Effects of glycopyrrolate on cardiorespiratory function in horses anesthetized with halothane and xylazine.
OBJECTIVE
To evaluate cardiopulmonary effects of glycopyrrolate in horses anesthetized with halothane and xylazine.


METHODS
6 horses.


METHODS
Horses were allocated to 2 treatment groups in a randomized complete block design. Anesthesia was maintained in mechanically ventilated horses by administration of halothane (1% end-tidal concentration) combined with a constant-rate infusion of xylazine hydrochloride (1 mg/kg/h, i.v.). Hemodynamic variables were monitored after induction of anesthesia and for 120 minutes after administration of glycopyrrolate or saline (0.9% NaCl) solution. Glycopyrrolate (2.5 microg/kg, i.v.) was administered at 10-minute intervals until heart rate (HR) increased at least 30% above baseline or a maximum cumulative dose of 7.5 microg/kg had been injected. Recovery characteristics and intestinal auscultation scores were evaluated for 24 hours after the end of anesthesia.


RESULTS
Cumulative dose of glycopyrrolate administered to 5 horses was 5 microg/kg, whereas 1 horse received 7.5 microg/kg. The positive chronotropic effects of glycopyrrolate were accompanied by an increase in cardiac output, arterial blood pressure, and tissue oxygen delivery. Whereas HR increased by 53% above baseline values at 20 minutes after the last glycopyrrolate injection, cardiac output and mean arterial pressure increased by 38% and 31%, respectively. Glycopyrrolate administration was associated with impaction of the large colon in 1 horse and low intestinal auscultation scores lasting 24 hours in 3 horses.


CONCLUSIONS
The positive chronotropic effects of glycopyrrolate resulted in improvement of hemodynamic function in horses anesthetized with halothane and xylazine. However, prolonged intestinal stasis and colic may limit its use during anesthesia.
Teixeira Neto
Francisco J
FJ
Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, ON, Canada, N1G 2W1.
McDonell
Wayne N
WN
Black
William D
WD
Duronghphongtorn
Sumit
S
D000759:Adjuvants, Anesthesia / Q000009:adverse effects / Q000494:pharmacology*; D000768:Anesthesia, General / Q000662:veterinary*; D019162:Anesthetics, Combined; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000187:drug effects; D005244:Fecal Impaction / Q000139:chemically induced; D006024:Glycopyrrolate / Q000009:adverse effects / Q000494:pharmacology*; D006221:Halothane; D006339:Heart Rate / Q000187:drug effects; D006452:Hemoglobinometry; D006736:Horses / Q000097:blood / Q000502:physiology*; D013318:Stroke Volume / Q000187:drug effects; D014991:Xylazine
D000759:Adjuvants, Anesthesia; D019162:Anesthetics, Combined; D014991:Xylazine; D006221:Halothane; D006024:Glycopyrrolate