Decreasing the toxic potential of intravenous regional anaesthesia

In an attempt to reduce the dose of local anaesthetic agent during intravenous regional anaesthesia (IVRA) of the upper limb, we have used a forearm tourniquet in 12 adult volunteers. The volume of the forearm venous system was predetermined angiographically. We performed IVRA with three solutions of lidocaine (0.25, 0.375, 0.5 per cent) administered in a volume equal to the forearm venous system. Angiographic results indicate that: a forearm tourniquet provides adequate vascular isolation; the volume of the forearm venous system can be correlated with body weight; the progression of the fluid in the venous system follows a pattern that is similar for all patients with the small veins of the distal forearm and proximal hand being filled last. With this technique, lidocaine 0.5 per cent resulted in a dose of 1.5 mg.kg-1 and provided excellent analgesia. Lower concentrations were unsatisfactory. We conclude that the use of a forearm tourniquet allows reduction of the local anaesthetic dose to a non-toxic level and thus increases the safety of IVRA.