Effects of isoflurane anesthesia with and without dexmedetomidine or remifentanil on quantitative electroencephalographic variables before and after nociceptive stimulation in dogs

Anne M. Kulka Small Animal Clinic, University of Veterinary Medicine Hannover, 30559 Hannover, Germany.

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Klaus A. Otto Central Laboratory Animal Facility, Medical School Hannover, 30625 Hannover, Germany.

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Carina Bergfeld Small Animal Clinic, University of Veterinary Medicine Hannover, 30559 Hannover, Germany.

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Martin Beyerbach Department of Biometry, Epidemiology and Information Processing, University of Veterinary Medicine Hannover, 30559 Hannover, Germany.

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Sabine B. R. Kästner Small Animal Clinic, University of Veterinary Medicine Hannover, 30559 Hannover, Germany.

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Abstract

Objective—To evaluate the influence of various anesthetic protocols and 3 multiples of isoflurane minimum alveolar concentration (MAC) before and after supramaximal stimulation on electroencephalographic (EEG) variables in dogs.

Animals—6 healthy adult Beagles (mean ± SD body weight, 16.3 ± 1.0 kg).

Procedures—All dogs underwent 3 anesthesia sessions with a minimum of 1 week separating sessions: isoflurane alone, isoflurane and a constant rate infusion of dexmedetomidine (3 μg/kg/h, IV; ID), and isoflurane and a constant rate infusion of remifentanil (18 μg/kg/h, IV; IR). The MAC of isoflurane was determined via supramaximal electrical stimulation. Quantitative variables (frequency bands and their ratios, median frequency, 95% spectral edge frequency [SEF], and an EEG index) were determined directly before and after supramaximal stimulation at 0.75, 1.0, and 1.5 times the MAC for each session of 20-second epochs.

Results—Mean ± SD isoflurane MACs for isoflurane alone, ID, and IR were 1.7 ± 0.3%, 1.0 ± 0.1%, and 1.0 ± 0.1%, respectively. Prestimulation 95% SEF decreased significantly with increasing MAC during the isoflurane alone and ID sessions. Significant decreases in δ frequency band (0.5 to 3.5 Hz) presence and significant increases in β frequency band (> 12.5 Hz) presence, median frequency, and 95% SEF after stimulation were dependent on the MAC and anesthetic protocol. The EEG index had the strongest correlation with increasing MAC during the isoflurane-alone session (ρ = −0.89) and the least in the IR session (ρ = −0.15).

Conclusions and Clinical Relevance—Anesthesia with isoflurane alone resulted in the greatest overall EEG depression of all protocols. Use of remifentanil depressed the EEG response to nociceptive stimulation more strongly than did dexmedetomidine. The EEG variables evaluated did not appear useful when used alone as indicators of anesthetic depth in dogs.

Abstract

Objective—To evaluate the influence of various anesthetic protocols and 3 multiples of isoflurane minimum alveolar concentration (MAC) before and after supramaximal stimulation on electroencephalographic (EEG) variables in dogs.

Animals—6 healthy adult Beagles (mean ± SD body weight, 16.3 ± 1.0 kg).

Procedures—All dogs underwent 3 anesthesia sessions with a minimum of 1 week separating sessions: isoflurane alone, isoflurane and a constant rate infusion of dexmedetomidine (3 μg/kg/h, IV; ID), and isoflurane and a constant rate infusion of remifentanil (18 μg/kg/h, IV; IR). The MAC of isoflurane was determined via supramaximal electrical stimulation. Quantitative variables (frequency bands and their ratios, median frequency, 95% spectral edge frequency [SEF], and an EEG index) were determined directly before and after supramaximal stimulation at 0.75, 1.0, and 1.5 times the MAC for each session of 20-second epochs.

Results—Mean ± SD isoflurane MACs for isoflurane alone, ID, and IR were 1.7 ± 0.3%, 1.0 ± 0.1%, and 1.0 ± 0.1%, respectively. Prestimulation 95% SEF decreased significantly with increasing MAC during the isoflurane alone and ID sessions. Significant decreases in δ frequency band (0.5 to 3.5 Hz) presence and significant increases in β frequency band (> 12.5 Hz) presence, median frequency, and 95% SEF after stimulation were dependent on the MAC and anesthetic protocol. The EEG index had the strongest correlation with increasing MAC during the isoflurane-alone session (ρ = −0.89) and the least in the IR session (ρ = −0.15).

Conclusions and Clinical Relevance—Anesthesia with isoflurane alone resulted in the greatest overall EEG depression of all protocols. Use of remifentanil depressed the EEG response to nociceptive stimulation more strongly than did dexmedetomidine. The EEG variables evaluated did not appear useful when used alone as indicators of anesthetic depth in dogs.

Contributor Notes

This manuscript represents a portion of a dissertation submitted by the first author to the University of Veterinary Medicine Hannover as partial fulfillment of the requirements for a Dr med vet degree.

Dr. Kulka was supported by a scholarship from Cusanuswerk.

Presented in abstract form at the 56th Jahreskongress der Deutschen Gesellschaft für Kleintiermedizin, Berlin, November 2009; and the Association of Veterinary Anaesthetists Spring Conference, Cambridge, England, March 2010.

Address correspondence to Dr. Kulka (anne_kulka@gmx.de).
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