Cardiopulmonary effects of a tiletamine-zolazepam combination in sheep

Abstract

Summary To assess the effects on heart and lung function, a tiletamine-zolazepam (tz) anesthetic combination was evaluated in 10 Dorset-type ewes. Ewes were randomly allotted to 2 equal groups. Ewes of groups 1 and 2 were given a single bolus of tz (12 and 24 mg/kg of body weight, iv, respectively) at time zero. Hemodynamic, pulmonary, and ventilation variables were measured at 15-minute intervals to 120 minutes. Blood gas variables were evaluated at 5-minute intervals for the first 30 minutes, then at 15-minute intervals to 120 minutes. In all sheep, tz administration induced rapid, smooth induction, with gradual and unremarkable recovery. Anesthesia duration was not significantly different between groups (mean ± sd, 39 ± 5 and 40 ± 14 minutes for groups 1 and 2, respectively). Immediate drug effects included apnea, decreased mean arterial blood pressure, and arterial hypoxemia. Cardiac output was significantly decreased in both groups at all times after drug administration. Significant changes in group-1 ewes included increased pulmonary and systemic vascular resistances and decreased inspired minute ventilation, tidal volume, and respiratory airflow. Significant changes in group-2 ewes included increased systemic vascular resistance and decreased pulmonary arterial pressure, inspired minute ventilation, and respiratory airflow. Both drug dosages induced apneustic breathing patterns and caused significant changes in arterial and venous blood hemoglobin concentrations and pcv. Tiletamine-zolazepam is useful for intermediate-duration anesthesia in sheep. However, because of alterations in cardiopulmonary function, its use at the dosages evaluated by us is not recommended in studies, in which minimal effects on heart and lung function are required, or in sheep with compromised heart or lung function.