Persistent changes in arterial blood gases in fetal sheep.

Two anaesthetic protocols were compared using pregnant sheep. In both groups of animals, anaesthesia was induced using an intravenous (i.v.) injection of diazepam and ketamine. The ewes were then intubated for positive pressure ventilation using 0.8 L/min of nitrous oxide and 2 L/min oxygen with 1.1–1.8% halothane. If the ewe showed any signs of awakening, one of two protocols was followed. First, the halothane concentration was increased to 2–3% until the ewe was completely anaesthetized. Second, the halothane concentration was not altered, but the ewe was given doses of i.v. diazepam (0.1 mg/kg) and ketamine (1 mg/kg) until again completely anaesthetized. At the completion of surgery, maternal recovery was rapid and similar between the two groups. However, five days after surgery, the fetal arterial Po2 and oxygen content of the fetuses receiving additional halothane (1.9 ± 0.2 kPa and 4.4 ± 1.0 mL/100 mL) were statistically significantly depressed when compared with the fetuses receiving additional dia...