Equine Sedation and Anaesthesia Flashcards
what should be done when preparing horses for sedation?
check passport assess signalment and temperament assess cardio and respiratory systems establish duration of sedation required and anticipated pain level consider facilities and handlers
why must a horses passport be checked before sedation?
due to their food production status to ensure that there is a hold placed on them if they are given specific drugs
do horses need to have food withheld before sedation?
no
should horses have food withheld after sedation?
restriction until they are adequately recovered
why is a calm, quiet environment required when sedating horses?
to enable drugs to take effect properly and so that sedation works as expected
with what type of sedation is a quiet environment key?
alpha - 2 agonists as they compete with adrenaline at receptors
how should you approach sedation of horses?
calm, quiet environment schedule enough time be aware of safety issues prepare all equipment ensure it is a positive interaction
why is it crucial that horses interaction with veterinary personnel is positive?
can easily become needle shy which poses a problem for any further veterinary treatment
what is acepromazine a derivative of?
phenothiazine
what level of sedation is offered by acepromazine?
mild
what is acepromazine used for in horses?
only takes the edge off so used for mild procedures or premed for GA
what is the speed of onset of acepromazine?
slow onset for IM and IV - 30 mins
how long is the duration of action of acepromazine?
4-6 hours
what is the key side effect of acepromazine?
vasodilation
why is acepromazine problematic in breeding stallions?
can cause priapism
why should acepromazine be avoided in shocked or hypovolaemic patients?
cause alpha adrenergic blockade which prevents contraction of smooth muscles so leads to vasodilation
what are the main types of sedatives used in horses?
alpha-2 adrenoreceptor agonists
what are the effects of alpha-2 adrenoreceptoragonists?
sedation muscle relaxation analgesia cardiovascular effects hypoinsulinaemia decreased GI motility sweating
what area of the brain is targeted by alpha2-adrenoreceptors?
pons (locus ceruleus)
where do alpha2-adrenoreceptor agonists have their analgesic effect?
dorsal horn of spinal cord
what are the cardiovascular effects of alpha2-adrenoreceptor agonists?
bradycardia
second degree AV block
initial hypertension then hypotension
what is the sign of adequate sedation with alpha2-adrenoreceptor agonists in horses?
5 point stance
ataxia
swaying
what receptors do alpha2-adrenoreceptor agonists bind to?
not totally alpha 2 specific, will also bind to alpha 1
how long do alpha2-adrenoreceptor agonists take to achieve full effect?
2-5 mins
what is the most specific alpha2-adrenoreceptor agonist?
romifidine
what is the least specific alpha2-adrenoreceptor agonist?
Xylazine
what is the fastest acting alpha2-adrenoreceptor agonist?
xylazine
what is the slowest acting alpha2-adrenoreceptor agonist?
romifidine
what is the alpha2-adrenoreceptor agonist that causes the most ataxia?
xylazine
what is the alpha2-adrenoreceptor agonist that causes the least ataxia?
romifidine
what alpha2-adrenoreceptor agonist has the shortest action?
xylazine
what alpha2-adrenoreceptor agonist has the longest action?
romifidine
how are alpha2-adrenoreceptor agonists administered?
IV or IM
care as absorbed across MM
what are the effects of opioids on horses when given with an alpha2-adrenoreceptor agonist?
have synergistic effect on analgesia and sedation depth
increased ataxia
possibility that animals are less likely to kick?!
what is the most popular opioid used in horses?
butorphanol
does butorphanol provide good analgesia to horses?
no so other analgesic must be given alongside
what is a better opioid to use in horses for it’s analgesic effect?
ketamine
what are the issues with using buprenorphine?
controlled drug
increased volume required so administration is more difficult
what is pethidine used for in horses?
relief of spasmodic colic, given IM only
can methadone be given to horses?
yes but on cascade as only licenced in small animals
when may remote IM sedation be used in horses?
unhandled or fractious horses
what combination of drugs may be given in a remote IM injection technique?
detomidine - 20-60 micrograms/kg
butorphanol - 50 micrograms/kg
acepromazine - 50 micrograms/kg
how must oral sedatives be prescribed?
for each individual horse for each time of use following a clinical exam by VS
what should be arranged when prescribing oral sedatives?
safe disposal of any unused product
what should be done when handling oral sedatives?
wear gloves
what is involved in gaining informed owner consent for sedation for paraprofessionals?
establish proposed procedures
warn owner about risks and define limits of responsibility
advise client that it’s prefurrable for the vet to be present throughout the period of sedation
advise about legal aspects of performing invasive veterinary surgery
ensure advice is provided verbally and in writing - record this
what is the calculated total mortality from peri-operative complications in horses?
