Onset and progression of intravenous regional anesthesia with dilute lidocaine

Intravenous regional anesthesia was induced in seven healthy volunteers using dilute lidocaine solution. Onset and progression were documented by sequential detailed neurologic examinations and compared with changes following intravenous regional administration of normal saline. On average, lidocaine produced sensory loss earliest on the radial forearm and in the first dorsal web space, although the sequence of development of analgesia was variable, e.g., fingertip analgesia could occur before or after forearm sensory loss. Motor paralysis could precede or follow sensory loss in tissues supplied by the same peripheral nerve; the only consistent finding was persistence of strength in the flexor digitorum profundus of the little finger. The pattern of development of intravenous regional anesthesia was related to the anatomic distribution of the peripheral nerves; it is hypothesized that the primary mechanism of action is block of the small distal nerve branches.