Evaluation of analgesia and cardiorespiratory effects of epidurally administered butorphanol in isoflurane-anesthetized dogs

Abstract

Objective - To determine variations in minimal alveolar concentration (MAC) of isoflurane and analgesic and cardiorespiratory effects of lumbosacral epidural administration of 0.25 mg of butorphanol/kg of body weight in dogs. Animals - 16 healthy male dogs. Procedure - Dogs were anesthetized with isoflurane alone. Eight dogs received butorphanol (group B) and the others an equal volume of isotonic saline solution (group S) administered by a catheter inserted in the lumbosacral epidural space. Isoflurane MAC was determined before and 30 minutes after the epidural injection, along with noxious stimulation to the fore- and hind limbs. Cardiorespiratory variables were recorded prior to and until 120 minutes after epidural administration. At that time, isoflurane anesthesia was ended, and nocicepticn (toe pinch and pin-prick responses) was evaluated for 7 hours. Dogs were observed for 3 days to determine presence of neurologic side effects. Results - For group-B dogs, isoflurane MAC decreased by 31 ± 8.6% after butorphanol was administered. Cutaneous insensitivity (to pin-prick nociceptive test) persisted for 3 hours after the end of isoflurane anesthesia in group-B dogs. No response was observed to toe pinch stimulation for 30 minutes after anesthesia. Conclusions - Epidural administration of 0.25 mg of butorphanol/kg in dogs was safe; minimal cardiorespiratory and no neurologic side effects were observed, and analgesia and an isoflurane-sparing effect were apparent. Clinical relevance - The short duration of action of epidurally administered butorphanol limits its value for clinical practice.