الفهرس 
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Abstract
Phenylephrine is a pure alpha-adrenergic receptor agonist with no beta-adrenergic receptor activity. It can effectively prevent or treat post spinal hypotension. Despite it could decrease utero-placental perfusion; recent studies have proven that it can improve neonatal outcome by maintaining maternal mean arterial blood pressure and organs perfusion pressure [14].
Norepinephrine has weak beta-adrenergic receptor agonistic properties, other than alpha adrenergic receptor agonist property. It has favourable effect on maternal heart rate and CO, rendering it a promising alternative to phenylephrine in obstetric anesthesia [12,15]
Ephedrine’s action is mainly indirect, via stimulating release of norepinephrine from sympathetic nerve terminals, because the uteroplacental circulation is largely devoid of direct sympathetic innervation, it is relatively resistant to the vasoconstrictive effects of ephedrine. These observations explain why most studies show that ephedrine increases blood pressure with minimal effect on uteroplacental blood flow. It has limited efficacy, and large doses may be required to maintain blo od pressure and prevent maternal symptoms. (15)
Simple randomization using a randomization table created by a computer software program was used to allocate parturients into 3 equal parallel groups according to the type of vasopressor drug. Phenylephrine (P) group: 25 parturients received phenylephrine (Phenylephrine HCL® 10mg/1ml STEROP, Belgium) infused at 0.1 ug/kg/min I.V. Norepinephrine (N) group: 25 parturients received norepinephrine (Levophrine® 4mg/4ml, EgyPharma, Egypt) infused at 0.05 ug/kg/min I.V. Ephedrine (E) group: 25 parturients received ephedrine
Summary