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Background: Epidural administration of opioids and α2-adrenergic agonists allows the use of smaller doses when administered by other routes, providing analgesia during trans and post-anesthetic periods, reducing side effects and postoperative stress. Sufentanil in higher doses caused minimal hemodynamic changes in dogs. When given epidurally, clonidine produces analgesia without motor block by a non-opioid mechanism of action. The aim of this study was to evaluate the quality and duration of analgesia as well the cardiorespiratory changes resulting from administration of epidural clonidine or sufentanil in dogs anesthetized with halothane. Materials, Methods & Results: Twenty adult health dogs were used divided into two groups, clonidine (CLO) group and sufentanil (SUF) receiving 150 µg and 50 µg respectively epidural. After induction with thiopental and propofol in a mixture of equal parts (0.8 mg/kg), general anesthesia was maintained with halothane in a Bain circuit for further epidural administration of drugs. Heart rate and cardiac rhythm, respiratory rate, tidal volume, min volume, systolic arterial pressure, body temperature, oxygen saturation of oxyhemoglobin, halothane vaporization were evaluated at times T0 (baseline) and every 15 min until the end of the procedure (T1, T2, T3, T4). The arterial blood gas analysis was performed at T0G (baseline) and 30 min and 2 h after epidural (T1G, T2G) evaluating pH, PaO2, PaCO2, BE, HCO3 - and TCO2. Postoperative analgesia was assessed by the scale of Firth & Haldane (1999) every hour for five hours, starting one hour after the surgery. All parametric variables were analyzed by use of a 1-way ANOVA for repeated measures, followed by a Dunnet test to compare all sample collection times with baseline data (0 min). For comparisons among groups, for each time, test t was used. Differences were considered significant when P < 0.05. The results showed a significant reduction in heart rate after 15 min lasting for 60 min with a reduction in SAP, but no signs of hypotension. A reduction in respiratory rate was also observed in the SUF group and vaporization of halothane in both groups with increase in SpO2. There was no difference in cardiac rhythm and tidal volume, there was only an increase in minute volume at 60 min in the SUF group. Body temperature also decreases at all times. Discussion: The reduction in heart rate was observed since sufentanil have discrete sympatholytic and vagotonic activity and α2-adrenergic agonists may also cause bradycardia by vagomimetic effect. The drugs used can also cause a reduction in blood pressure, but hypotension was not observed in this study, corroborating with several authors. The lipophilic opioids suffer greater absorption by the blood vessels in the epidural region resulting in peak plasma concentration and early respiratory depression, while the α2-adrenergic agonists cause respiratory depression secondary to central nervous system depression. The observed reduction in vaporization is due to potentiation of drugs used. Analgesia in the intraoperative period can be proved since tachycardia, tachypnea, or hypertension during clamping of the ovarian pedicles was not observed and in the immediate postoperative period, both drugs proved effective with Firth & Haldane numerical scale. The doses employed by epidural reduced the need for halothane demonstrating intra-operative analgesic effect. Furthermore, sufentanil caused severe respiratory depression, however it is suggested greater efficacy when compared to clonidine in the immediate postoperative period. [ABSTRACT FROM AUTHOR]

Background: α2-adrenergic agonists stand out for their intense acting in the respiratory and hemodynamic parameters, which sometimes aggravates the already compromised patient. Clonidine is widely used in humans due to its sedation, minimal hemodynamic and respiratory changes and for analgesia. In veterinary medicine, clonidine has been studied recently specially for epidural analgesia. The study aimed to evaluate the physiological changes and the sedative effect of the intramuscular administration of clonidine in dogs, once there are no reports of intramuscularly use of clonidine. Materials, Methods & Results: Six adult healthy mongrel dogs (5 females and 1 male) were used, after hematological evaluation (complete hemogram) with an average weight of 12 ± 2.5 kg. The animals were randomly divided into four groups with a minimum interval of 10 days, where: control group (GC) received 5 mL of saline IM with the other three groups receiving different doses of clonidine, 5 µg/kg (CLO5), 15 µg/kg (CLO15) and 30 µg/kg (CLO30) intramuscularly. Heart and respiratory rate, oxygen saturation, systolic arterial pressure, rectal temperature and sedation by analogical descriptive scale were evaluated before administration (baseline), after 5 and 15 min and at 15 min intervals for a period of 90 min. For each group, all parametric variables were analyzed by use of a 1-way ANOVA for repeated measures, followed by a Dunnet test to compare all sample collection times with baseline data (0 min). For comparisons among groups, for each time, 1-way ANOVA was performed, followed by a Tukey test. Score sedation non parametrical variable were analyzed by Friedman test, followed by Dunn's. Differences were considered significant at P < 0.05. The results showed that clonidine caused a reduction in heart rate 5 min after administration lasting for 90 min with the three doses studied, with a reduction in systolic arterial pressure but with no signs of hypotension. There were respiratory reduction, but between normal values and decreased rectal temperature was observed, with no changes in oxygen saturation. Sedation scores were higher with the higher doses of clonidine. Discussion: The cardiovascular and respiratory effects of administration of α2-adrenergic agonists are characteristic, noting reduction in heart rate which is due mostly to decrease in sympathetic nervous system tonus, which was observed in all treated groups where a significant reduction in heart rate in a gradual manner and tending to be dose dependent since lower values were observed with higher doses, reaching bradycardia (HR <60 bpm) in group CLO30. Another common alteration of α2-adrenergic agonists are the changes in blood pressure, such as hypertension and subsequent hypotension and respiratory depression, frames not observed in this study. Reduction in body temperature is especially due to decrease in muscular activity as well interfering with thermoregulatory mechanisms. Another factor that may contribute is the room temperature, which remained close to 25 C. Intramuscular administration of clonidine caused light and mild sedation with the studies doses and cardiorrespiratory changes should be used in healthy animals. Further studies should be conducted with associations of other pharmacological class to promote a more pronounced level of sedation. [ABSTRACT FROM AUTHOR]