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We investigated the duration of labor analgesia produced by a small dose of spinal bupivacaine/fentanyl alone or in combination with a small dose of morphine. Sixty parturients were enrolled in this placebo-controlled, double-blinded, randomized trial. All women received a spinal injection of 12.5 μg of fentanyl with 2 mg of bupivacaine. The morphine group (MBF) also received 125 μg of morphine; the placebo group (BF) received saline. Pain scores were <3 of 10 within 10 min of injection. The median duration of analgesia was similar between groups (89 min versus 84 min; P = not significant), and only 20% of the MBF group experienced prolonged analgesia. During subsequent epidural analgesia, the MBF group had a significantly lesser rate of breakthrough pain (0.15 ± 0.14 episodes per hour versus 0.26 ± 0.18 episodes per hour; P = 0.02). Also, during the first 24 h postpartum, the MBF group required significantly fewer medications (3.3 ± 3.7 doses versus 4.7 ± 3.5 doses; P = 0.04). Intrathecal injection of this small dose of bupivacaine/fentanyl produced a rapid onset of labor analgesia; the addition of a small dose of morphine did not significantly prolong analgesia, but it improved subsequent pain relief, as measured by the rate of breakthrough pain and postpartum medication requirements. This may provide a clinically useful means of improving intra- and postpartum pain relief.