الفهرس 
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Abstract
Spinal anaesthesia is considered the standard anaesthetic technique for elective cesarean section. However, hypotension is a major limitation of this technique. The incidence of hypotension is more than 80% without any prophylactic measures. This hypotension with or without bradycardia has detrimental effects on both mother and foetus.
The incidence of hypotension can be lowered by several ways but till date, no single method completely prevents hypotension. Many articles emphasize on the arterial rather than venous circulation and show that the reduced systemic vascular resistance as the primary factor for the genesis of maternal hypotension. Over the last few years, there is a trend to rely more on vasopressors than either crystalloid or colloid alone.
Routinely, vasopressors such as ephedrine, metaraminol and phenylephrine have been given prophylactically preoperatively to combat maternal hypotension.
Ephedrine is sympathomimatic amine. The principle mechanism of its action relies on its indirect stimulation of the adrenergic receptors, which is part of sympathetic nervous system, by increasing the activity of noradrenaline at the post-synaptic α and β receptors. The presence of direct interactions with α-receptors is unlikely, but still controversial. L-Ephedrine and particularly its stereoisomer pseudoephedrine has indirect sympathomimetic effects and due its ability to cross blood brain barrier, it is CNS stimulant similar to amphetamines but with weaker effect, as it releases noradrenaline and dopamine in the substantia nigra.
Ephedrine is commonly used as a vasopressor during spinal anaesthesia to prevent maternal hypotension. Unlike direct acting α1 agonists ,ephedrine does not decrease uterine blood flow. This makes it the preferred vasopressor for most obstetric uses. Ephedrine has also been reported to posses’ antiemetic properties, particularly in association with hypotension following spinal anaesthesia.
Despite the use of prophylactic intravenous (i.v.) infusion or bolus ephedrine for the last three decades, a good number of failures have also been reported.
Phenylephrine is a selective α1 adrenergic receptor agonist used primarily as a decongestant, as an agent to dilate the pupil and as a vasopressor to increase the blood pressure in unstable patients with hypotension, phenylephrine is especially useful in counteracting the hypotensive effect of epidural and subarachnoid anesthetics. . It has the advantage of not being inotropic or chronotropic, and so it strictly elevates the blood pressure without increasing the heart rate or contractility (reflex bradycardia may result from the blood pressure increase). However this is especially useful if the heart is already tachycardic and/or has a cardiomyopathy .Its elimination half life is about 2.5 to 3 hours; while ephedrine is about 3 to 6 hours.The present study was carried out to compare between the effectiveness and the side effects of intravenous infusion of either phenylephrine or ephedrine in combating the effect of spinal anaesthesia on maternal hemodynamics as regard heart rate, systolic, diastolic and mean arterial blood pressure during elective cesarean section.