Effect of Epidural Infusion Bolus Delivery Rate on the Duration of Labor Analgesia: A Randomized Clinical Trial

Background: Programmed intermittent boluses of local anesthetic have been shown to be superior to continuous infusions for maintenance of labor analgesia. High-rate epidural boluses increase delivery pressure at the catheter orifice and may improve drug distribution in the epidural space. We hypothesized that high-rate drug delivery would improve labor analgesia and reduce the requirement for provider-administered supplemental boluses for breakthrough pain. Methods: Nulliparous women with a singleton pregnancy at a cervical dilation of less than or equal to 5 cm at request for neuraxial analgesia were eligible for this superiority-design, double-blind, randomized controlled trial. Neuraxial analgesia was initiated with intrathecal fentanyl 25 &mgr;g. The maintenance epidural solution was bupivacaine 0.625 mg/ml with fentanyl 1.95 &mgr;g/ml. Programmed (every 60 min) intermittent boluses (10 ml) and patient controlled bolus (5 ml bolus, lockout interval: 10 min) were administered at a rate of 100 ml/h (low-rate) or 300 ml/h (high-rate). The primary outcome was percentage of patients requiring provider-administered supplemental bolus analgesia. Results: One hundred eight women were randomized to the low- and 102 to the high-rate group. Provider-administered supplemental bolus doses were requested by 44 of 108 (40.7%) in the low- and 37 of 102 (36.3%) in the high-rate group (difference –4.4%; 95% CI of the difference, –18.5 to 9.1%; P = 0.67). Patient requested/delivered epidural bolus ratio and the hourly bupivacaine consumption were not different between groups. No subject had an adverse event. Conclusions: Labor analgesia quality, assessed by need for provider- and patient-administered supplemental analgesia and hourly bupivacaine consumption was not improved by high-rate epidural bolus administration.