EFFECTS OF ISOXSUPRINE ON MATERNAL AND FETAL ACID-BASE-BALANCE AND CIRCULATION

Prematurity is a large contributing factor to neonatal morbidity. An obstetric alternative to premature labor is administration of isoxsuprine, an effective inhibitor of uterine contractions. Six crossbred unanesthetized pregnant ewes were used to determine the effects on fetal and maternal cardiovascular and acid-base status of 10 maternal i.v. infusions of 30 mg isoxsuprine over 30 min (1 mg/min). Isoxsuprine caused slight maternal hypotension and a transient acidosis, both of which returned to baseline values within 60 min. Maternal tachycardia persisted throughout the experiment. A slight decrease in the O2 percent saturation of the hemoglobin and the calculated O2 content was observed after the infusion. There was no significant change in uterine blood flow. Maternal lactate concentration transiently increased at 60 min only. In the fetus, isoxsuprine caused transient hypotension and tachycardia. Fetal arterial PCO2, calculated HCO3- concentration and O2 content all decreased slightly at 45 min only. Fetal hyperglycemia was observed after the infusion throughout the experiment. All other fetal values returned to baseline levels within 60 min. Thirty mg isoxsuprine can cause tolerable maternal and fetal metabolic and physiologic effects when administered i.v. to the unanesthetized pregnant ewe.