Anesthesia induction agents

General anesthesia typically involves at least a sedative, an induction agent and a maintenance agent. Polypharmacy is common as it decreases the side effect of individual drugs; this means we often use multiple drugs for each part (sedation, induction and maintenance).

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, guaifenesin) that help to prolong the anesthetic 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 eventful due to the excitement phase of anesthesia. Unlike horses, ruminants do not exhibit much of an 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; this 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.

GG 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 associated with induction to humans

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 : GG is 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