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Effects of Alfaxalone Priming Before Induction in Cats

Rebecca Johnson, DVM, PhD, DACVAA, University of Wisconsin–Madison

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In the Literature

Lagos-Carvajal A, Queiroz-Williams P, Cremer J, et al. Effects of a priming dose of alfaxalone on the total anesthetic induction dose and cardiorespiratory function of sedated healthy cats. Am J Vet Res. 2020;81(11):850-855.


Injectable anesthetic induction agents can significantly alter patient physiology. For example, propofol and alfaxalone (even when titrated to effect for induction) can decrease systemic vascular resistance and blood pressure in cats.1-3 Further, both agents can cause respiratory depression and apnea.2,3 Thus, anesthetic procedures that minimize the total administered dose (eg, cardiopulmonary-sparing premedications, slow administration of the anesthetic induction agent, priming doses of the anesthetic induction agent) may help reduce these effects.

This study evaluated the cardiorespiratory effects and measured the total induction agent doses of alfaxalone in dexmedetomidine/methadone premedicated cats after administration of a priming dose of alfaxalone (0.25 mg/kg IV) or a control solution (0.9% saline; 0.025 mL/kg IV) over 60 seconds. After an additional 60 seconds, cats were given alfaxalone until tracheal intubation could be performed. Heart rate, mean arterial pressure (MAP), respiratory rate, tidal volume, and minute ventilation (among other parameters) were measured every 2 minutes after induction for 8 minutes. Cats primed with alfaxalone required significantly lower total alfaxalone than saline-primed cats (≈0.98 mg/kg vs ≈1.41 mg/kg, respectively). In addition, when considered over all time periods after induction, MAPs were significantly higher but heart rates were lower when alfaxalone versus saline was used as a primer. Overall tidal volume was also significantly reduced with alfaxalone priming, although minute ventilation did not differ between groups. No cats developed hypotension (MAP <60 mm Hg).

These data suggest that a small priming dose of alfaxalone administered over 60 seconds, which corresponded to ≈25% of the lowest recommended induction dose, before orotracheal intubation reduces the total amount of alfaxalone subsequently required; this may contribute to less hypotension associated with this induction agent in cats. Although these results appear promising in this sample of healthy cats, other factors may confound the results. For example, the effects of pre-existing pathology are unknown because cats with underlying conditions might be unable to mount compensatory physiologic responses. In addition, many cats are transitioned to inhalant anesthesia after alfaxalone induction, and these results may not hold true once the cardiorespiratory effects of inhalants are present. Further, blood pressure was measured noninvasively, which may not always reflect direct arterial pressure in cats.4 Despite these limitations, priming with alfaxalone before a bolus injection of alfaxalone and tracheal intubation may be a simple, clinically useful way to minimize overall dose and potentially deleterious effects (eg, decreased blood pressure, severe respiratory depression, including apnea).


Key pearls to put into practice:


In cats, alfaxalone for anesthetic induction is associated with decreased systemic vascular resistance and blood pressure, similar to other induction agents (eg, propofol).



Use of a slowly delivered priming dose of alfaxalone (over 60 seconds) before anesthetic induction with alfaxalone in cats reduces the total amount of anesthetic needed for orotracheal intubation and results in higher MAPs as compared with cats primed with saline.


Injectable anesthetic agent priming in cats is a simple, clinically useful technique associated with an overall reduction of the amount of anesthetic required, which may attenuate the deleterious effects of these agents.


For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

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