Determination of ED90 of Intrathecal Lidocaine for Adequate Anesthesia for Elective Cervical Cerclage Surgery

Overview

Cervical incompetence complicates approximately 1 in 500 pregnancies . Those women with cervical incompetence are at risk for second trimester spontaneous abortion and preterm labor. Cervical cerclage reduces these risks but must be performed under general or neuraxial anesthesia. Some anesthesiologists prefer neuraxial anesthesia, as it reduces fetal exposure to medications and avoids the risks associated with loss of maternal airway reflexes under general anesthesia. Spinal anesthesia, in particular, has the added advantage of being technically simple while still providing a rapid, dense sensory block. For cerclage placement, patients require a sensory block from the T10 to S4 dermatome in order to cover sensation from the cervix as well as the vagina and perineum. Patients presenting for cerclage under spinal anesthesia pose a dosing challenge given the physiologic changes associated with pregnancy. As women progress with their pregnancy, they require lower doses of intrathecal local anesthetic to achieve similar block level. Multiple studies have demonstrated that these changes start during the second trimester. Inadequate sensory coverage with a spinal anesthetic typically necessitates conversion to general anesthesia, causing additional time wasted and added risk to the patient and fetus. Anecdotally, this is the reason why some anesthesiologists choose general anesthesia for patients undergoing cerclage over a spinal anesthetic. As there is currently no literature determining the correct dosage for these patients, we propose a dose-response study to determine the ED90 of intrathecal lidocaine for adequate anesthesia for elective cervical cerclage placement.The findings of this study will help determine the minimum dose of intrathecal lidocaine necessary to provide adequate spinal anesthesia for cervical cerclage for 90% of women. This will help decrease the frequency of inadequate anesthesia for cervical cerclage.