Tehran University Medical Journal

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Background: 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.

Keywords: Bispectral index, aging, awake, sedation

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