Equine and Ruminant General Anesthesia Flashcards
what are the two MAIN options for equine anesthesia and how common are they
A) sedation +/- local anesthesia = very common
B) general anesthesia +/- local anesthesia = moderately common
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
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
what are the physiological consequences of general anesthesia and recumbency in the horse during the recovery phase
- decreased coordination
- decreased mm strength
- altered mentation
it is important to assess the horses environment before anesthesia for (5)
- cleanliness
- safety
- minimal dust/particles
- quiet
- assistance
what is the purpose of a demand valve
provides positive pressure ventilation when using an E tank
in an ideal situation, how long should an adult horse be fasted before general anesthesia
12h
what are some important management factors for the horse prior to general anesthesia
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
in the history, it is important to gather _________ about the horse
concurrent medications and when they were last dewormed
what does the anesthetic plan include in horses
1) drugs
2) airway management
3) monitoring
4) supportive measures
5) emergency preparation
6) post-operative analgesia
what are the 3 typical drug plans for adult horses:
1) 10-15 min procedure
2) <1h procedure
3) >1h procedure
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
what do we never give horses to pre-med and why
anti-cholinergics; can lead to colic
what are the 3 main induction options in horses for GA and what duration of effect will they have
1) ketamine
2) ketamine + diazepam
3) ketamine + guaifenesin
10-15 mins
we commonly give ketamine following…
sedation with an alpha-2 agonist (smooth)
how is ketamine metabolized and eliminated
metabolized by liver and eliminated in kidney
what are the effects of ketamine when used alone for induction (after giving a pre-medication) vs in combination
1) skeletal mm relaxation
2) mm weakness -> ataxia, recumbency
3) excitement in adult horses
In combination: improved skeletal mm relaxation
both guaifenesin and diazepam/midazolam are
centrally acting mm relaxants (and both have minimal CVS effects)
what are the maintenance options for anesthesia in the horse
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)
what should you never give as a top-up to maintain anesthesia in the horse
just ketamine/diazepam
if using GXK to maintain anesthesia in horses what is the recommendation
- give supplemental O2
- give via an IV catheter
- limit the duration of anesthesia to under 1h
what is an example of a drug plan for a horse with a 10-15 min duration procedure
pre-med: alpha-2 (xylazine, romifidine, detomidine) and an opioid
induction: ketamine and diazepam
maintenance: ketamine and alpha-2 bolus
what is an example of a drug plan for a horse with a <60 min duration procedure
pre-med: alpha-2 (xylazine, detomidine, romifidine) + opioid
induction: ketamine + diazepam
maintenance: ketamine + alpha-2 bolus OR GXK drip OR inhalant
what is an example of a drug plan for a horse with a >60 min duration procedure
pre-medication: alpha-2 (xylazine, romifidine, detomidine) + opioid
induction: ketamine + diazepam or ketamine + guaifenesin
maintenance: inhalant
how do you decide which anesthetic machine to use for horses and cows:
1) SA machine
2) LA machine
SA machine: <150-200 kg
LA machine: >200 kg
what is the GA plan in a foal <2 weeks old
pre-med: diazepam
induction: ketamine
maintenance: inhalant (isoflurane)
what is the GA plan in a foal >2weeks old
If unhealthy follow same protocol for foals < 2 weeks (diazepam + ketamine + inhalant)
If healthy:
Premed: alpha-2 (xylazine)
Induction: ketamine + diazepam
Maintenance: inhalant (isoflurane)
what are the 2 methods for airway management in horses
nasotracheal or orotracheal
how do we typically do airway management:
1) in the field
2) in hospital
1) we don’t: manage risk with positioning
2) orotracheal common; done blind
what are some commonly used ionotropes to support equine anesthesia (4)
- dobutamine
- dopamine
- ephedrine
- calcium
what fluids are commonly given horses during GA
balanced elecrolyte solutions (ex. lactated ringer) or hypertonic saline if dehydrated
