General pharmacology

Anesthesia induction agents

Induction agents are used to move from standing sedation to recumbency. The most common LA induction agents are ketamine, telazol, and guaifenesin (GG). Propofol is used occasionally in camelids or small ruminants. Masking with isoflurane can be used to induce anesthesia (and is used with pigs) but is higher risk to the environment and to people in the environment.

Ketamine

Schedule III

Ketamine is a dissociative anesthetic agent used to induce recumbency after sedation when given at higher doses.

It is commonly combined with other drugs (xylazine, diazepam or midazolam, guafenesin) to prolong the aneshetic duration and to enhance relaxation.

Ketamine is a relatively safe drug with minimal cardiovascular or respiratory depressant effects. “It is hard to kill with ketamine.” Horses must be well sedated before ketamine is given; otherwise life gets a bit too exciting due to the excitement phase of anesthesia. Unlike in horses, there is minimal excitement phase in ruminants. Both the sedative and induction agents can be combined in the same syringe (eg ketamine/diazepam or xylazine/ketamine) and given at the same time.

Telazol

Schedule III

Telazol is a combination of tiletamine (dissociative agent like ketamine) and zolazepam (benzodiazepine like diazepam). It lasts longer than ketamine/diazepam but is more expensive.

The drug needs to be reconstituted prior to use and then has a limited shelf life.
It can be administered intramuscularly (can be handy at times).

Guaifenesin (GG)

Guaifenesin is a muscle relaxant that helps counteract the rigidity associated with ketamine. GG must be compounded and can be explosive if done incorrectly.

It can be used for induction (0.5-2 ml/kg) but has a slightly delayed effect so overdosing is a risk. However, the gradual induction minimizes the apnea risk.

GG is combined with xylazine and ketamine to form “triple drip” or with just ketamine to form “double drip” (see maintenance protocols). The combinations are used more commonly than is GG alone.

Side effects : Very irritating perivascularly. Use a catheter. Overdoses of GG can lead to increased muscle tone, making the animal appear too light vs too deep.

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See the next chapter for species specific links

 

License

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Large Animal Surgery - Supplemental Notes by Erin Malone, DVM, PhD; Elaine Norton, DVM PhD; Erica Dobbs, DVM; and Ashley Ezzo, DVM is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.