The effects of terbutaline on the acid base balance and circulation of chronically instrumented pregnant sheep.

Terbutaline is considered an effective beta agonist with beta 2 character, for the inhibiton of labor. Its safety was evaluated in twelve infusions of 1,500 micrograms over 30 min, to 8 'steady state' pregnant sheep of 110--134 days of gestation. Experimentation was performed at least 4 days postoperatively. Maternal (n = 12) and fetal (n = 7) arterial blood samples were drawn at 0, 10, 20, 30, 60- and 90 min from the start of the infusion. Uterine blood flow (UBF), blood pressure (BP), and heart rate (HR) were monitored continuously. Maternal pCO2, bicarbonate (HCO-3), and base excess (BE) decreased significantly during the infusion. Maternal pH, pO2, and O2% saturation of the hemoglobin (O2%) remained constant. Maternal hemoglobin (Hb) increased significantly at 10 min. A significant maternal hypotension and tachycardia followed the infusion. UBF decreased by 26% at the end of infusion, recovering by 60 min. Fetal pH, pCO2, Hb, O2%, BP, HR, HCO-3, BE, and CO2 content all remained stable for the duration of the experiment. Fetal arterial pO2 transiently increased at 10 min. No other significant fetal effects were observed.