[Alkalinization of mepivacaine for axillary plexus anesthesia using a catheter]

Abstract

One disadvantage of perivascular axillary block using a catheter technique is delayed temporal development of the blockade. Some clinical studies have concluded that pH-adjusted solutions of local anesthetics produce a more rapid onset of blockade. Alkalinization of mepivacaine for brachial block produced conflicting results. In the present study, we attempted to define the effect of alkalinization of mepivacaine 1% on clinical efficacy, onset, and regression in patients undergoing upper extremity surgery with axillary block using the catheter technique. METHODS. Sixty consecutive adult patients (ASA I-II) scheduled for upper extremity surgery under axillary block, were randomly assigned to one of two groups. In a double-blind fashion, 30 patients received 40 ml 1% mepivacaine, the pH of which had been raised to 7.25 by adding 4 ml 8.4% NaHCO3, and 30 received 40 ml commercially prepared 1% mepivacaine hydrochloride solution containing 4 ml 0.9% NaCl (pH 6.0). All patients received axillary block using the catheter technique. After placement of the block, a blinded observer tested sensory and motor blockade after 2 min, 5 min and then every 5 min for 30 min in each of the terminal nerves of the brachial plexus. Sensory blockade was determined by pinprick and graded in accordance with the scale proposed by Hollmèn: 0: Normal sensation of pinprick. 1: pinprick felt as sharp-pointed but weaker compared with the same area in the other upper extremity. 2: Pinprick recognized as touch with a blunt object. 3: No perception of touch. The gradation of motor blockade was 0: normal muscular function; 1: slight depression in muscular function compared with preanesthetic strength; 2: very weak action persisting in muscles; and 3: complete block. The results for each group were compared at every time interval. Duration of blockade was compared by evaluating the rate of regression within the first 2 h after placement of the block in each group. Mepivacaine plasma levels were measured by HPLC in 10 patients of each group prior to injection and 5, 10, 15, 20, 30, 60, and 120 min thereafter. Statistical comparison was made using the chi 2 and t tests. Differences were considered statistically significant when P-values were less than 0.05. RESULTS. The bicarbonate and saline groups were similar with respect to age, height, weight, and sex distribution. Significantly more patients in the bicarbonate group showed onset of motor blockade (grade 1) after 2 min with respect in the axillary, musculocutaneous, radial, and median nerves as well as onset of sensory blockade in the same nerves with a significant difference in blockade of the radial nerve. (ABSTRACT TRUNCATED AT 400 WORDS)