Cardiopulmonary effects of xylazine and acepromazine in pregnant cows in late gestation.
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.


METHODS
8 cows between 219 and 241 days of gestation.


METHODS
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
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.
Hodgson
David S
DS
Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80523, USA.
Dunlop
Colin I
CI
Chapman
Phillip L
PL
Smith
John A
JA
D000075:Acepromazine / Q000494:pharmacology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002417:Cattle / Q000502:physiology*; D018492:Dopamine Antagonists / Q000494:pharmacology*; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006400:Hematocrit / Q000662:veterinary; D006439:Hemodynamics / Q000187:drug effects*; D010100:Oxygen / Q000097:blood; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000187:drug effects / Q000502:physiology*; D012119:Respiration / Q000187:drug effects*; D014599:Uterus / Q000098:blood supply*; D014991:Xylazine / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D018492:Dopamine Antagonists; D014991:Xylazine; D000075:Acepromazine; D010100:Oxygen