Anesthesia for Population Control: Doing it Well and Cheap
World Small Animal Veterinary Association Congress Proceedings, 2018
Anderson Favaro da Cunha, DVM, MS, DACVAA
Professor and Chief, Veterinary Anesthesia and Analgesia, Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA

Non-client-owned, shelter animals often require sedation, anesthesia and analgesia for orchiectomy (neuter) or ovariohysterectomy (spay) prior to adoption. The Association of Shelter Veterinarians published a guideline regarding the anesthesia of shelter animals with emphasis on patient care and welfare, including anesthesia, analgesia and postoperative care.

There are also several websites elucidating ways to preserve and protect the animal rights at shelters. They are:

Many studies show that the anesthesia-related mortality rate is reduced with in-depth understanding of the patient’s history and pre-op examinations. However, when animals present for surgeries in shelters, they usually lack that important clinical history. Performing full blood work for all animals prior to surgery is cost prohibitive, and most feral animals do not allow the veterinarian to approach for a complete physical exam prior to drug injection. Therefore, the anesthesia-related mortality rate in shelters is higher. However, there are several simple techniques that can be used for the anesthesia management of feral and shelter animals in order to improve their survival rate.

1.  The most important techniques you can add to your practice in order to increase survival rates in the face of a lack of pre-op clinical information are:

a.  Vital signs monitoring during anesthesia

b.  Personnel training to recognize any possible cardiovascular and respiratory complications

c.  Readiness for aggressive treatments of possible complications

2.  Before the beginning of your anesthesia management, it is important to provide a stress-free environment. Stress leads to catecholamine release and arrhythmias that can be exacerbated by anesthesia. Keep cats away from dogs and dogs away from cats. That alone can help to reduce the stress of those animals significantly. Consider this: Outsmart your patient, but do not out-power them. You must stay calm, use your brain and be sneaky. Do not use brute force to restrain the animal. That will only cause frustrations for you and your team and stress for your patients. Remember: With cats, the less restraint the better. Also, do not use a catch poll for cats. That causes too much stress for them. Search for a “Freeman cat net”—this is a great device to help you to reduce the animal stress. Squeeze cages can also help you get your injections with minimum stress for both ends: you and your patient.

3.  It is acceptable to anesthetize pregnant or lactating patients, animals in estrus, and animals that have pyometra, mild infectious or noninfectious diseases (i.e., upper respiratory tract disease, parasite infestation or subclinical heartworm infection). However, additional monitoring should be available for those patients. For these cases you should consider running blood work and obtaining a complete physical exam before the beginning of anesthesia, when possible.

4.  Fasting helps to reduce the chances of regurgitation and aspiration pneumonia. It is recommended 2–4 hours of fasting for pediatric animals and 6–8 hours for adult animals. Exceptions may be made for feral cats in traps when it is not safe to remove food from traps due to human safety. Removing water is neither necessary nor recommended.

5.  Many cats have hyperthermia during anesthesia recovery. The mechanism triggering the post-op hyperthermia is not well understood. Stress, opioids and ketamine could be trigger factors. Also, there is a belief that under anesthesia, the more hypothermic the patients are, the more hyperthermic they will be during recovery. Therefore, consider checking the body temperature as soon as possible and throughout the recovery phase as well. Provide heat when necessary. To treat the hyperthermia: nonsteroidal anti-inflammatory drugs work well; consider reversing any opioid medication. If you do reverse the opioids with naloxone, then the patient may suffer from pain. Butorphanol is a partial antagonist of the mu opioid receptors and can be used for the reversal of the hydromorphone and morphine as well. When butorphanol is used as a reversal agent, the patient will have some analgesia. Use water instead of alcohol since alcohol only causes peripheral vasoconstriction that prevents heat loss. Also a simple fan helps to get the temperature down.

6.  When you are planning your anesthetic protocol for your shelter program, consider safe and efficient protocols. Balanced anesthesia should always be the goal, with analgesia as the first priority. Choose safe drugs with wide therapeutic indexes. Ketamine and tiletamine are great examples of safe anesthetic drugs that provide potent analgesia. When ketamine or tiletamine is used in combination with a benzodiazepine (diazepam, midazolam or zolazepam) and an opioid (butorphanol, morphine, hydromorphone, buprenorphine) or an alpha-2 agonist, the animal gets good muscle relaxation, immobilization, effective analgesia and loss of consciousness without patient compromise. Another advantage of ketamine over other induction agents like propofol and alfaxalone is in regard to the necessity of endotracheal intubation. Ketamine leads to a maintenance of the laryngeal reflexes, which help the prevention of aspiration pneumonia.

7.  After sedation, make sure someone trained is observing the animal to have fast treatment when necessary. Oxygen supplementation could significantly reduce shelter mortality.

8.  Finances are important. When designing anesthetic protocols, check local prices and pick the least expensive drugs; however, do not forget that anesthesia is not analgesia, and to be fair, the shelter animals need both. Think about cheap opioids and nonsteroidal anti-inflammatories. Also to reduce cost, check with your local pharmaceutical representative if they have programs to help shelters and other organizations to either provide the drugs for free or at least with a subsidized cost.

9.  Eye lube is very important. Animals cannot generate tears while under general anesthesia, and corneal ulcers may form if eyes are not well lubricated after anesthesia induction.

10.  Besides the surgical procedure, consider the use of flea medicine when necessary. We recommend the identification of the surgical site with a tattoo to prevent possible future surgeries in the same animal. Some areas allow ear notches to identify the castrated animals; however, that technique tends to reduce the likelihood of adoptions afterward.

11.  Communication between staff is essential. You need a well-trained team where everyone involved knows exactly what to do. Someone should be responsible for double-checking drug labels, concentrations and volumes. Usually the total drug volume is based on estimated bodyweight, and to speed up the process, there are ways to precalculate drug volumes per kilogram.

12.  Use local anesthesia. An intratesticular block with lidocaine is a safe, cheap, fast and efficient analgesic protocol. There is no described local analgesia technique for OHE. Incisional local anesthesia has been described, but it usually causes a prolongation of surgical site healing and is contraindicated, especially for cats and dogs that will be released after the surgery and no veterinary care will be available.

13.  Mask induction can be performed; however, there is a major concern with environmental air pollution in the OR. Males don’t have to be orotracheal intubated if the surgeon is fast; however, females should always be intubated and ventilated. Remember, isoflurane, and another inhalant by itself does not provide analgesia and should not be used by itself.


References are available upon request.


Speaker Information
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Anderson Favaro da Cunha, DVM, MS, DACVAA
Department of Veterinary Clinical Sciences
School of Veterinary Medicine
Louisiana State University
Baton Rouge, LA, USA

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