Anesthetic, cardiorespiratory, and metabolic effects of four intravenous anesthetic regimens induced in horses immediately after maximal exercise.
OBJECTIVE
To determine the anesthetic, cardiorespiratory, and metabolic effects of 4 IV anesthetic regimens in Thoroughbred horses recuperating from a brief period of maximal exercise.


METHODS
6 adult Thoroughbreds.


METHODS
Horses were preconditioned by exercising them on a treadmill. Each horse ran 4 simulated races, with a minimum of 14 days between races. Races were run at a treadmill speed that caused horses to exercise at 120% of their maximal oxygen consumption. Horses ran until fatigued or for a maximum of 2 minutes. Two minutes after exercise, horses received a combination of xylazine hydrochloride (2.2 mg/kg of body weight) and acepromazine maleate (0.04 mg/kg) IV. Five minutes after exercise, horses received 1 of the following 4 IV anesthetic regimens: ketamine hydrochloride (2.2 mg/kg); ketamine (2.2 mg/kg) and diazepam (0.1 mg/kg); tiletamine hydrochloride-zolazepam hydrochloride (1 mg/kg); and guaifenesin (50 mg/kg) and thiopental sodium (5 mg/kg). Treatments were randomized. Cardiopulmonary indices were measured, and samples of blood were collected before and at specific times for 90 minutes after each race.


RESULTS
Each regimen induced lateral recumbency. The quality of induction and anesthesia after ketamine administration was significantly worse than after other regimens, and the duration of anesthesia was significantly shorter. Time to lateral recumbency was significantly longer after ketamine or guaifenesin-thiopental administration than after ketaminediazepam or tilet-amine-zolazepam administration. Arterial blood pressures after guaifenesin-thiopental administration were significantly lower than after the other regimens.


CONCLUSIONS
Anesthesia can be safely induced in sedated horses immediately after maximal exercise. Ketamine-diazepam and tilet-amine-zolazepam induced good quality anesthesia with acceptable perturbations in cardiopulmonary and metabolic indices. Ketamine alone and guaifenesin-thiopental regimens are not recommended.
Hubbell
J A
JA
Department of Veterinary Clinical Sciences, The College of Veterinary Medicine, The Ohio State University, Columbus 43210, USA.
Hinchcliff
K W
KW
Schmall
L M
LM
Muir
W W
WW
Robertson
J T
JT
Sams
R A
RA
D000075:Acepromazine / Q000494:pharmacology; D000771:Anesthesia, Intravenous / Q000379:methods / Q000662:veterinary*; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D000818:Animals; D001774:Blood Chemical Analysis; D001794:Blood Pressure / Q000187:drug effects; D001831:Body Temperature / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D003975:Diazepam / Q000494:pharmacology; D005260:Female; D006140:Guaifenesin / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006736:Horses; D007649:Ketamine / Q000494:pharmacology; D008297:Male; D010805:Physical Conditioning, Animal; D005082:Physical Exertion / Q000187:drug effects*; D015656:Respiratory Mechanics / Q000187:drug effects*; D012420:Running; D013874:Thiopental / Q000494:pharmacology; D013992:Tiletamine / Q000494:pharmacology; D014991:Xylazine / Q000494:pharmacology; D015041:Zolazepam / Q000494:pharmacology
D018686:Anesthetics, Intravenous; D014991:Xylazine; D013992:Tiletamine; D006140:Guaifenesin; D000075:Acepromazine; D007649:Ketamine; D015041:Zolazepam; D013874:Thiopental; D003975:Diazepam