Determining the ED90 for Intrathecal 3% Chloroprocaine for Elective Cervical Cerclage Surgery

Cervical cerclage is a procedure performed on pregnant women with cervical incompetence to reduce the risk of second trimester spontaneous abortion and preterm labor. This outpatient procedure is performed commonly under both general and regional anesthesia. In an effort to ensure rapid discharge some institutions prefer the use of general anesthesia; however, this has the disadvantage of exposing the fetus to general anesthetic drugs, increased risk of aspiration and a higher requirement for opioid analgesia post operatively. The benefits of neuraxial anesthesia for cerclage placement includes rapid onset of a dense sensory block, reduced fetus exposure to medications, and maintenance of maternal airway reflexes. Successful analgesia for cerclage placement requires a sensory block from S4-T10 dermatomes. Inadequate sensory coverage with a spinal anesthetic typically necessitates the conversion to general anesthesia adding risk to the mother and fetus while increasing intraoperative times and resources. Currently there are no studies determining optimum dose of spinal chloroprocaine for cervical cerclage. The investigators propose a dose determining study to determine the ED90 of intrathecal lidocaine and chloroprocaine which will help decrease incidence of inadequate anesthesia for cervical cerclage.

This is a multicenter, double blinded, dose ranging, biased-coin design study. Usual practice for regional anesthesia for cerclage placement consists of a mixture of 3% chloroprocaine and fentanyl. The exact dosing of the local anesthetic mixture used is dependent on the anesthesiologist's preference. Chloroprocaine provides a rapid onset of surgical anesthesia with little need for intraoperative analgesic supplementation. If there are contraindications for spinal anesthesia or patient refusal than general anesthesia is offered as an alternative.

The aim of this study is to assess the anesthetic quality of various doses chloroprocaine and in elective cerclage placement. Chloroprocaine is licensed and commonly administered intrathecally for cerclage placement.

To mitigate against the occurrence of inadequate analgesia in this ED90 study, a combined spinal-epidural technique will be utilized in order to provide supplemental analgesia via epidural top up if needed.

The investigators propose testing the hypothesis in patients scheduled for elective cervical cerclage placement. Participants will receive standard of care for anesthesia but in the context of a clinical trial with the addition of randomization, blinding, and more comprehensive evaluation of the trial outcomes (see outcomes objectives below).