Determination of the ED 50 and ED 95 of intravenous bolus of norepinephrine for the treatment of hypotension during spinal anesthesia for cesarean delivery.

Norepinephrine is considered as a potential alternative for blood pressure stabilization during spinal anesthesia for cesarean delivery, as it maintains a better maternal heart rate and cardiac output compared with phenylephrine. However, its use as a bolus dose for hypotension treatment remains largely unexplored. Therefore, the present study investigated the ED50 and ED95 of norepinephrine as a bolus for maternal hypotension during cesarean delivery. In the present prospective trial, 42 patients were enrolled for elective delivery under spinal anesthesia. The dose of norepinephrine was decided by the up-and-down sequential allocation method (UDM) with an initial dose of 0.075 µg/kg and a 0.025 µg/kg increment. The 42 patients received a bolus of norepinephrine when systolic blood pressure fell to <80% of baseline. The ED50 was calculated by the sequential method and the probit regression model. The ED95 was then calculated using the probit regression model. The ED50 of norepinephrine, which was determined by the UDM, was 0.067 µg/kg (95% CI, 0.056-0.081). The probit regression model calculated an ED50 of 0.072 µg/kg (95% CI, 0.056-0.088) and an ED95 of 0.121 µg/kg (95% CI, 0.1-0.207). In summary, the present results suggested the ED50 of a bolus norepinephrine for preventing hypotension in elective CD is 0.067 µg/kg (95% CI, 0.056-0.081), with an ED95 of 0.121 µg/kg (95% CI, 0.1-0.207).