Duration of nonresponse to noxious stimulation after intramuscular administration of butorphanol, medetomidine, or a butorphanol-medetomidine combination during isoflurane administration in dogs
Ka. Grimm et al., Duration of nonresponse to noxious stimulation after intramuscular administration of butorphanol, medetomidine, or a butorphanol-medetomidine combination during isoflurane administration in dogs, AM J VET RE, 61(1), 2000, pp. 42-47
Objective-To assess duration of actions of butorphanol, medetomidine, and a
butorphanol-medetomidine combination in dogs given subanesthetic doses of
isoflurane (ISO).
Animals-6 healthy dogs.
Procedure-Minimum alveolar concentration (MAC) Values for ISO were determin
ed, for each dog. Subsequently, 4 treatments were administered to each dog
(saline [0.9% NaCl] solution, butorphanol [0.2 mg/kg of body weight], medet
omidine [5.0 mu g/kg], and a combination of butorphanol [0.2 mg/kg] and med
etomidine [5.0 mu g/kg]). All treatments were administered IM to dogs concu
rrent with isoflurane; treatment order was determined, using a randomized c
rossover design. Treatments were given at 7-day intervals. After mask induc
tion with ISO and instrumentation with a rectal temperature probe, end-tida
l CO2 and anesthetic gas concentrations were analyzed. End-tidal ISO concen
tration was reduced to 90% MAC for each dog. A tail clamp was applied 15 mi
nutes later. After a positive response, 1 of the treatments was administere
d. Response to application of the tail clamp was assessed at 15-minute inte
rvals until a positive response again was detected.
Results-Duration of nonresponse after administration of saline solution, bu
torphanol, medetomidine, and butorphanol-medetomidine (mean +/- SD) was 0.0
+/- 0.0, 1.5 +/- 1.5, 2.63 +/- 0.49, and 5.58 +/- 2.28 hours, respectively
. Medetomidine effects were evident significantly longer than those for sa
line solution, whereas effects for bulorphanol-medetomidine were evident si
gnificantly longer than for each agent administered alone.
Conclusion and Clinical Relevance-During ISO-induced anesthesia, administra
tion of medetomidine, but not butorphanol, provides longer and more consist
ent analgesia than does saline solution, and the combination of butorphanol
-medetomidine appears superior to the use of medetomidine or butorphanol al
one.