Current sedation assessment methods
are subject to variability depending upon the observer (Habibi
and Coursin 1996). RSS is not sensitive or specific enough
to determine agitation and over-sedation (Habibi and Coursin 1996). Furthermore,
evaluation using RSS is hard to duplicate in a busy ICU since it
can be time-consuming and can agitate the patient (Habibi and Coursin
1996). On the contrary, BIS is an objective, non-invasive
method of continuously monitoring the patients sedation level.
Finally, RSS cannot be used to evaluate sedation levels in intubated patients
(Polland 1993). Many patients in the ICU require mechanical ventilation
and/or muscle relaxants. Patients who are on ventilators and who receive
muscle relaxants cannot communicate effectively. RSS is an inadequate method
of determining sedation level in such patients since the patients cannot respond
(Polland 1993; Spencer et al. 1994). BIS would be a good alternative
for intubated patients and/or patients who are receiving muscle relaxants. An
EEG would provide non-invasive, continuous monitoring of sedation levels without
requiring the patient to respond verbally. Apparently, using BIS analysis
could be the vehicle of providing objective sedation assessment in both intubated
and non-intubated patients. Using BIS analysis, doctors and nurses may be able
to achieve the ideal level of sedation that "provides a degree of sleepiness
from which the patient is easily aroused and remains cooperative and responsive
to commands" (Habibi and Coursin 1996).
The usefulness of other EEG parameters in determining sedation has also been
investigated (Lui et al. 1996). Our results also showed that SEF, MPF,
Absolute alpha, Absolute beta, and EMG are statistically different between
responders and non-responders. However, these parameters are not as
specific as BIS; similar to RSS, they may only be able to differentiate between
responders and non-responders (Lui et al. 1996). Also, the other power
spectrum variables did not correlate with RSS as well as BIS did (Table 4). According
to a previous study, these simple EEG analyses are not effective; little correlation
was found between MPF, SEF, and sedation score in critically ill patients (Spencer
et al. 1994). Similarily, another study concluded that BIS provided the best
correlation with the sedation scaling system used, and that only BIS consistently
increased as anesthetic wore off (Spencer et al. 1994). Other EEG parameters
do not correlate with RSS as well as BIS and hence, are not as effective in
measuring sedation (Polland 1993; Spencer et al. 1994).
Other objective measures of sedation are also being investigated. One
study found that cardiac beat-to-beat variability (RR variability) correlates
well with RSS in ICU patients (Haberthur et al. 1996). It is an objective,
continuous method that can be used to monitor intubated
patients (Haberthur et al. 1996). More research needs to be done on alternative
methods of assessing sedation in an objective manner. Presently,
BIS can be used effectively to determine sedation in ICU patients. Other clinical
uses of BIS are also being studied. For example, one study concluded
that BIS can be used to measure effects anesthetics have on EEG wave patterns
(Billard et al., 1997).
is definitely useful in a clinical setting and may become the
new method of monitoring depth of anesthesia in the ICU
and possibly even in the operating room.
The author would like to thank Patricia
Embree and all other staff at ASPECT Medical Systems for the support and for providing all
the mechanical equipment necessary to complete this study.
Aspect Medical Systems. Technology
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