Field Anesthesia and Chemical Restraint

Question 1

T/F: recumbency is required for short surgical procedures

Answer 1

true

Question 2

IV anesthesia can be safely used for up to ____ hr.

Answer 2

1

Question 3

Mortality rate in horses undergoing anesthesia is higher. What are the 4 contributing factors?

Answer 3

1. age (foals, older)
2. duration of surgery (>3 hr risky)
3. drugs used for sedation
4. inhalants

Question 4

Preanesthetics MUST induce …

Answer 4

a state of calmness

You should NEVER anesthetize an excited horse!! If you’ve given pre-sedation and the horse is still excited, then give something else prior to induction/anesthesia.

Question 5

Pre-anesthetic physical examination should focus on what 2 body systems and why?

Answer 5

respiratory and cardiovascular.

This is because 1) subclinical respiratory disease can become overt after anesthesia and 2) You should ensure you are aware of any arrhythmias and murmurs (and ensure HR is >20)

Question 6

How long should horses be fasted prior to undergoing anesthesia?

Answer 6

4-6 hours for adults

some surgeries require 24-48 hr (ex. laporoscopic cryptorchid)

Question 7

What are 3 commonly used drug groups for standing sedation and premedication?

Answer 7

1. alpha-2 agonists (xylazine, detomidine)
2. phenothiazines (ace)
3. opioids

Question 8

Which of the following statements is FALSE about alpha-2 agonists?
A. they can be administered PO, IM, or IV
B. they produce sedation, muscle relaxation, and analgesia
C. they increase HR and CO which can lead to first and second degree AV blocks
D. peak effect is in 3-5 min (IV) or 10-15 min (IM)
E. they can decrease GI motility
F. they increase urination
G. they are reversible

Answer 8

C. they increase HR and CO which can lead to first and second degree AV blocks

they DECREASE heart rate and cardiac output, which can lead to 1st and 2nd degree AV blocks

Question 9

How do you know when a horse is adequately sedated with pre-meds?

Answer 9

they assume the 5-point stance
head is down, eyelids and lips are droopy

Question 10

T/F: detomidine is more potent than xylazine and therefore is a better drug

Answer 10

false – it is more potent, but it is not necessarily a “better” drug. Higher potency simply means that less is required to achieve the same effects.

Question 11

what are the reversal agents for alpha-2 agonists?

Answer 11

1. yohimbine
2. atipamazole/ antisedan
3. tolazoline

Question 12

Detomidine can be given orally in applesauce, molasses, or alone but it takes ______ to take effect.

Answer 12

45 min

Question 13

Which of the following statements is FALSE about a phenothiazine (acepromazine) as a pre-medication?
A. it can be given PO, IV, or IM
B. it produces a calming, relaxing effect, but horse can still be rousable
C. can create hypotension
D. onset is 5-10 minutes, duration is 6-10 hours
E. it produces very minimal muscle relaxation or ataxia
F. it does not provide analgesia
G. when combined with alpha-2 agonist, can enhance sedation

Answer 13

D. onset is 5-10 minutes, duration is 6-10 hours

onset is actually 15-30 minutes, duration is 6-10 hrs

Question 14

Why are opioids (butorphanol, morphine, TD fentanyl) used in conjunction with tranquilizers such as xylazine?

Answer 14

When opiods are given alone, they can cause excitement.

Question 15

Why are dissociatives like ketamine used as induction agents in horses?

Answer 15

their onset is rapid and the induction and recovery are very smooth if used with alpha-2’s (xylazine, detomidine)

Question 16

T/F: ketamine should only be given IV

Answer 16

true

Question 17

T/F: you should combine xylazine and ketamine in the same syringe when using them in conjunction for induction

Answer 17

false

give xylazine first, then ketamine.

Question 18

Which of the following statements is TRUE about the xylazine + ketamine combination?
A. good muscle relaxation is achieved
B. tachypnea is common but resolves within the first 5 minutes
C. Adding diazepam provides smoother induction and greater muscle relaxation
D. major surgeries can be performed with this combo alone

Answer 18

C. Adding diazepam provides smoother induction and greater muscle relaxation

A is false because ket + xylazine alone has poor muscle relaxation
B is false because ket + xylazine can actually cause apneustic breathing
D is false because only minor surgeries should be performed with this combo

Question 19

When using telazol (tiletamine/zolazepam) + xylazine, why are the recoveries “rough” or prolonged?
How could you improve this?

Answer 19

The xylazine is already gone and they are recovering off of the dissociative.

To improve that, you can used detomidine + telazol because detomidine lasts longer than xylazine.

Question 20

what is the BEST / smoothest drug protocol for laying a horse down in the field?

Answer 20

xylazine + ketamine

Question 21

T/F: TKD will induce recumbency in 1 minute and the animal will be back standing in 40 minutes. The combination is ideal because it requires less of each drug. However, this combo should not be used alone for surgery.

Answer 21

true

Question 22

What are the benefits / purpose of use of Guaifenesin?

Answer 22

GG is a muscle relaxant.
It does not induce unconsciousness or analgesia and should not be used alone.
BUT, it allows for other drug amounts to be decreased.

Question 23

What are the signs of GG overdose?

Answer 23

• extension of forelimbs
• labored breathing
• respiratory and cardiac arrest

it looks like the horse is “getting light”

Question 24

What is the purpose of adding diazepam or midazolam into your anesthetic protocol?

Answer 24

provides additional muscle relaxation in conjunction with other agents.
It should NEVER be used alone.

Question 25

T/F: there is not really any difference between midazolam and diazepam in terms of their effectiveness.

Answer 25

true

Question 26

Propofol can be cost-prohibitive in horses due to the large volume required to achieve effect. What can you combine propofol with to reduce the dose required?

Answer 26

guaifenisin or ketamine

but note that respiratory depression still limits usefulness of propofol in the field.

Question 27

To prolong xylazine/ketamine anesthesia, what are 4 potential options to add to the protocol?

Answer 27

1. give 1/3-1/2 orginal dose of xylazine and ketamine
2. add guaifenisin/ket or GKX
3. use detomidine instead of xylazine (from the beginning)
4. give 1/4-1/2 ketamine and diazepam

Question 28

what is included in “triple drip”?
(give amounts of each too)

Answer 28

1 L of 5% guaifenisin or x amt of midazolam
500 mg xylazine
1-2 grams ketamine

Question 29

Triple drip can be used to induce or maintain anesthesia safely for up to _____.

Answer 29

1 hr

but you should give supplemental oxygen if surgery is longer than 30 min.

Question 30

Monitoring can be challenging for non-hospital situations. What are the most important components of monitoring for field anesthesia?

Answer 30

1. provide proper padding, remove halter, protect eyes
2. use IV catheter if doing TIVA
3. All TIVA agents should be administered “to effect” (brisk palpebral, tearing, occasional nystagmus present)
4. provide muscle relaxation
5. digital pulse palpation, CRT, and MM color
6. observe respiratory rate and rhythm

Question 31

why is respiratory rate MORE reliable indicator of changing planes of anesthesia than heart rate is?

Answer 31

heart rate changes very little in horses during changing planes of anesthesia, whereas respiratory rate will become rapid and forceful as the horse gets lighter.

Question 32

T/F: all recumbent horses are hypoxic to some degree

Answer 32

true

however, healthy horses can tolerate this hypoxia for short periods (45-60 min), oxygen supplementation should be provided to compromised patients.

Question 33

When do most injuries occur during horse procedures?

Answer 33

during induction and recovery
especially if the horse is trying to stand early, so you must combine physical and chemical restraint methods to slow this process and protect them.