Potential use of dexmedetomidine for different levels of sedation, analgesia and anaesthesia in dogs

Abstract

A combination of drugs may be preferred over the use of a single agent to induce deep sedation. A synergistic interaction between the drugs reduces the dose requirements of the drugs thereby minimising the unwanted side effects associated with each drug and improving recovery. The present study was undertaken to evaluate the suitability of dexmedetomidine and dexmedetomidine in combination with midazolam-fentanyl or midazolam-fentanyl-ketamine for different levels of sedation, analgesia and anaesthesia in dogs. In a prospective, blinded, randomised clinical trial, 12 mixed breed dogs were divided into three groups. Animals of Group I were injected with dexmedetomidine 20 μg/kg. Animals of Group II received 20 μg/kg dexmedetomidine + 0.2 mg/kg midazolam + 4 μg/kg fentanyl and animals of Group III were administered with 20 μg/kg dexmedetomidine + 0.2 mg/kg midazolam + 4 μg/kg fentanyl + 10 mg/kgketamine. All the drugs were given simultaneously via the intramuscular route. Jaw relaxation, palpebral reflex, pedal reflex and response to intubation were recorded and graded on a numerical scale. Values of heart rate, respiratory rate, rectal temperature and mean arterial pressure were recorded at baseline and then at predetermined intervals up to 120 min. Onset of sedation time, onset of recumbency time, time to return of righting reflex, standing recovery time and complete recovery time were recorded. Maximal muscle relaxation, sedation and analgesia were observed in animals of Group III, which was followed in decreasing order by Groups II and I. Heart rate decreased significantly (P < 0.05) after administration of drugs in Groups I and II but a significant (P < 0.05) increase was recorded in Group III. Respiratory rate decreased significantly (P < 0.05) in all the groups. Rectal temperature decreased non-significantly in all the groups. Mean arterial pressure initially increased significantly (P < 0.01) in Groups I and III followed by a decrease in Group I, but in Group III it remained above the base line. In Group II, MAP decreased throughout the study period. Onset of sedation time and onset of recumbency time were significantly (P < 0.05) shorter in Group III as compared to Group I. Time to return of righting reflex, standing recovery time and complete recovery time did not differ significantly between the groups. It is concluded that dexmedetomidine provides a reliable moderate sedation and analgesia. Addition of midazolam and fentanyl enhances sedation, analgesia and muscle relaxation induced by dexmedetomidine. Addition of ketamine produced deep sedation and complete anaesthesia with lesser cardiopulmonary depression. Thus, dexmedetomidine can be used safely in combination with midazolam, fentanyl and ketamine for different levels of sedation, analgesia and anaesthesia in dogs.