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Abstract

Objective—To determine whether infusion of xylazine and ketamine or xylazine and propofol after sevoflurane administration in horses would improve the quality of recovery from anesthesia.

Animals—6 healthy adult horses.

Procedures—For each horse, anesthesia was induced by administration of xylazine, diazepam, and ketamine and maintained with sevoflurane for approximately 90 minutes (of which the last 60 minutes were under steady-state conditions) 3 times at 1-week intervals. For 1 anesthetic episode, each horse was allowed to recover from sevoflurane anesthesia; for the other 2 episodes, xylazine and ketamine or xylazine and propofol were infused for 30 or 15 minutes, respectively, after termination of sevoflurane administration. Selected cardiopulmonary variables were measured during anesthesia and recovery. Recovery events were monitored and subjectively scored.

Results—Cardiopulmonary variables differed minimally among treatments, although the xylazine-propofol infusion was associated with greater respiratory depression than was the xylazine-ketamine infusion. Interval from discontinuation of sevoflurane or infusion administration to standing did not differ significantly among treatments, but the number of attempts required to stand successfully was significantly lower after xylazine-propofol infusion, compared with the number of attempts after sevoflurane alone. Scores for recovery from anesthesia were significantly lower (ie, better recovery) after either infusion, compared with scores for sevoflurane administration alone.

Conclusions and Clinical Relevance—Xylazine-ketamine or xylazine-propofol infusion significantly improved quality of recovery from sevoflurane anesthesia in horses. Xylazine-ketamine or xylazine-propofol infusions may be of benefit during recovery from sevoflurane anesthesia in horses for which a smooth recovery is particularly critical. However, oxygenation and ventilation should be monitored carefully.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine the effect of a constant-rate infusion of fentanyl on minimum alveolar concentration (MAC) of isoflurane and to determine the interaction between fentanyl and a benzodiazepine agonist (diazepam) and antagonist (flumazenil) in isoflurane-anesthetized dogs.

Animals—8 mixed-breed adult dogs.

Procedure—Dogs were anesthetized with isoflurane 3 times during a 6-week period. After a 30-minute equilibration period, each MAC determination was performed in triplicate, using standard techniques. Fentanyl was administered as a bolus (10 µg/kg of body weight, IV) that was followed by a constant infusion (0.3 µg/kg per min, IV) throughout the remainder of the experiment. After determining isoflurane-fentanyl MAC in triplicate, each dog received saline (0.9% NaCl) solution, diazepam, or flumazenil. After 30 minutes, MAC was determined again.

Results—Fentanyl significantly decreased isoflurane MAC (corrected to a barometric pressure of 760 mm Hg) from 1.80 ± 0.21 to 0.85 ± 0.14%, a reduction of 53%. Isoflurane-fentanyl-diazepam MAC (0.48 ± 0.29%) was significantly less than isoflurane-fentanylsaline MAC (0.79 ± 0.21%). Percentage reduction in isoflurane MAC was significantly greater for fentanyldiazepam (74%), compared with fentanyl-saline (54%) or fentanyl-flumazenil (61%). Mean fentanyl concentrations for the entire experiment were increased over time and were higher in the diazepam group than the saline or flumazenil groups.

Conclusion and Clinical Relevance—Fentanyl markedly decreased isoflurane MAC in dogs. Diazepam, but not flumazenil, further decreased isoflurane-fentanyl MAC. Our results indicate that diazepam enhances, whereas flumazenil does not affect, opioid-induced CNS depression and, possibly, analgesia in dogs. (Am J Vet Res 2001;62:555–560)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate effects of injection with a nonsteroidal anti-inflammatory drug (NSAID) followed by oral administration of an NSAID on the gastrointestinal tract (GIT) of healthy dogs.

Animals—6 healthy Walker Hounds.

Procedures—In a randomized, crossover design, dogs were administered 4 treatments consisting of an SC injection of an NSAID or control solution (day 0), followed by oral administration of an NSAID or inert substance for 4 days (days 1 through 4). Treatment regimens included carprofen (4 mg/kg) followed by inert substance; saline (0.9% NaCl) solution followed by deracoxib (4 mg/kg); carprofen (4 mg/kg) followed by carprofen (4 mg/kg); and carprofen (4 mg/kg) followed by deracoxib (4 mg/kg). Hematologic, serum biochemical, and fecal evaluations were conducted weekly, and clinical scores were obtained daily. Endoscopy of the GIT was performed before and on days 1, 2, and 5 for each treatment. Lesions were scored by use of a 6-point scale.

Results—No significant differences existed for clinical data, clinicopathologic data, or lesion scores in the esophagus, cardia, or duodenum. For the gastric fundus, antrum, and lesser curvature, an effect of time was observed for all treatments, with lesions worsening from before to day 2 of treatments but improving by day 5.

Conclusions and Clinical Relevance—Sequential administration of NSAIDs in this experiment did not result in clinically important gastroduodenal ulcers. A larger study to investigate the effect of sequential administration of NSAIDs for longer durations and in dogs with signs of acute and chronic pain is essential to substantiate these findings.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate μ-opioid receptors in synovial membranes of horses and determine whether these receptors are up-regulated in nerve endings during inflammation.

