Canadian Journal of Anesthesia, Vol 15, 56-62, Copyright © 1968 by Canadian Anesthesiologists' Society

Neuromuscular Effects of Six Local Anaesthetics on Anaesthetized Subjects

¹ Department of Anesthesiology, University of Miami School of Medicine and Jackson Memorial Hospital, Miami, Florida

Procaine, lidocaine, mepivacaine, prilocaine, tetracaine, and dibucaine were injected into the brachial or radial artery of surgical patients under halothane-nitrous-oxide-oxygen anaesthesia. The adductor pollicis muscle was electrically stimulated either indirectly, via the ulnar nerve, or directly, and the contraction recorded.

All local anaesthetics produced an immediate reduction of the single twitch tetanic muscle tension. The minimum paralysing dose for procaine, lidocaine, prilocaine, and mepivacaine ranged from 0.4 to 0.6 mg./kg. and for dibucaine and tetracaine from 0.2 to 0.3 mg./kg. The directly elicited contraction was depressed by doubling or tripling the minimal paralysing dose. Tetracaine and dibucaine had a significantly longer duration of action and a marked cumulative effect. No adverse effects of the experiments were observed.

The results suggest that the duration of muscle paralysis may be related to the strength of binding of local anaesthetics to myoneural junctional receptors. The possibility of a prejunctional site of action on the motor nerve terminal is discussed.