[Comparative study of 1% prilocaine and 1% mepivacaine in axillary plexus anesthesia]

In a randomized double-blind study, the latency period and spread of axillary brachial plexus block using 40 ml mepivacaine hydrochloride (1% solution), or prilocaine (1% solution) was studied in 60 patients scheduled for surgery of the hand and forearm regions. The sensory block of the axillary, musculocutaneus, radial, median, ulnar and medial brachial cutaneous nerves was recorded using the pin-prick test every 5 min after injection and the motor block was assessed by testing the power of the corresponding muscles up to 30 min after injection. The degree of intraoperative analgesia attained was also determined. The venous methemoglobin level was determined before and 2 h after the administration of the local anesthetic agent. The development of sensory blockade was significantly faster after 10 min and 15 min in the radial nerve, and the development of motor blockade after 15 min and 20 min in the axillary nerve, using mepivacaine. After 30 min, there were no significant differences in the degree of sensory or motor block attained between the two groups. Intraoperative analgesia was attained in 27 patients of the mepivacaine group, versus 23 patients of the prilocaine group (NS). The methemoglobin level was always elevated following prilocaine, but not following mepivacaine. Two patients had an increase of the methemoglobin concentration to more than 11% after the administration of prilocaine. Neither the higher toxicity to the central nervous and cardiovascular systems from mepivacaine, nor the methemoglobin formed by prilocaine seems to be of clinical significance with the dosage and technique employed.