Motor nerve conduction in intravenous regional anaesthesia with bupivacaine hydrochloride

Motor nerve conduction (MNC) from proximal and distal points of the median and ulnar nerve was examined in 14 patients receiving a total of 29 i.v. regional anaesthetics (IRA) with bupivacaine hydrochloride in doses ranging from 100 to 300 mg. Conduction was tested during and following vascular obstruction, until MNC returned to pre-IRA value. After 20 min of obstruction, MNC was unobtainable in most patients, an effect which was dose-related. The action of bupivacaine on MNC persisted for up to 3 h after cuff release, depending on the dose, and paralleled voluntary movements. MNC block began at the proximal point of both nerves, the median nerve being affected earlier. Based on the clinical and electrical findings, bupivacaine 200 mg proved to be optimum dose for producing safe and prolonged IRA.