The role of vasopressors in the management of hypotension induced by spinal and epidural anaesthesia

Abstract

Although spinal and epidural blocks provide excellent anaesthesia for many operations, they are frequently accompanied by hypotension. This is largely the result of sympathetic nerve blockade. Excessive hypotension may potentially produce myocardial and cerebral ischaemia, and is associated with neonatal acidaemia in obstetric practice. How to prevent and treat this hypotension has been the subject of much investigation and controversy. One of the mainstays of management is the use of vasopressor agents and those currently available are not perfect. In this review, the role of vasopressor agents is discussed and possible future management strategies are commented upon. Ephedrine was the first agent used for this purpose and it has withstood the test of time: it is the agent against which all others are compared. It remains the first-line agent in obstetric anaesthesia as it does not affect the fetus adversely, but it cannot be relied upon to be 100% successful and other agents must be considered when it is inadequate. It is best given by infusion. In non-obstetric practice, ephedrine has a good track record but again its success rate is less than 100%. As there is no fetus to consider, it may be more appropriate to consider using a pure vasoconstrictor agent such as methoxamine or phenylephrine as a first-line therapy in such cases. This judgment can only be made on an individual patient basis as ephedrine produces a tachycardia while phenylephrine and methoxamine both produce bradycardia.