INVIVO DETERMINATION OF CONCENTRATION-EFFECT CURVES OF LOCAL-ANESTHETICS IN MAN

In clinical use, the concentrations of local anaesthetics at the site of action are unknown. With the method described here, concentrations of local anaesthetics can be predetermined and kept constant at the si te of action. In six volunteers, a blister was raised on the ventral s urface of the forearm. After removal of the epithelium, the blister ba se was rinsed continuously with carbogenated Tyrode's solution with an d without increasing concentrations of bupivacaine (Carbostesin) for 1 5 min each. The effects of bupivacaine were determined by changes in t he perception (tactile sensation) of drops falling on the blister base from increasing heights. The minimal height at which the drops were j ust perceived characterized the threshold of perception. With increasi ng bupivacaine concentrations, threshold increased until the drops wer e no longer perceived, at a median concentration of 2.48 mmol litre-1 (range 1.24-3.10 mmol litre-1). After the blister base was rinsed with Tyrode's solution, threshold of perception reached baseline values, w hich was in accordance with an intact blister base.