Background: Single-shot spinal anesthesia is commonly used for cesarean delivery. Achieving adequate anesthesia throughout surgery needs to be balanced with associated complications. We investigated the optimal dose of intrathecal hyperbaric bupivacaine, co-administered with opioids, for anesthesia for cesarean delivery.
Methods: This prospective, randomized, double-blinded, dose-ranging trial included parturients scheduled to undergo cesarean delivery under spinal anesthesia. An epidural catheter was first inserted at the T11-12 vertebral interspace, followed by spinal anesthesia at the L2-3 or L3-4 vertebral interspace. Subjects were randomly assigned to one of seven doses of intrathecal hyperbaric bupivacaine 0.5% (6, 7, 8, 9, 10, 11 or 12mg), with added 15μg fentanyl and 75μg morphine. Successful induction of anesthesia (successind) was defined as achievement of bilateral sensory loss to cold at the T6 dermatome or higher, within 10 minutes. Successful maintenance of anesthesia (successmain) was defined by no epidural supplementation within 60 minutes of intrathecal injection. The effective doses for 50% (ED50) and 95% (ED95) of patients were estimated using logistic regression analysis.
Results: The ED50 and ED95 for successmain were 6.0mg (95% CI: 4.5 to 7.5mg) and 12.6mg (95% CI: 7.9 to 17.2mg), respectively. The incidence of respiratory discomfort and maternal satisfaction scores did not differ significantly between dose groups. Phenylephrine dose and nausea/vomiting incidence increased with increasing doses of bupivacaine.
Conclusion: Under study conditions, our results suggest that 12.6mg of intrathecal bupivacaine, administered with fentanyl and morphine, is required to achieve adequate intraoperative analgesia without the need for epidural supplemention.
Keywords: Cesarean delivery; Hyperbaric bupivacaine; Spinal anesthesia.
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