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Abstract

Objective

To examine effects of atipamezole on detomidine midsacral subarachnoidally-induced analgesia, cardiovascular and respiratory activity, head ptosis, and position of pelvic limbs in healthy mares.

Animals

10 healthy mares.

Procedure

Using a randomized, blinded, crossover study design, mares received detomidine (0.03 mg/kg of body weight, diluted in 3 ml of CSF) midsacral subarachnoidally, followed by atipamezole (0.1 mg/kg [test]) or sterile saline (0.9% NaCl) solution (control), IV 61 minutes later and saline solution (3 ml, midsacral subarachnoidally) on a separate occasion, at least 2 weeks later. Analgesia was determined by lack of sensory perception to electrical stimulation at the perineal dermatome and no response to needle-prick stimulation extending from the coccygeal to T15 dermatomes. Arterial acid-base (pH, standard bicarbonate, and base excess values), gas tensions (PO2 , PCO2 ), PCV, total solids concentration, heart and respiratory rates, rectal temperature, and arterial blood pressure were determined, and mares were observed for sweating and urination. Mean scores of perineal analgesia, head ptosis, position of pelvic limbs, and cardiovascular and respiratory data were compared for the 3-hour test period.

Results

Subarachnoidally administered detomidine induced perineal analgesia (mean ± SD onset, 9.0 ± 4.6 minutes; duration, 130 ± 26 minutes), marked head ptosis, moderate changes in pelvic limb position, cardiovascular and respiratory depression, sweating in analgesic zones, and diuresis. Intravenously administered atipamezole significantly reduced mean scores of detomidine-induced perineal analgesia, head ptosis, pelvic limb position, sweating and diuresis; partially antagonized detomidine-induced bradycardia; and did not effect detomidine-induced bradypnea.

Conclusions and Clinical Relevance

Most effects of midsacral subarachnoidally administered detomidine, except bradycardia and bradypnea, were reversed by atipamezole (0.1 mg/kg, IV), indicating that most of the actions of detomidine were mediated via activation of α2-adrenergic receptors. (Am J Vet Res 1998;59:468–477)

Free access
in American Journal of Veterinary Research

Objective

To determine the analgesic agents administered to animals frequently used in biomedical research.

Design

Telephone survey.

Sample Population

Diplomates of the American College of Laboratory Animal Medicine.

Procedure

200 of 429 active diplomates listed in the 1993 directory of the American College of Laboratory Animal Medicine were selected at random for telephone interviews. Diplomates were asked to identify the species that they cared for and the dosages, dosing intervals, and routes of administration for analgesic agents.

Results

90 of 200 (45%) diplomates completed the survey. Twenty-two analgesic agents were identified for use in 472 applications in 16 species. Opioid analgesics were the most frequently selected agents, with buprenorphine hydrochloride and butorphanol being most frequently used. Intramuscular and subcutaneous routes of administration were used most frequently.

Clinical Implications

Among diplomates of the American College of Laboratory Animal Medicine, opioids are the most frequently selected agents used to induce analgesia in animals used in biomedical research. Dosages and dosing intervals used vary widely among animals of various species as well as for animals in each species. (J Am Vet Med Assoc 1996,209: 918-921)

Free access
in Journal of the American Veterinary Medical Association

Abstract

Objective

To examine and compare effects of 2α2 - adrenergic receptor agonists, xylazine and detomidine, administered into the sacrococcygeal epidural space to induce safe and effective perineal analgesia on cardio-vascular and respiratory functions, head ptosis, and po-sition of pelvic limbs in healthy mares.

Animals

8 healthy mares.

Procedure

Blood samples were drawn and systemic hemodynamics were determined, including cardiac output and pulmonary arterial, systemic arterial, and right atrial pressures. Two-way ANOVA with repeated measures was used to detect significant (P < 0.05) differences between mean scores of perineal analgesia, cardiorespiratory variables, head ptosis, and position of pelvic limbs in mares before and during a 3-hour testing period. Analgesia was determined by lack of sensory perception to electrical stimulation at the perineal dermatome and no response to needle prick stimulation in dermatomes extending from the coccyx to T15. Avoidance responses to electrical current and needle prick stimulation and behavioral changes (head ptosis, position of pelvic limbs) were quantitatively assessed by use of a scoring system.

