THE EFFECTS OF SPINAL ANESTHESIA ON THE FETAL HEART RATE.

The effect of spinal anesthesia on fetal heart rate is due to maternal hypotension and subsequent fetal hypoxia. Maternal hypotension of 80 mm of mercury for five minutes almost always results in hypoxic fetal bradycardia. This bradycardia is gradual in onset, and may be preceded by a short period of fetal tachycardia. There is a lag in the return of fetal heart rate to normal after maternal blood pressure has normalized. Similar bradycardia has been observed in maternal syncope unassociated with anesthesia. Maternal hypotension should be prevented, and if it occurs should be corrected early. Administration of a vasopressor drug is the treatment of choice, with oxygen and fluids as indicated.