Effect of Cephalic Pressure on Fetal Cerebral Blood Flow

ABSTRACT

During vaginal delivery, the fetus is exposed to a variety of stresses including pressure applied to the fetal skull. In order to study the effects of this stress on fetal homeo-stasis, we monitored the response to external cephalic compression applied to the acutely prepared near-term fetal lamb. In response to cephalic pressure, we noted initial bradycardia followed by sustained tachycardia. Mean arterial pressure and pulse pressure rose during cephalic pressure and gradually returned to baseline levels. Cerebral blood flow fell approximately 95% early in the period of compression. This fall in total cerebral blood flow was accompanied by a redistribution of cerebral flow. During this time, a smaller percentage of cerebral blood flow was found in the cortex and a greater percentage was directed to the brainstem.