The Hemodynamic Response of Calves to Tiletamine-Zolazepam Anesthesia

Six isoflurane-anesthetized calves were instrumented for hemodynamic studies and allowed to recover from anesthesia. When the mean arterial blood pressure rose to 100 mmHg or when vigorous movement occurred, a 1:1 tiletamine-zolazepam mixture (4 mg/kg) was administered intravenously (IV). Values for cardiac output, cardiac index, stroke index, central venous pressure, and right ventricular stroke work index did not change significantly. Systolic, mean, and diastolic arterial blood pressures and systemic vascular resistance were significantly decreased below baseline at 5 minutes; they were significantly increased above baseline at 20 minutes and remained so throughout the 60 minute study. Changes in left ventricular stroke work index and rate pressure product were similar to those of arterial blood pressure and systemic vascular resistance, although they were not significant. Heart rate and pulmonary capillary wedge pressure decreased significantly but gradually returned to baseline at 40 minutes and then increased significantly above baseline by the end of the study. Minor venous-arterial shunting or perhaps mismatching of ventilation and perfusion appeared to have developed in the later stages of the study. This was reflected in a minor increase in the arterial partial pressure of carbon dioxide (PaCO2) and a decrease in the arterial partial pressure of oxygen (PaO2) and arterial pH. At the dose administered, the hemodynamic changes induced by tiletamine-zolazepam were minimal and were compatible with safe anesthesia in calves.