The median local analgesic dose of intrathecal bupivacaine with hydromorphone for labour: a double-blind randomized controlled trial.

PURPOSE: Neuraxial hydromorphone has been reported to provide rapid onset of labour analgesia, effective segmental pain relief, and a longer duration of action than commonly used lipophilic opioids. This study was conducted to test the hypothesis that intrathecal hydromorphone reduces the dose requirement for intrathecal bupivacaine to induce rapid analgesia for women in the first stage of labour. METHODS: In this double-blind randomized controlled sequential allocation trial, 88 labouring parturients received combined spinal-epidural analgesia at 2-6 cm cervical dilation. Participants received intrathecal bupivacaine alone or bupivacaine plus hydromorphone 100 µg with the bupivacaine dose determined using up-down sequential allocation. An effective dose was defined as a visual analogue pain score of ≤10 mm (on a 100-mm pain scale) reported within 20 min of injection. The median effective doses were calculated using the formula of Dixon and Massey and verified using isotonic regression. RESULTS: A decrease was observed in the median local analgesic doses (effective dose [ED50]) estimated according to the formulas of Dixon and Massey, with a between-group difference of -0.45 mg. The precision of the estimate was wide-ranging (95% confidence interval -1.23 to 0.33), so no definitive conclusion can be drawn. CONCLUSION: Further research is needed to determine whether or not intrathecal hydromorphone 100 µg changes the dose of intrathecal bupivacaine required to induce labour analgesia within 20 min. TRIAL REGISTRATION: The trial was conducted in 2007 prior to widespread acceptance of the standard for clinical trial registration.