Vasopressor Therapy for Hypotension due to Epidural Anesthesia for Cesarean Section

Abstract

Comment Based primarily on uterine blood flow studies in sheep, anesthesiologists have been rigidly taught that maternal hypotension resulting from spinal or epidural block treated with primarily a-agonists (phenylephrine, methoxy-amine, norepinephrine) resulted in decreased uteroplacental perfusion and further fetal deterioration. These two investigators using human mothers undergoing elective cesarean section with epidural block measured cardiac parameters including cardiac output with the noninvasive technique of impedance electrocardiography. Based on maternal cardiac parameters, umbilical venous and arterial blood gases at birth, and neonatal 1 and 5 min Apgar scores, 100 jug i.v. boluses of phenylephrine were as safe and as effective from maternal and fetal standpoints as were 5 mg i.v. boluses of ephedrine in treating mild maternal hypotension following sympathetic block. The authors are to be congratulated on this excellent clinical research in a not inconsiderable number (n = 127) of mothers. However, despite these results, we would still favor at present the use of ephedrine over neo-synephrine in the treatment of postsympathetic block maternal hypotension for the following reasons: 1. The safety and efficacy of ephedrine has been tested and proven in both humans and animals over many years. Additional studies confirming the authors' findings, including neonatal neuroadaptive capacity scoring, are required to establish the safety of drugs such as phenyleph-rine. 2. Should Ergot preparations be required for postpartum uterine contraction, previous use of a-agonists has been documented to be associated with severe hypertension. This effect is far less severe with ephedrine. 3. Elective uncomplicated parturients not in labor were studied. The effect of phenylephrine on parturients in labor and on uterine contractions needs to be examined. 4. The safety of phenylephrine in the high risk parturient, (e.g., preeclampsia, prematurity, diabetes, increased maternal age, etc) needs to be established while the safety of ephedrine has been reasonably well proven in these patients. 5. A considerable amount of 1:200,000 epineph-rine in the local anesthetic was used to establish the epidural for cesarean section. Such amounts of epinephrine have been shown in nonpregnant humans to have primarily agonistic effects which could account for failure of phenylephrine not lowering cardiac output in these patients. Hence, similar studies are required in patients having spinal block or epidural block using epi-nephrine-free local anesthetics. Despite these reservations the results of this study certainly give evidence of phenylephrine's maternal and fetal safety when its use is indicated should ephedrine be ineffective or should maternal tachycardia be avoided. Brett B. Gutsche, M.D. Theodore G. Cheek, M.D.