During elective lower segment Caesarean section under spinal anaesthesia, the mother develops hypotension to 85/50 mmHg. Which vasopressor is preferred for first line correction and why?
- A Phenylephrine infusion, because it corrects blood pressure with less fetal acidosis than ephedrine ✓
- B Ephedrine, because it preserves uteroplacental perfusion through beta agonism
- C Mephentermine, because it crosses the placenta least
- D Adrenaline bolus, because alpha activity is required at this dose
Correct answer: A. Phenylephrine infusion, because it corrects blood pressure with less fetal acidosis than ephedrine
Explanation
Randomised trials and current obstetric anaesthesia practice favour phenylephrine as the first line vasopressor for spinal induced hypotension at Caesarean delivery. It maintains maternal pressure with a higher umbilical artery pH and less fetal acidosis than ephedrine, because ephedrine crosses the placenta and stimulates fetal metabolism directly. Ephedrine remains acceptable when the mother is bradycardic, since phenylephrine's pure alpha effect lowers heart rate.
Reference: Chestnut's Obstetric Anesthesia, 6th ed.
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