Carotid arterial blood flow in the ovine fetus as a continuous measure of cerebral blood flow.

Objective: The purpose of this study was to establish a continuous measure of cerebral blood flow in the ovine fetus with a transit time flow probe.
Methods: Seven chronically catheterized fetal sheep were studied near term with placement of a 3R Transonic flow probe on the external carotid artery, just proximal to the internal maxillary artery. Blood flow changes were induced by altering maternal inspired oxygen and carbon dioxide concentrations, with cerebral and extracerebral blood flows also determined by the microsphere technique.
Results: Although absolute carotid and cerebral blood flow values were only modestly related under the present study conditions (r = 0.60, P < .05), both the percent change and the actual change in carotid arterial blood flow showed a strong linear correlation with that for cerebral blood flow (r = 0.84, P < .01, and r = 0.72, P < .02) but less so with that for extracerebral blood flow (r = 0.44 and r = 0.28).
Conclusion: Measurements of carotid blood flow as studied with a transit time flow probe and induced blood gas changes can provide for a continuous assessment of changes in blood flow to the ovine fetal brain.