[Clinical effectiveness and systemic toxicity of various mixtures of prilocaine and bupivacaine in axillary plexus block].

The presently existing local anesthetics (LA) do not guarantee a rapid onset and simultaneously a long duration of action. The combination of a medium-long acting LA with bupivacaine, a long-acting LA with slow onset, could be means to achieve these aims. Prilocaine was chosen as the medium-long acting LA because it has the lowest toxicity of this group and for pharmacological reasons. METHODS. In a prospective, controlled double-blind study 100 patients scheduled for axillary block for elective surgical procedures of the hand or wrist were randomly assigned to five groups. Twenty patients in each group received either 40 ml prilocaine 1.5%; 40 ml bupivacaine 0.375%; 20 ml prilocaine 1% + 20 ml bupivacaine 0.5%; 20 ml prilocaine 2% + 20 ml bupivacaine 0.5%; or 20 ml prilocaine 2% + 20 ml bupivacaine 0.375%. The LA mixtures were freshly mixed 15 min prior to the axillary block. The blocks were performed using an immobile, short-beveled needle by anesthesiologists who were familiar with this technique. Analgesia was classified using the pin-prick method with 0 = no analgesia, 1 = analgesia, 2 = anesthesia. Motor blockade was classified with 0 = no motor block, 1 = paresis, 2 = paralysis. The following nerves were analyzed: ulnar, radial, median, musculocutaneous, and medial antebrachial. In 6 patients of each group plasma levels of the LA were measured by gas chromatography and methemoglobinemia was determined. Statistical analysis of the data was performed using the Student t-test and chi-square test on a level of significance of P less than 0.05. Results. All surgical procedures could be performed as planned in regional anesthesia. Twenty minutes after injection of the LA only 15% of the blocks were sufficient in the bupivacaine group, while in the other four groups 40%-50% of the blocks were complete (P less than 0.05). The degree of analgesia was deeper in the groups with 2% prilocaine and prilocaine alone than in the group with 1% prilocaine. Forty minutes after injection there were no significant differences between the groups. Motor blockade after 20 min was significantly lower in the bupivacaine group than in the prilocaine group (P less than 0.05). After 4 h all three prilocaine-bupivacaine mixtures showed a significantly more pronounced analgesia of the median nerve than the prilocaine group (P less than 0.02-0.001).(ABSTRACT TRUNCATED AT 400 WORDS)