Avaliação da analgesia pós-operatória da dexmedetomidina isolada e associada à morfina quando utilizada na medicação pré-anestésica em cadelas submetidas à ovarissalpingohisterectomia eletiva

Abstract

Background: α-2-agonists and opioids are commonly used on preemptive analgesia in small medicine. Dexmedetomidine is an α-2-agonist used as sedative, muscle relaxant and analgesic. The aim of the present study was to evaluate, through Glasgow modified pain scale and Melbourne pain scale, the analgesic efficacy of 5 μg/kg dexmedetomidine and its possible potentiation in association with 0.3 mg/kg morphine when used as a preanesthetic medication in bitches undergoing elective ovariosalpingohisterectomy. Materials, Methods & Results: Twenty bitches were used in this study, weighing between 5 and 15 kg, age between 1 and 6 years and classified as ASA I according to the American Society of Anesthesiology. The animals were housed in kennels for 24 h before the experiment to set up and interact with the trained and blinded observers. During the experiment, the bitches were allocated in two groups (10 bitches / each) who received preanesthetic medication with isolated 2 dexmedetomidine (5 μg/kg - GD) or dexmedetomidine associated with morphine (0.3 mg/kg - GDM) intramuscularly (IM). After 30 min they were submitted to anesthetic induction with propofol dose-effect and general inhalation anestesia, with isoflurane, for elective ovariosalpingohisterectomy, procedure with an average duration of 45 min. The bitches were evaluated before 5 min of the treatments and 1, 2, 4, 8, 12 and 24 h after extubation through the Glasgow Scale Modified (GSM), Melbourne Scale (MS) and Dobbins Sedation Scale (DS). If the GSM score was higher than 3.3, an analgesic rescue of morphine (0.5 mg/kg – IM) was administered. It could be observed an increase in the scoring of the pain scales in both groups from the T1, with significant difference only of the T1 in relation to the T0 in the GSM of GDM. Two rescues were performed in T1 of GD and three rescues in T1 and one rescue in T3 of GDM. There was no significant difference between the groups in relation to this variable, as the result of P=0.62. Discussion: Based on the results of this study, dexmedetomidine (0.5 μg/Kg – IM) does not have adequate analgesic effect for use in preemptive analgesia of bitches submitted to elective OSH due to the high number of analgesic rescues. A small increase in GSM and MS scores from T1 can be expected compared to values prior to the surgical procedure since there was no nociceptive stimulation. This increase was only significant in T1 of GDM, moment of greatest rescue number (n = 3). The absence of significant difference between the groups proves that the analgesic effect of dexmedetomidine was not potentiated by the association with morphine at the dose and route used in this experiment. Although morphine is widely used and proven to be effective for the surgical procedure of OSH, both when used alone and in combination with other drugs, this fact has not been proven in the present study. This fact may have occurred due to the low dose of dexmedetomidine used or due to its short duration. Therefore, dexmedetomidine at the dose used as preanesthetic medication did not produce an adequate analgesic effect in the postoperative period of bitches submitted to elective OSH. The 3 effects of the same were not potentiated by the association with morphine, at the dose used. Not being recommended for postoperative analgesic control of elective OSH in bitches. However, further studies are needed to better evaluate the analgesic effect of this α-2-agonist.