Bonnie D. Wright, DVM, DACVAA
Approach to anesthesia, sedation, and analgesia in wild vs. domesticated animals is on a continuum. Rather than lumping entirely based upon species, I prefer to think about whether a patient is amenable to a titrated approach of anesthesia or requires a ‘big hammer’ that takes the animal very quickly through the stages of anesthesia and renders them unconscious as fast as possible.
Examples of the grey zone: aggressive domesticated cat vs. injection trained lioness.
Aside from behavior training that is blessedly making its way into zoo animal management, most exotic exotics are in danger of hurting themselves or others if anesthesia isn’t swift and strong. Therefore, the inherent risk of anesthetic drugs becomes relatively less threatening/more manageable than the alternative (titration approach). This will be the aspect that I discuss today, and within this paradigm, only drugs that can be absorbed IM are addressed.
Four major classes of drugs in the ‘big hammer’ approach to anesthesia:
1. Alpha-two agonists exert agonist activity at central and peripheral alpha-2 adrenergic receptors, which result in a decrease norepinephrine from adrenergic terminals in CNS and periphery. The cause sedation, decreased sympathetic activity, analgesia, vasoconstriction, bradycardia, decrease contractility, decrease perfusion. Species variation in dose generally combined.
2. Opioids - ultra-potent and others: µ receptor subtypes mediate supraspinal analgesia, euphoria, dependence, tolerance, respiratory depression (dose dependent), hypothermia, bradycardia, miosis, increased sphincter tone (urinary retention, constipation, pylorus), altered GI motility, vomiting. ĸ receptor subtypes mediate spinal analgesia, sedation, and limited respiratory depression.
3. Cyclohexamines (ketamine, tiletamine): Antagonize the NMDA receptor. Some areas of the CNS are depressed (neo corticothalamic) while others are stimulated (limbic). Activity is mediated in part by antagonizing the NMDA receptors in the brain and spinal cord. This activity also moderates up-regulation of the pain response (wind-up) and inhibits glial activation and hyperactivity.
4. Neurosteroids (alfaxalone): Recently approved for dogs - growing data in zoo and wildlife. Currently the concentration is too dilute, and it is not available at wildpharm.com. However, for an IM compatible drug, this has significant cardiovascular and respiratory sparing effects. Awaiting more concentrated formulation - so far reported use in deer.
Additions (modify but do not provide profound effects, in most cases):
Benzodiazapines are GABA receptor agonists in the central nervous system, decreasing CNS stimulation and activity. They also provide muscle relaxation via internuncial neurons in the spinal cord.
1. They are anti-convulsive and create minimal cardiopulmonary effects.
2. Unfortunately, in veterinary medicine they also tend to be ineffective tranquilizers when used alone in most species (except pigs, neonatal foals, goats and sheep). Severe excitation and mania are likely unless the animal is already sedate from disease or other drugs.
3. These drugs are most commonly use as adjucts to other drugs, either for premedication of ill patients, or to augment induction with most other drugs.
a. Highly protein bound, hepatic metabolism, renal elimination.
b. Diazepam is non-soluble and comes formulated in propylene glycol- a vascular irritant. IM absorption is slow and unpredictable. Long-term IV administration may result in thrombophlebitis and scarring. Occasional reactions to propylene glycol are reported (hypotension, shock).
c. Midazolam is more potent than diazepam, is water soluble, and may be given by any route.
d. Telazol is formulated with tiletamine (a dissociative drug) and zolazepam. Zolazepam is not available as an isolated drug.
Butyrophenones: formulations compounded and provided by zoopharm.
Droperidol, azaperone, haloperidol: Potent dopamine receptor antagonists with mild anti-histamine and serotonin antagonism. Anti-psychotic properties possible.
Analgesic considerations in zoo animals:
Improving data in many zoo species
Administration challenges, solutions
- Non-drug options - acupuncture, motion