Der Einfluss von Bupivacain und Adjuvanzien auf die Mikrozirkulation von peripheren Nerven

Background Regional anesthesia and especially peripheral nerve blocks have become increasingly important in past years. Due to increasing numbers, the complications of these techniques have attracted more and more attention. A complication of peripheral nerve blocks is the nerve injury caused by an ischemia of the nerve tissue. The vascular supply to peripheral nerves is derived by a dense capillary network in the endoneurium. This intrinsic vascular system anastomoses with the extrinsic vascular system in the epineurium. Both local anesthetics and the adjuncts, epinephrine and clonidine, can affect the local microcirculation. With the combination of laser Doppler flowmetry and spectrophotometry, nerve blood flow and hemoglobin oxygen saturation in microcirculation can be determined in the same place at the same time. The present study investigated the effects of bupivacaine alone or in combination with the adjuncts, epinephrine and clonidine, on the nerval microcirculation. Methods Brachial plexus was exposed in anaesthetised swine. The parameters of microcirculation (nerve blood flow, hemoglobin oxygen saturation, relative hemoglobin amount) were recorded. After 10min for stabilization, 1ml of one of the experimental solutions was applied locally. In the standard group, this was bupivacaine 0.5%, in the intervention groups, bupivacaine 0.5% with epinephrine 10 μg/ml (1:100 000) and bupivacaine 0.5% together with clonidine 3.75 μg/ml. In the negative control group isotonic sodium chloride solution was used. The study was continued for an additional 60min. The statistical tests for the parameters of nerval microcirculation were performed with the Mann-Whitney-U test. The data of the intervention groups and the negative control group were compared with those of the bupivacaine standard group. For nerve blood flow and hemoglobin oxygen saturation, a significance test was also carried out within the groups with the Wilcoxon signed-rank test. The distribution of the vital parameters (mean arterial blood pressure, peripheral oxygen saturation and heart rate) was analysed using the Kruskal-Wallis test. Results Bupivacaine 0.5% significantly reduced nerve blood flow and hemoglobin oxygen saturation compared to negative control. Comparing the intervention groups (epinephrine, clonidine) with the standard group (bupivacaine), no significant differences were found for nerve blood flow and hemoglobin oxygen saturation. The relative hemoglobin amount was not affected by bupivacaine alone or in combination with the adjuncts compared to the negative control. In individual cases, the application of bupivacaine with epinephrine resulted in marked reductions of nerve blood flow and hemoglobin oxygen saturation. Conclusion Bupivacaine reduced both nerve blood flow and hemoglobin oxygen saturation in peripheral nerves. The adjuncts, epinephrine and clonidine, did not lead to any further decrease in nerve blood flow or hemoglobin oxygen saturation compared to bupivacaine alone. Clonidine prolongs the effect of long-acting local anesthetics. This makes clonidine a safe and appropriate adjunct in peripheral nerve blocks. Application of epinephrine led in individual cases to marked decreases of nerve blood flow and hemoglobin oxygen saturation. Despite a lack of statistical significance, a potential risk for ischemic nerve injury can be assumed. Epinephrine does not prolong the effect of long-acting local anesthetics. The eligibility for epinephrine as an adjunct in peripheral nerve blocks is questionable.