[New viewpoints on the mode of action of intravenous regional anesthesia]

The site of action of intravenous regional analgesia is controversial. We developed a new method to investigate if the local anaesthetic primarily blocks the peripheral nerve endings or the main nerve trunks. Intravenous regional analgesia was carried out in six volunteers who received 4 mg/kg prilocaine 1.5%. An additional finger tourniquet was placed at the third finger. While in the other four fingers complete analgesia was observed after five minutes, no adequate analgesia could be detected in the third finger distal of the finger tourniquet. This observation proves that the principal site of action of intravenous regional analgesia is at the peripheral nerve endings. Two further studies, with contrast media and radio isotopes, were carried out to investigate the spread of the injected volume. Both investigations show that the injected volume spreads distally into the fingers.