Why Question Established Practice?
*Emeritus Professor and Former Chair of Anesthesiology, Wake Forest School of Medicine, Winston-Salem, North Carolina.Anesthesiology (Impact Factor: 5.88). 10/2012; 117(6). DOI: 10.1097/ALN.0b013e31826e05bb
During hypotension resulting from conduction anesthesia in gravid ewes, uterine blood flow (UBF) decreased roughly in proportion to the decrease in maternal blood pressure. Ephedrine or mephentermine significantly increased UBF over that accomplished by metaraminol. Presumably, the preferential effects of these agents were the result of increased cardiac output owing to inotropic and chronotropic actions. However, UBF never exceeded 90% of prespinal levels with any vasoactive agent, and, for a given maternal system, the UBF response was variable, generally increasing but frequently remaining constant or decreasing. For these reasons, all other methods of combating hypotension should be used initially. If vasopressors are still required, agents of choice are those whose principal mode of action lies in cardiac stimulation rather than peripheral vasoconstriction.
- Anesthesiology 08/1970; 33(1):25-34. DOI:10.1097/00000542-197007000-00010 · 5.88 Impact Factor
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ABSTRACT: Phenylephrine is effective for the management of spinal anesthesia-induced hypotension in parturients undergoing cesarean delivery under spinal anesthesia. While ephedrine was previously considered the vasopressor of choice in obstetric patients, phenylephrine is increasingly being used. This is largely due to studies suggesting improved fetal acid-base status with the use of phenylephrine as well as the low incidence of hypotension and its related side effects with prophylactic phenylephrine regimens. This review highlights the effects of phenylephrine compared with ephedrine on maternal hemodynamics (arterial blood pressure, heart rate, and cardiac output), and occurrence of intraoperative nausea and vomiting. The impact of the administration of phenylephrine as a bolus for the treatment of established hypotension compared with its administration as a prophylactic infusion is discussed. This article also reviews the impact of phenylephrine compared with ephedrine on uteroplacental perfusion, and fetal outcomes such as neonatal acid-base status and Apgar scores. The optimum dosing regimen for phenylephrine administration is also discussed.Anesthesia and analgesia 11/2011; 114(2):377-90. DOI:10.1213/ANE.0b013e3182373a3e · 3.47 Impact Factor
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ABSTRACT: To evaluate the safety of prophylactic vasopressor administration prior to obstetric conduction anesthesia, equipotent doses of ephedrine, metaraminol, mephentermine, and methoxamine were administered to 16 nonanesthetized pregnant ewes near term. When the maternal blood pressure was increased by 50%, uterine blood flow was unchanged with ephedrine and was reduced 20% with mephentermine (P > 0.05); 45% with metaraminol (P < 0.05) and 62% with methoxamine (P > 0.05). Metaraminol and methoxamine consistently decreased uterine blood flow at all levels of maternal blood pressure elevation. No significant change in fetal blood gas and acid base variables was demonstrated.Anesthesiology 05/1974; 40(4):354-70. DOI:10.1097/00000542-197404000-00009 · 5.88 Impact Factor
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