Objective—To determine effects of sedation
achieved by xylazine (XYL) or acepromazine (ACE) on
cardiopulmonary function and uterine blood flow in
cows in late gestation.
Animals—8 cows between 219 and 241 days of gestation.
Procedure—Doses of ACE (0.02 mg/kg) or XYL (0.04
mg/kg) were administered IV. Measurements were
obtained to determine cardiopulmonary effects and
oxygen delivery to the uterus.
Results—Heart rate was not significantly affected by
administration of ACE, but it decreased markedly after
administration of XYL. Uterine artery flow was
decreased at all times by XYL and was always less
than for ACE. Xylazine increased uterine vascular
resistance through 30 minutes and caused reduced
PaO2 and increased PaCO2 at all time periods.
Acepromazine caused a 5% decrease in PaO2 only at
5 minutes. Xylazine reduced oxygen delivery by 59%
at 5 minutes and 32% at 45 minutes. In contrast, ACE
caused a nonsignificant reduction of oxygen delivery
by 16% at 15 minutes and a return to baseline values
by 45 minutes
Conclusions and Clinical Relevance—Xylazine
markedly reduces flow and availability of oxygenated
blood to the uterus, which may critically impair delivery
of oxygen to the fetus at a stressful and important time
of development or delivery. Acepromazine was associated
with slight reductions of much shorter duration.
When XYL is used to sedate pregnant cows, it could
impose physiologic distress on the fetus and potentially
increase fetal morbidity and mortality. When sedation
of the dam is desirable, ACE could be an alternative
to XYL. (Am J Vet Res 2002;63:1695–1699)