Cardiovascular effects, induction and recovery characteristics and alfaxalone dose assessment in alfaxalone versus alfaxalone-fentanyl total intravenous anaesthesia in dogs.

Objective: To compare cardiovascular effects and anaesthetic quality of alfaxalone alone or in combination with a fentanyl constant rate infusion (CRI) when used for total intravenous anaesthesia (TIVA) in dogs.

Study Design: Prospective, blinded, randomized, experimental study.

Animals: A group of 12 intact female dogs.

Methods: Following intramuscular dexmedetomidine (10 μg kg) and methadone (0.1 mg kg) administration, anaesthesia was induced intravenously with alfaxalone (2 mg kg) (group AP) or alfaxalone (2 mg kg) preceded by fentanyl (2 μg kg) (group AF). Anaesthetic maintenance was obtained with an alfaxalone variable rate infusion (VRI) started at 0.15 mg kg minute (group AP) or an alfaxalone VRI (same starting rate) combined with a CRI of fentanyl (10 μg kg hour) (group AF). The alfaxalone VRI was adjusted every 5 minutes, based on clinical assessment. Cardiovascular parameters (recorded every 5 minutes) and recovery characteristics (using a numerical rating scale) were compared between groups. A mixed model statistical approach was used to compare the mean VRI alfaxalone dose and cardiovascular parameters between groups; recovery scores were analysed using the Wilcoxon rank-sum test (α = 0.05).

Results: The mean CRI alfaxalone dose for anaesthetic maintenance differed significantly between treatments [0.16 ± 0.01 mg kg minute (group AP) versus 0.13 ± 0.01 mg kg minute (group AF)]. Overall heart rate, systolic, mean and diastolic arterial pressures were lower in group AF than in group AP (p < 0.0001, p = 0.0058, p < 0.0001 and p < 0.0001, respectively. Recovery quality scores did not differ significantly and were poor in both groups.

Conclusions And Clinical Relevance: In combination with a fentanyl CRI, an alfaxalone TIVA provides a cardiovascular stable anaesthesia in dogs. The addition of fentanyl results in a significant dose reduction. The quality of anaesthetic recovery remains poor.