[Diffusion of bupivacaine into the intercostal muscle following interpleural analgesia]

To test the hypothesis that local anesthetic solution diffuses across the parietal pleura into the intercostal nerves in interpleural analgesia, tissue bupivacaine concentrations were assayed after interpleural injection of bupivacaine in rabbits. Thirty animals were killed at 10, 20, or 30 min after administration of 0.5% bupivacaine (1 ml.kg-1) into the left pleural cavity. The left intercostal muscle (lt-ICM), right intercostal muscle (rt-ICM) and femoral muscle (FM) were sampled immediately after killing the animals. Bupivacaine concentrations were analyzed by high-performance liquid chromatography. Mean bupivacaine concentrations in lt-ICM were 10.8 micrograms.g-1 at 10 min, 15.2 micrograms.g-1 at 20 min and 11.8 micrograms.g-1 at 30 min. On the other hand, the bupivacaine concentrations in rt-ICM and FM were less than 2.0 micrograms.g-1 at any sampling time. (P < 0.01 vs. lt-ICM). These results indicate that bupivacaine administered interpleurally diffuses from the pleural space into the ipsilateral intercostal muscle. Direct diffusion of bupivacaine could cause intercostal nerve block following interpleural analgesia.