The site of action of lidocaine in intravenous regional anesthesia.

Despite vast clinical experience and success with intravenous regional anaesthesia (IVRA), the site and mode of action of the local anesthetic agents remains controversial. Many investigations have been published, but conclusions are variable. The principal site of action of lidocaine in IVRA was studied using 15 ASA I-II patients receiving surgical operation on the hands and forearms. A 22 gauge plastic cannula was inserted into the median cubital vein at the elbow. A double cuff tourniquet was secured on the upper arm, as described by Bier and modified by Homes. Another single tourniquet was then applied on the forearm as near the plastic catheter as possible. Two different concentrations of lidocaine (0.5% and 2%) in a total dose of 3 mg kg-1 was slowly injected into the vein via the catheter after the limb was exsanguinated and the tourniquets were inflated. The results showed that 0.5% lidocaine produced analgesia only on the intercuff area; there was no analgesic response noted on the forearm distal to the third tourniquet after a 15 minutes observation. However patients who received 2% lidocaine experienced in analgesia rapidly on the intercuff area and also slowly on the forearm and hand. The anesthesia developed from the fingertips upward. Based on this evidence, we concluded that the principal site of action of lidocaine in IVRA depends on concentration. The lower concentration acts on the sensory nerve endings and the small nerves. Whereas, the higher concentration acts on both nerve trunks and nerve endings.