title: Effects of isoflurane anesthesia with and without dexmedetomidine or remifentanil on quantitative electroencephalographic variables before and after nociceptive stimulation 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.
  
  
  METHODS
  6 healthy adult Beagles (mean ± SD body weight, 16.3 ± 1.0 kg).
  
  
  METHODS
  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
  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.
authors.affiliation: Small Animal Clinic, University of Veterinary Medicine Hannover, Hannover, Germany. anne_kulka@gmx.de
authors.forename: Anne M
authors.initials: AM
authors.lastname: Kulka
authors.forename: Klaus A
authors.initials: KA
authors.lastname: Otto
authors.forename: Carina
authors.initials: C
authors.lastname: Bergfeld
authors.forename: Martin
authors.initials: M
authors.lastname: Beyerbach
authors.forename: Sabine B R
authors.initials: SB
authors.lastname: Kästner
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000008:administration & dosage*; D000701:Analgesics, Opioid / Q000008:administration & dosage*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000818:Animals; D001784:Blood Gas Analysis; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D020927:Dexmedetomidine / Q000008:administration & dosage*; D004285:Dogs; D004569:Electroencephalography / Q000662:veterinary; D005260:Female; D007530:Isoflurane / Q000008:administration & dosage*; D008297:Male; D059225:Nociception; D010880:Piperidines / Q000008:administration & dosage*; D011650:Pulmonary Alveoli / Q000378:metabolism; D000077208:Remifentanil; D014457:Ulna / Q000502:physiology
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D000701:Analgesics, Opioid; D018685:Anesthetics, Inhalation; D010880:Piperidines; D020927:Dexmedetomidine; D007530:Isoflurane; D000077208:Remifentanil