The influence of atropine on the cardiopulmonary effects of a xylazine-ketamine combination in dogs.

The effect of atropine on cardiopulmonary changes induced by xylazine-ketamine anesthesia was studied in 7 male dogs. A consecutive i.v. injection of xylazine (1.1 mg/kg) and ketamine (11 mg/kg) induced an anesthesia of approximately 20 min, and increased PaCO2 but decreased PaO2 and pHa for 20 min. The xylazine-ketamine administration increased heart rate for 5 min, which was followed by a small but significant decrease at 30 min posttreatment. The xylazine-ketamine injection decreased left ventricular and mean aortic pressure for 1 to 2 min. The low pressures returned to normal and became higher than base line levels at 5 min posttreatment. The xylazine-ketamine injection increased peripheral resistance and decreased cardiac output and cardiac index for at least 40 min. An i.v. injection of atropine sulfate (0.04 mg/kg) potentiated the effect of xylazine-ketamine on PaCO2 and PaO2, but did not change the effect of xylazine-ketamine on pHa. The atropine injection did not change the transient low left ventricular and mean aortic pressures immediate after the xylazine-ketamine administration, but did potentiate the duration of the increased heart rate, left ventricular and mean aortic pressures induced by xylazine-ketamine between 5 to 40 min. Atropine did not change the effect of xylazine-ketamine on peripheral resistance. Atropine partially antagonized the effect of xylazine-ketamine on cardiac output and cardiac index. Interpretation of the results indicates that atropine may increase cardiac work and may potentiate the pulmonary effect of i.v. administration of xylazine-ketamine.