Paravertebral brachial plexus blockade in cats: a cadaver study

Objectives: The aims of this study were to describe the paravertebral brachial plexus (PBP) blockade in cats, and compare the spread of bupivacaine–methylene blue solution (BMS) using two volumes of injection into the PBP. Methods: Six cadavers (4.4 ± 1.8 kg) randomly received 0.15 ml/kg (LOW) or 0.2 ml/kg (HIGH) per injection of BMS into the PBP. The first injection was made ventral to the transverse process of the sixth cervical vertebra (nerves C6 and C7) at the emergence of nerve roots. A second injection was performed at the edge of the cranial border of the scapula and directed ventrally towards the first rib (C8 and T1). Cadavers were dissected and the presence of BMS in contact with the nerves (success rate) and length of staining were evaluated for each nerve (C6/C7/C8/T1). Length of target nerves in contact with BMS was measured and <15 mm was considered fair, ⩾15 mm sufficient and >40 mm excessive. Complications (aspiration of blood, staining of pleural space and/or spinal cord) were recorded. Paired t-test, Mann-Whitney U-test and χ ² test were used for statistical analysis when appropriate (P <0.05). Results: Eleven hemilateral brachial plexuses were injected. Aspiration of blood occurred during one injection. Inadvertent pleural or spinal staining was not observed. Success rates (positive nerve staining) in the LOW and HIGH groups, respectively, were as follows: C6: 83% and 80%; C7: 66% and 100%; C8: 66% and 100%; T1: 50% and 60% (P >0.05). Median (range) length of nerve staining was 22 mm (15–39 mm) for LOW and 21 mm (13–35 mm) for HIGH (P >0.05). Excessive nerve staining was not recorded. Conclusions and relevance: This study describes the PBP blockade in cats with acceptable nerve staining and minimal complications. Success rate and length of nerve staining were not significantly different between the LOW and HIGH groups.