title: Effects of isoflurane, sevoflurane and methoxyflurane on the electroencephalogram of the chicken.
abstract: OBJECTIVE
  Anaesthetics have differing effects on mammalian electroencephalogram (EEG) but little is known about the effects on avian EEG. This study explored how inhalant anaesthetics affect chicken EEG.
  
  
  METHODS
  Experimental study.
  
  
  METHODS
  Twelve female Hyline Brown chickens aged 6-11 weeks.
  
  
  METHODS
  Each chicken was anaesthetized with isoflurane, sevoflurane, and methoxyflurane. For each, anaesthesia was adjusted to 1, 1.5 and 2 times Minimum Anaesthetic Concentration (MAC). Total Power (Ptot), Median Frequency (F50), Spectral Edge Frequency (F95) and Burst Suppression Ratio (BSR) were calculated at each volume concentration. BSR data were analyzed using doubly repeated measures anova. Neither isoflurane nor sevoflurane could be included in analysis of F50, F95 and Ptot because of extensive burst suppression; Methoxyflurane data were analyzed using RM anova.
  
  
  RESULTS
  There was a significant interaction between anaesthetic and concentration on BSR [F(4,22) = 10.65, p < 0.0001]. For both isoflurane and sevoflurane, BSR increased with concentration. Isoflurane caused less suppression than sevoflurane at 1.5 MAC and at final 1 MAC while methoxyflurane caused virtually no burst suppression. Methoxyflurane concentration had a significant effect on F50 [F(2,20) = 3.83, p = 0.04], F95 [F(2,20) = 4.03, p = 0.03] and Ptot [F(2,20) = 5.22, p = 0.02]. Decreasing methoxyflurane from 2 to 1 MAC increased F50 and F95. Ptot increased when concentration decreased from 1.5 to 1 MAC and tended to be higher at 1 MAC than at 2 MAC.
  
  
  CONCLUSIONS
  Isoflurane and sevoflurane suppressed chicken EEG in a dose-dependent manner. Higher concentrations of methoxyflurane caused an increasing degree of synchronization of EEG. Isoflurane and sevoflurane suppressed EEG activity to a greater extent than did methoxyflurane at equivalent MAC multiples. Isoflurane caused less suppression than sevoflurane at intermediate concentrations. These results indicate the similarity between avian and mammalian EEG responses to inhalant anaesthetics and reinforce the difference between MAC and anaesthetic effects on brain activity in birds.
authors.affiliation: Animal Welfare Science and Bioethics Centre/Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North, New Zealand.
authors.forename: Amanda E
authors.initials: AE
authors.lastname: McIlhone
authors.forename: Ngaio J
authors.initials: NJ
authors.lastname: Beausoleil
authors.forename: Craig B
authors.initials: CB
authors.lastname: Johnson
authors.forename: David J
authors.initials: DJ
authors.lastname: Mellor
mesh_terms: D000769:Anesthesia, Inhalation / Q000662:veterinary; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D001921:Brain / Q000187:drug effects; D002645:Chickens; D004562:Electrocardiography / Q000187:drug effects / Q000662:veterinary; D004569:Electroencephalography / Q000187:drug effects / Q000662:veterinary*; D005260:Female; D006321:Heart / Q000187:drug effects; D007530:Isoflurane / Q000494:pharmacology*; D008733:Methoxyflurane / Q000494:pharmacology*; D008738:Methyl Ethers / Q000494:pharmacology*; D000077149:Sevoflurane
chemical_list: D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D008733:Methoxyflurane; D000077149:Sevoflurane; D007530:Isoflurane
keywords: EEG; anaesthesia; burst suppression; chicken; frequency analysis