• G Frawley, K R Smith, and P Ingelmo.
• Department of Paediatric Anaesthesia and Pain Management, Royal Children's Hospital, Anaesthesia Research, Murdoch Childrens Research Institute, Melbourne, Australia. geoff.frawley@rch.org.au
• Br J Anaesth. 2009 Nov 1;103(5):731-8.

BackgroundComparing the relative potency of new local anaesthetics such as levobupivacaine and ropivacaine with bupivacaine by the minimum local analgesic concentration model has not been described for neonatal spinal anaesthesia. This information is important to compare agents and to determine the most effective spinal dose.MethodsWe performed a two-stage study to determine the ED50, the ED95, and the relative analgesic potency of isobaric spinal bupivacaine, levobupivacaine, and ropivacaine in infants. In phase 1, 81 infants were randomized in a Dixon-Massey study to describe the minimum local analgesic dose. In phase 2, a further 70 patients were randomly allocated to receive spinal anaesthesia with doses in the upper dose-response range to define the ED95.ResultsThe ED50 doses for bupivacaine, levobupivacaine, and ropivacaine were estimated by isotonic regression to be 0.30 mg kg(-1) [95% confidence interval (CI) 0.25-0.43], 0.55 mg kg(-1) (0.50-0.64), and 0.50 mg kg(-1) (0.43-0.64), respectively. The ED(95), respectively, of bupivacaine, levobupivacaine, and ropivacaine were 0.96 mg kg(-1) (95% CI 0.83-0.98), 1.18 mg kg(-1) (1.05-1.22), and 0.99 mg kg(-1) (0.73-1.50). The relative potency ratios at the ED(50) were bupivacaine:levobupivacaine 0.55 (95% CI 0.39-0.88), bupivacaine:ropivacaine 0.61 (0.41-1.00), and levobupivacaine:ropivacaine 1.09 (0.84-1.45).ConclusionsAppropriate doses for infant spinal anaesthesia are 1 mg kg(-1) of isobaric 0.5% bupivacaine and ropivacaine and 1.2 mg kg(-1) of isobaric 0.5% levobupivacaine.

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