Field Anesthetic Techniques Flashcards
Why are induction and recovery from anesthesia especially difficult in horses?
- recumbency is unnatural for them
- they try to escape the unfamiliar
How long can IV anesthesia be administered safely in the field?
Up to an hour
- if longer, refer to hospital where they can be hooked up to gas anesthesia and ventilator
What horses have a higher mortality rate compared to other species when under anesthesia? What is the average risk?
Age: foals <10 days, and old patients at higher risk
Duration of surgery: longer procedures have worse prognosis (try to keep elective procedures under 3 hrs)
Drugs for sedation: decreased risk with Ace, increased risk with inhalants? Depends more on individual case and anesthesia team
*Average mortality around 0.5-1%- should not be barrier if surgery provides better prognosis for survival
What are the primary goals of pre-medications for field anesthesia?
-Premeds should result in sedation, analgesia, and muscle relaxation
-pre-anesthetics must induce a state of calmness
-NEVER anesthetize an excited horse
How should you prepare before an anesthetic procedure?
-complete physical exam with special intention to the respiratory and cardiovascular systems
-subclinical respiratory disease can become overt after anesthesia (may need to rebreathe to evaluate)
-evaluate clinical signs, perform bloodwork if needed
-careful auscultation of heart
TRY TO ONLY ANESTHETIZE HEALTHY HORSES IF POSSIBLE
What are the most common arrythmias in horses? What about murmurs?
1st and 2nd degree AV block, Atrial fibrillation (irregularly irregular-sounds like tennis shoes in dryer)
- afib is the only one that warrants much further examination
Murmurs: Innocent murmurs (from PDA), VSD, or mitral/aortic insufficiency
Why does HYPP or tying up increase anesthetic risk?
These horses have hyperkalemia which can cause heart problems, especially under anesthesia
- they are easily worked up
- need to heavily sedate these horses pre-op
How long should you fast horses prior to field anesthesia?
-4-6 hours is ok in most cases
- some surgeries require 24-48 hours, such as abdominal procedures
T/F: The medications that we use for standing sedation in horses are different than the medications we use for pre-meds prior to anesthesia
False- we use the same medications (alpha 2 agonists, opioids, benzodiazepines)
What are the routes that alpha-2 agonists can be given? What are its effects and when is their peak effect?
PO, IM, or IV
-results in sedation, muscle relaxation and analgesia
-results in the 5 point stance
-peak effect 3-5 min after being given IV, 10-15 min after being given IM
Describe some of the effects that alpha 2s have on the heart and other organs.
-Decreased HR and CO, can cause first and second degree AV block- be sure to monitor HR when under
-increased urination (osmotic diuresis from hyperglycemia, inhibition of ADH)
Which is more potent: detomidine or xylazine?
Detomidine
What are the reversal agents for alpha 2s?
Yohimbine, atipamazole, tolazoline
-not often used due to risk of getting too excited post op leading to injury
-only use in emergency situations
T/F: you need to restrain horses under the effects of alpha 2s
True- they can always react and kick even while sedated
T/F: you can give detomidine orally
True
- injectable form can be given PO with applesauce, molasses or alone
- also a gel is available, but this has fallen out of favor
Describe how you would give a detomidine CRI
-Give to effect (dont need fancy syringe pumps)
-using a catheter is ideal
-good option if you dont have a lot of help
Describe the features of phenothiazines (aka acepromazine)
-Given PO, IM, IV
-results in a calm and relaxed horse which can be aroused
-minimal muscle relaxation or ataxia
-no analgesia
-there is a potential for hypotension when combined with inhalants
What is the onset of action and duration of action for acepromazine?
-onset of 25-30 min after being given IV
-duration of action of 6-10 hours
When is acepromazine indicated?
Usually combined with alpha 2 agonists to enhance sedation
What is a reason that you should use caution when using acepromazine in breeding stallions?
Priapism is a potential side effect
Describe the common opioids used in horses and when they should be used.
Butorphanol, Morphine, Transdermal fentanyl
-use as adjuncts to tranquilizers (can cause excitement when used alone)
What are the mainstays for induction in horses?
Dissociatives: Ketamine and telazol
- can add on muscle relaxants (such as benzodiazepines and guaifenesin) or propofol
Describe the features of dissociatives
-onset of action is rapid
-induction and recovery is generally smooth when used in conjunction with alpha 2 agonists
-duration of ketamine-alpha 2 anesthetics is generally 15-20 minutes
-alpha 2s are more effective as an adjunct to dissociatives
Describe the xylazine ketamine protocol for induction.
Xylazine followed by ketamine (1 mg/kg IV xylazine, then 2 mg/kg ketamine IV)- don’t give together
-success depends on xylazine producing sedation, not giving ketamine to an excited horse, not disturbing the horse until recovered and only giving ketamine IV
-muscle relaxation can be poor, apneustic breathing is common
-can be used for minor surgeries
-adding diazepam can lead to smoother induction and greater muscle relaxation
