Objective-To evaluate the effects of subarachnoidally administered hyperbaric morphine, buprenorphine, and methadone on avoidance threshold to noxious electrical stimulation of the perineal, sacral, lumbar, and thoracic regions in horses. Animals-6 healthy adult horses. Procedures-Horses were assigned to receive subarachnoid administration of hyperbaric morphine (0.01 mg/kg), buprenorphine (0.001 mg/kg), methadone (0.01mg/kg), or 10% dextrose solution in equal volumes (5 mL). Electrical stimulation was applied every 10 minutes for 60 minutes and every 30 minutes for 120 minutes after subarachnoid injection over the dermatomes of the perineal, sacral, lumbar, and thoracic regions, and the avoidance threshold voltage was recorded. Heart and respiratory rate, blood gas tensions, serum electrolyte concentrations, and sedative effects were also evaluated. Results-Administration of 10% dextrose solution did not change the avoidance threshold. Morphine and methadone significantly increased the avoidance threshold by 10 minutes after injection, which lasted until 120 minutes after subarachnoid administration in the perineal, sacral, lumbar, and thoracic regions. Profound analgesia (avoidance threshold > 40 V) was achieved in all regions. Buprenorphine also significantly increased the avoidance threshold by 10 minutes (36 V) after injection, which lasted 60 minutes and was considered moderate. Heart rate, blood pressure, respiratory rate, and blood gas tensions stayed within reference range. No ataxia, signs of sedation, or CNS excitement were observed. Conclusions and Clinical Relevance-Subarachnoid administration of hyperbaric morphine or methadone produces intense analgesia for 120 minutes over the dermatomes of the perineal, sacral, lumbar, and thoracic areas without cardiorespiratory depression, ataxia, or CNS excitement in horses.

Objective-To determine the effects of meloxicam and butorphanol on minimum alveolar concentration of isoflurane (MAC(ISO)) in rabbits. Animals-10 healthy young adult female rabbits. Procedure-Rabbits were anesthetized with isoflurane on 3 occasions in a blinded, randomized complete block design to determine the MAC(ISO) associated with administration of meloxicam (0, 0.3, or 1.5 mg/kg, PO) and butorphanol (0.4 mg/kg, IV). The MAC(ISO) was determined by use of a paw clamp technique as the end-tidal concentration of isoflurane halfway between the values that allowed or inhibited purposeful movement. Rectal temperature, end-tidal CO2 concentration, heart rate, oxygen saturation, and arterial blood pressure were measured to evaluate cardiopulmonary function. Results-Mean +/- SE MAC(ISO) in saline (0.9% NaCl) solution-treated rabbits was 2.49 +/- 0.07% and was not significantly different from that associated with administration of meloxicam at 0.3 mg/kg (2.56 +/- 0.07%) or 1.5 mg/kg (2.66 +/- 0.07%). Butorphanol significantly reduced the MAC(ISO) to 2.30 +/- 0.07% when administered with saline solution alone, 2.27 +/- 0.07% when administered with 0.3 mg of meloxicam/kg, and 2.33 +/- 0.07% when administered with 1.5 mg of meloxicam/kg. The percentage reduction in MAC(ISO) was significantly greater for rabbits that received butorphanol and meloxicam at either dose, compared with butorphanol and saline solution. Conclusions and Clinical Relevance-Results indicated that meloxicam does not have a direct isoflurane-sparing effect and does not interfere with the anesthetic-sparing effect of butorphanol in rabbits.