HEMODYNAMIC-EFFECTS OF INTRAVENOUS ISOPROTERENOL VERSUS EPINEPHRINE IN THE CHRONIC MATERNAL-FETAL SHEEP PREPARATION

Isoproterenol 5 mu g may be an effective marker of accidental intravas cular injection in women in labor; however, before isoproterenol can b e incorporated in routinely used epidural test doses, the safety and u sefulness should be determined in an animal model. This study was desi gned to examine the hemodynamic effects of isoproterenol in comparison with epinephrine in the pregnant ewe. Five doses of isoproterenol wer e tested and compared with two doses of epinephrine in a randomized cr oss-over fashion. After administration of isoproterenol there was a sm all decrease of uterine blood flow (UBF) and maternal mean arterial pr essure (MMAP), which both almost immediately returned to baseline. Whe n epinephrine was used a more pronounced and more prolonged decrease o f UBF occurred. Increasing doses of isoproterenol resulted in dose-dep endent increases in maternal heart rate (MHR), while with epinephrine this was not the case. A significant increase in the cardiac output wa s seen after isoproterenol. Neither isoproterenol nor epinephrine affe cted fetal heart rate (FHR), fetal mean arterial pressure (FMAP), amni otic fluid pressure (Amn-pr), blood gases, or acid base status in the mother and the fetus. Provided that neurotoxic effects are absent, iso proterenol might be a better alternative than epinephrine as a test do se for possible intravenous placement of an epidural catheter in pregn ant women.