Effect of Manipulation of the Programmed Intermittent Bolus Time Interval and Injection Volume on Total Drug Use for Labor Epidural Analgesia: a Randomized Controlled Trial

Traditionally, neuraxial labor analgesia was maintained for the duration of labor with manual intermittent bolus injection of anesthetic by the anesthesiologist via an in-dwelling epidural catheter. During the last decade, there has been a transition to maintenance of analgesia with a continuous epidural infusion. Analgesia is maintained with fewer episodes of breakthrough pain and parturient satisfaction is increased. The anesthesiologists' workload is less. More recently, use of patient controlled epidural analgesia (PCEA) has become popular; usually a continuous infusion is supplemented by patient-activated bolus injections.

Studies have compared the intermittent manual epidural bolus technique to continuous infusion, continuous infusion to PCEA without a background infusion, and PCEA with and without a background infusion. Studies vary in the epidural solution local anesthetic mass (volume and concentration), and lock-out intervals. The incidence and intensity of motor blockade is greater with continuous infusion compared to bolus administration of the same concentration/mass local anesthetic per unit time, whether the bolus is administered manually or by PCEA. Consumption of local anesthetic is less with bolus administration (manual or PCEA) compared to continuous infusion. Therefore, lower concentrations of local anesthetic are frequently used for continuous infusions.

Current pump technology supports continuous epidural infusion, PCEA without a background infusion, and PCEA with a background infusion. Current pump technology does not support programmed intermittent bolus administration with or without supplemental PCEA. Further study in this area may motivate pump manufacturers to redesign their pumps to support this type of drug administration.

The purpose of the study is to determine how manipulation of the programmed intermittent time interval and volume influences total drug use, quality of analgesia, and patient satisfaction during maintenance of labor analgesia.

Eligible women were asked to participate shortly after admission to the Labor and Delivery Unit at Prentice Women's Hospital immediately following the routine preanesthetic interview. Informed, written consent was obtained. At the time of request for labor analgesia the cervix was examined and a baseline Visual Analog Scale (VAS) for pain (100 mm unmarked line with the end points labeled "no pain" and "worst pain imaginable") was determined. Labor analgesia was initiated with a routine combined spinal epidural (CSE) technique. The VAS for pain was determined 10 minutes after the intrathecal injection. If the VAS was less than 10 mm, the parturient was randomized (by a computer generated random number table) to one of three programmed intermittent epidural bolus analgesia maintenance techniques: 2.5 mL every 15 minutes, 5 mL every 30 minutes, or 10 mL every 60 minutes. All epidural solutions consisted of bupivacaine 0.0625% with fentanyl 1.95 micrograms/mL. The initial programmed intermittent bolus dose was initiated 30 minutes after the intrathecal injection in all groups.