The effect of ketamine anaesthesia on the acidotic fetal lamb.

The following study in pregnant ewes was done to examine the effects of ketamine-oxygen anaesthesia on the fetal lamb made acidotic by partial occlusion of the umbilical cord. Fifteen pregnant ewes were instrumented under general anaesthesia to allow continuous measurement of maternal and fetal mean arterial pressure and pulse rate and for withdrawal of arterial blood samples for blood gas analysis. An occlusion loop was loosely secured around the umbilical cord. Following a recovery period of 48 hours, a tracheostomy was performed on each ewe. After a control period, the umbilical occlusion loop was slowly inflated until fetal pH had decreased to 7.12-7.15. Following inflation the animals were divided into groups A and B. Group A received no anaesthesia. In Group B, the ewes received ketamine 3 mg X kg-1 intravenously and controlled ventilation with FIO2 of 1.0. After ten minutes ketamine 1 mg X kg-1 was given. In both groups radioactive microspheres were injected into the fetus at 0, 5, and 15 minutes. Ketamine anaesthesia in the pregnant ewe abolished the fetal hypertension and bradycardia produced by partial cord occlusion. All fetuses survived the 15 minutes of ketamine anaesthesia and there were no significant changes in arterial blood gases or pH. Blood flows determined by the microsphere method to the brain, heart, and kidneys were not significantly altered by ketamine. We conclude that ketamine-oxygen anaesthesia does not cause further deterioration in the acidotic fetal lamb.