Equine and Ruminant General Anesthesia

Question 1

what are the two MAIN options for equine anesthesia and how common are they

Answer 1

A) sedation +/- local anesthesia = very common

B) general anesthesia +/- local anesthesia = moderately common

Question 2

what are the physiological consequences (in lungs, in heart, in GI) of general anesthesia and recumbency in the horse during the maintenance phase… what is the overall (net) effect

Answer 2

overall effect: decreased oxygen delivery to tissues

in lungs:
- decreased alveolar ventilation
- decreased oxygenation

in heart:
- decreased cardiac output
- decreased blood pressure

in GI
- decreased motility

Question 3

what are the physiological consequences of general anesthesia and recumbency in the horse during the recovery phase

Answer 3

• decreased coordination
• decreased mm strength
• altered mentation

Question 4

it is important to assess the horses environment before anesthesia for (5)

Answer 4

• cleanliness
• safety
• minimal dust/particles
• quiet
• assistance

Question 5

what is the purpose of a demand valve

Answer 5

provides positive pressure ventilation when using an E tank

Question 6

in an ideal situation, how long should an adult horse be fasted before general anesthesia

Answer 6

12h

Question 7

what are some important management factors for the horse prior to general anesthesia

Answer 7

1) mouth flush before intubating
2) should ideally not be shod or put bandages over the shoes
3) keep the mare and foal together until one is anesthetized
4) fasting

Question 8

in the history, it is important to gather _________ about the horse

Answer 8

concurrent medications and when they were last dewormed

Question 9

what does the anesthetic plan include in horses

Answer 9

1) drugs
2) airway management
3) monitoring
4) supportive measures
5) emergency preparation
6) post-operative analgesia

Question 10

what are the 3 typical drug plans for adult horses:
1) 10-15 min procedure
2) <1h procedure
3) >1h procedure

Answer 10

1) pre-medication followed by induction with an IV anesthetic agent

2) pre-medication followed by induction with an IV anesthetic agent followed by an IV bolus/CRI anesthetic agent OR inhalant

3) pre-medication followed by induction with an IV anesthetic followed by inhalant

Question 11

what do we never give horses to pre-med and why

Answer 11

anti-cholinergics; can lead to colic

Question 12

what are the 3 main induction options in horses for GA and what duration of effect will they have

Answer 12

1) ketamine
2) ketamine + diazepam
3) ketamine + guaifenesin

10-15 mins

Question 13

we commonly give ketamine following…

Answer 13

sedation with an alpha-2 agonist (smooth)

Question 14

how is ketamine metabolized and eliminated

Answer 14

metabolized by liver and eliminated in kidney

Question 15

what are the effects of ketamine when used alone for induction (after giving a pre-medication) vs in combination

Answer 15

1) skeletal mm relaxation
2) mm weakness -> ataxia, recumbency
3) excitement in adult horses

In combination: improved skeletal mm relaxation

Question 16

both guaifenesin and diazepam/midazolam are

Answer 16

centrally acting mm relaxants (and both have minimal CVS effects)

Question 17

what are the maintenance options for anesthesia in the horse

Answer 17

A. IV: ketamine/alpha-2 bolus; ketamine/alpha-2/guaifenesin triple drip; other infusion

B. Inhalant (halothane or isoflurane +/- MAC reducing agents like lidocaine or alpha-2s)

Question 18

what should you never give as a top-up to maintain anesthesia in the horse

Answer 18

just ketamine/diazepam

Question 19

if using GXK to maintain anesthesia in horses what is the recommendation

Answer 19

• give supplemental O2
• give via an IV catheter
• limit the duration of anesthesia to under 1h

Question 20

what is an example of a drug plan for a horse with a 10-15 min duration procedure

Answer 20

pre-med: alpha-2 (xylazine, romifidine, detomidine) and an opioid

induction: ketamine and diazepam

maintenance: ketamine and alpha-2 bolus

Question 21

what is an example of a drug plan for a horse with a <60 min duration procedure

Answer 21

pre-med: alpha-2 (xylazine, detomidine, romifidine) + opioid

induction: ketamine + diazepam

maintenance: ketamine + alpha-2 bolus OR GXK drip OR inhalant

Question 22

what is an example of a drug plan for a horse with a >60 min duration procedure

Answer 22

pre-medication: alpha-2 (xylazine, romifidine, detomidine) + opioid

induction: ketamine + diazepam or ketamine + guaifenesin

maintenance: inhalant

Question 23

how do you decide which anesthetic machine to use for horses and cows:

1) SA machine
2) LA machine

Answer 23

SA machine: <150-200 kg

LA machine: >200 kg

Question 24

what is the GA plan in a foal <2 weeks old

Answer 24

pre-med: diazepam

induction: ketamine

maintenance: inhalant (isoflurane)

Question 25

what is the GA plan in a foal >2weeks old

Answer 25

If unhealthy follow same protocol for foals < 2 weeks (diazepam + ketamine + inhalant) If healthy: Premed: alpha-2 (xylazine) Induction: ketamine + diazepam Maintenance: inhalant (isoflurane)

Question 26

what are the 2 methods for airway management in horses

Answer 26

nasotracheal or orotracheal

Question 27

how do we typically do airway management: 1) in the field 2) in hospital

Answer 27

1) we don't: manage risk with positioning 2) orotracheal common; done blind

Question 28

what are some commonly used ionotropes to support equine anesthesia (4)

