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Programmed intermittent epidural bolus for labor analgesia during first stage of labor: A sequential trial to determine the optimum bolus dose of bupivacaine 0.0625% plus fentanyl 2 mcg/ml at fixed intervals of 40 minutes
Abstract Number: O-07
Abstract Type: Original Research
Background: The effective PIEB interval time for 10 ml boluses of bupivacaine 0.0625% + fentanyl 2 mcg/mL has been suggested to be 40 minutes. This regimen has shown to be effective without the use of PCEA in 90% of women during first stage of labor (1). However, although not associated with hypotension or motor block, 34% of women undergoing this regimen exhibited a sensory block to ice above T6. It is unknown whether it is possible to reduce the PIEB volume while keeping the PIEB interval at 40 minutes and still provide adequate analgesia. We sought to study the effective PIEB volume of bupivacaine 0.0625% + fentanyl 2 mcg/mL at a fixed interval of 40 minutes to provide effective analgesia in 90% of women (EV90) during the first stage of labor, without the use of PCEA.
Methods: This was a prospective double-blind dose-finding study using the biased coin up-down sequential allocation method (2). Inclusion criteria included nulliparous women requesting epidural analgesia with a term singleton pregnancy. Ultrasound assisted epidural catheter insertion was at either the L2-3 or L3-4 interspace. A test dose of 3 mL of bupivacaine 0.125% + fentanyl 3.3 mcg/mL was administered, followed by a loading dose of 12 mL of the same solution. In order to remain eligible for the study, women had to achieve a Verbal Numerical Rating Score ≤ 1/10 within 20 minutes of completion of the loading dose. Labor analgesia was maintained with bupivacaine 0.0625% + fentanyl 2 mcg/mL. The first PIEB bolus was given 1 hour after the completion of the loading dose and all subsequent PIEB boluses were given at a fixed interval of 40 minutes. The first patient enrolled in the study received a PIEB bolus of 7 mL. Subsequent patients received 7, 8, 9, 10, 11 or 12 mL, based on the biased-coin allocation. The primary outcome was adequate analgesia, defined as no use of PCEA or request for manual boluses for 6 hours after the loading dose or until the patient’s cervix was fully dilated, whichever occurred first. Secondary outcomes included motor block, hypotension, and sensory level to ice and pinprick.
Results: We studied 40 women. The estimated EV90 was 11 mL (95% CI 10.32-11.65) with the Isotonic Regression Method and 10.65 mL (95% CI 10.27-11.03) with the Truncated Dixon and Mood Method. Overall, sensory block was above T6 in 18/40 women when assessed by ice and in 11/40 women when assessed by pinprick. Overall, 37/40 women exhibited no motor block. No patient required treatment for hypotension.
Discussion: It is not possible to reduce the PIEB volume from 10 mL in our current PIEB regimen without compromising the quality of analgesia. Not surprisingly, a significant proportion of women will exhibit sensory block above T6 to both ice and pinprick. Sensory block to pinprick may be more reassuring in this context. Motor block and hypotension requiring treatment were virtually non-existent.
References: 1)Anesth Analg, 2017;124:537-541 2)Anesthesiology, 2007;107:144-152