The axillary sheath and single-injection axillary block

Failure to block the terminal nerves of the brachial plexus, the circumferential type of incomplete axillary brachial plexus block, is the main problem of the single-injection technique. Two studies were carried out to observe the internal anatomy of the axillary sheath and the effect of different volumes of dye injected into the sheath in cadavers. In our first study, the internal arrangement of the axillary sheath and its septae were examined microscopically by slicing the sheath longitudinally and transversely. In the second study, boluses of 10, 20, and 40 cc of methylene-blue were injected into one of the compartments of the axillary sheath. The axillary sheath was dissected out and sliced transversely to observe the spread of the dye in the injected and in the adjacent compartments. The specimens of the axillary sheath were then opened longitudinally and the septae excised and examined at x10 magnification to see the effect of the various volumes of the injection bolus. This study shows that septae from the deep surface of the axillary sheath form compartments for each nerve. The septae function as barriers under physiologic conditions. By increasing the injected volume of solutions, bubble-like defects are produced in the septae in the compartments into which leakage was demonstrated.