Comparison of Bispectral Index Values Produced by Isoflurane and Halothane at Equal End-tidal MAC Concentrations

Abstract

The bispectral index (BIS) has been validated as a measure of hypnotic effect for various anaesthetic agents. There are limited data correlating the BIS with minimum alveolar concentration (MAC) of different volatile anaesthetics. We compared the BIS values using halothane and isoflurane at equal end-tidal MAC multiples. Forty adult patients of ASAI-II undergoing elective abdominal surgeries were randomly assigned into two groups. After a standardized induction, anaesthesia was maintained with either halothane (Group H) or isoflurane (Group I) in combination with nitrous oxide 66% in oxygen and fentanyl.BIS values were measured before induction, during anaesthesia at 0.5 MAC, 1 MAC, 1.5 MAC concentration of the volatile anaesthetics and then at awakening of the patient. BIS measurements were made after meeting steady state concentrations of volatile anaesthetic agents. BIS values at 0.5 MAC, 1.0 MAC and 1.5 MAC for patients receiving halothane exceeded those for patients receiving isoflurane. BIS value at awakening did not differ between the halothane and isoflurane groups. We concluded that at equal MAC concentrations of halothane and isoflurane BIS values were significantly lower with isoflurane.

Keywords

• Bispectral index; Halothane; Isoflurane
• Minimum alveolar concentration