Despite the widespread use of an epinephrine-containing test dose to detect
intravascular catheter placement, its use in obstetric anesthesia remains
controversial. Reasons for this controversy include a reduced chronotropic
response to P-adrenergic agents during pregnancy, increased maternal heart
rate variability during uterine contractions, and the observed reduction of
uterine blood flow in animal models after the administration of epinephrin
e. Additional concerns include the use of epinephrine in preeclamptic patie
nts who show an increased response to vasoactive drugs with the risk of a p
ossible hypertensive crisis with i.v, injection of epinephrine. In these pa
tients a further reduction of the already compromised uterine blood flow ma
y subject the fetus to an increased risk of asphyxia. Isoproterenol, as a p
ure P-adrenergic drug, may offer several advantages. It leads to a more rel
iable heart rate increase in parturients without an increase in mean or dia
stolic blood pressure, and uterine blood flow is enhanced with i.v. injecti
on. This would suggest a larger safety margin for mother and fetus. However
, because there are insufficient data to rule out potential neurotoxicity,
the use of isoproterenol has not been approved for epidural or intrathecal
use and its place in obstetric anesthesia remains to be demonstrated. As no
other safer substitute for epinephrine is currently available, an increasi
ng number of anesthesiologists omit a standard test dose containing epineph
rine in laboring patients and rely on close clinical observation, frequent
aspiration through a multi-orifice catheter and fractionated injections. (C
) 2001 Harcourt Publishers Ltd.