Administração intravenosa contínua de dexmedetomidina em caprinos – determinação da taxa de infusão mínima e efeitos fisiológicos, sedativo e analgésico.

Abstract

In order to determine the minimum rate of continuous intravenous infusion of dexmedetomidine in goats and its analgesic and sedative effects and on physiologic, hemogasometric, hematological, biochemical and electrocardiographic parameters, this thesis was divided into three chapters. In the prelude, a systematic review and metaanalysis was carried out in order to detail the cardiorespiratory alterations of ruminants under the action of dexmedetomidine. To this do so, two independent evaluators performed a broad research in the databases: Pubmed, ScienceDirect, Scielo, Google Scholar and PLOS One, using the combination of keywords: dexmedetomidine AND effect AND (goat OR sheep OR cow OR ruminant). The results showed that there are evidences that dexmedetomidine reduces heart rate, mean blood pressure, cardiac output and arterial oxygen tension in addition to increasing arterial carbon dioxide tension, considering pooled effect. In the second chapter, the average intensity of electrical stimulus required to elicit painful reaction in Moxotó breed goats and the minimum rate of intravenous infusion of dexmedetomidine that abolished the reaction to the harmful stimulus were determined. To determine the minimum intensity of the electrical stimulus, two electrodes were positioned on the right flank of the animal and the stimulus was started at 10 mA. The intensity was high in increments of 5 mA, until the moment a positive response to the stimulus was elicited. The mean trigger intensity was obtained by the arithmetic mean of the minimum intensities in which each animal reacted. The minimum infusion rate of dexmedetomidine that abolished the response to the trigger stimulus was determined by the arithmetic mean between the highest infusion rate that did not abolish the voluntary movement to the painful stimulus and that which abolished this movement in each animal, and finally, the arithmetic mean of all animals was obtained. Continuous intravenous infusion of dexmedetomidine at a dose of 2,1 μg/kg/h, without prior bolus, was able to abolish the voluntary response to the 21 mA electrical stimulus considered trigger in nonsedated goats. In the third chapter, the effects of intravenous continuous infusion of dexmedetomidine were evaluated at a dose of 2,1 μg/kg/h for 90 minutes in 10 goats, with no oxygen supply. Heart rate (HR), respiratory rate (ƒ), systolic, diastolic and mean blood pressure (SAP, DAP and MAP, respectively), rectal temperature (RT), partial oxyhemoglobin saturation (SpO2), ruminal motility (RM), sedation scores, muscle relaxation and analgesia, hemogasometric, hematological, biochemical and electrocardiographic parameters were recorded. There was a significant reduction in the following parameters: HR, DAP, RT, ƒ, SpO2, hematocrit, hemoglobin and red blood cells, and an increase in pH, in glycemia and QRS complex and QT interval durations. Only bradycardia represented clinical significance, but without repercussion in the other parameters. Sedation, analgesia and myorelaxation scores were satisfactory, although with prolonged latency period. There was no clinical relevance in the hematological and biochemical alterations evaluated. It can be concluded that the continuous infusion of dexmedetomidine in goats at the rate of 2,1 μg/kg/h without previous bolus promoted levels of sedation, muscle relaxation and analgesia appropriate to procedures performed in field condition, since associated with other analgesics or local anesthetics. There was no respiratory depression or hematological and biochemical impact; however the bradycardia observed implies contraindication in a nonhealthy patient, especially with hemodynamic instability. Thus, dexmedetomidine could be useful for surgical procedures, provided that the prolonged latency period, its impact on HR and the need for analgesic complementation are considered.