BJA Advance Access published online on April 19, 2004
British Journal of Anaesthesia, doi:10.1093/bja/aeh155
© 2004 by The Board of Management and Trustees of the British Journal of Anaesthesia
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1 Department of Anaesthesia, Clinica Città di Roma, Roma, Italy; Department of Anaesthesia Città di Roma Hospital Via Maidalchini 20, 00152 Roma, Italy
* To whom correspondence should be addressed. E-mail: michela_camorcia{at}yahoo.it.
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).
Clinical Investigation
Epidural test dose with levobupivacaine and ropivacaine: determination of ED50 motor block after spinal administration
2 Department of Anaesthesia, Clinica Città di Roma, Roma, Italy
3 Department of Anaesthesia, St James’ University Hospital, Leeds, UK
4 Department of Anaesthesia and Intensive Care, South Manchester University Hospital, Wythenshawe, UK
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