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To determine whether hemodynamic responses of halothane-anesthetized horses undergoing surgical procedures depended on anesthetic induction protocols used, and to determine whether hemodynamic responses to surgical manipulation could be detected.


Prospective experimental study without controls.


36 clinically normal horses.


Horses were allotted to 5 groups according to anesthetic induction protocol: acepromazine/guaifene-sin/thiamylal, acepromazine/guaifenesin/ketamine, xyla-zine/guaifenesin/thiamylal, xylazine/guaifenesin/ketamine, and xylazine/diazepam/ketamine. Anesthesia was maintained with halothane. Hemodynamic measurements and blood gas values were obtained prior to the start of surgery, during surgery, and after surgery.


Few differences in hemodynamic measurements existed between horses in which anesthesia was induced by 5 anesthetic induction protocols, whether prior to the start of surgery or for pooled values for all 3 measurement periods. Hemodynamic responses to surgical manipulation were marked and included increased mean arterial pressure and systemic vascular resistance, and decreased cardiac index and oxygen delivery.

Clinical Implications—

Choice of anesthetic induction protocol has little impact on hemodynamic function during surgery in halothane-anesthetized horses. Surgical stimulation may increase blood pressure, but does not improve cardiac index or oxygen delivery. (J Am Vet Med Assoc 1996;208:252-257)

Free access
in Journal of the American Veterinary Medical Association


Objective—To determine the effects of clenbuterol, at a dosage of up to 3.2 μg/kg for 14 days, PO, on skeletal and cardiac muscle in healthy horses undergoing treadmill exercise.

Animals—12 healthy horses from 3 to 10 years old.

Procedures—Horses were randomly assigned to a control group (n = 6) or clenbuterol group (6) and received either saline (0.9% NaCl) solution or clenbuterol, PO, every 12 hours for 14 days. Horses were subjected to submaximal treadmill exercise daily during treatment. Muscle biopsy specimens were collected before and after treatment for determination of apoptosis. Echocardiographic measurements, serum clenbuterol and cardiac troponin I concentrations, and serum activities of creatine kinase and aspartate aminotransferase were measured before, during, and after treatment. Jugular venous blood samples were collected every 3 days during treatment. Echocardiography was repeated every 7 days after beginning treatment. Response variables were compared between treatment groups and across time periods.

Results—No significant effect of clenbuterol or exercise on response variables was found between treatment and control groups at any time point or within groups over time.

Conclusions and Clinical Relevance—Results did not reveal any adverse effects of treatment with an approved dose of clenbuterol on equine cardiac or skeletal muscle in the small number of horses tested.

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in American Journal of Veterinary Research