Regional cerebral blood flow changes during severe fetal asphyxia produced by slow partial umbilical cord compression

We studied the effects of severe partial asphyxia on regional cerebral blood flow and arterial blood pressure in the unanesthetized, physiologically stable fetal lamb. Cerebral blood flow was measured by the microsphere technique before and during partial umbilical cord compression. Asphyxia sufficient to decrease pH from 7.40 to 7.04 and reduce oxygen saturation from 50% to 19% increased cerebral blood flow to all areas of the brain with the largest increases going to the brain stem (275% of control) and deep cerebral structures (240% of control). Fetal arterial blood pressures increased from a mean of 58 mm Hg to a mean of 71 mm. Hg during asphyxia. The blood pressure increases correlated closely with the regional cerebral blood flow increases. There was a poor correlation between cerebral blood flow increases and changes in Paco2' pH, or oxygen saturation. We conclude that during severe fetal asphyxia arterial blood pressure is the critical factor in determining cerebral blood flow.