Fetal carotid blood flow during videofetoscopy

Intracranial bleeding has been reported as one of the complications of both open and minimally invasive fetal surgery and putatively attributed to intraoperative fluctuations of carotid blood flow. The aim of this study was to look at fetal carotid blood flow and its relationship with umbilical blood flow, blood pressure, oxygen delivery, and acid-base status in the fetus at various intraamniotic pressures with both liquid and gas media during fetoscopic surgery.

Six 115- to 130-day-gestation ewes underwent continuous invasive systemic blood pressure monitoring in the descending aorta. A hysterotomy was performed. A 6-mm ultrasonic blood flow probe was placed around the common umbilical artery at its origin from the fetal aorta. This was followed by placement of a double-lumen, 4F catheter in the fetal descending aorta through a femoral artery. A 4-mm ultrasonic blood flow probe was then placed around the fetal left common carotid artery. A pressure-monitoring, multiperforated catheter was placed inside the amniotic cavity. The fetus was repositioned inside the uterus, which was then closed. The abdominal wall was closed loosely. No further manipulation was performed for 1 hour. Intraamniotic pressure was raised from 0 to 30 mm Hg at 5-mm Hg intervals by infusing either warmed saline or medical air. Common umbilical artery and left carotid artery blood flows, blood pressure, blood gases, bicarbonate, sodium, and hematocrit were recorded in all fetuses at each 5-mm Hg interval. Maternal systemic blood pressure, O2 saturation, and temperature were kept constant.

Carotid blood flow remained stable within the intra-amniotic pressure range studied (0 to 30 mm Hg), despite the significant drop in common umbilical artery blood flow uniformly observed above 20 mm Hg when saline was infused and above 15 mm Hg when air was infused. There was fetal hypoxemia and hypercarbia concomitant with decreased common umbilical artery blood flow (however, without fetal acidosis, because of compensatory elevation of bicarbonate). Within the intraamniotic pressure range studied, fetal aortic blood pressure, sodium, and hematocrit did not vary significantly, even when there was decreased umbilical blood flow.

Fetal carotid blood flow is protected, possibly autoregulated, remaining stable even after umbilical blood flow decreases as a consequence of elevated intrauterine pressures up to 30 mm Hg during videofetoscopy. These data suggests that perioperative intracranial bleeding related to videofetoscopic surgery is caused by factors other than fluctuations of cerebral blood flow.