Phenylephrine

Phenylephrine is approximately 13 times less potent than norepinephrine, requiring a concentration of 100 µg/mL versus 8 µg/mL at the same infusion rate. A prior study found higher umbilical vein glucose concentrations in the norepinephrine group versus phenylephrine, suggesting differential effects on maternal-fetal glucose regulation, but did not directly measure maternal blood glucose or insulin levels. If no significant metabolic difference between the two vasopressors is found, vasopressor choice could instead be guided by norepinephrine's potential advantage in preserving fetal acid-base balance. Phenylephrine does not have consensus support as the first-line vasopressor, and institutional practice varies widely. Phenylephrine has historically been the dominant first-line agent for intraoperative hypotension. Phenylephrine is described as a pure alpha-1 agonist with vasopressor-only activity. Phenylephrine has been associated with worsened cardiac indices and outcomes in critical care and obstetric settings, but this has not been thoroughly studied in intraoperative surgery. Phenylephrine is one of two vasopressors most widely used to counteract spinal anaesthesia-induced hy…