Objective—To investigate spontaneous locomotor activity (SLA) and antinociceptive effects of buprenorphine in horses. Animals—6 healthy adult horses. Procedures—Horses received each of 3 treatments (10 mL of saline [0.9% NaCl] solution, 5 μg of buprenorphine/kg, or 10 μg of buprenorphine/kg).Treatments were administered IV. Order of treatments was randomized, and there was a 10-day interval between subsequent treatments. Spontaneous locomotor activity was investigated in a behavioral box by use of infrared photoelectric sensors connected to a computer, which detected movement of each horse. Antinociceptive effect was investigated by hoof-withdrawal reflex latency (HWRL) and skin-twitching reflex latency (STRL) after painful stimulation with a heat lamp. Results—Moderate excitement was observed in all horses from 5 to 10 minutes after the administration of both dosages of buprenorphine. The SLA increased significantly for 6 and 14 hours after IV administration of 5 and 10 μg of buprenorphine/kg, respectively. Values for HWRL increased significantly only at 30 minutes after injection of 5 μg of buprenorphine/kg, whereas STRL and HWRL each increased significantly from 1 to 6 hours (except at 2 and 4 hours) and 11 hours, respectively, after injection of 10 μg of buprenorphine/kg. Conclusions and Clinical Relevance—IV injection of buprenorphine caused a dose-dependent increase in SLA, but only the dose of 10 μg/kg induced analgesia on the basis of results for the experimental method used.

Objective—To compare the renal and cardiorespiratory effects of IV treatment with lactated Ringer's solution (LRS) or physiologic saline (0.9% NaCl) solution (PSS) in severely decompensated cats with urethral obstruction (UO). Animals—14 cats (4 cats were used only to establish infusion rates). Procedures—An occluded urethral catheter was used to induce UO in each cat. After development of severe metabolic acidosis, hyperkalemia, and postrenal azotemia, the obstruction was relieved (0 hours); LRS or PSS (5 cats/group) was administered IV (gradually decreasing rate) beginning 15 minutes before and continuing for 48 hours after UO relief. Ten minutes before urethral catheter placement (baseline), at start of fluid therapy (SFT), and at intervals during fluid administration, various physical and clinicopathologic evaluations were performed. Results—Metabolic acidosis was detected in the PSS-treated group at SFT and 2 hours after relief of UO and in the LRS-treated group only at SFT The PSS-treated group had significantly lower blood pH and bicarbonate concentrations at 8 through 48 hours and lower base excess values at 2 through 48 hours, compared with the LRS-treated group. Hypocalcemia and hypernatremia were detected in the PSS-treated group at 2 and 12 hours, respectively. Absolute serum potassium and chloride concentrations did not differ significantly between groups at any time point. Conclusions and Clinical Relevance—Treatment with LRS or PSS appeared to be safe and effective in cats with experimentally induced UO; however, LRS was more efficient in restoring the acid-base and electrolyte balance in severely decompensated cats with UO.

Objective—To investigate the effects of buprenorphine on cardiopulmonary variables and on abdominal auscultation scores in horses. Animals—6 healthy adult horses. Procedures—Horses were restrained in stocks and allocated to 2 treatments in a randomized crossover design, with 1-week intervals between each treatment. Saline (0.9% NaCl) solution was administered IV as a control, whereas buprenorphine (10 μg/kg, IV) was administered to the experimental group. Cardiopulmonary data were collected for 120 minutes after buprenorphine or saline solution administration. Abdominal auscultation scores were monitored for 2 and 12 hours after drug administration in the control and experimental groups, respectively. Results—Following control treatment, horses remained calm while restrained in the stocks and no significant changes in cardiopulmonary variables were observed throughout the study. Buprenorphine administration caused excitatory phenomena (restlessness and head shaking). Heart rate, cardiac index, and arterial blood pressure were significantly increased after buprenorphine administration until the end of the observational period (120 minutes). Minimal changes were found in arterial blood gas tensions. Abdominal auscultation scores decreased significantly from baseline for 4 hours after buprenorphine administration. Conclusions and Clinical Relevance— Buprenorphine induced excitement and hemodynamic stimulation with minimal changes in arterial blood gas tensions. These effects may impact the clinical use of buprenorphine in horses. Further studies are indicated to investigate the effects of buprenorphine on gastrointestinal motility and fecal output.

Objective—To compare the ability of a sidestream capnograph and a mainstream capnograph to measure end-tidal CO₂ (ETCO₂) and provide accurate estimates of PaCO₂ in mechanically ventilated dogs. Design—Randomized, double Latin square. Animals—6 healthy adult dogs. Procedure—Anesthesia was induced and neuromuscular blockade achieved by IV administration of pancuronium bromide. Mechanical ventilation was used to induce conditions of standard ventilation, hyperventilation, and hypoventilation. While tidal volume was held constant, changes in minute volume ventilation and PaCO₂ were made by changing the respiratory rate. Arterial blood gas analysis was performed and ETCO₂ measurements were obtained by use of either a mainstream or a sidestream capnographic analyzer. Results—A linear regression model and bias analysis were used to compare PaCO₂ and ETCO₂ measurements; ETCO₂ measurements obtained by both capnographs correlated well with PaCO₂. Compared with PaCO₂, mainstream ETCO₂ values differed by 3.15 ± 4.89 mm Hg (mean bias ± SD), whereas the bias observed with the sidestream ETCO₂ system was significantly higher (5.65 ± 5.57 mm Hg). Regardless of the device used to measure ETCO2, bias increased as PaCO₂ exceeded 60 mm Hg. Conclusions and Clinical Relevance—Although the mainstream capnograph was slightly more accurate, both methods of ETCO₂ measurement correlated well with PaCO₂ and reflected changes in the ventilatory status. However, ETCO₂ values > 45 mm Hg may inaccurately reflect the severity of hypoventilation as PaCO₂ may be underestimated during conditions of hypercapnia (PaCO₂ > 60 mm Hg). (J Am Vet Med Assoc 2002;221:1582–1585)

Continuous-rate infusion (CRI) of drugs results in more stable plasma drug concentrations than administration of intermittent boluses, thus providing greater stability of physiological parameters. The aim of this study was to evaluate the physiologic and analgesic effects of the administration of morphine, butorphanol, tramadol or methadone by CRI in horses with induced synovitis of the radiocarpal joint. Increased values of cardiorespiratory parameters and body temperature were observed in all groups after initiation of opioid administration, and these increases were sustained throughout the CRI period. Morphine, butorphanol and methadone each caused a reduction in gut sounds, and this effect was greatest in animals that received morphine. Administration of morphine or methadone reduced the degree of lameness after the end of intravenous infusion. Administration of tramadol did not alter the degree of lameness in the animals. CRI of morphine or methadone, but not butorphanol or tramadol, provided analgesia in horses with carpal synovitis. All of these opioids increased cardiovascular and respiratory parameters and reduced gut sounds during CRI.