Observations of the potency and duration of vecuronium in isoflurane-anesthetized horses.
OBJECTIVE
To evaluate the potency and duration of three subparalyzing doses of vecuronium (VEC) in isoflurane-anesthetized horses.


METHODS
Prospective experimental study.


METHODS
Thirteen healthy adult horses undergoing arthroscopic surgery.


METHODS
During isoflurane anesthesia, horses received one of three doses of vecuronium (25, 50, or 100 μg kg(-1)). Neuromuscular transmission was monitored with acceleromyography (AMG) with train-of-four (TOF) stimulation of the radial nerve. Maximal depression of the first twitch (T1), and onset time were recorded for each dose. Recovery time to a TOF ratio >90% was also evaluated.


RESULTS
Vecuronium 25 μg kg(-1) produced no observable T1 depression in four horses. VEC 50 μg kg(-1) (n = 5) produced a maximal T1 depression of [median (min, max)] 41 (20, 71) % in four horses, and no neuromuscular block was seen in the fifth. VEC 100 μg kg(-1) was given to four horses and produced a T1 depression of 73 (64, 78) %. Of the four horses in which VEC 50 μg kg(-1) produced a measurable neuromuscular block, three recovered spontaneously 43 (40, 52) minutes after VEC administration; a fourth subject received edrophonium to reverse residual block at the end of the surgery. Spontaneous recovery after VEC 100 μg kg(-1) occurred by 112 minutes in one horse, and had to be facilitated by edrophonium in the remaining three horses, more than 2 hours after VEC had been given.


CONCLUSIONS
A dose of 100 μg kg(-1) VEC in isoflurane anesthetized horses failed to produce complete paralysis. The partial neuromuscular block lasted at least 2 hours after this dose had been administered. Edrophonium was required to reverse the neuromuscular block in three of four horses. It is likely that more than 100 μg kg(-1) VEC would be necessary for complete neuromuscular blockade in horses, and that this dose will last >2 hours.
Department of Clinical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, NY, USA. mm459@cornell.edu
Manuel
M
Martin-Flores
Monique D
MD
Pare
Wendy
W
Adams
Luis
L
Campoy
Robin D
RD
Gleed
D000769:Anesthesia, Inhalation / Q000662:veterinary*; D018685:Anesthetics, Inhalation; D000818:Animals; D001182:Arthroscopy / Q000662:veterinary; D004305:Dose-Response Relationship, Drug; D006734:Horse Diseases / Q000601:surgery; D006736:Horses; D007103:Immobilization / Q000379:methods / Q000662:veterinary; D007262:Infusions, Intravenous / Q000662:veterinary; D007530:Isoflurane; D003473:Neuromuscular Nondepolarizing Agents / Q000008:administration & dosage* / Q000494:pharmacology; D014673:Vecuronium Bromide / Q000008:administration & dosage* / Q000494:pharmacology
D018685:Anesthetics, Inhalation; D003473:Neuromuscular Nondepolarizing Agents; D014673:Vecuronium Bromide; D007530:Isoflurane