The Effect of pH Adjustment of 2% Mepivacaine on Epidural Anesthesia

Two-hundred men, scheduled for elective meniscectomy under epidural anesthesia, were randomly assigned to receive either a standard 2% mepivacaine solution (n = 100) or a pH adjusted 2% mepivacaine solution (pHAS, n = 100). The pHAS was freshly prepared before the block by adding 0.1 mEq of NaHCO3 per ml of mepivacaine solution. After a test-dose, the anesthetic solution was injected to produce a level of sensory anesthesia to T10. The mean duration of anesthesia and the mean dose of mepivacaine used were comparable between the groups. Patients in the pHAS group showed a significant shortening of onset time in T10 and in S2 segment (p less than .001). Grade 3 motor blockade was achieved in the same number of patients, but a faster motor block was observed in the pHAS group (p less than .05). Regression of both sensory and motor blockade in the two groups was not significantly different.