Association Between Bolus Rate and the Adequacy of Labor Analgesia Using Timed-intermittent Boluses

Overview

Administration of anesthetic solution into the epidural space is usually accomplished by a combination of continuous infusion, provider-administered boluses and patient-administered boluses (patient controlled epidural analgesia \[PCEA\]). The optimal method for maintaining labor analgesia is unknown. Several studies have demonstrated that timed-intermittent boluses, in combination with patient-controlled epidural analgesia (PCEA), provide superior maintenance of labor analgesia than maintenance with a continuous infusion with PCEA. Epidural infusion pumps capable of delivering timed boluses of local anesthetic with PCEA recently became commercially available. Several infusion rates are available for delivering the timed bolus, and the optimal bolus rate is unknown.

Cervical dilation will be confirmed by a member of the obstetric team prior to epidural catheter placement as is routinely done at our institution. A baseline pain visual analog scale (VAS) score will be obtained using a 100-mm unmarked line with the end points labeled "no pain" and "worst pain imaginable. Labor analgesia will be initiated using CSE analgesia with 25 mcg of intrathecal fentanyl. An epidural test dose will be performed as routine (1.5% lidocaine with epinephrine 1:200, 3 mL). Labor analgesia will be maintained using timed-intermittent boluses of local anesthetic with PCEA using the CADD-Solis pump (Smiths Medical). An unblinded anesthesia research nurse will program the epidural pump and initiate the maintenance of labor analgesia. Fifteen minutes following the intrathecal dose, a VAS score and a sensory level of analgesia will be obtained. The following information will be obtained hourly until complete cervical dilation (10 cm): VAS pain score, sensory level, a modified Bromage score (0 - no motor paralysis; 1 - inability to raise extended leg, but able to move knee and foot; 2 - inability to raise extended leg and to move knee, but able to move foot; 3 - inability to raise extended leg or to move knee and foot). The time to the first request for supplemental analgesia will be recorded on the study data sheet. The time, type and volume of local anesthetic used, and VAS scores before and 15 minutes after the redose will be recorded. All other clinical management will be as per routine, and study participation will not interfere with anesthetic or obstetric care. Anesthesiologists will manage breakthrough pain in the usual manner (assessment of stage of labor and extend/density of neuraxial blockade, followed by the appropriate maneuver to reestablish adequate analgesia). Following delivery, the patient will be asked to give one final VAS score and her overall satisfaction with labor using a 100 mm unmarked line. Mode of delivery, as well as the duration of the 1st and 2nd stage of labor will be recorded by study personnel. Patient Controlled Epidural Analgesia (PCEA) pump utilization data will be downloaded from epidural pumps after delivery. This will include the time to first PCEA request, the number of PCEA demands, the number of times that PCEA boluses were delivered, the total amount of local anesthetic consumed.