Abstract
Objective—To evaluate the effect of intratesticular administration of lidocaine on cardiovascular responses and cremaster muscle tension during castration of isoflurane-anesthetized stallions.
Animals—28 healthy stallions (mean ± SD age, 4.2 ± 2.8 years) with no testicular abnormalities that were scheduled for castration.
Procedure—Each horse was given acepromazine (20 μg/kg, IM), romifidine (50 μg/kg, IV), and butorphanol (20 μg/kg, IV). Anesthesia was induced with ketamine (2.5 mg/kg, IV) and midazolam (50 μg/kg, IV) and maintained with isoflurane (1.7% end-tidal concentration). After 10 minutes at a stable anesthetic plane, a needle was placed in each testicle and either no fluid or 15 mL of 2% lidocaine was injected; 10 minutes after needle placement, surgery was commenced. Pulse rate and arterial blood pressures were measured invasively at intervals from 5 minutes prior to castration (baseline) until 5 minutes after the left spermatic cord was clamped. The surgeon subjectively scored the degree of cremaster muscle tension. In 2 horses, lidocaine labeled with radioactive carbon (C14) was used and testicular autoradiograms were obtained.
Results—Compared with baseline values, castration significantly increased blood pressure measurements; intratesticular injection of lidocaine decreased this blood pressure response and cremaster muscle tension. In 2 horses, autoradiography revealed diffuse distribution of lidocaine into the spermatic cord but poor distribution into the cremaster muscle.
Conclusions and Clinical Relevance—In isoflurane-anesthetized stallions, intratesticular injection of lidocaine prior to castration appeared to decrease intraoperative blood pressure responses and cremaster muscle tension and may be a beneficial supplement to isoflurane anesthesia.
