Chemical restraint and sedation in leporids

Leporids are a family of the order of lagomorphs including rabbits and hares, known for being easily stressed, panicked or traumatized. These species present major difficulties to being anesthetized safely, reporting unacceptable intra- and post-operative mortality with a variety of anesthetic techniques. A moderate to severe respiratory depression has been reported in leporids with almost any anesthetic molecule and combination, like ketamine/alpha2 agonists/ opioids (1, 2). As a consequence, lagomorph sedation and anesthesia always demand continuous administration of oxygen throughout the anesthetic procedure (1, 2, 3). In general, leporids exhibit peculiar and inconstant responses to anesthetic molecules displaying unreliable signs and reflexes as indicators of anesthetic depth. Sedation scales are normally used in non-cooperative humans and in animals. To assess the level of sedation and analgesia in leporids we modified a numeric rating scale including rabbit’s posture, loss of the righting reflex, palpebral reflex and reactions to other stimuli (Appendix 1) (3). The most popular anesthetic molecules used in lagomorphs include ketamine, medetomidine, benzodiazepines and opioids. In 2002 Hedenqvist et al. verified the level of sedation produced by administering intramuscular (IM) or subcutaneous (SC) ketamine/medetomidine or ketamine/butorphanol in rabbits. These Authors reported dose dependent effects, whose onset was surprisingly unaffected by the administration route (1). As in other species, medetomidine produces mild to marked bradycardia at sedative doses in lagomorphs, and when associated with fentanyl and midazolam a 35% drop compared with conscious animals has been reported (2). Several factors play key roles on the absorption and distribution of anesthetic drugs in lagomorphs, among which stress and injection route significantly affect pharmacodynamics. Standard drug administration routes such as IM and intravenous (IV) achieve comparable planes of anesthesia, but their performance produce distress in lagomorphs, while SC injection is better tolerated but lacks predictable absorption and action onset (4). Multiple IM injections of anesthetic molecules do increase absorption rate but can be harmful and stressful (4). Alternative effective and well-tolerated routes for drug administration in rabbits have been reported in literature, such as transmucosal and intranasal routes (5). Considering the above drawbacks, we developed a powerful sedation protocol for hares and rabbits aimed at reducing distress and at preventing panic in captive, untamed subjects (3). A combination of dexmedetomidine (0.1 mg/kg) midazolam (2 mg/kg) and butorphanol (0.4 mg/kg) was administered via transnasal route by means of a thin catheter advanced to the nasopharyngeal region, in a group of 8 hares and two groups of 8 rabbits. A rapid, deep and flexible analgo-sedation ensued after 30-120’’ lasting about 70 minutes (3). Prolonged recovery could be prevented because the effects of each component can be reversed at any time according to needs (3). Leporids sedation is a challenging practice due to species peculiarities. Fitting anesthetic equipment, a sound drug choice and an observant anesthetist improve lagomorph’s anesthetic safety. Chemical restraint by a mixture of agents allows the synergistic potentiation of each component, reducing their individual doses and side effects.