Results

Epidurally administered xylazine induced perineal analgesia and variable bilateral caudal analgesia extending from the coccyx to S3 dermatome, with minimal cardiovascular and respiratory depression, head ptosis, changes in position of pelvic limbs, and no urination in standing mares. Epidurally administered detomidine in-duced perineal analgesia, variable bilateral analgesia with dermatomal spread ranging from coccyx to S3 and coccyx to T15, with cardiovascular depression, marked head ptosis, changes in position of pelvic limbs, and diuresis in standing mares. Onset of perineal analgesia after xylazine and detomidine administrations was 13.1 ± 3.7 and 12.5 ± 2.7 minutes (mean ± SD), respectively. The period of perineal analgesia was significantly (P < 0.05) longer in mares after epidural xylazine administration than after epidural detomidine administration (165 to > 180 minutes vs 160 ± 8 minutes).

Conclusions

Caudal epidurally administered xylazine (0.25 mg/kg of body weight in 8 ml of 0.9% NaCI) offers the most desirable conditions in mares: long-term perineal analgesia (> 2.5 hours), with minimal cardiopulmonary depression, head ptosis, changes in pelvic limb position, and no urination in standing mares during a 3- hour test period. (Am J Vet Res 1996;57:1338-1345)

Free access
in American Journal of Veterinary Research

Abstract

Objective

To examine effects of 0.25 mg of xylazine/kg of body weight diluted to a total volume of 6 ml/450 kg with sterile 0.9% NaCl, administered into the epidural space of the sacrococcygeal joint on perineal analgesia, sedation, ataxia, and respiratory and cardiovascular function in standing mares:

Design

Randomized, blinded study, using xylazine (treatment) and 0.9% NaCl (controls). At least 2 weeks elapsed between the treatments.

Animals

Eight healthy mares.

Procedure

Blood samples were drawn. Systemic hemodynamics were determined, including cardiac output and pulmonary arterial, systemic arterial, and right atrial pressures. Two-way ANOVA with repeated measures was used to detect significant (P < 0.05) differences between mean scores of analgesia, sedation, ataxia, and cardiorespiratory variables before and during a 3-hour testing period. Analgesia was determined by lack of sensory perception to electrical stimulation at the perineal dermatome and no response to needle prick stimulation extending from coccyx to S3 dermatomes. Sedation was determined by head ptosis.

Results

Epidurally administered xylazine induced variable bilateral caudal analgesia extending from coccyx to S3, with minimal sedation, ataxia, and cardiovascular and respiratory depression in standing mares. Analgesia was attained at 15 ± 6 minutes and lasted for 165 to over 180 minutes. Heart and respiratory rates, systolic, diastolic, and mean arterial blood pressure, PCV, hemoglobin concentration, arterial oxygen content, and oxygen transport were decreased after xylazine, but not 0.9% NaCl, treatment. Cardiac output, stroke volume, mean right atrial pressure, mean pulmonary artery pressure, systemic vascular resistance, pulmonary vascular resistance, arterial and mixed venous pH and gas tensions (Po2 and Pco2 ), oxygen consumption, blood temperature, and rectal temperature did not change significantly (P < 0.05) after epidural administration of xylazine or 0.9% NaCl.

Conclusions

Caudal epidurally administered xylazine (0.25 mg/kg in 6 ml of 0.9% NaCl) can be given safely to induce prolonged (> 2 hours) caudal analgesia with minimal sedation, ataxia, and circulatory and respiratory disturbances in conscious, standing mares.

Free access
in American Journal of Veterinary Research

SUMMARY

Six horses were subjected to 3 hours of low-flow ischemia and 3 hours of reperfusion of the large colon. After induction of anesthesia, the large colon was exteriorized through a ventral midline celiotomy. Colonic blood flow was measured continuously, using Doppler ultrasonic flow probes placed on the colonic arteries supplying the dorsal and ventral colons and was allowed to stabilize for 15 to 30 minutes after instrumentation. Low-flow ischemia was induced by reducing colonic arterial blood flow to 20% of baseline (bl) flow. Colonic mucosal, seromuscular, and full-thickness blood flow were determined on a tissue-weight basis by injecting colored microspheres proximally into the colonic artery supplying the ventral colon. Reference blood samples were obtained at a known flow rate from the colonic artery and vein at a site more distal to the site of injection. Left ventral colon biopsy specimens were harvested at bl, 3 hours of ischemia, and 15 minutes of reperfusion. Blood and tissue samples were digested and filtered to collect the microspheres, and dimethylformamide was added to release the colored dyes. Dye concentration in blood and tissue samples was measured by use of spectrophotometry, and tissue-blood flow was calculated. Data were analyzed, using two-way anova for repeated measures; statistical significance was set at P < 0.05. Doppler blood flow decreased to approximately 20% of BL, whereas microsphere blood flow ranged between 13.7 and 15.5% of bl at 3 hours of ischemia. Doppler-determined blood flow increased immediately on restoration of blood flow, reached 183% of bl at 15 minutes of reperfusion, and remained at or above bl throughout 3 hours of reperfusion. This reactive hyperemia was also detected, using the colored microspheres; blood flow increased to 242 and 327% of bl at 15 minutes of reperfusion in the mucosal and seromuscular layers, respectively. Mucosal blood flow was not different from seromuscular blood flow at any time, indicating relatively equal distribution of blood flow between these 2 layers. As determined from the venous reference samples, there was no evidence of arteriovenous anastomoses.

