Volume and dose of local anesthetic necessary to block the axillary brachial plexus using ultrasound guidance.

摘要

IN this issue of Anesthesiology, O'Donnell and Iohotn report a successful block of the brachial plexus at the axilla with as little as 1 ml of 2% lidocaine per nerve. Their findings are at odds with the conventional experience in which axillary brachial plexus block has been typically associated with a variable success rate ranging from 50% to 100%, even when substantially larger volumes of local anesthetics are used. Before the introduction of electrolocalization and/or ultrasound guidance, blind injection of the local anesthetic around the axillary artery (transarterial technique) was the predominant method used to block the axillary brachial plexus. Failures or incomplete blocks were thought to be caused by imprecise needle placement or septation of the brachial plexus sheath, leading to malposition of the local anesthetic. In 1961, De Jong showed that success of the axillary perivascular technique depends on the injection of a sufficient volume of local anesthetic and recommended that 42 ml of local anesthetic was necessary to fill the axillary brachial plexus sheath. To increase the success rate, larger volumes of local anesthetic, as much as 80 ml in some reports, have been used, with techniques using multiple injections. Only few investigators reported the ability of small aliquots of local anesthetic (e.g., 5 mlerve) to result in successful block.