Alkalinization of mepivacaine accelerates onset of interscalene block for shoulder surgery

Reports evaluating the effect of alkalinization of mepivacaine on the onset of regional anesthesia have been controversial. The effect of alkalinization of mepivacaine on the onset of interscalene block has not been reported and is the subject of this study. Forty patients received an interscalene block by elicitation of paresthesia with 25-gauge, blunt level needle. Twenty patients received 40 ml 1.4% mepivacaine, which contained epinephrine (1:200,000). Another 20 patients received 40 ml 1.4% mepivacaine, epinephrine (1:200,000), and 4 mEq of NaHCO3. Time to onset of block was determined by awareness of cold, and loss of pain perception and motor function at the shoulder, elbow and hand. The duration of block for each observation was determined. The onset was significantly faster for all tested modalities in the pH-adjusted group. No statistically significant differences in the duration of either motor or sensory were found between the study and control groups.