Ultrasound-guided pudendal block in the dog: a cadaver study and case report

This case report describes the approach and use of an ultrasound-guided pudendal nerve block in dogs. The technique was first performed in the cadaver of a 14 kg male castrated Miniature Australian Shepherd dog. The ultrasound probe was placed in transverse orientation on midline between the anus and ischiatic arch. Methylene blue (0.05 mL kg^-1) was injected around the pudendal nerves bilaterally via an in-plane technique, with the following landmarks identified: urethra, perineal arteries, and internal obturator, bulbospongiosus and retractor penis muscles. Postinjection dissection revealed diffuse staining of the ischiorectal fossae and staining of an approximately 25 mm length of each pudendal nerve. A 1-year-old castrated male Labradoodle dog presented for urethral resection and anastomosis due to necrotic prolapse of the distal urethra. An ultrasound-guided pudendal nerve block was performed with 0.5% bupivacaine (0.05 mL kg^-1 per site) before surgery. The dog was premedicated with methadone [0.3 mg kg^-1 intravenously (IV)] and dexmedetomidine (2 μg kg^-1 IV), and general anesthesia was induced with ketamine (1 mg kg^-1 IV) followed by propofol (titrated to effect; total 1.4 mg kg^-1 IV). The trachea was intubated and anesthesia maintained with isoflurane carried in oxygen. The dog was given carprofen (2.2 mg kg^-1 subcutaneously) on extubation. The dog did not require intra- or postoperative rescue analgesic interventions in the 18 hours after surgery until hospital discharge. This technique appeared successful in desensitizing the distal urethra. Further investigation of this locoregional technique is warranted.