Sample Population—Synovial tissue obtained from 39 client-owned horses during arthroscopy and 14 research horses during necropsy; brain and synovial tissues were obtained during necropsy from 1 horse, and control tissues were obtained from a mouse.

Procedure—Horses were classified into 7 groups on the basis of histologically determined degree of inflammation. Binding of primary rabbit antibody developed against μ-opioid receptors in equine synovial tissue was studied, using western blot analysis. Synovial membranes were tested for μ-opioid receptors by immunohistochemical staining, using a diaminobenzidine-cobalt chloride chromogen. Homogenates of synovial membranes were evaluated by use of radioligand binding.

Results—Examination of western blots of equine thalamus revealed that rabbit antibody developed against μ-opioid receptors yielded a band (molecular weight, 55 kd) that corresponded with that of other opioid receptors. Use of immunohistochemical staining of synovial tissue revealed considerable staining in the proliferative lining layer and in regions surrounding vascular structures. Specific radioligand binding of tissue homogenates was found in all groups. We did not detect significant differences in binding between horses with inflammation and horses without inflammation.

Conclusions and Clinical Relevance—Results of immunohistochemical analysis and radioligand binding of tissue homogenates suggest that there are opioid receptors in synovial membranes of horses. Our results support the practice of intra-articular administration of opioids to relieve pain after arthroscopic surgery in horses. (Am J Vet Res 2001;62:1408–1412).

Full access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate the use of xylazine and ketamine for total IV anesthesia in horses.

Animals—8 horses.

Procedure—Anesthetic induction was performed on 4 occasions in each horse with xylazine (0.75 mg/kg, IV), guaifenesin (75 mg/kg, IV), and ketamine (2 mg/kg, IV). Intravenous infusions of xylazine and ketamine were then started by use of 1 of 6 treatments as follows for which 35, 90, 120, and 150 represent infusion dosages (µg/kg/min) and X and K represent xylazine and ketamine, respectively: X35+K90 with 100% inspired oxygen (O2), X35+K120-O2, X35+K150-O2, X70+K90-O2, K150-O2, and X35+K120 with a 21% fraction of inspired oxygen (ie, air). Cardiopulmonary measurements were performed. Response to a noxious electrical stimulus was observed at 20, 40, and 60 minutes after induction. Times to achieve sternal recumbency and standing were recorded. Quality of sedation, induction, and recovery to sternal recumbency and standing were subjectively evaluated.

Results—Heart rate and cardiac index were higher and total peripheral resistance lower in K150-O2 and X35+K120-air groups. The mean arterial pressure was highest in the X35+K120-air group and lowest in the K150-O2 group (125 ± 6 vs 85 ± 8 at 20 minutes, respectively). Mean PaO2 was lowest in the X35+K120-air group. Times to sternal recumbency and standing were shortest for horses receiving K150-O2 (23 ± 6 minutes and 33 ± 8 minutes, respectively) and longest for those receiving X70+K90-O2 (58 ± 28 minutes and 69 ± 27 minutes, respectively).

Conclusions and Clinical Relevance—Infusions of xylazine and ketamine may be used with oxygen supplementation to maintain 60 minutes of anesthesia in healthy adult horses. (Am J Vet Res 2005;66:1002–1007)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To assess the pharmacokinetics and pharmacodynamics of morphine in llamas.

Animals—6 healthy adult llamas.

Procedures—Llamas received morphine sulfate in a randomized crossover design. In phase 1, they received IV or IM administration of morphine at 0.05 or 0.5 mg/kg, respectively; in phase 2, they received IV administration of morphine at 0.05, 0.25, or 0.5 mg/kg. Plasma morphine and morphine-6-glucuronide concentrations were determined by validated methods. Body temperature, heart rate, respiratory rate, sedation, and analgesia were assessed and compared with plasma concentrations by regression analysis.

Results—Total body clearance was similar between IV administration of morphine sulfate at 0.25 and 0.5 mg/kg (mean ± SD, 25.3 ± 6.9 mL/min/kg and 27.3 ± 5.9 mL/min/kg, respectively), and linearity was demonstrated between these doses. Bioavailability of morphine following IM administration at 0.5 mg/kg was 120 ± 30%. Body temperature and sedation increased as the dose of morphine administered increased. Heart rate was unaffected by varying doses. Respiratory rate decreased as dose increased. Analgesia was difficult to assess as a result of high individual variability. Intravenous administration of morphine at 0.25 mg/kg provided the most consistent increase in tolerance to electric stimulation. Pharmacodynamic modeling revealed a sigmoidal relationship between plasma concentration and sedation score.

Conclusions and Clinical Relevance—Morphine was characterized by a large apparent volume of distribution and high systemic clearance in llamas. A prolonged half-life was observed with IM injection. Intravenous administration of morphine sulfate at 0.25 mg/kg every 4 hours is suggested for further study.

Full access
in American Journal of Veterinary Research