ED90 of 3% Chloroprocaine for Cervical Cerclage

"Initial Patient (A#X) 45mg (1.5mL) of Chloroprocaine 3% (Nesacaine - Fresenius Kabi), will be drawn up into a 3 ml syringe (a 1 ml 'TB syringe' will be used to aspirate the drug in aliquots to ensure accuracy). The following additive will be added: 10 mcg (0.2ml) of fentanyl (50 mcg/ml) 0.3 ml of sterile 0.9% sodium chloride Thus the total volume in the syringe will be 2 ml. Study drugs will be prepared by one anesthesiologist (un-blinded) and administered by another anesthesiologist (blinded).~Subsequent Patient (A#X+1) The dose of Chloroprocaine 3% based on outcome from prior subject and calculations mentioned previously will be added to 10 mcg (0.2ml) of fentanyl (50 mcg/ml). Sterile 0.9% sodium chloride will be added until the total volume in the syringe is 2 ml."