29: LA

Anatomic considerations when doing LA anesthesia

Many are obligate nasal breathers

Why is induction and recovery often so dramatic with large animals

They are prey animals with a very strong fight or flight response

Inhalant that cannot be used in large animals

Nitric oxide → accumulates in rumen or cecum

How long should a horse be fasted for before anesthesia

3-6 hours

Typical premed sedative in horses

α2 agonists

How do you know if a horse is sedate enough to anesthetize

• Head down: “nostrils at the level of your knees”

• Lip drooping

• Ears in the neutral position

• Non-reactive to stimuli

How do we accomplish standing chemical restraint for standing procedures where we aren’t using general anesthesia

α2 agonist/other sedative and an opioid, often as a CRI

Common pre-med + induction combo for field anesthesia

α2 agonist + ketamine

Meds in a “triple drip” CRI for maintenance

• Guaifenesin: muscle relaxant

• Ketamine: dissociative

• Xylazine: sedative

Primary induction agent in equine medicine

Ketamine

Why do we like ketamine so much for horses

They move through the phases of induction very quickly and without dysphoria

What HAS to be given with ketamine for induction

A muscle relaxant, commonly benzodiazepines

T/F: equine intubation is done blind

True

How long can you maintain anesthesia in a horse with triple trip

MAX 1 hour

Why can’t you do TIVA/triple drip anesthesia in a horse longer than an hour

We worry about the accumulation of IV anesthetics

What organs are we most worried about in horses with anesthetic hypotensive episodes

Muscles and limbs

Standard monitoring for BP during anesthesia in horses

Invasive arterial BP

Sites in a horse where we measure arterial BP

• Facial artery

• Metatarsal artery

• Transverse facial artery

How do you know a horse is in an adequate plane of anesthesia

Slow palpebral reflex and present of nystagmus

T/F: inhalant anesthetics can be adjusted to put a horse back in a deeper plane of anesthesia

F; it is too slow. You need to use injectable

Why do we worry about anesthetic positioning so much in horses

Because they are so big, they can end up with myopathies and neuropathies if positioned poorly

Most risky part of equine anesthesia

Recovery

Why might you need to sedate a horse that is recovering from anesthesia

They will try to stand before they are ready

Why should you fast a horse for 1-3 hours post-anesthesia

They will have GIT dyskinesia for a while and can end up with choke

Opioids commonly used for equine anesthetic analgesia

Butorphanol and morphine

Why is morphine a controversial choice for equine pain management

Some people think morphine causes colic (but Dr. M says a painful horse is much more likely to colic, so he is pro-morphine)

Why are ruminants at a higher anesthetic risk of aspiration and reflux

They salivate a lot and they don’t have a strong LES

Why is positioning during anesthesia important in ruminants

Their large GIT can compress the lungs and result in hypoventilation → hypoxemia

How long should you fast a ruminant before anesthesia

24-48 hours

What can happen if you fast a ruminant longer than 48 hours

You can have problems with GIT bacteria → ketoacidosis

Meds that are NOT a good idea to give to ruminants

Anticholinergics

How can you position a ruminant to decrease the risk of aspiration pneumonia

Keep the nose below the larynx

How can you prevent nasal edema in ruminants

Spray phenylephrine in the nasal cavity to shrink mucosa

What do you do if a ruminant shows signs of respiratory obstruction

Give more induction agent and try to re-intubate, or to a tracheostomy if that isn’t working

Preferred site for IV access in ruminants

Jugular vein

Meds that ruminants (especially sheep!) are very sensitive to

α2 agonists

Side effects of α2 agonists in ruminants (especially sheep)

• Acute pulmonary edema

• Hypoxemia

Better choice for a sedative in ruminants

Benzodiazepines

Common induction combinations in ruminants

Ketamine + guaifenesin/propofol/midazolam

Induction combo that can be given IM in ruminants

Telazol reconstituted with ketamine and xylazine

T/F: ruminants easily get hypotensive under anesthesia, like small animals

F

Anesthetic complication in ruminants that is more common than hypotension

Hypoxia

When should you extubate a ruminant that is recovering from anesthesia

When they are rejecting the tube

When should you stop monitoring a ruminant that is recovering from anesthesia

When they can eructate

How long should you fast swine before anesthesia

6-12 hours

Considerations when intubating a pig

• Small glottis and trachea

• Well developed lateral ventricles

• Prone to laryngospasm

Most common premed combo in swine

Telazol + ketamine + xylazine