[Motor block determination for the identification of accidental spinal injection of levobupivacaine: a study on the minimum efficient test-dose (ED50)].

Background: The aim of this study was to determine the ED50 for the dose of levobupivacaine 0,5% that, if given intrathecally will not cause total spinal anesthesia but will give a reliable and reproducible clinical sign to differentiate intrathecal from epidural injection.
Methods: Thirty women at term undergoing elective cesarean section under a combined spinal-epidural technique (CSE) were enrolled into this sequential allocation study. The dose in each test dose was determined by the response of the previous patient to the higher or lower dose in her test syringe, according to up-down sequential allocation. The exception to this was the first woman in each group, for whom the starting dose was chosen to be 4 mg. The end point was the occurrence of any motor block, in any side, within 5 minutes from intrathecal injection of the test dose. Test dose efficacy was assessed using a modified Bromage scale every minute for 5 minutes. The median effective dose of levobupivacaine was estimated from the up-down sequences using the formula of Dixon and Massey.
Results: The MAD of the test dose for levobupivacaine was of 4,8 mg (4,4 to 5,2; 95% C.I.).
Discussions: This study may help to determine the appropriate dose for a test dose for inadvertent spinal levobupivacaine.