Blind perineural injection for sciatic and femoral nerve block in cats: anatomical study and in vivo application

ABSTRACT: This study investigated staining of sciatic (SN) and femoral (FN) nerves in feline cadavers following injection of two different volumes of methylene blue, and the application of one chosen volume in vivo using lidocaine in healthy sedated cats. Fourteen adult feline cadavers weighing 2.8 ± 1.2 kg and 10 healthy adult cats weighing 3.5 ± 1.2 kg were used in the study. First, an anatomical study of the SN and FN was carried out on six feline cadavers to measure depth of each nerve, followed by injection of 1% methylene blue on another eight cadavers to compare 0.2 with 0.3 mL/kg on each pelvic limb. The volume associated with staining ≥ 2 cm of the nerves was considered adequate for application in vivo. Based on the cadaveric study, 10 healthy cats received 1.25% lidocaine on one side and saline on the contralateral side at 0.2 mL/kg to assess efficacy of perineural block. Injections were performed between the semimembranosus and semitendinosus muscles for the SN and in the femoral triangle, next to the iliopsoas muscle, for the FN. Motor assessment included a score of ataxia and patellar reflex testing. Sensory assessment comprised proprioception and skin clamping at the leg. Data were analyzed using paired t test. Results showed insufficient in vivo block, demonstrated by lack of difference between sides (P > 0.05). In conclusion, SN and FN block cannot be successfully performed in cats without the aid of imaging modalities or neurostimulation using low volumes of solution (0.2 mL/kg).