Biomedical Engineering Reference
In-Depth Information
CHAPTER 9
EEG Signal Analysis in Anesthesia
Ira J. Rampil
After nearly 80 years of development, EEG monitoring has finally assumed the sta-
tus of a routine aid to patient care in the operating room. Although the EEG has
been used in its raw form for decades in surgery that risks the blood supply of the
brain in particular, it is only recently that processed EEG has developed to the point
where it can reliably assess the anesthetic response in individual patients undergoing
routine surgery and can predict whether they are forming memories or can respond
to verbal commands. Reducing the incidence of unintentional recall of
intraoperative events is an important goal of modern patient safety-oriented anes-
thesiologists. This chapter provides an overview of the long gestation of EEG and
the algorithms that provide clinical utility.
9.1
Rationale for Monitoring EEG in the Operating Room
Generically, patient monitoring is performed to assess a patient's condition and, in
particular, to detect physiological changes. The working hypothesis is that early
detection allows for timely therapeutic intervention after changes and preservation
of good health and outcome. It is, of course, difficult to demonstrate this effect in
practice due to many confounding factors. In fact, data demonstrating a positive
effect on actual patient outcomes does not exist for electrocardiography, blood
pressure monitoring, or even for pulse oximetry. Despite this lack of convincing evi-
dence, monitoring physiological variables is the international standard of care dur-
ing general anesthesia. Among the available variables, the EEG has been used to
target three specific and undesirable physiological states: hypoxia/ischemia, local-
ization of seizure foci, and inadequate anesthetic effect. Many forms of EEG analy-
sis have been proposed for use during anesthesia and surgery over the years, the vast
majority as engineering exercises without meaningful clinical trials. Because clinical
medicine has become ever more results oriented, the chapter points out, where data
are available, which techniques have been tested in a clinical population and with
what results.
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