Assessment of the Bilateral Block of the Trunk of the Pudendal Nerve in Cats with Urethral Obstruction
Background: Clinical care of cats with urethral obstruction is a common routine in feline clinical medicine and the re-establishment of urinary flow is essential for long-lasting correction of the pathophysiological alterations presented. For this chemical restraint is usually employed, that together with the alteration, increases the anesthetic risk of these patients. Improvement in anesthetic techniques, especially the loco-regional, may contribute to reducing the anesthetic risk of these patients and facilitate maneuvers to clear the obstruction. Thus the objective of the present study was to describe and assess the bilateral block technique of the pudendal nerve in 16 cats with urethral obstruction.
Materials, Methods & Results: Sixteen male crossbred cats were used, with partial or total urethral obstruction, attended at the Veterinary Hospital of the Federal University of Campina Grande, PB, Brazil. The anesthetic block of the pudendal nerve trunk was carried out by placing the local anesthetic close to the ventral foramen of the second sacral vertebra, using a 13 x 0.45 mm needle attached to a 1 mL syringe. To assess the effectiveness of the bilateral block, the analgesia promoted was assessed using the substitute (“Reaction to Palpating the Surgical Wound” of subscale 1 (pain expression) of the “Compound Multi-dimensional Scale to Assess Post Operational Pain in Cats”. This assessment was made before the bilateral block (M0) and 10 min afterwards (M1) and the scores ranged from 0 to 3. In addition, a segmental assessment of the urethra was made, where, by passing a probe the sensitivity was assessed of the urethral ostium, penile and pelvic urethra and the relaxing of the external urethral sphincter. This assessment was made at M1 and classified as present or absent. In the cases where the bilateral block was inefficient, the technique was repeated, in the same locations and at the same dose as initially administered, and a new assessment (M2) was made 10 minutes after the second administration. In 12 of the 16 patients assessed the bilateral block was made once. The following were observed in these patients at M1: reduction in the reaction to penile manipulation (P = 0.003), total relaxation of the external urethral sphincter and absence of sensitivity to passing the probe through the penile urethra (P = 0.000) and insensitivity of the ostium urethrae (P = 0.006). In the animals in which the anesthetic bilateral block was repeated (4/16) the value of p adjusted for penile manipulation was 0.05. There was no reaction to the probe passage through the ostium urethrae and the penile urethra or contraction of the external urethral sphincter in 3 of the 4 animals (P = 0.625). Considering the total number of animals assessed, the urethral obstruction of the pudendal nerve trunk, carried out one or twice, caused statistically significant (P = 0.004) insensitivity to penile manipulation, probing of the ostium urethrae and the penile urethra and total relaxation of the external urethral sphincter in 14 of the 16 animals. In three patients concomitant anesthetic bilateral block was observed of the sciatic nerve, bilateral (two animals) or unilateral (one animal).
Discussion: studies on the feline pudendal nerve have demonstrated that the sensitive and motor bilateral block of this nerve is possible, as corroborated by the present study. Although an atomic study had shown the possibility of concomitant bilateral block of the sciatic nerve, and therefore, according to the authors, the technique should not be recommended, this finding did not demonstrate great clinical relevance, because in most cases the patients remained under fluid therapy throughout the anesthetic recovery period (about two hours) and therefore with restricted movement. Nevertheless, studies should be carried out to improve this technique.
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