A healthy 29-year-old undergoes elective lower segment Caesarean section under spinal anaesthesia. Ten minutes after subarachnoid block her blood pressure falls to 88/52 mmHg with a heart rate of 92/min. There is no fetal distress. The vasopressor of FIRST choice is:

• A Ephedrine bolus
• B Adrenaline bolus
• C Mephentermine bolus
• D Phenylephrine bolus or infusion ✓

Explanation

Randomised trials in healthy parturients show alpha agonists such as phenylephrine maintain maternal blood pressure with equal efficacy to ephedrine but produce better fetal pH and base excess, because ephedrine crosses the placenta and increases fetal metabolic demand causing acidosis. Phenylephrine is therefore first line unless the mother has a low heart rate or fixed cardiac output state. Adrenaline is never used for routine spinal hypotension, and mephentermine has largely been superseded.

Reference: Chestnut's Obstetric Anesthesia, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.