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine effects of IV administered yohimbine on perineal analgesia, cardiovascular and respiratory activity, and head and pelvic limb position in healthy mares following epidural administration of detomidine hydrochloride solution.

Animals

8 healthy mares.

Procedure

Each mare received detomidine hydrochloride (0.06 mg/kg of body weight), administered in the caudal epidural space, followed 61 minutes later by yohimbine (0.05 mg/kg; test) or sterile saline (0.9% NaCl) solution (control), administered IV, in a randomized, crossover study design with ≥ 2 weeks between treatments. Analgesia was determined by lack of sensory perception to electrical stimulation of perineal dermatomes and needle-prick stimulation of coccygeal to 15th thoracic dermatomes. Arterial pH, Paco2, Pao2, heart and respiratory rates, rectal temperature, arterial blood pressure, and cardiac output were determined, and mares were observed for sweating and urination. Mean scores obtained for test and control groups were compared.

Results

Intravenously administered yohimbine significantly reduced mean scores of detomidine-induced perineal analgesia, head ptosis, changes in pelvic limb position, and sweating and diuresis; antagonized detomidine-induced decreases in heart rate and cardiac output; but did not affect detomidine-induced decrease in respiratory rate.

Conclusions and Clinical Relevance

Most effects of epidurally administered detomidine, except bradypnea, were antagonized by yohimbine, suggesting that detomidine may influence respiratory rate by mechanisms other than stimulation of α2-adrenoceptors, or that yohimbine induces respiratory depressant effects. Yohimbine may be an effective α2-adrenoceptor antagonist for all but respiratory depression following epidural administration of detomidine to mares. (Am J Vet Res 1999;60:1262–1270)

Free access
in American Journal of Veterinary Research

Summary

The cardiorespiratory effects of thiamylal (10 mg/kg of body weight, iv) and the effects of preanesthetic medication with diazepam, acepromazine, detomidine, or xylazine administered prior to a thiamylal dosage of 6 mg/kg, iv, were evaluated in 6 adult horses. The quality of recovery from thiamylal anesthesia also was evaluated. Intravenous administration of thiamylal at a dosage of 10 mg/kg increased heart rate, systemic arterial, pulmonary artery, and central venous blood pressures, as well as cardiac output and arterial partial pressure of CO2 (PaCO2 ). The maximal rate of right ventricular pressure increase (RVdP/ dtmax), respiratory rate, and arterial partial pressure of Ο2 (PaO2 ) decreased, whereas arterial pH and systemic vascular resistance remained unchanged. Preanesthetic medication with diazepam prior to iv administration of thiamylal (6 mg/kg) did not change the pattern of this response, but diazepam did increase heart rate, cardiac output, and respiratory rate during the recovery period. Administration of acepromazine (0.1 mg/kg, iv) prior to administration of thiamylal increased heart rate and decreased systemic arterial and central venous blood pressures and systemic vascular resistance. Detomidine (10 μg/kg, iv), administered prior to thiamylal, decreased heart rate, cardiac output, and respiratory rate, and increased right atrial blood pressure. Administration of xylazine (0.5 and 1.0 mg/kg, iv) prior to thiamylal induced effects qualitatively similar to detomidine. Thiamylal decreased RVdP/dtmax and PaO2 in horses that received diazepam, acepromazine, detomidine, or xylazine.

Horses receiving 10 mg of thiamylal/kg, iv, or 0.1 mg of diazepam/kg, iv, prior to thiamylal (6 mg/kg, iv) had the most difficulty in attaining a standing position. Horses receiving 10 mg of thiamylal/kg, iv, or acepromazine, detomidine, or xylazine (1 mg/kg, iv) prior to thiamylal (6 mg/kg, iv) had the longest anesthesia time. Results indicated that bolus injections of thiamylal used to induce short-term anesthesia in horses increase heart rate, systemic arterial, pulmonary artery, and central venous pressures, as well as PacO2 , but decrease RVdP/dtmax, respiratory rate, and PaO2 . Further, the recovery process was improved by administration of acepromazine, detomidine, or xylazine, but not diazepam, as preanesthetic medication.

