Bupivacaine augments intrathecal fentanyl for labor analgesia

Background: Intrathecal fentanyl has been shown to be an effective analgesi c for labor; this study investigated the analgesic effect of low-dose bupiv acaine added to intrathecal fentanyl for labor analgesia Methods: Ninety parturients in active labor who requested regional analgesi a were randomized to receive an intrathecal injection of either fentanyl, 2 5 mu g; bupivacaine, 1.25 mg, with fentanyl, 25 mu g; or bupivacaine, 2.5 m g, with fentanyl, 25 mu g, as part of a combined spinal-epidural technique. Visual analog pain scores were recorded before and at intervals after inje ction until the patient requested further analgesia. Maternal blood pressur e and fetal heart rate were recorded before and at intervals after injectio n. Lower-extremity muscle strength was tested before and 30 min after injec tion; anesthetic level to cold sensation and the presence and severity of p ruritus were recorded. Results: Duration of analgesia was longer in the group receiving bupivacain e, 2.5 mg, and fentanyl, 25 mu g, than the group receiving plain fentanyl ( 108 vs. 92 min; P < 0.05). Onset of analgesia was faster in both groups rec eiving bupivacaine compared with plain fentanyl(P < 0.05). No differences i n muscle strength after injection were found in any group, although anesthe tic levels to cold were documented In all patients in the bupivacaine group s, and 21 of 30 in the plain fentanyl group. Baseline fetal heart rates did not change after injection in any group, and maternal blood pressure was u nchanged. Conclusions: The addition of 2.5 mg isobaric bupivacaine to 25 pg fentanyl for intrathecal labor analgesia modestly increases duration and speeds onse t of analgesia compared with plain intrathecal fentanyl.