Intrathecal clonidine in obstetrics: sheep studies.

Clonidine may be administered intrathecally as an adjunct to local anesthetics or accidentally during attempted epidural analgesia. To examine clonidine's acute maternal and fetal effects, the authors injected clonidine (100, 300, 750, 1500 micrograms cumulative dose at 15-min intervals) intrathecally in nine chronically prepared near-term ewes. Unlike intrathecal saline injection, which did not alter any parameters, clonidine altered maternal blood pressure in a biphasic manner (depression at lower doses and return to baseline after the highest dose). Clonidine produced a dose-dependent decrease in maternal and fetal heart rate. After the highest dose, 1500 micrograms, PO2 decreased in both ewe and fetus, accompanied by fetal hypertension and bradycardia. Clonidine increased maternal and fetal serum glucose, but not cortisol. Although clonidine-induced hypoxemia and hyperglycemia occur only in sheep, fetal bradycardia may limit the usefulness of clonidine in large doses (greater than 10 micrograms/kg) in obstetrics. Lower doses, such as may be used to enhance spinal anesthesia, are well tolerated in sheep.