Free access
in Journal of the American Veterinary Medical Association

SUMMARY

The ventricular arrhythmogenic dose of epinephrine (ade) was determined in 6 dogs anesthetized with halothane alone or with halothane after injection of tiletamine/zolazepam (tz). Respiratory rate and tidal volume were controlled and sodium bicarbonate was administered to maintain arterial pH and blood gas values within reference range. Heart rate and arterial blood pressure were recorded during determination of the ade. The ade (mean ± sd) was no different during anesthesia with use of halothane alone (8.9 ± 4.3) than it was when injections of tz preceded administration of halothane (6.7 ± 2.8). Tiletamine/zolazepam was also administered iv immediately after determination of the ade during halothane-induced anesthesia. The tz administered in this manner did not alter the ade. Blood pressure and heart rate were significantly greater during infusion of epinephrine than immediately prior to infusion. The administration of tz did not alter blood pressure response.

The ade was also determined in 6 cats anesthetized with halothane preceded by administration of tz. The ade (mean ± sd) was 0.7 ± 0.23 μg/kg, a value similar to that reported for cats during anesthesia with halothane alone.

Free access
in American Journal of Veterinary Research

SUMMARY

The cardiovascular effects of xylazine and detomidine in horses were studied. Six horses were given each of the following 5 treatments, at 1-week intervals: xylazine, 1.1 mg/kg, iv; xylazine, 2.2 mg/kg, im; detomidine, 0.01 mg/ kg, iv; detomidine, 0.02 mg/kg, iv; and detomidine, 0,04 mg/kg, im. All treatments resulted in significantly decreased heart rate, increased incidence of atrioventricular block, and decreased cardiac output and cardiac index; cardiac output and cardiac index were lowest following iv administration of 0.02 mg of detomidine/kg. Mean arterial pressure was significantly reduced for various periods with all treatments; however, iv administration of 0.02 nig of detomidine/kg caused hypertension initially. Systemic vascular resistance was increased by all treatments. Indices of ventricular contractility and relaxation, + dP/dt and − dP/dt, were significantly depressed by all treatments. Significant changes were not detected in stroke volume or ejection fraction. The pcv was significantly reduced by all treatments. Respiratoiy rate was significantly decreased with all treatments, but arterial carbon dioxide tension did not change. Arterial oxygen tension was significantly decreased briefly with the 3 iv treatments only.

Free access
in American Journal of Veterinary Research

Abstract

Objective—To evaluate the cardiovascular effects of total IV anesthesia with propofol (P-TIVA) or ketamine-medetomidine-propofol (KMP-TIVA) in horses.

Animals—5 Thoroughbreds.

Procedures—Horses were anesthetized twice for 4 hours, once with P-TIVA and once with KMP-TIVA. Horses were medicated with medetomidine (0.005 mg/kg, IV) and anesthetized with ketamine (2.5 mg/kg, IV) and midazolam (0.04 mg/kg, IV). After receiving a loading dose of propofol (0.5 mg/kg, IV), anesthesia was maintained with a constant rate infusion of propofol (0.22 mg/kg/min) for P-TIVA or with a constant rate infusion of propofol (0.14 mg/kg/min), ketamine (1 mg/kg/h), and medetomidine (0.00125 mg/kg/h) for KMP-TIVA. Ventilation was artificially controlled throughout anesthesia. Cardiovascular measurements were determined before medication and every 30 minutes during anesthesia, and recovery from anesthesia was scored.

Results—Cardiovascular function was maintained within acceptable limits during P-TIVA and KMP-TIVA. Heart rate ranged from 30 to 40 beats/min, and mean arterial blood pressure was > 90 mm Hg in all horses during anesthesia. Heart rate was lower in horses anesthetized with KMP-TIVA, compared with P-TIVA. Cardiac index decreased significantly, reaching minimum values (65% of baseline values) at 90 minutes during KMP-TIVA, whereas cardiac index was maintained between 80% and 90% of baseline values during P-TIVA. Stroke volume and systemic vascular resistance were similarly maintained during both methods of anesthesia. With P-TIVA, some spontaneous limb movements occurred, whereas with KMP-TIVA, no movements were observed.

Conclusions and Clinical Relevance—Cardiovascular measurements remained within acceptable values in artificially ventilated horses during P-TIVA or KMP-TIVA. Decreased cardiac output associated with KMP-TIVA was primarily the result of decreases in heart rate.

Full access
in American Journal of Veterinary Research