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

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).