Objective—To evaluate the influence of epidural
administration of xylazine hydrochloride on the minimum
alveolar concentration of isoflurane (MACISO)
and cardiopulmonary system in anesthetized dogs.
Animals—6 clinically normal dogs.
Procedure—Dogs were anesthetized with isoflurane
in oxygen after randomly being assigned to receive 1
of the following 4 treatments: epidural administration
of saline (0.9% NaCl) solution or xylazine at a dose of
0.1, 0.2, or 0.4 mg·kg–1. Experiments were performed
on 5 occasions with at least a 1-week interval
between experiments; each dog received all 4 treatments.
Following instrumentation, the concentration
of isoflurane was maintained constant for 15 minutes
at the MACISO that had been determined for each dog,
and data on heart rate, arterial blood pressure, respiratory
rate, tidal volume, minute volume, arterial partial
pressure of oxygen, arterial partial pressure of carbon
dioxide, and arterial pH were collected. The
epidural treatment was administered, and 30 minutes
later, data were again collected. From this point on,
determination of the MACISO following epidural treatment
(ie, MACISO + EPI) was initiated. Cardiopulmonary
data were collected before each electrical supramaximal
stimulus during MACISO + EPI determinations.
Results—The mean (± SD) MACISO was 1.29 ±
0.04%. The epidural administration of xylazine at
doses of 0.1, 0.2, and 0.4 mg·kg−1 decreased the
MACISO, respectively, by 8.4 ± 2.4%, 21.7 ± 4.9%,
and 33.4 ± 2.64%. Cardiopulmonary effects were limited.
Conclusions and Clinical Relevance—Epidural
administration of xylazine decreases the MACISO in a
dose-dependent manner and is associated with few
cardiopulmonary effects in anesthetized dogs. (Am J
Vet Res 2004;65:854–859)