Site of action of `intravenous regional anaesthesia'

Abstract

Electro-physiological studies of the effect of lignocaine on neuromuscular conduction in the forearm are reported. Motor nerve conduction was examined by stimulating the ulnar nerve at the wrist and elbow and electromyographically recording potentials from the abductor digiti minimi. Sensory nerve excitability was examined by recording the action potential from the median nerve at the wrist following stimulation of the skin of the thumb. Regional anesthesia was produced in an ischemic limb by injecting 40 ml of 0.5% lignocaine. Results suggested that lignocaine acts on the peripheral parts of the neuron. Following stimulation of the ulnar nerve at the wrist an increase in the latency of the action potential in the hypothenar muscles was consistently observed. The action of lignocaine was not reversed by neostigmine and seems to have a dual effect both inhibiting acetylcholine production and opposing its action.