Updated: Jul 21, 2019
In this post, Dr. Erik Hofmeister discusses his approach to chemical restraint of aggressive animals.
We’ve all been there. You’re at a cabin in the woods with your friends when you hear some wolves howling at night. Suddenly, a werewolf crashes through a window and attacks your group. Being a well-prepared anesthetist going to werewolf-infested woods, you flip the cap off your needle and plunge a syringe of drugs into its thigh. It backhands you into the kitchen while your friend fends it off with a chair. The werewolf’s movements become slower, its snarls becoming slurred, and finally it falls face-first onto the floor in a relaxed, unconscious heap. You dispose of it with a silver knife at sunrise. But what was in the syringe?
I have one guiding light when it comes to sedating aggressive animals: “Aggressive animals are like terrorists: we don’t negotiate with them.”
Very often I see clinicians using “gentle” doses of sedatives on aggressive animals and being unsuccessful in getting them sedated. The therapeutic index on our sedative drugs is massive. I say go big or go home. Failing to start with an appropriate dose and combination from the outset leads to stressed out patients, stressed out staff, and an unsuccessful sedation. Just hit them with a big drug hammer from the outset.
Here are my favorite chemical restraint protocols for aggressive carnivores (cat, dog, bear, etc.):
I use ketamine 10 mg/kg, dexmedetomidine 0.02 mg/kg, and opioid type and dose of your choice. This is my go-to protocol because it’s highly effective (I had one cat not sedate on this: I doubled everything and stuck him again and he was out), it is inexpensive, and provides good cardiorespiratory stability in healthy patients.
The only drawback may be the volume in larger animals. In a 20kg dog, this will be ~3.2mL if you use butorphanol 0.2 mg/kg.
I use tiletamine/zolazepam 4 mg/kg, dexmedetomidine 0.02 mg/kg, and opioid type and dose of your choice. I rarely use tiletamine/zolazepam, mostly due to the expense. The only advantage over the prior protocol is the volume. For a 20kg dog, this will be ~2mL using the above butorphanol dose.
I use ketamine 10 mg/kg, midazolam 0.5 mg/kg, and opioid type and dose of your choice. This is my go-to if I want to avoid dexmedetomidine for whatever reason, for example, if a dog has a known heart murmur and the increae in systemic vascular resistance caused by dexmed might be deleterious to cardiac output.
I use alfaxalone 3 mg/kg, midazolam 0.5 mg/kg, and high dose opioid (e.g. butorphanol 0.4 mg/kg, hydromorphone 0.2 mg/kg). One of my sayings is, “Aggressive sick patients are why God gave us alfaxalone.” If you have a cat with HCM or CRF or a patient you are worried about giving ketamine to, this is a nice protocol. It’s not as reliable as the others: depending on the patient , you may want to increase the alfaxalone dose. In my hands it has about an 80% success rate. Volume gets to be an issue with animals over about 5 kg.
The above combinations are great for healthy through sick patients, as noted. What about brachycephalic dogs? I always worry about heavily sedating these patients, because they’re already only able to breathe by the grace of God. My typical choice is high-dose opioid, preferably methadone at 1 mg/kg. have used dexmedetomidine successfully, but I always worry about it. One of the Uga dogs was aggressive - he even bit his orthopod- so we had to sedate him each time. Each time I thought, “I’m going to be the one that kills Uga.” How do you handle that?
Any time you sedate an aggressive animal, you should have a conversation with the client. Explain that you will use the safest option available but, given the limited ability to do a physical exam or obtain bloodwork, and the high degree of stress the patient is experiencing, they are a higher risk patient than normal. I feel this is doubly true of mean brachycephalic dogs. I think the options above are good, and I have had good success with them, but no protocol is perfect and the client should understand the higher risk involved.
Also, be prepared to intervene to stabilize the patient when you are heavily sedating or providing chemical restraint. It is a slippery slope from fully aware to fully dead, and it is possible that a patient might unexpectedly stop breathing or become very hypotensive and need you to support their respiratory and/or cardiovascular systems. Have flow-by oxygen available, be ready to intubate, and have some sort of objective monitor such as a pulse oximeter or Doppler flow probe to keep on the patient. It also makes sense to have reversal agents at hand.
So what was in the syringe given the werewolf? I would have used tiletamine/zolazepam/dexmedetomidine. A relatively small volume, fast onset, and highly reliable. I’d hate to have a half-sedated or unsedated werewolf to contend with!
Remember: the first time you sedate is your best bet. Go big initially with appropriate drugs after discussing with the client and you set yourself up for success.