Alfaxalone as a Total Intravenous Anesthesia Protocol in New Zealand White Rabbits (Oryctolagus cuniculus) Improves Cardiovascular Stability Compared to Isoflurane.

Abstract

Alfaxalone has been studied for anesthetic induction of rabbits with rapid onset and a short duration of action; however, it has been minimally evaluated as an option for anesthetic maintenance. This study compared alfaxalone-based total intravenous anesthesia maintenance protocols against inhaled isoflurane, the current standard for anesthetic maintenance in rabbits. Twenty-four male New Zealand White rabbits were assigned to 1 of 3 treatment groups: isoflurane alone, alfaxalone with buprenorphine, or alfaxalone with midazolam. All rabbits were premedicated with buprenorphine HCl (0.02 mg/kg SC) and induced with alfaxalone (6 mg/kg IM). Following intubation and with supplementation of 100% O2, rabbits were maintained for 1 h on either isoflurane (2.5%) or alfaxalone continuous rate infusion (CRI) (0.2 mg/kg/min). For rabbits on the alfaxalone CRI, boluses of buprenorphine HCl (0.01 mg/kg IV or SC) or midazolam (0.1 to 0.3 mg/kg SC) were given upon induction or adjunctively as needed dependent on positive tail-pinch responses that were conducted at timepoints t0, t15, t30, t45, and t60. Heart rate, invasive blood pressure, respiratory rate, end-tidal CO2, percent O2 saturation, and temperature were recorded every 5 min. Surgical plane of anesthesia was characterized by lack of positive response to a tail clamp and was reached in all anesthetic groups. Results showed significant reduction in heart rate of the alfaxalone groups while there was no significant difference in mean arterial pressure compared with the isoflurane groups. However, respiratory rate in the alfaxalone groups was decreased with associated increases in end-tidal CO2 levels. There were no significant differences noted between alfaxalone treatment groups. The results confirmed that CRI alfaxalone (total intravenous anesthesia) should be considered as a potential anesthetic alternative to isoflurane anesthesia in rabbits, although special attention to respiratory monitoring and management is warranted.