Foetal deterioration following thiopentone-nitrous oxide anaesthesia in the pregnant ewe

Six pregnant sheep were chronically prepared with indwelling catheters in maternal and foetal vessels and a flow probe around a maternal uterine artery. They were anaesthetized the following day with thiopentone and nitrous oxide (70 per cent)--oxygen (30 per cent) maintenance with tracheal intubation. Maternal uterine blood flow fell about 20 per cent following induction of anaesthesia. This resulted from uterine vasoconstriction which, in turn, probably resulted from maternal catecholamine release during light anaesthesia. The foetus in utero developed a mixed metabolic and respiratory acidosis and a fall in oxygen saturation. The possibility that light maternal anaesthesia increases rather than decreases neonatal depression is discussed.