Intrathecal Morphine Reduces Breakthrough Pain During Labor Epidural Analgesia

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Intrathecal Morphine Reduces Breakthrough Pain During Labor Epidural Analgesia
A. Vasudevan, C.E. Snoman, S. Sundar, T.W. Sarge, and P.E. Hess
(Br J Anaesth, 98:241-245, 2007)
Department of Anesthesia, Critical Care and Pain Medicine, Beth Israel Deaconess Medical Center, Boston, MA
Although combined spinal-epidural (CSE) labor analgesia is widely used, breakthrough pain is often reported by parturients after the spinal medication has receded. A previous study by the authors found that morphine added to a spinal injection did not prolong the duration of the spinal component of analgesia but improved the effectiveness of subsequent epidural analgesia. The current randomized, double-blind, placebo-controlled trial examined the effect of a small dose of intrathecal morphine in reducing breakthrough pain in 55 of 60 healthy parturients enrolled in the study.
The patients were of mixed parity and requested neuraxial analgesia; they were in active labor with a term, singleton fetus in vertex position. A midline CSE was performed at the L3-4 or L4-5 interspace using the needle-through-needle technique. Fentanyl 12.5 mg (0.25 mL) with bupivacaine 2.0 mg (0.8 mL) plus either 100 mg (0.2 mL) for the morphine group (MS) or an equal volume of saline for the placebo group (PLCB) was injected through a 25-gauge Sprotte needle. After this injection and the removal of the Sprotte needle, an epidural catheter was placed and tested with 3.0 mL of 1.5% lidocaine containing 1:200,000 epinephrine. Promptly after confirmation of negative intrathecal or intravenous injection, the epidural catheter was infused at 15 mL/h with a solution containing 0.04% bupivacaine, fentanyl 1.7 mg/mL, and 1:600,000 epinephrine. Initial treatment of breakthrough pain was by epidural injection of 0.125% bupivacaine (8 mL) with fentanyl 100 mg (2 mL). If required, 15 minutes later, a second epidural injection of 0.125% bupivacaine was given; a final assessment was made 15 minutes later and a final 10 mL of 0.125% bupivacaine was injected if indicated. The primary end point was the number of breakthrough incidents per patient. Determinations were also made for the number of supplemental epidural injections, the use of analgesics in the first 24 hours postpartum, and side effects. Failure of adequate pain relief would result in a replacement of the epidural catheter and elimination from further study. Pain and side effects were evaluated every 4 hours for 24 hours after delivery.
Fifty-five patients could be evaluated; the MS and PLCB groups did not differ in maternal and obstetric characteristics. Vital signs, analgesic level to cold and pinprick, motor block, and pain scores were similar in both groups. The MS group had 0.6 episodes of breakthrough pain per patient compared with 1.1 episodes for the PLCB group. The hourly rate of breakthrough pain was lower in the MS group, and the median time from spinal injection to the first episode of breakthrough pain was 300 minutes in the MS group compared with 180 minutes in the PLCB patients, a statistically significant difference. The incidence of all side effects during labor was similar. At the 24-hour follow-up, the MS group had slightly more nausea, but the incidences of other side effects were similar. Requirements for postpartum pain medications were reduced in the MS group. Among those who had a successful vaginal delivery, there was a 40% reduction in the doses of pain medication administered and a 75% reduction in the use of oral opioid pain medications. The investigators concluded that a small dose of intrathecal morphine added to a spinal injection of fentanyl and bupivacaine appeared to increase the effectiveness of epidural labor analgesia.

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