Alternative Techniques for Alfaxalone Anesthesia Induction in Dogs and Cats
Alfaxalone is a neuroactive synthetic steroid (Brewster & Bodor, 1990) that produces anesthetic induction with dose- and speed-dependent cardiorespiratory depression in dogs and cats (Chiu et al. 2016; Warne et al., 2015). At clinical doses in unpremedicated dogs (2 mg kg-1) and cats (5 mg kg-1), alfaxalone induces a mild decrease in systemic vascular resistance, systemic blood pressure (Muir et al., 2009; Muir et al., 2008), apnea, hypoventilation, and hypoxemia (Muir et al. 2009; Muir et al., 2008). The cardiorespiratory side effects from alfaxalone induction could be prevented by reducing the total dose of alfaxalone necessary to produce general anesthesia. Therefore, the overall objective of this research dissertation was to investigate the reduction of alfaxalone induction dose by using it in two alternative anesthesia induction techniques, as follows: 1- priming principle of alfaxalone, in dogs and cats, and 2- co-induction of midazolam with a low dose of alfaxalone, in cats. This study also aims to investigate the cardiorespiratory effect of these alternative techniques of induction in dogs and cats.
Priming principle (Djaniani & Ribes-Pastor, 1999) consists on the administration of a pre-calculated low dose of an induction agent, administered prior to the following dose administration of the same induction agent until anesthesia is achieved (Kataria et al., 2010). The present study used priming principle with alfaxalone IV to achieve tracheal intubation in dogs and cats premedicated with dexmedetomidine and methadone. As results, the total dose of alfaxalone was significantly reduced by 27% in dogs and 25% in cats. Cardiorespiratory depression was not observed during the study.
Co-induction is the concomitant administration of two or more drugs with additive or synergistic effect (Sdrales & Miller, 2013). In humans, this induction technique has been well described using midazolam (Liao et al., 2017). The present study investigated the effective dose (ED50) of midazolam to be used as co-induction with alfaxalone in cats. It was determined that the ED50 of midazolam is 0.08 ± 0.04 mg kg-1 when co-administered with a low dose of alfaxalone (0.25 mg kg-1) in premedicated cats with methadone and dexmedetomidine.