Objective—To evaluate the use of xylazine and ketamine
for total IV anesthesia in horses.
Procedure—Anesthetic induction was performed on
4 occasions in each horse with xylazine (0.75 mg/kg,
IV), guaifenesin (75 mg/kg, IV), and ketamine
(2 mg/kg, IV). Intravenous infusions of xylazine and
ketamine were then started by use of 1 of 6 treatments
as follows for which 35, 90, 120, and 150 represent
infusion dosages (µg/kg/min) and X and K represent
xylazine and ketamine, respectively: X35+K90
with 100% inspired oxygen (O2), X35+K120-O2,
X35+K150-O2, X70+K90-O2, K150-O2, and X35+K120
with a 21% fraction of inspired oxygen (ie, air).
Cardiopulmonary measurements were performed.
Response to a noxious electrical stimulus was
observed at 20, 40, and 60 minutes after induction.
Times to achieve sternal recumbency and standing
were recorded. Quality of sedation, induction, and
recovery to sternal recumbency and standing were
Results—Heart rate and cardiac index were higher
and total peripheral resistance lower in K150-O2 and
X35+K120-air groups. The mean arterial pressure was
highest in the X35+K120-air group and lowest in the
K150-O2 group (125 ± 6 vs 85 ± 8 at 20 minutes,
respectively). Mean PaO2 was lowest in the
X35+K120-air group. Times to sternal recumbency
and standing were shortest for horses receiving
K150-O2 (23 ± 6 minutes and 33 ± 8 minutes, respectively)
and longest for those receiving X70+K90-O2
(58 ± 28 minutes and 69 ± 27 minutes, respectively).
Conclusions and Clinical Relevance—Infusions of
xylazine and ketamine may be used with oxygen supplementation
to maintain 60 minutes of anesthesia in
healthy adult horses. (Am J Vet Res 2005;66:1002–1007)