Hypotension associated with spinal anaesthesia for caesarean section.

Spinal anaesthesia for Caesarean section is associated with an unacceptably high incidence of hypotension despite the administration of an intravenous fluid preload and the use of uterine displacement. The theoretical benefits of preventing hypotension as opposed to treating it as it occurs are the avoidance o f considerable maternal discomfort, a reduced risk o f serious cardiovascular or respiratory depression and the avoidance of transient foetal asphyxia. The use of prophylactic intramuscular ephedrine prior to spinal anaesthesia has been recommended but not well studied. The advantages o f the intramuscular route for ephedrine administration are its simplicity and its favourable pharmacokinetic profile. Cardiovascular support is sustained throughout the surgery and into the post operative period. Opposition to the use o f intramuscular ephedrine in the prevention of hypotension is based on two studies in which spinal anaesthesia was not used [1,2]. These studies showed an unacceptably high incidence o f hypertension, a deleterious effect on foetal gas exchange and a lack of efficacy when intramuscular ephedrine was used in epidural and general anaesthesia respectively. This research report describes a randomised, double blind, interventional study designed to assess the safety (prevalence of hypertension, tachycardia or foetal compromise) and efficacy (prevalence of hypotension) o f 37,5mg of ephedrine given prior to spinal anaesthesia for Caesarean section. Forty patients who had given informed consent were entered into the study. Blood pressures and pulse rates were recorded for 90 minutes after ephedrine administration, samples o f umbilical venous blood were collected and Apgar scores assessed. This study found that giving 37,5mg of intramuscular ephedrine prior to spinal anaesthesia was safe from a maternal point of view in that it was not associated with reactive hypertension or tachycardia. When the ephedrine was given 10 minutes prior to induction of the spinal the technique proved to be effective in reducing the incidence and severity of hypotension. When used in the above manner the technique was not associated with foetal depression or acidosis.