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Equi-MAC concentrations of halothane and isoflurane do not produce similar bispectral index values

Ganne S Umamaheswara Rao1, Zulfiqar Ali, Madhusudan Ramamoorthy

  • 1Department of Neuroanaesthesia, National Institute of Mental Health and Neurosciences, Bangalore, India. gsuma@nimhans.kar.nic.in

Journal of Neurosurgical Anesthesiology
|April 7, 2007
PubMed

Insights

Bispectral Index (BIS) values are lower with isoflurane compared to halothane anesthesia at equivalent Minimum Alveolar Concentration (MAC) levels. BIS and SEF95 decrease with increasing anesthetic concentrations for both agents.

Area of Science:

  • Anesthesiology
  • Neurophysiology

Background:

  • Minimum Alveolar Concentration (MAC) traditionally measures inhalational anesthetic potency.
  • Bispectral Index (BIS), derived from electroencephalogram, quantifies anesthesia's hypnotic component.

Purpose of the Study:

  • To compare BIS values produced by equi-MAC concentrations of halothane and isoflurane.
  • To assess BIS and SEF95 during anesthetic wash-in and wash-out phases.

Main Methods:

  • 34 patients undergoing spinal surgery were studied.
  • BIS and SEF95 were recorded at 0.5, 0.75, and 1.0 MAC of halothane or isoflurane.
  • Measurements were taken during both wash-in and wash-out phases.

Main Results:

  • BIS and SEF95 significantly decreased with increasing concentrations of both anesthetics (P<0.001).
  • Isoflurane produced significantly lower BIS and SEF95 values than halothane at equivalent MAC concentrations (P<0.001).
  • BIS values were comparable during wash-in and wash-out for a given agent and MAC.

Conclusions:

  • BIS values are significantly lower with isoflurane compared to halothane at similar MAC concentrations.
  • BIS monitoring provides a reliable measure of hypnotic effect across different inhalational agents.

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