title: Maternal and fetal effects of isoproterenol in the gravid ewe.
abstract: Detection of the intravascular placement of epidural catheters is an important but difficult task. In this study, we evaluated maternal and fetal hemodynamic responses to intravenous (i.v.) and epidural injection of isoproterenol (ISO), a proposed chronotropic test dose, in gravid ewes. Near-term, chronically instrumented, gravid ewes with single fetuses were studied at least 48 h after surgery. We continuously recorded maternal heart rate (MHR), systemic and pulmonary blood pressures, uterine blood flow (UBF), and fetal blood pressure and heart rate. Maternal cardiac output was measured by thermodilution. In random sequence, each ewe (n = 11) received i.v. injections of saline, epinephrine (EPI) 15 microg; ISO 4, 16, and 80 microg; or epidural (n = 9 ewes) injections of saline, ISO 4 microg and ISO 40 microg. All variables returned to baseline between experiments. Sections of lumber spinal cord were harvested from five animals for later histopathological study. I.v. ISO caused a dose-related increase in MHR. Cardiac output also increased transiently after all doses of ISO but not after EPI. Maternal diastolic blood pressure decreased after ISO 16 and 80 microg. UBF decreased significantly for 120 s after EPI 15 microg. Epidural ISO did not significantly change maternal systemic or pulmonary blood pressure, cardiac output, or UBF. The 40-microg dose increased MHR significantly. No histopathological changes were seen in three ISO-exposed and two control spinal cords. I.v. ISO reliably induces maternal tachycardia in nonstressed gravid ewes. Unlike EPI, I.v. ISO lacks a statistically significant effect on UBF. However, ISO seems to be rapidly absorbed from the epidural space. Identifying the source of maternal tachycardia after epidural injection of a large dose of ISO could be difficult. If the absence of histopathological change is confirmed, ISO represents an alternative to EPI as a chronotropic test dose.
authors.affiliation: Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. Norrism@notes.wustl.edu
authors.forename: M C
authors.initials: MC
authors.lastname: Norris
authors.forename: V A
authors.initials: VA
authors.lastname: Arkoosh
authors.forename: R
authors.initials: R
authors.lastname: Knobler
mesh_terms: D000322:Adrenergic Agonists / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D002316:Cardiotonic Agents / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004388:Dura Mater / Q000187:drug effects / Q000473:pathology; D004837:Epinephrine / Q000008:administration & dosage / Q000494:pharmacology; D005260:Female; D005333:Fetus / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D006340:Heart Rate, Fetal / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects; D007268:Injections, Epidural; D007275:Injections, Intravenous; D007545:Isoproterenol / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000187:drug effects*; D011651:Pulmonary Artery / Q000187:drug effects; D011897:Random Allocation; D012039:Regional Blood Flow / Q000187:drug effects; D015203:Reproducibility of Results; D012756:Sheep; D016037:Single-Blind Method; D012965:Sodium Chloride; D013116:Spinal Cord / Q000187:drug effects / Q000473:pathology; D013610:Tachycardia / Q000139:chemically induced; D013815:Thermodilution; D014599:Uterus / Q000098:blood supply / Q000187:drug effects
chemical_list: D000322:Adrenergic Agonists; D002316:Cardiotonic Agents; D012965:Sodium Chloride; D007545:Isoproterenol; D004837:Epinephrine