The effect of fentanyl on the end-tidal sevoflurane concentration needed to prevent motor movement in dogs.
OBJECTIVE
The objectives of this study were to determine the effects of fentanyl on the end-tidal concentration of sevoflurane needed to prevent motor movement (MACNM ) in response to noxious stimulation, and to evaluate if acute tolerance develops.


METHODS
Randomized cross-over experimental study.


METHODS
Six healthy, adult (2-3 years old), intact male, mixed-breed dogs weighing 16.2 ± 1.1 kg.


METHODS
Six dogs were randomly assigned to receive one of three separate treatments over a 3 week period. After baseline sevoflurane MACNM (MACNM-B) determination, fentanyl treatments (T) were administered as a loading dose (Ld) and constant rate infusion (CRI) as follows: T1-Ld of 7.5 μg kg(-1) and CRI at 3 μg kg(-1) hour(-1); T2-Ld of 15 μg kg(-1) and CRI at 6.0 μg kg (-1) hour(-1); T3-Ld of 30 μg kg(-1) and CRI at 12 μg kg(-1) hour(-1). The MACNM was defined as the minimum end-tidal sevoflurane concentration preventing motor movement. The first post-treatment MACNM (MACNM-I) determination was initiated 90 minutes after the start of the CRI, and a second MACNM (MACNM - II) determination was initiated 3 hours after MACNM-I was established.


RESULTS
The overall least square mean MACNM-B for all groups was 2.66%. All treatments decreased (p < 0.05) MACNM, and the decrease from baseline was 22%, 35% and 41% for T1, T2 and T3, respectively. Percentage change in T1 differed (p < 0.05) from T2 and T3; however, T2 did not differ from T3. MACNM-I was not significantly different from MACNM-II within treatments.


CONCLUSIONS
Fentanyl doses in the range of 3-12 μg kg(-1) hour(-1) significantly decreased the sevoflurane MACNM. Clinically significant tolerance to fentanyl did not occur under the study conditions.
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.
Sabrina
S
Reilly
Reza
R
Seddighi
Christine M
CM
Egger
Barton W
BW
Rohrbach
Thomas J
TJ
Doherty
Wen
W
Qu
James R
JR
Johnson
D000759:Adjuvants, Anesthesia / Q000008:administration & dosage / Q000494:pharmacology*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D018592:Cross-Over Studies; D004285:Dogs / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005283:Fentanyl / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage / Q000494:pharmacology*; D009043:Motor Activity / Q000187:drug effects*; D000077149:Sevoflurane
D000759:Adjuvants, Anesthesia; D018685:Anesthetics, Inhalation; D008738:Methyl Ethers; D000077149:Sevoflurane; D005283:Fentanyl