Chemical Restraint of Ruminants – Ketamine Stun Technique

The Ketamine Stun is simply the addition of a small dose of ketamine to any injectable chemical restraint technique. I initially developed the Ketamine Stun technique in the early 1990's to cover my limited cat handling abilities. My first exposure to camelid patients came when I left equine practice to teach at Ohio State. The recalcitrant behavior they frequently exhibited 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). I named this technique the Ketamine Stun (aka Ket Stun) because of the stunned effect it produced in patients when administered at doses that produce recumbency. These patients appear to be awake, but seem oblivious to surroundings and procedure being performed. The intravenous effect is quite brief (approximately15 minutes) and patients typically stand and appear fairly normal at that time. I initially referred to this state as semianesthetized, but perhaps chemical hypnosis is more appropriate. Because of the success in camelid patients the Ketamine Stun technique was adjusted for use in ruminants (less xylazine) and proved to be just as useful (2, 3). Equine applications have proven more challenging. Dramatic improvement in cooperation evident a minute or two after the IV bolus of ketamine is administered in patients that were totally uncooperative under the prior detomidine-morphine sedation suggests the potential of this technique. Unfortunately, the effective sedation-ketamine levels are not far removed from those that produce instability. Alpha2-adrenergic agonists possess potent sedative and analgesic effects. Opioids are typically thought of as analgesic drugs, but they possess central nervous system effects that when combined with a tranquilizer or sedative produces a greater level of mental depression. Ketamine is a N-methyl-D-aspartate (NMDA) receptor antagonist that possesses potent analgesic effects at subanesthetic doses. 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 one is able to use smaller doses of the individual components 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 ruminants and camelid patients I typically use a combination of xylazine, butorphanol, and ketamine. In equine patients I generally use detomidine, morphine, and ketamine. Morphine is used to provide analgesic relief in food animal patients and is much cheaper than butorphanol.