Effect of intratesticular injection of lidocaine on cardiovascular responses to castration in isoflurane-anesthetized stallions.
OBJECTIVE
To evaluate the effect of intratesticular administration of lidocaine on cardiovascular responses and cremaster muscle tension during castration of isoflurane-anesthetized stallions.


METHODS
28 healthy stallions (mean +/- SD age, 4.2 +/- 2.8 years) with no testicular abnormalities that were scheduled for castration.


METHODS
Each horse was given acepromazine (20 microg/kg, IM), romifidine (50 microg/kg, IV), and butorphanol (20 microg/kg, IV). Anesthesia was induced with ketamine (2.5 mg/kg, IV) and midazolam (50 microg/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 (C(14)) 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
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.
Haga
Henning A
HA
Department of Companion Animal Clinical Sciences, Norwegian School of Veterinary Science, PO Box 8146 Dep, N-0033 Oslo, Norway.
Lykkjen
Sigrid
S
Revold
Tobias
T
Ranheim
Birgit
B
D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects*; D006736:Horses / Q000502:physiology*; D007267:Injections; D007530:Isoflurane / Q000494:pharmacology*; D008012:Lidocaine / Q000008:administration & dosage* / Q000494:pharmacology*; D008297:Male; D009919:Orchiectomy / Q000662:veterinary*
D000779:Anesthetics, Local; D008012:Lidocaine; D007530:Isoflurane