Introduction: Stress response, whether exaggerated or insufficient can be detrimental in the critical care setting. Various drugs used in this setting are known to affect stress response.

Background: Alfaxalone and propofol are commonly used anaesthetics in emergency and critical care. Studies in a variety of species and with diverse designs have shown controversial results regarding the effects of both drugs on stress response. Alfaxalone and propofol effects on cortisol production have not been investigated in cats. Salivary cortisol measurements have been used as a noninvasive alternative to serum cortisol measurements.

Objective: To assess the effects of alfaxalone or propofol administration on salivary cortisol in healthy cats.

Design: Prospective, blinded, cross-over experimental study.

Methods: After undergoing one week of adaptation to single metabolic cages, fifteen male castrated cats were randomized to receive intravenous continuous rate infusion of alfaxalone (4–8 mg/kg/h) propofol (6–12 mg/kg/h), producing similar levels of sedation or control (buffered balanced isotonic crystalloid, 1.2 ml/kg/h) for 30 minutes. Salivary samples were collected at T 0, T 30’, T 1 h, T 3 h, T 6 h, T 12 h and T 24 h. The study was carried out in three intervention groups with a washout period of six days. Cortisol concentrations were measured using an in-house ELISA method. An area under the curve (AUC) was generated for the time points T 0 through to T 6 h.

Statistical analyses included one way repeated measures ANOVA of log data and Tuckey’s multiple comparison test using commercial software. Significance was set as p<0.05.

Results: No significant difference was found in the baseline AUC between groups (p=0.9410).

There was no significant difference in the AUC between the propofol group and the control group (p=0.1631). The AUC in the alfaxalone group was significantly higher compared to the control (p=0.0065) and propofol group (p=0.0471), respectively. T 12 h and T 24 h cortisol concentrations returned to baseline.

Discussion: In this study, alfaxalone increased short-term cortisol production compared to a control whereas propofol did not. Whether alfaxalone has a direct stimulatory effect on the hypothalamus-pituitary-adrenal axis, or acts indirectly remains unknown.

Conclusions: Alfaxalone increases salivary cortisol concentrations in healthy cats. Further studies in critically-ill cats are necessary to assess the clinical significance of these results.