Cardiorespiratory and Hemodynamic Effects of Medetomidine or Xylazine with Atropine and Diazepam Premedication for Total Intravenous Anesthesia Induced and Maintained with Propofol/Fentanyl in Dogs Undergoing Surgery

The aim of this study was to compare the effects of different premedication protocols followed by a propofol/fentanyl TIVA on cardio-respiratory and hemodynamic changes in twenty-four dogs randomly divided into two groups (AMD-group: medetomidine, atropine and diazepam; AXD-group: xylazine, atropine and diazepam). Cardiorespiratory variables, acid-base indices, quality of sedation, induction, intubation and recovery were recorded throughout the experiment. Significant changes were observed for the pO₂ level, which was increased in the AMDgroup from 90 min. (*P< 0.05) to 120 min. (**P< 0.01) of anesthesia. This can be explained by a reduction of the administration rate of propofol/fentanyl TIVA and oxygenation initiated due to excessively deep anesthesia detected by an anesthetsiologist, leading to improved ventilation and increased pO₂. The pCO₂ (*P < 0.05) reached more preferable values during the first 30 min. and pH (**P< 0.01) was significantly improved within the first 60 min. in the AXD-group thanks to less depressant effects of xylazine. Within the first 30 min. of anesthesia a significant heart rate difference between the groups was accompanied with significantly higher BP (hypertension) in the AXD-group (10 min. ***P< 0.001, 30 min. **P< 0.01). This points to the possibility of atropine application only in the case of a tendency to bradycardia followed by hypotension. It can be concluded that xylazine is a better option for the premedication of a propofol/ fentanyl TIVA in dogs undergoing a prolonged surgical intervention, in spite of the fact that lower sedation scores were attained. We have detected significantly less adverse cardio-respiratory and hemodynamic effects of xylazine, and a shorter recovery time when compared to medetomidine