The effect of body condition on alfaxalone induction dosage requirement in dogs

Alfaxalone is commonly used in veterinary anesthesia for the induction of general anesthesia (GA) in dogs. However, it has been associated with dose-dependent cardiovascular depression. Therefore, the administration of liposoluble, intravenous (IV)-administered injectable induction agents, such as alfaxalone, is recommended to be based on the dog's lean body mass (LBM).

To determine the influence of body condition score (BCS) on IV alfaxalone dose requirements to achieve endotracheal intubation in dogs.

Prospective clinical study. A group of 34 dogs undergoing GA for diagnostic and/or surgical procedures, body weight (BW) > 4 kg, BCS > 2, age 1-14 years, American Society of Anesthesiologists (ASAs) classification I-III. Dogs were allocated to two different groups according to their BCS: non-overweight group (NOW) BCS: 3-5 and over-weight group (OW) BCS: 6-9. All dogs were premedicated IV with methadone 0.2 mg kg^-1, and anesthesia was induced by a slow IV infusion of alfaxalone at 1 mg kg^-1 minute^-1, delivered with a syringe driver, until loss of jaw tone and no/minimal gagging reflex sufficient to allow endotracheal intubation was achieved. The total dose of alfaxalone and the occurrence of post-induction apnoea were recorded.The Shapiro-Wilk test was performed to test for normality. A Chi-square test was performed to compare the incidence of post-induction apnoea between groups, and the Mann-Whitney U test was performed to compare the induction dose of alfaxalone between groups. A p-value < 0.05 was considered statistically significant.

The mean dose ± standard deviation of alfaxalone in NOW was 2.18 ± 0.59 mg kg^-1, and in OW, it was 1.63 ± 0.26 mg kg^-1 (p = 0.002). The sedation score did not differ between groups. Postinduction apnoea (PIA) occurred in 6 of 17 animals in NOW and 15 of 17 in OW (p = 0.002).

The dose of IV alfaxalone per kg of total body mass required to achieve endotracheal intubation was lower in overweight dogs, suggesting that LBM should be considered when calculating IV anesthetic doses. The incidence of post-induction apnoea was higher in overweight/obese dogs with alfaxalone administered at a rate of 1 mg kg^-1 minute^-1.