Objective To determine the influence on the distribution of the volume of a local anaesthetic-methylene blue solution at three different nerve block sites in the dog.
Study design Randomized, controlled, blinded experimental trial.
Animals 23 hound-cross dogs weighing 16–40 kg and aged 2 ± 0 years (mean ± SD).
Methods Dogs were anaesthetized and randomly assigned to three groups of seven or eight dogs each, based on volume administered: low, medium and high volume (L, M and H). Using electrolocation, the injection was performed after a positive response was elicited (flexion of the elbow for the brachial plexus block, quadriceps contractions for the lumbar plexus and dorsiflexion/plantar extension of the foot for the sciatic nerve block). At the brachial plexus site, groups L, M and H received 0.075, 0.15 and 0.3 mL kg−1, respectively. At the lumbar plexus site, groups L, M and H received 0.1, 0.2 and 0.4 mL kg−1, respectively. At the proximal sciatic nerve site, groups L, M and H received 0.05, 0.1 and 0.25 mL kg−1, respectively. Necropsies were performed immediately following euthanasia. Staining of ≥2 cm along the nerve was considered sufficient; the proportions sufficient were compared with Fisher’s exact test. The volume was recommended when all the relevant nerves were stained sufficiently in all or all but one of the dogs within the group.
Results In the brachial plexus, only in group H were all the nerves stained sufficiently. In the lumbar plexus site, no statistical difference was found, but we suggest the H group volume to balance sufficient and excessive staining. At the sciatic nerve site, all volumes tested produced sufficient staining in all (or all but one) dogs.
Conclusions and clinical relevance Volumes of 0.3 and 0.05 mL kg−1 produced sufficient distribution for performing brachial plexus, and sciatic nerve blocks, respectively. Additionally, a volume of 0.4 mL kg−1 might also be adequate for a lumbar plexus block (no statistical significance was reached).