Answer 28

- dobutamine - dopamine - ephedrine - calcium

Question 29

what fluids are commonly given horses during GA

Answer 29

balanced elecrolyte solutions (ex. lactated ringer) or hypertonic saline if dehydrated

Question 30

what are some examples of analgesic drugs for horses post-op

Answer 30

1) local anesthetics 2) opioids 3) alpha-2 4) NSAIDs

Question 31

what are 3 consequences of decreased oxygen delivery to tissues during horse GA

Answer 31

myopathy, cardiopulmonary arrest, post-operative ileus and colic

Question 32

relative to horses, how common is general anesthesia +/- local anesthesia in cows

Answer 32

uncommon/rare compared to moderately common in horses -> the indications for it are incredibly rare

Question 33

what are the physiological consequences of general anesthesia and recumbancy in ruminants and what is the overall effect

Answer 33

respiratory: - decreased alveolar ventilation - decreased oxygenation - airway obstruction/aspiration CVS: - decreased cardiac output GI: - decreased motility - increased regurgitation Overall effect: - decreased oxygen delivery to tissues - bloat/regurgitation/aspiration - cardiopulmonary arrest - neuropathies

Question 34

mature ruminants almost always require:

Answer 34

ventilatory support

Question 35

what is a very critical history question for ruminant GA

Answer 35

are they pregnant or not

Question 36

how long should you fast: - cow/bull - sheep/goat - calf

Answer 36

cow/bull: 24-48h sheep/goat: 12-18h calf: 2-8h

Question 37

similar to horses, it is important to ask ruminant owners about _______ prior to GA

Answer 37

concurrent medications and dewormers

Question 38

in addition to the requirements of the anesthetic plan in horses, what is added to the anesthetic plan in ruminants

Answer 38

drug withdrawal times

Question 39

T/F we can give ruminants anticholinergics

Answer 39

F

Question 40

what alpha-2s can we use in ruminants

Answer 40

xylazine

Question 41

if we use benzodiazepines for pre-medication in ruminants, what route should they be given

Answer 41

IV

Question 42

T/F xylazine is an analgesic

Answer 42

T

Question 43

when is xylazine contraindicated in large animals

Answer 43

- 3rd trimester of pregnancy - debilitated animal - hypoxemic or hypovolemic - urinary obstruction

Question 44

what is the order of sensitivity to xylazine in ruminants from most to least sensitive: llama, sheep, goat, cow

Answer 44

goats sheep cow llama

Question 45

T/F xylazine does not provide analgesia but is reversible whereas acepromazine provides analgesia but is irreversible

Answer 45

F; xylazine has analgesia and is reversible; acepromazine has no analgesia and is not reversible

Question 46

when is acepromazine contradindicated

Answer 46

hypovolemic patients

Question 47

what is an important potential side effect of acepromazine in ruminants

Answer 47

regurgitation

Question 48

when are benzos used in ruminants and how

Answer 48

in sick adults or in calves for moderate sedation to premedicate; cannot give diazepam IM but can give midazolam IM

Question 49

when would we use anticholinergics and which do we usually use in ruminants

Answer 49

to treat bradycardia; glycopyrrolate better than atropine (longer acting, less placental transfer) Note; NOT COMMONLY DONE

Question 50

what are the induction options in ruminants

Answer 50

- ketamine - ketamine and diazepam - ketamine and guaifenesin - propofol (small ruminants and calves only)

Question 51

is guaifenesin or diazepam more commonly used in ruminants

Answer 51

guaifenesin better mm relaxant

Question 52

what are maintenance options for ruminant GA

Answer 52

IV - GXK - repeat boluses of injectable agents Inhalant

Question 53

T/F every domestic ruminant placed under GA should have their airway protected, even if not using inhalant maintenance anesthetic

Answer 53

T

Question 54

it is important to prevent yourself from doing what during intubation of small ruminants/calves

Answer 54

intubating only the right main stem bronchus (to the R cranial lung lobe)

Question 55

how does the larynx in ruminants differ from horses and what is the consequence

Answer 55

more caudal and sloping in ruminants; makes blind intubation hard

Question 56

how do we intubate ruminants

Answer 56

- blind (sheep and calves) - direct visualization (sheep and calves) - palpation (mature cows) - fiberoptic

Question 57

what are the main anesthetic plans for a healthy mature cow/bull

Answer 57

premed: xylazine induction: GG/ketamine or diazepam/ketamine maintenance: GXK or inhalant

Question 58

what are the main anesthetic plans for a calf

Answer 58

premed: xylazine induction: ketamine/diazepam maintenance: inhalant or GXK or ketamine bolus or propofol CRI premed: diazpeam induction: ketamine maintenance: inhalant or GXK or bolus ketamine or propofol CRI

Question 59

what are the main anesthetic plans for a sheep

Answer 59

premed: none, xylazine, acepromazine or benzodiazepine induction: ketamine +/- benzodiazepine OR propofol +/- benzodiazepine maintenance: inhalant

Question 60

how do we recover ruminants to ensure no aspiration

Answer 60

1) examine the airway and remove debris if present 2) maintain airway until sternal and strong swallow reflex 3) extubate with cuff partially inflate

Question 61

how can we prevent bloat in ruminants during GA

Answer 61

off-feed; place ororuminal tube

Question 62

what are the toxic doses of the following local anesthetics: - lidocaine - mepivacaine - bupivacaine

Answer 62

lidocaine: 10 mg/kg mepivacaine: 10 mg/kg bupivacaine: 2 mg/kg

Question 63

why should you avoid benzocaine

Answer 63

causes methemoglobinemia in ruminants