Hemodynamic effects of intravenous isoproterenol versus epinephrine in the chronic maternal-fetal sheep preparation.

ABSTRACT

Isoproterenol 5 micrograms may be an effective marker of accidental intravascular injection in women in labor; however, before isoproterenol can be incorporated in routinely used epidural test doses, the safety and usefulness should be determined in an animal model. This study was designed to examine the hemodynamic effects of isoproterenol in comparison with epinephrine in the pregnant ewe. Five doses of isoproterenol were tested and compared with two doses of epinephrine in a randomized cross-over fashion. After administration of isoproterenol there was a small decrease of uterine blood flow (UBF) and maternal mean artery pressure (MMAP), which both almost immediately returned to baseline. When epinephrine was used a more pronounced and more prolonged decrease of UBF occurred. Increasing doses of isoproterenol resulted in dose-dependent increases in maternal heart rate (MHR), while with epinephrine this was not the case. A significant increase in the cardiac output was seen after isoproterenol. Neither isoproterenol nor epinephrine affected fetal heart rate (FHR), fetal mean arterial pressure (FMAP), amniotic fluid pressure (Amn-pr), blood gases, or acid base status in the mother and the fetus. Provided that neurotoxic effects are absent, isoproterenol might be a better alternative than epinephrine as a test dose for possible intravenous placement of an epidural catheter in pregnant women.