Pharmacokinetic Simulation of Remifentanil Dosing at Different Effect-Site Targets During Target-Controlled Infusion for Cesarean Delivery.

Background/Objectives: Remifentanil may be useful during general anesthesia for cesarean delivery, although the amount administered before delivery using target-controlled infusion (TCI) at different effect-site targets has not been well quantified. This pharmacokinetic study investigated how much remifentanil would be delivered before birth at different initial effect-site targets. Methods: This retrospective simulation study used demographic data from 50 women undergoing cesarean delivery. Remifentanil TCI (Minto model) was simulated with initial effect-site targets of 1, 2, 4, and 6 ng/mL. One minute after the simulated plasma peak, the target was reduced to 1 ng/mL (t0). Doses before t0, duration of the infusion pause, and total dose before delivery were calculated. Simulated dosing patterns were summarized overall and stratified by elective and emergency procedures. Results: Infusion pauses after target reduction lasted 175, 346, and 503 s after initial targets of 2, 4, and 6 ng/mL, respectively. Delivery occurred during these pauses in 16%, 46%, and 72% of cases (19%, 71%, and 90% in emergency cases). Mean remifentanil dose at delivery was 33.7, 43.0, 70.0, and 101.0 μg for initial targets of 1, 2, 4, and 6 ng/mL, respectively. Following target reduction, the additional remifentanil administered before delivery decreased from a mean of 17.0 μg with an initial effect-site target of 1 ng/mL to 0.9 μg with an initial target of 6 ng/mL. Conclusions: This simulation demonstrated that only modest additional doses of remifentanil would be delivered to the mother between induction and delivery during target-controlled infusion for cesarean delivery, with the exact amount depending on the initial effect-site target concentration.