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The effects of maternal plasma dobutamine levels on fetal oxygenation in anaesthetized sheep
Authors:Ec Butler DVM    Pf Moon DVM Dip ACVA    Rd Gleed BVSc  DVA  Dip ACVA  Dip ECVA    Jw Ludders DVM  Dip ACVA    Xy Ding MD    Pw Nathanielsz MD  PhD    Hn Erb DVM  PhD
Institution:College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA
Abstract:ObjectiveTo measure the effects of dobutamine infusion on fetal oxygenation during isoflurane anaesthesia in pregnant ewes.Study designProspective randomized experimental study.AnimalsSeven clinically normal adult pregnant Rambouillet-Dorset cross ewes with fetuses of 117–122 days gestational age.MethodsThe ewes were anaesthetized with ketamine (2 mg kg?1) IM, and isoflurane (FE′ISO 2.0%) in oxygen. After instrumentation and stabilization, dobutamine was infused at 4 µg kg?1minute?1 for 60 minutes and 10 µg kg?1minute?1 for 60 minutes 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.ResultsMaternal mean systemic carotid arterial pressure was 60 mm Hg prior to dobutamine infusion. After 5 minutes 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 4 µg kg?1minute?1 and to 0.70 (0.20–0.73) at a dose of 10 µg kg?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.ConclusionsDobutamine at 4 µg kg?1minute?1 increases fetal oxygenation that is not improved by a dose of 10 µg kg?1minute?1. This increase is largely due to an increase in maternal haemoglobin concentration that, in turn, increases oxygen delivery to the placenta.Clinical relevanceThe use of dobutamine to treat hypotension in pregnant sheep during isoflurane anaesthesia improves fetal oxygenation. This may be true in other species.
Keywords:Anaesthesia  dobutamine  pregnancy  sympathomimetics  sheep
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