Antagonism by flumazenil of midazolam-induced changes in quantitative electroencephalographic data from isofluraneanesthetized dogs

R. D. Keegan From the Department of Veterinary Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6610.

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S. A. Greene From the Department of Veterinary Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6610.

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M. P. Moore From the Department of Veterinary Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6610.

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L. V. Gallagher From the Department of Veterinary Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman, WA 99164-6610.

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Summary

Quantitative electroencephalography (qeeg) was assessed in 5 dogs anesthetized with 1.6% end-tidal concentration of isoflurane and after subsequent administration of the benzodiazepine midazolam (0.2 mg/kg of body weight, iv). Ventilation was controlled to maintain normocapnia. Effect of the benzodiazepine antagonist, flumazenil (0.04 mg/kg, iv), on qeeg in midazolam-isoflurane-anesthetized dogs was determined. Heart rate, arterial blood pressure, esophageal temperature, arterial pH and blood gas tensions, endtidal CO2 concentration, and end-tidal isoflurane concentration were monitored throughout the study. A 21-lead linked-ear montage was used for recording the eeg data. Quantitative eeg data were stored on an optical disk for later analysis. Values for absolute power of eeg were determined for δ-, θ-, α-, and β-frequencies. Cardiovascular variables remained stable throughout the study. Midazolam administration was associated with decreased absolute power in all frequencies of eeg at all electrode sites. Administration of flumazenil antagonized midazolam-induced decreased absolute power of eeg in all frequencies at all electrode sites. We conclude that qeeg provides a noninvasive, objective measure of midazolamand flumazenil-induced changes in cortical activity during isoflurane anesthesia.

Summary

Quantitative electroencephalography (qeeg) was assessed in 5 dogs anesthetized with 1.6% end-tidal concentration of isoflurane and after subsequent administration of the benzodiazepine midazolam (0.2 mg/kg of body weight, iv). Ventilation was controlled to maintain normocapnia. Effect of the benzodiazepine antagonist, flumazenil (0.04 mg/kg, iv), on qeeg in midazolam-isoflurane-anesthetized dogs was determined. Heart rate, arterial blood pressure, esophageal temperature, arterial pH and blood gas tensions, endtidal CO2 concentration, and end-tidal isoflurane concentration were monitored throughout the study. A 21-lead linked-ear montage was used for recording the eeg data. Quantitative eeg data were stored on an optical disk for later analysis. Values for absolute power of eeg were determined for δ-, θ-, α-, and β-frequencies. Cardiovascular variables remained stable throughout the study. Midazolam administration was associated with decreased absolute power in all frequencies of eeg at all electrode sites. Administration of flumazenil antagonized midazolam-induced decreased absolute power of eeg in all frequencies at all electrode sites. We conclude that qeeg provides a noninvasive, objective measure of midazolamand flumazenil-induced changes in cortical activity during isoflurane anesthesia.

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