Background: Bispectral index (BIS index) shows the depth of anesthesia. The effects of drugs on BIS and amnesia are different. This study was performed to evaluate the association between two different sedative regimens on BIS and amnesia.
Methods: In this clinical trial, 60 patients who needed elective orthopedic surgery under regional anesthesia with intravenous sedation were elected. Patients divided in two equal groups based on sedation protocol by block randomization method: midazolam plus fentanyl group (MF group) or propofol group (P group). Dose of sedative drugs were adjusted according to clinical findings of sedation. Depth of sedation in all patients, preserved in four based on modified Ramsey Sedation Score. Patients questioned about spontaneous recall after full awakening in recovery room. Recall of any event during operation considered as failed amnesia. Correlation of BIS index with recall was measured in two different groups separately.
Results: The frequency of recall was 2 (6.7%) in P group and 10 (33.3%) in MF group (p=0.01). The mean± SD of BIS in P group was 76±5 (68-91) and in MF group was 93.4±5 (77-98) (p<0.001). The difference of BIS in patients without amnesia (p=0.019) and with amnesia (p<0.001) in two groups were significant, respectively. No delay in recovery was observed.
Conclusion: Although the Modified Ramsey Sedation Score and clinical sedation indices were the same, but BIS in patients varied in a wide range. Hypnotic drug was a main determinant of BIS score and amnesia.