Ultrasound-guided ischiorectal fossa block targeting the pudendal nerve in dogs: a cadaveric study.

OBJECTIVE

To describe an ultrasound-guided (USG) regional anesthesia technique for perineural injection of the pudendal nerve (PdN) in dogs.

STUDY

DESIGN

Prospective, randomized, anatomic study.

ANIMALS: A total of seven thawed and 15 fresh canine cadavers.

METHODS

Anatomical dissection, sonography and computed tomography (CT) techniques were used. In this study, 17 cadavers (11 males and six females), with body mass of 25.2 ± 6.3 kg (mean ± standard deviation) were used: four for anatomical study and approach development and 13 administered bilateral USG transgluteal injections. Using a dorsomedial-to-ventrolateral needle trajectory, the ischiorectal fossa was targeted medial to the ischiatic spine. Each hemipelvis was randomized to be administered high (HV, 0.2 mL kg-1) or low (LV, 0.1 mL kg-1) volume injections of ropivacaine-dye solution. Following injection, cadavers were dissected. Successful PdN staining (>1 cm nerve length stained) and inadvertent staining of the sciatic nerve, or rectal, urethral or intravascular puncture was recorded. Volumes were compared using a mixed effects ordinal logistic regression model (p < 0.05 considered significant).

RESULTS

We excluded five cadavers owing to poor tissue preservation. The neurovascular bundle containing PdN and landmarks for ischiorectal fossa were defined using CT. Sonographically, landmarks were identified and dye solution injected into the fossa. Complete staining of the PdN was achieved in 69.2% (HV) and 58.3% (LV) of injections. There was no significant difference in nerve staining between groups (p = 0.864). There was no significant difference in sciatic nerve staining between HV (7.7%) and LV (8.3%) (p = 0.71). Rectal, urethral or intravascular puncture was not observed.

CONCLUSIONS AND CLINICAL RELEVANCE: This is the first description of an USG ischiorectal fossa block using a transgluteal approach targeting the PdN in dogs. The described USG technique could provide anesthesia of the urethra and perineal region. Further studies are necessary to investigate this approach in live animals.