Evaluation of antinociceptive and sedative effects of methadone or morphine combined with ketamine-midazolam in rabbits undergoing elective orchiectomy
DOI:
https://doi.org/10.5380/avs.v29i4.97168Keywords:
anesthesiology, lagomorphs, nociception, opioids, sedationAbstract
Abstract: The objective of the study was to evaluate the effects of adding methadone or morphine to an anesthetic protocol combined with ketamine and midazolam in rabbits undergoing elective orchiectomy. Twenty-four animals were used, evenly distributed into three groups, receiving 15mg/kg of ketamine and 2mg/kg of midazolam (GCON), associated or not with 2mg/kg of methadone (GMET) or morphine (GMOR), intramuscularly. Cardiorespiratory parameters, blood gas analysis, and sedation depth were recorded at baseline (T-15); 15 minutes after premedication (T0); 5 minutes after local block (T1); clamping of the first spermatic cord (T2); second (T3), and immediately after scrotorraphy (T4). Sedation depth was assessed via posture (PS); resistance to dorsal recumbency (RD); jaw tone (JT); palpebral reflex (PR); total sedation score (TS); muscle relaxation (MR), and stimuli response (RS). The inclusion of a µ-agonist opioid enhanced sedation quality without negatively affecting anesthetic recovery. Results showed that methadone provided deeper sedation and greater respiratory depression, while morphine had a similar but less pronounced effect. GMET exhibited a significant reduction in respiratory rate (p<0.0001) and an increase in PaCO2 (p<0.0001), indicating more pronounced respiratory depression compared to the other groups. HR remained within normal limits for GMOR and GMET, whereas GCON showed a significant increase (p=0.0221). No significant changes in blood pressure or rectal temperature were observed between groups. Sedation quality was significantly higher in GMET compared to GCON (p=0.0018). It is concluded that opioids improved sedation quality without compromising cardiovascular stability, though oxygen therapy was required due to respiratory depression, particularly with methadone.
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