[Axillary plexus block by simultaneous blockade of several nerves. I. Influence of the volume of the anesthetic solution].

The influence of the volume of local anaesthetic solution on axillary blockade was investigated in a prospective randomized double-blind study including 120 patients presenting for upper limb surgery. A peripheral nerve stimulator was used to carry out the axillary block with a multiple injection technique. The musculocutaneous, radial, median and ulnar nerves were routinely stimulated. Four criteria were monitored: quality of sensory blockade, degree of motor blockade, time of onset and duration of anaesthesia. The patients were randomly allocated into two groups (n = 60 each). In the first, patients received 25 ml per m2 of body surface area of carbonated 1% lignocaine, 0.25% bupivacaine or a 1 to 1 mixture of both. Patients in the other group were given the same amount of local anaesthetic in half the volume, i.e. 12.5 ml.m-2 of carbonated 2% lignocaine, 0.5% bupivacaine or a 1 to 1 mixture of both these. Adrenaline (1 in 400,000) was added to half the anaesthetic solutions used in each group. The data demonstrated that, for a same amount of local anaesthetic, the larger volumes provided better quality sensory blockade than the smaller ones (p < 0.03). However, the volume of solution used affected neither the time of onset nor the duration of anaesthesia, nor the degree of motor blockade. It is concluded that, despite the use of a neurostimulator and simultaneous infiltration of several nerve trunks, the volume required to ensure a reliable degree of sensory block with the technique of axillary block is comprised between 40 and 50 ml (25 ml.m-2).