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Objective—To assess duration of actions of butorphanol, medetomidine, and a butorphanol-medetomidine combination in dogs given subanesthetic doses of isoflurane (ISO).

Animals—6 healthy dogs.

Procedure—Minimum alveolar concentration (MAC) values for ISO were determined. for each dog. Subsequently, 4 treatments were administered to each dog (saline [0.9% NaCl] solution, butorphanol [0.2 mg/kg of body weight], medetomidine [5.0 mg/kg], and a combination of butorphanol [0.2 mg/kg] and medetomidine [5.0 mg/kg]). All treatments were administered IM to dogs concurrent with isoflurane; treatment order was determined, using a randomized crossover design. Treatments were given at 7-day intervals. After mask induction with ISO and instrumentation with a rectal temperature probe, endtidal CO2 and anesthetic gas concentrations were analyzed. End-tidal ISO concentration was reduced to 90% MAC for each dog. A tail clamp was applied 15 minutes later. After a positive response, 1 of the treatments was administered. Response to application of the tail clamp was assessed at 15-minute intervals until a positive response again was detected.

Results—Duration of nonresponse after administration of saline solution, butorphanol, medetomidine, and butorphanol-medetomidine (mean ± SD) was 0.0 ± 0.0, 1.5 ± 1.5, 2.63 ± 0.49, and 5.58 ± 2.28 hours, respectively. Medetomidine effects were evident significantly longer than those for saline solution, whereas effects for butorphanol-medetomidine were evident significantly longer than for each agent administered alone.

Conclusion and Clinical Relevance—During ISOinduced anesthesia, administration of medetomidine, but not butorphanol, provides longer and more consistent analgesia than does saline solution, and the combination of butorphanol-medetomidine appears superior to the use of medetomidine or butorphanol alone. (Am J Vet Res 2000;61:42–47)

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in American Journal of Veterinary Research


Objective—To determine the relationship between bispectral index (BIS) and minimum alveolar concentration (MAC) multiples of isoflurane after IM injection of medetomidine or saline (0.9% NaCl) solution in anesthetized dogs.

Animals—6 dogs.

Procedure—Each dog was anesthetized 3 times with isoflurane. First, the MAC of isoflurane for each dog was determined by use of the tail clamp method. Second, anesthetized dogs were randomly assigned to receive an IM injection of medetomidine (8 µg · kg–1) or an equal volume of isotonic saline (0.9% NaCl) solution 30 minutes prior to beginning BIS measurements. Last, anesthetized dogs received the remaining treatment (medetomidine or isotonic saline solution). Dogs were anesthetized at each of 4 MAC multiples of isoflurane. Ventilation was controlled and atracurium (0.2 mg/kg followed by 6 µg/kg/min as a continuous infusion, IV) administered. After a 20-minute equilibration period at each MAC multiple of isoflurane, BIS data were collected for 5 minutes and median values of BIS calculated.

Results—BIS significantly decreased with increasing MAC multiples of isoflurane over the range of 0.8 to 2.0 MAC. Mean (± SD) MAC of isoflurane was 1.3 ± 0.2%. During isoflurane-saline anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 65 ± 8, 60 ± 7, 52 ± 3, and 31 ± 28, respectively. During isoflurane-medetomidine anesthesia, mean BIS measurements at 0.8, 1.0, 1.5, and 2.0 MAC were 77 ± 4, 53 ± 7, 31 ± 24, and 9 ± 20, respectively.

Conclusions and Clinical Relevance—BIS monitoring in dogs anesthetized with isoflurane has a predictive value in regard to degree of CNS depression. During isoflurane anesthesia, our results support a MAC-reducing effect of medetomidine. (Am J Vet Res 2003;64:316–320)

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in American Journal of Veterinary Research


Objective—To determine the hemodynamic consequences of the coadministration of a continuous rate infusion (CRI) of medetomidine with a fentanyl bolus in dogs.

Animals—12 healthy sexually intact male dogs weighing 30.3 ± 4.2 kg (mean ± SD).

Procedure—Dogs received either fentanyl alone (15.0 µg/kg, IV bolus) or the same dose of fentanyl during an 11-hour CRI of medetomidine (1.5 µg/kg/h, IV). Prior to drug administration, dogs were instrumented for measurement of cardiac output, left atrial pressure, and systemic arterial blood pressures. Additionally, blood samples were collected from the pulmonary artery and left atrium for blood gas analysis.

Results—Medetomidine infusion reduced the cardiac index, heart rate, and O2 delivery while increasing left atrial pressure. Subsequent fentanyl administration further decreased the cardiac index. The PaO2 was not significantly different between the 2 treatment groups; however, fentanyl transiently decreased PaO2 from baseline values in dogs receiving a CRI of medetomidine.

Conclusions and Clinical Relevance—Because of the prolonged hemodynamic changes associated with the CRI of medetomidine, its safety should be further evaluated before being clinically implemented in dogs. (Am J Vet Res 2005;66:1222–1226)

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in American Journal of Veterinary Research


Objective—To evaluate the incidence of and factors associated with complications following rectal pull-through (RPT) surgery and the outcome for dogs with rectal tumors.

Design—Retrospective case series.

Animals—74 dogs with rectal masses.

Procedures—Information regarding signalment, history, diagnostic testing, type of rectal disease, surgical details, and postoperative complications, treatments, and outcomes was obtained from medical records and follow-up communications. Survival times were calculated. Descriptive statistics were generated. Regression analyses were used to evaluate the effect of various variables on the development of postsurgical complications and survival time.

Results—58 (78.4%) dogs developed postsurgical complications, the most common of which was fecal incontinence with 42 (56.8%) dogs affected, of which 23 (54.8%) developed permanent incontinence. Other complications included diarrhea (n = 32), tenesmus (23), stricture formation (16), rectal bleeding (8), constipation (7), dehiscence (6), and infection (4). The rectal tumor recurred in 10 dogs. The median survival time was 1,150 days for all dogs and 726 days for dogs with malignant tumors. The 2 most common rectal masses were rectal carcinoma and rectal carcinoma in situ, and the dogs with these tumors had median survival times of 696 and 1,006 days, respectively.

Conclusions and Clinical Relevance—Dogs with rectal diseases that underwent RPT surgery had a high incidence of complications; however, those dogs had good local tumor control and survival times. The risk and impact of postsurgical complications on the quality of life and oncological outcomes should be discussed with owners before RPT surgery is performed in dogs with rectal masses.

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in Journal of the American Veterinary Medical Association