Preferential channelling of anaesthetic solution injected within the perivascular axillary sheath

Preferential channelling of anaesthetic solution injected into the perivascular axillary sheath was investigated in 40 patients undergoing elective orthopaedic upper-limb surgery. Three needles, with different approaches and inclinations, were inserted near the three main terminal branches of the brachial plexus using an axillary approach. Separate boluses of anaesthetic solution (12 ml of a mixture of equal parts of 0.5% bupivacaine with 1:200,000 adrenaline and 2% lignocaine) were injected in random order through each needle, and back flow through the other two needles was noted. Back flow was observed, mainly in the needle nearest to the radial nerve during injection of the anaesthetic solution in the superior and inferior aspects of the brachial artery, and in the needle close to the ulnar nerve when the injection was performed posterior to the artery, near the radial nerve. These results could be related to the trapping of anaesthetic solution in unconnected compartments and to the slope of the needle injecting the anaesthetic solution which spreads preferentially along a gradient following the needle shaft direction.