Comparison of 5% with dextrose, 1.5% with dextrose, and 1.5% dextrose-free lidocaine solutions for spinal anesthesia in human volunteers.

The use of lidocaine in concentrations less than 5% for spinal anesthesia may be advantageous but has not been carefully studied. Lidocaine 50 mg (1.5% with dextrose and 1.5% dextrose-free) was administered to eight volunteers in a randomized, double blind, cross-over fashion. All of these subjects had previously received 5% lidocaine with dextrose using the same experimental protocol. Sensory analgesia was assessed with pinprick, transcutaneous electrical stimulation (TES) equivalent to surgical incision, and duration of tolerance of pneumatic thigh tourniquet. Motor block was assessed with isometric force dynamometry. Peak dermatomal level was the highest and duration until regression of pinprick the longest with the 5% solution (P < 0.05). Duration of tolerance to TES was increased (33 +/- 10 min) with the 5% solution (P < 0.04). Duration of tolerance to tourniquet pain was increased (11 +/- 3 min) with the 5% solution (P < 0.02). Duration of motor block was increased (45 +/- 9 min) with the 5% and the 1.5% without dextrose solutions (P < 0.04). Time to void was increased (33 +/- 5 min) with the 5% solution (P < 0.03). In conclusion, the use of different solutions of lidocaine for spinal anesthesia results in significant differences in sensory and motor block and time until recovery of micturition.