Chemical Restraint of Camelids
Ketamine Stun
The Ketamine Stun is basically the addition of a small dose of ketamine to any injectable chemical restraint technique. I initially developed the Ketamine Stun technique in the early 1990s to cover my limited handling abilities with regard to cats. My first exposure to camelid patients occurred when I left equine practice to teach at Ohio State. Their frequent recalcitrant behavior quickly led to experimentation with low-dose ketamine protocols to improve the level of patient cooperation during diagnostic and therapeutic procedures. Success was immediately evident, and the technique became wildly popular with the food animal clinicians, residents, and students charged with the care of these patients.1 Because of the success in camelid patients, the Ketamine Stun technique was adjusted for use in ruminants (lower dose of xylazine) and proved to be just as useful.2 Equine applications have proven more challenging. Dramatic improvement in cooperation evident a minute or two after an IV bolus of ketamine is administered to patients that were totally uncooperative under the prior detomidine–morphine sedation suggests the potential of the Ketamine Stun technique in horses.3,4 Unfortunately, the effective chemical restraint levels of ketamine are not far removed from those that produce instability in horses. The Ketamine Stun technique has been shown to reduce stress response to castration and dehorning in calves.5,6
α2-adrenergic agonists possess potent sedative and analgesic effects. Opioids are typically thought of as analgesic drugs, but they possess central nervous system (CNS) effects, which, when combined with a tranquilizer or sedative, produce a greater level of mental depression. Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist that possesses potent analgesic effects at subanesthetic doses.7 Ketamine was initially included in the stun technique for its analgesic properties but likely contributes to the mental aspects of the enhanced cooperation exhibited by patients under the influence of the Ketamine Stun technique. By combining drugs, smaller doses of the individual components can be used while still achieving the desired level of patient control. Dosing must be more conservative when using the ketamine stun technique in standing patients. This limits the degree of systemic analgesia relative to what can be achieved in recumbent patients but still provides improved patient cooperation when compared with more traditional methods of standing chemical restraint in both ruminants and horses.
In ruminants and camelid patients, I use a combination of xylazine, butorphanol, and ketamine. In equine patients, I use detomidine, morphine, and ketamine. Morphine is used to provide analgesic relief in food animal patients and is much less expensive than butorphanol. I have used morphine (0.05–0.06 mg/kg) in ruminant stuns. In standing adult cattle stuns, a similar level of cooperation is achieved with either opioid, but patients appear less obtunded when morphine is used. Some practitioners may find the obtunded appearance useful because it allows them to monitor decay over time in the level of chemical restraint. Deterioration in the level of patient cooperation also may be used to determine when supplemental drug administration would be required. The systemic analgesia provided by the Ketamine Stun technique is not limited to purely chemical restraint applications. Small doses of ketamine (0.22 mg/kg, IV) layered over a mild level of xylazine sedation provide dramatic short-term (15 minutes) relief from moderate colic pain in horses.8
Intravenous Ketamine Stun
TABLE 45-1
IM, Intramuscular; IV, intravenous.
*Doses of the individual drugs are relatively small, which permits them to be safely rounded up in most instances (e.g., 14 mg becomes 15 mg; 17 mg becomes 20 mg; etc.). Rounding makes drawing doses and the record keeping involved easier. A 1-mL syringe should be used, which requires the use of large animal xylazine (100 mg/mL).
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