Distribution of local anesthetic solutions in retromediastinal blockPreliminary experimental results

Background and Objectives Interpleural anesthesia blocks pain perception from the thoracoabdominal wall without impairment of leg function. Bilateral interpleural anesthesia is not recommended because of possible bilateral impairment of respiratory function. Infiltration of the retromediastinum with local anesthetic might cause bilateral thoracoabdominal somatic block and block of sympathetic afferents from the abdominal cavity without impairing respiration. Method Distribution of stained fluid was studied after injection into the retromediastinum through a catheter placed about 10 cm cephalad to the diaphragm via the esophageal hiatus in three human cadavers of normal size and in six anesthetized pigs of 20-30 kg. In the pigs, serum levels of bupivacaine were measured after injection of 10 mL of 0.5% bupivacaine stained with 1 mL of methylene blue. Results The injected Dye stained intercostal nerves 6-11 in cadavers and 5-12 in pigs symmetrically on both sides, along with the adjacent parts of the sympathetic chain and both vagal nerves but not the phrenic nerves. During the sampling period of 50-60 minutes, bupivacaine serum concentrations rose slowly to a maximum of 4.2 μg/mL. Conclusions Block of pain perception from the abdominal wall and cavity is possible by injection of local anesthetic into the retromediastinum via a catheter introduced through the esophageal diaphragm hiatus. The block would not be expected to impair respiratory or leg function. Its efficacy and safety have yet to be established.