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Uptake of halothane by the foetal lamb in utero

Abstract:

The uptake of halothane by the normal foetus in utero was determined, using the pregnant ewe as an experimental animal model. Six pregnant ewes of 125-135 days gestation were surgically prepared under general anaesthesia. Potyvinyl catheters were placed in the maternal femoral artery and vein and in the foetal femoral artery and vein and the axillary artery. Each animal was allowed to recover for 24-36 hours prior to study. On the day of the experiment a tracheostomy was performed and after a control period, the ewe was anesthetized with 1.5 per cent halothane in oxygen. During each study, maternal and foetal blood pressure were continuously recorded. Simultaneous maternal and foetal arterial halothane concentrations were measured to construct an uptake curve for the foetus. During the study, foetal mean arterial blood pressure fell significantly (27per cent). There were no significant changes in foetal or maternal pulse rate or acidbase status. Halothane appeared in the foetal blood by two minutes but foetal halothane levels remained significantly lower than maternal for 24 minutes. We conclude that halothane crosses the placenta rapidly and produces a decrease in foetal blood pressure but no change in foetal oxygenation or acid-base status. © 1983 Canadian Anesthesiologists.