Effect of medetomidine administration on bispectral index measurements in dogs during anesthesia with isoflurane.
OBJECTIVE
To determine the relationship between bispectral index (BIS) and minimum alveolar concentration (MAC) multiples of isoflurane after IM injection of medetomidine or saline (0.9% NaCl) solution in anesthetized dogs.


METHODS
6 dogs.


METHODS
Each dog was anesthetized 3 times with isoflurane. First, the MAC of isoflurane for each dog was determined by use of the tail clamp method. Second, anesthetized dogs were randomly assigned to receive an IM injection of medetomidine (8 microg x kg(-1)) or an equal volume of isotonic saline (0.9% NaCl) solution 30 minutes prior to beginning BIS measurements. Last, anesthetized dogs received the remaining treatment (medetomidine or isotonic saline solution). Dogs were anesthetized at each of 4 MAC multiples of isoflurane. Ventilation was controlled and atracurium (0.2 mg/kg followed by 6 microg/kg/min as a continuous infusion, IV) administered. After a 20-minute equilibration period at each MAC multiple of isoflurane, BIS data were collected for 5 minutes and median values of BIS calculated.


RESULTS
BIS significantly decreased with increasing MAC multiples of isoflurane over the range of 0.8 to 2.0 MAC. Mean (+/- SD) MAC of isoflurane was 1.3 +/- 0.2%. During isoflurane-saline anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 65 +/- 8, 60 +/- 7 52 +/- 3, and 31 +/- 28, respectively. During isoflurane-medetomidine anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 77 +/- 4, 53 +/- 7, 31 +/- 24, and 9 +/- 20, respectively.


CONCLUSIONS
BIS monitoring in dogs anesthetized with isoflurane has a predictive value in regard to degree of CNS depression. During isoflurane anesthesia, our results support a MAC-reducing effect of medetomidine.
Greene
Stephen A
SA
Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, IL 61802, USA.
Tranquilli
William J
WJ
Benson
G John
GJ
Grimm
Kurt A
KA
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D000818:Animals; D002490:Central Nervous System / Q000187:drug effects* / Q000502:physiology; D018592:Cross-Over Studies; D004285:Dogs; D004347:Drug Interactions; D007530:Isoflurane / Q000494:pharmacology*; D020926:Medetomidine / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D018685:Anesthetics, Inhalation; D007530:Isoflurane; D020926:Medetomidine