Journal Article

Epidural test dose with levobupivacaine and ropivacaine: determination of ED50 motor block after spinal administration

M. Camorcia, G. Capogna, G. Lyons and M. Columb

in BJA: British Journal of Anaesthesia

Published on behalf of the British Journal of Anaesthesia

Volume 92, issue 6, pages 850-853
Published in print June 2004 | ISSN: 0007-0912
Published online June 2004 | e-ISSN: 1471-6771 | DOI: https://dx.doi.org/10.1093/bja/aeh155
Epidural test dose with levobupivacaine and ropivacaine: determination of ED50 motor block after spinal administration

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Background. When a test is required to detect a possible intrathecal catheter, many would seek to use the same local anaesthetic as that used for epidural analgesia. The rapid onset of inappropriate motor block after a local anaesthetic administered epidurally implies intrathecal spread. Because of claims of greater sensory–motor separation, or because of reduced potency compared with bupivacaine, the efficacy of the new local anaesthetics in intrathecal testing has been questioned. The aim of this study was to establish the feasibility of a test dose for an inadvertent intrathecal catheter using ropivacaine and levobupivacaine, and to establish the dose required.

Methods. Sixty women undergoing elective Caesarean section with a combined spinal– epidural technique were enrolled into this prospective, double‐blind sequential allocation study. The women were randomized to receive plain levobupivacaine 0.5% or ropivacaine 0.5% intrathecally. The dose was determined according to up–down sequential allocation. The end‐point was any evidence of lower limb motor block within 5 min of injection.

Results. The ED50 motor block at 5 min was 4.8 mg (95% CI, 4.49, 5.28) for levobupivacaine and 5.9 mg (95% CI, 4.82, 6.98) for ropivacaine (95% CI difference, 0.052, 1.98) (P=0.04). The estimated ED95 motor block was 5.9 mg (95% CI 5.19, 6.71) for levobupivacaine and 8.3 mg (95% CI, 6.30, 10.44) for ropivacaine. The potency ratio between the two drugs was 0.83 (95% CI, 0.69, 0.99).

Conclusions. Both local anaesthetics produce evidence of motor block within 5 min of intrathecal injection and could serve as tests of intrathecal administration. Derived ED95 values suggest 10 mg doses should be effective, but this study did not measure predictive value. Ropivacaine is less potent for motor block than levobupivacaine by a factor of 0.83 (P<0.04).

Br J Anaesth 2004; 92: 850–3

Keywords: anaesthetics local, levobupivacaine; anaesthetics local, ropivacaine; analgesia, obstetric; analgesic techniques, epidural

Journal Article.  2445 words.  Illustrated.

Subjects: Anaesthetics

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