 186-192.

[4] Wiebe, S., “Effectiveness and Safety of Epilepsy Surgery: What Is the Evidence?” CNS Spec-

trums, Vol. 9, No. 2, February 2004, pp. 126-132.

[5] Tellez-Zenteno, J. F., et al., “Long-Term Outcomes in Epilepsy Surgery: Antiepileptic

Drugs, Mortality, Cognitive and Psychosocial Aspects,” Brain, Vol. 130, Pt. 2, February
2007, pp. 334-345.

[6] Rampil, I. J., “A Primer for EEG Signal Processing in Anesthesia,” Anesthesiology, Vol. 89,

No. 4, October 1998, pp. 980-1002.

[7] Liu, W. H., et al., “Incidence of Awareness with Recall During General Anaesthesia,”

Anaesthesia, Vol. 46, No. 6, June 1991, pp. 435-437.

[8] Sandin, R. H., et al., “Awareness During Anaesthesia: A Prospective Case Study,” Lancet,

Vol. 355, No. 9205, February 26, 2000, pp. 707-711.

[9] Sebel, P. S., et al., “The Incidence of Awareness During Anesthesia: A Multicenter United

States Study,” Anesthesia and Analgesia, Vol. 99, No. 3, September 2004, pp. 833-839.