what are some examples of analgesic drugs for horses post-op
1) local anesthetics
2) opioids
3) alpha-2
4) NSAIDs
what are 3 consequences of decreased oxygen delivery to tissues during horse GA
myopathy, cardiopulmonary arrest, post-operative ileus and colic
relative to horses, how common is general anesthesia +/- local anesthesia in cows
uncommon/rare compared to moderately common in horses -> the indications for it are incredibly rare
what are the physiological consequences of general anesthesia and recumbancy in ruminants and what is the overall effect
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
mature ruminants almost always require:
ventilatory support
what is a very critical history question for ruminant GA
are they pregnant or not
how long should you fast:
- cow/bull
- sheep/goat
- calf
cow/bull: 24-48h
sheep/goat: 12-18h
calf: 2-8h
similar to horses, it is important to ask ruminant owners about _______ prior to GA
concurrent medications and dewormers
in addition to the requirements of the anesthetic plan in horses, what is added to the anesthetic plan in ruminants
drug withdrawal times
T/F we can give ruminants anticholinergics
F
what alpha-2s can we use in ruminants
xylazine
if we use benzodiazepines for pre-medication in ruminants, what route should they be given
IV
T/F xylazine is an analgesic
T
when is xylazine contraindicated in large animals
- 3rd trimester of pregnancy
- debilitated animal
- hypoxemic or hypovolemic
- urinary obstruction
what is the order of sensitivity to xylazine in ruminants from most to least sensitive: llama, sheep, goat, cow
goats
sheep
cow
llama
T/F xylazine does not provide analgesia but is reversible whereas acepromazine provides analgesia but is irreversible
F; xylazine has analgesia and is reversible; acepromazine has no analgesia and is not reversible
when is acepromazine contradindicated
hypovolemic patients
what is an important potential side effect of acepromazine in ruminants
regurgitation
when are benzos used in ruminants and how
in sick adults or in calves for moderate sedation to premedicate; cannot give diazepam IM but can give midazolam IM
when would we use anticholinergics and which do we usually use in ruminants
to treat bradycardia; glycopyrrolate better than atropine (longer acting, less placental transfer)
Note; NOT COMMONLY DONE
what are the induction options in ruminants
- ketamine
- ketamine and diazepam
- ketamine and guaifenesin
- propofol (small ruminants and calves only)
is guaifenesin or diazepam more commonly used in ruminants
guaifenesin better mm relaxant
what are maintenance options for ruminant GA
IV
- GXK
- repeat boluses of injectable agents
Inhalant
T/F every domestic ruminant placed under GA should have their airway protected, even if not using inhalant maintenance anesthetic
T
it is important to prevent yourself from doing what during intubation of small ruminants/calves
intubating only the right main stem bronchus (to the R cranial lung lobe)
how does the larynx in ruminants differ from horses and what is the consequence
more caudal and sloping in ruminants; makes blind intubation hard
how do we intubate ruminants
- blind (sheep and calves)
- direct visualization (sheep and calves)
- palpation (mature cows)
- fiberoptic
what are the main anesthetic plans for a healthy mature cow/bull
premed: xylazine
induction: GG/ketamine or diazepam/ketamine
maintenance: GXK or inhalant
what are the main anesthetic plans for a calf
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
what are the main anesthetic plans for a sheep
premed: none, xylazine, acepromazine or benzodiazepine
induction: ketamine +/- benzodiazepine OR propofol +/- benzodiazepine
maintenance: inhalant
how do we recover ruminants to ensure no aspiration
1) examine the airway and remove debris if present
2) maintain airway until sternal and strong swallow reflex
3) extubate with cuff partially inflate
how can we prevent bloat in ruminants during GA
off-feed; place ororuminal tube
what are the toxic doses of the following local anesthetics:
- lidocaine
- mepivacaine
- bupivacaine
lidocaine: 10 mg/kg
mepivacaine: 10 mg/kg
bupivacaine: 2 mg/kg
why should you avoid benzocaine
causes methemoglobinemia in ruminants
