The effect of aging on bispectral index before and after sedation: A prospective study

The Bispectral Index (BIS) is an EEG-derived value that measures the
sedative and hypnotic component of the anesthetic state. The effects of age on the
bispectral index have not been well documented. The objective of the present study
was to determine the influence of age on hypnotic requirement and bispectral index in
awake and in patients with sedation induced by midazolam.
Methods: Eighty patients were enrolled in this prospective observational study. The
patients in study group were aged more than 70 years, and the age in control group
ranged 20-40 years. Baseline recording of BIS was taken in awake patients in two
groups for few minutes. Five minutes after administration of 0.02 mg/kg IV midazolam
the BIS value also was taken and recorded.
Results: In the study group, patients had a mean base BIS 94±3 compared with 97.3±1
in the control group (p< 0.0001). Five minutes after administration of 0.02 mg/kg
midazolam the value were 80.9±6 and 90.4±3 respectively (p< 0.0001).
Conclusion: When BIS is used as a monitor of hypnosis in the elderly, we recommend
that a baseline recording be taken before induction for a few minutes to alert the
anesthesia provider to the possibility of low initial values. Further studies are needed to
verify if the recommended range of 50-60 of BIS during clinical anesthesia is also
adequate in the elderly with low initial baseline BIS or if this range needs adjusting in
view of reduced initial BIS value.