Objective To measure the effects of dobutamine infusion on fetal oxygenation during isoflurane anaesthesia in pregnant ewes. Study design Prospective randomized experimental study. Animals Seven clinically normal adult pregnant Rambouillet-Dorset cross ewes with fetuses of 117–122 days gestational age. Methods The ewes were anaesthetized with ketamine (2mgkg−1) IM, and isoflurane (FE′ISO 2.0%) in oxygen. After instrumentation and stabilization, dobutamine was infused at 4µgkg−1minute−1 for 60minutes and 10µgkg−1minute−1 for 60minutes in random order, separated by a 20-minute washout period. Catheters were placed in the maternal and fetal carotid arteries; these were used for continuous blood pressure measurement and intermittent blood sampling. Results Maternal mean systemic carotid arterial pressure was 60mmHg prior to dobutamine infusion. After 5minutes of dobutamine infusion, fetal oxygen saturation increased (p<0.05) from 0.62 (0.17–0.71, minimum–maximum) to 0.72 (0.28–0.78) at a dose of 4µgkg−1minute−1 and to 0.70 (0.20–0.73) at a dose of 10µgkg−1minute−1. These increases were maintained during the infusion and were not significantly different between doses. Maternal oxygen saturation remained constant at 1.0 before and during all infusions. Although maternal heart rate and blood pressure increased (p<0.05) by 90% and 25%, respectively, with dobutamine, this stimulant effect was not evident in the corresponding fetal variables. Maternal haemoglobin concentration increased 30% (p<0.05) with each infusion. Conclusions Dobutamine at 4µgkg−1minute−1 increases fetal oxygenation that is not improved by a dose of 10µgkg−1minute−1. This increase is largely due to an increase in maternal haemoglobin concentration that, in turn, increases oxygen delivery to the placenta. Clinical relevance The use of dobutamine to treat hypotension in pregnant sheep during isoflurane anaesthesia improves fetal oxygenation. This may be true in other species.
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