[Determination of median effective dose of lidocaine to control the onset time of sciatic nerve blockade using up-and-down sequential method].

Objective: To determine the median effective dose (ED50) of 2% lidocaine to control the onset time of sciatic nerve blockade within 15 min by using 2% lidocaine and 0.75% ropivacaine 10 ml.

Methods: Fifty patients underwent sciatic nerve blockade and lumbar plexus blockade for operations of unilateral lower extremities. 2% lidocaine was allocated into 7 ranks in geometric proportion between 4.2 ml and 12.5 ml. The observed index was the blockade onset time less than 15 min of the lateral cutaneous branch of sural nerve, fibular nerve, and rami calcanei medicales nervi tibialis. The ED50 of 2% lidocaine was determined respectively in the patients in which dorsiflexion or plantarflexion was elicited by in up-and-down sequential method.

Results: Combined with ropivacaine, the values of ED50 of 2% lidocaine in the patients in which dorsiflexion and plantarflexion were elicited by up-and-down sequential method were 6.88 ml and 6.19 ml respectively when the onset time of blockade of sciatic nerve was within the range of 15 min.

Conclusion: The dosage to elicit plantarflexion is similar to the dosage to elicit dorsiflexion in sciatic nerve blockade.