Ultrasound-guided sciatic nerve block injections in barred owl (Strix varia) cadavers

Objective

To describe an ultrasound-guided approach to the sciatic nerve and the distribution of nerve staining using two injectate volumes of dye in barred owls.

Study design

Descriptive, randomized, assessor-blinded, cadaveric study.

Animals

Twelve barred owl cadavers.

Methods

The sciatic nerve was visualized with a 13-6 MHz linear ultrasound probe placed on the medial aspect of the proximal femur in barred owl cadavers. A needle was inserted at the proximal caudal thigh, and cranially advanced in-plane until the tip was immediately adjacent and ventral to the sciatic nerve. Eleven owls were injected bilaterally with a 1:1 solution of 1% methylene blue and 0.5% ropivacaine, with high-volume (HV; 0.4 mL kg^–1) and low-volume (LV; 0.2 mL kg^–1) treatments. Nerve staining ≥ 1 cm circumferentially was determined by dissection 15 minutes post-injection. The coelom was then opened to inspect for aberrant dye spread. In one barred owl cadaver, a 1:1 solution of 1% methylene blue and 74% ioversol contrast was injected, and computed tomography was performed immediately before and 15 minutes after injection for evaluation of injectate spread.

Results

The HV treatment (0.4 mL kg^–1) resulted in successful nerve staining in 100% of injections, whereas the LV treatment (0.2 mL kg^–1) resulted in successful nerve staining in 91% of injections. There was no leakage of injectate into undesired locations (e.g. coelomic cavity) in any cadaver.

Conclusions and clinical relevance

In barred owls, the sciatic nerve can be visualized with ultrasound and injecting a ropivacaine/dye solution under ultrasound guidance successfully stained the sciatic nerve in the majority of cases. This technique holds potential for providing analgesia distal to the stifle joint; however, further investigations are necessary to evaluate its practical application in a clinical setting.