Lateral ultrasound-guided axillary RUMM block in cats: a pilot cadaveric study

Objectives This study aimed to describe the prominent landmarks for an in-plane ultrasound-guided lateral approach to an axillary RUMM block in cats and document the anatomical distribution of injected solution in cadavers. Methods Eleven mixed breed, frozen-thawed cat cadavers were used. The ultrasound probe was placed on the lateral aspect of the forelimb. A spinal needle was used to inject either methylene blue 5 mg/ml or permanent tissue dye 1:10 within the focal clustering point of the radial (R), ulna (U), median (M) and musculocutaneous (Mc) nerves. The block was approached from either a cranial or caudal direction. Specimens were immediately dissected. A successful block was defined as > 20 mm of continuous stain on all nerves (R, U, M and Mc), a partial block as one or more nerves stained > 20 mm continuously and a negative block failed to stain any nerve > 20 mm. Results The cranial approach stained the R 8/9, U 6/9, M 6/9 and Mc 8/9 nerves successfully, while the caudal approach stained the R 7/9, U 8/9, M 7/9 and Mc 5/9 nerves successfully. There were no statistical differences on staining rates between approaches or limbs used. Conclusions and relevance The lateral approach to an axillary RUMM block is feasible in cats and may be a useful alternative to current approaches used for brachial and antebrachial desensitisation. Both cranial and caudal approaches produced similar results; however, further research in live animals will determine the clinical applicability.