Assessment of the effects of intramuscular administration of alfaxalone with and without medetomidine in Horsfield's tortoises (Agrionemys horsfieldii)

Abstract

Objective: To characterise four different intramuscular (IM) anaesthetic protocols, two with alfaxalone and two with alfaxalone in combination with medetomidine in terrestrial tortoises. Study design: Blinded, randomized, cross-over experimental study. Animals: Nine healthy adult male Horsfield's tortoises (Agrionemys horsfieldii). Methods: Each tortoise was randomly assigned to one of four different protocols: 1) 10 mg kg-1 alfaxalone; 2) 10 mg kg-1 alfaxalone + 0.10 mg kg-1 medetomidine; 3) 20 mg kg-1 alfaxalone; and 4) 20 mg kg-1 alfaxalone + 0.05 mg kg-1 medetomidine. During the experiment, the following variables were recorded: heart rate; respiratory rate; peripheral nociceptive responses; muscle strength; ability to intubate; palpebral, corneal and tap reflexes; and cloacal temperature. Results: Protocols 1 and 2 resulted in moderate sedation with no analgesia, and moderate to deep sedation with minimal analgesia, respectively. Protocols 3 and 4 resulted in deep sedation or anaesthesia with variable analgesic effect; these two protocols had the longest total anaesthetic time and allowed intubation in 6/9 and 8/9 tortoises respectively. The total anaesthesia/sedation time produced by alfaxalone was significantly increased (p < 0.05) by the addition of medetomidine. There were no significant differences regarding time to plateau phase and duration of plateau phase. Baseline heart rate of 53 ± 6 beats minute-1 decreased significantly (p < 0.05) with all protocols, and was lower (p < 0.05) in protocols 3 and 4. Heart rate increased after atipamezole administration, but the increase was transient. In two tortoises, extreme bradycardia with no cardiac activity for 10 minutes was observed with protocols 3 and 4. Conclusion and clinical relevance: Alfaxalone 10 and 20 mg kg-1 IM can be used for sedation for non-painful procedures. Alfaxalone in combination with medetomidine can be used for deeper sedation or anaesthesia, but the observed respiratory and cardiovascular depression may limit its use. © 2013 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesia and Analgesia.