Document Detail

Comparison of the effects of halothane, isoflurane and methoxyflurane on the electroencephalogram of the horse.
MedLine Citation:
PMID:  10193288     Owner:  NLM     Status:  MEDLINE    
We have investigated in eight ponies the effects of three different end-tidal concentrations of halothane, isoflurane and methoxyflurane on median (F50) and 95% spectral edge (F95) frequencies of the EEG and the second differential (DD) of the middle latency auditory evoked potential (MLAEP). The three concentrations of each agent were chosen to represent approximately the minimum alveolar concentration (MAC), 1.25 MAC and 1.5 MAC for each agent. During halothane anaesthesia, F95 decreased progressively as halothane concentration increased, from mean 13.9 (SD 2.6) at 0.8% to 11.9 (1.1) at 1.2%. DD was lower during anaesthesia with the highest concentration (21 (6.5)) compared with the lowest (27.6 (11.4)). There were no significant changes in F50. During isoflurane anaesthesia, there was a small, but significant increase in F95 between the intermediate and highest concentrations (10.2 (1.5) to 10.8 (1.6)). There were no changes in F50 and DD. Values of F95, F50 and DD at all isoflurane concentrations were similar to those of halothane at the highest concentration. During methoxyflurane anaesthesia, F95 and F50 decreased progressively as methoxyflurane concentration was increased, from 21.3 (0.7) and 6.5 (1), respectively, at 0.26%, to 20.1 (0.6) and 5.6 (0.8), respectively, at 0.39%. DD was lower during anaesthesia with the highest concentration of methoxyflurane (25.7 (7.8)) compared with the lowest (39.7 (20.6)). Values of F95, F50 and DD at all methoxyflurane concentrations were higher than those seen with halothane at the lowest concentration. The different relative positions of the dose-response curves for EEG and MLAEP changes compared with antinociception (MAC) changes suggest differences in the mechanisms of action of these three agents. These differences may explain the incomplete adherence to the Meyer-Overton rule.
C B Johnson; P M Taylor
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Publication Detail:
Type:  Comparative Study; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  British journal of anaesthesia     Volume:  81     ISSN:  0007-0912     ISO Abbreviation:  Br J Anaesth     Publication Date:  1998 Nov 
Date Detail:
Created Date:  1999-04-20     Completed Date:  1999-04-20     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0372541     Medline TA:  Br J Anaesth     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  748-53     Citation Subset:  IM    
Department of Clinical Veterinary Science, University of Bristol, Langford.
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MeSH Terms
Anesthetics, Inhalation / pharmacology*
Dose-Response Relationship, Drug
Electroencephalography / drug effects,  veterinary*
Evoked Potentials, Auditory / drug effects
Halothane / pharmacology
Horses / physiology*
Isoflurane / pharmacology
Methoxyflurane / pharmacology
Reg. No./Substance:
0/Anesthetics, Inhalation; 151-67-7/Halothane; 26675-46-7/Isoflurane; 76-38-0/Methoxyflurane

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