Xylazine and xylazine-ketamine in dogs.

The cardiopulmonary consequences of IV administered xylazine (1.0 mg/kg) followed by ketamine (10 mg/kg) were evaluated in 12 dogs. Xylazine caused significant decreases in heart rate, cardiac output, left ventricular work, breathing rate, minute ventilation, physiologic dead space, oxygen transport, mixed venous partial pressure of oxygen, and oxygen concentration. It caused significant increases in systemic blood pressure, central venous pressure, systemic vascular resistance, tidal volume, and oxygen utilization ratio. The subsequent administration of ketamine was associated with significant increases in heart rate (transient increase), cardiac output, the alveolar-arterial PO2 gradient and venous admixture (transient increase), and arterial PCO2 (transient increase). It caused significant decreases in stroke volume (transient decrease), left ventricular stroke work (transient decrease), effective alveolar ventilation, arterial PO2 and oxygen content (transient decrease).