Phenylephrine

Regarding the use of phenylephrine following central neuraxial block in obstetric

anaesthesia, the following statements are true EXCEPT which one?

a) Continuous infusion produces fewer periods of hypotension than intermittent boluses

b) It results in less umbilical artery acidaemia than ephedrine

c) It produces less bradycardia compared to ephedrine

d) It produces less supraventricular tachycardia compared to ephedrine

e) It has not been shown to exhibit tachyphylaxis

Answer: c

Explanation

Following an inversion of what would have seemed heresy ten years ago, phenylephrine has become widely established as the drug for maintaining blood pressure following regional block in obstetric anaesthesia. This α1 agonist gives smoothest blood pressure control as an infusion. Studies have shown that phenylephrine produces less acidosis on umbilical sampling, although there is conflicting evidence as to whether it produces less actual foetal acidosis. Phenylephrine produces less maternal supraventricular tachycardias but more bradycardias. There are some rare reports of tachyphylaxis outside of the obstetric literature.