The Effect of Propofol Injection Pain on Auditory Evoked Potential Index and Bispectral Index

Background: The electroencephalogram (EEG) methods are being used widely, to monitor of the depth of awareness. Among them, auditory evoked potential (AEP index) and the bispectral index (BIS) were adopted as specific EEG methods in many clinics. We evaluated the effect of propofol injection pain on AEP index and BIS in mildly sedated patients with midazolam who undergo general anesthesia.

Methods: 38 patients (18 to 65 age, ASA I or II grade) were separated in two groups randomly (group AEP and group BIS). Atropine 0.5 mg and midazolam 0.05 mg/kg were intramuscular injected as a premedication before going to operating room. Anesthesia was induced with propofol by target-controlled infusion. We had checked AEP index and BIS every 10 s till 90 s after propofol injection began.

Results: With propofol injection pain, BIS was not increased, but decreased at 70, 80 and 90 s. Whereas AEP index was increased significantly at 30, 40 and 50 s, and decreased significantly after that.

Conclusions: AEP index is more sensitive and reliable method to monitor depth of awareness during anesthesia induction phase in real time.