1.9% died within 7 days of surgery
what are the top 3 factors responsible for anaesthetic death in horses?
cardiac arrest 33%
fracture 23%
myopathy 7%
what type of surgery is highly risky in horses?
colic
what are the risk factors associated with equine anaesthesia?
drugs used age of animal duration of anaesthesia time of surgery operation type
what drug may have a protective effect against anaesthetic related death?
acepromazine
why is TIVA protective in equine anaesthesia?
TIVA is only safe in shorter procedures (<2 hrs)
is there a difference in risk between isoflurane and halothane when used in horses?
no difference found
what age of horse is associated with lowest risk of anaesthetic death?
2-7 years
what effect does time of surgery have on risk of anaesthetic death?
middle of the night (tend to be emergencies anyway)
towards the end of the day (4pm)
what effect does duration of anaesthesia have on anaesthetic risk?
longer anesthesia = increased risk of death
what factors should be considered when deciding whether a procedure will be carried out in the field or the theatre?
temperament of horse
procedure to be performed (how invasive/sterility needed/post op care)
duration of procedure
facilities available (hospital or at yard)
whether transport is possible
what should be done to prepare a horse for anaesthesia?
full physical exam obtain owner consent removal of large haynet 12 hours before anaesthesia groom to remove mud remove shoes weigh antibiotics at least 30 mins before anaesthesia rinse mouth tetanus antioxin if required
should horses be starved prior to anaesthesia?
remove large haynet 12 hours before, leave small amount of food in stable and provide small breakfast to reduce stress
why must any antibiotics that are going to be administered be given at least 30mins before anaesthesia?
as they can lead to hypotension
why should horses have their mouth rinsed before anaesthesia?
prevent advancement of debris into the trachea leading to trauma
where should an IV catheter be inserted into a horse/
left jugular vein
describe the correct technique for jugular IV catheter insertion
strict aseptic technique (inc.gloves)
clip, scrub and use spirit
vein should be raised close to point of insertion
secure in place (suture or glue)
what equipment is required for equine anaesthesia?
padded headcollar and leadrope
towel and ophthalmic equipment
drugs drawn up and labelled
ET tubes and gag
what size ET tubes are required for an adult horse?
20-30mm
what size ET tubes are required for a pony?
25mm
what size ET tubes are required for a small pony?
20mm
what aspects of the theatre environment must be prepared before anaesthesia?
table in correct position
anaesthetic machine ready
monitoring equipment ready including ECG and invasive BP
when is acepromazine given during anaesthesia?
20-30 mins before induction in normovolaemic patients
where is alpha2-agonist sedation given during anaesthesia?
in induction box
what alpha-2 agonist is preferable in abdominal pain patients requiring anaesthesia?
xylozine as it has best analgesic effects
what is vital about the induction area?
should be quiet to ensure full effectiveness of drugs
what drugs may be used to induce anaesthesia in horses?
ketamine/diazepam
thiopental
+/- GGE
what state should the horse be in before induction of anaesthesia is attempted?
profound sedation (5 mins post alpha2 agonist) - 5 point stance
what methods can be used to manage the horse as it goes down following induction?
free fall - handler supports head
tilt table
gate/padded stall
how should intubation be performed in horses?
head and neck extended
blind technique
usually oral
when may nasotracheal intubation be performed in horses?
if access to the mouth/airway is required during surgery
when may GGE be used?
during induction/maintenance of equine anaesthesia
what is GGE?
centrally acting muscle relaxant
what neurons does GGE act at?
internuncial neurones of spinal cord, brainstem and subcortical areas of the brain
does GGE have any anaesthetic/analgesic properties?
no - only used in combinatio with other drugs
via what route can GGE be given?
IV only as causes tissue damage if given perivascularly
how can anaesthesia of horses be maintained?
TIVA
sevoflurane (not licenced)
isoflurane
what combination of drugs can be used for TIVA of horses?
GGE, ketamine and alpha2-agonist
what are the impacts of isoflurane on horses cardiovascular and pulmonary systems?
respiratory depression
hypotension
why is the rapid recovery from anaesthesia not ideal in horses?
they need to recover slowly to reduce the risk of injury when they attempt to stand or injury to any handlers
how long can TIVA be used for?
1-2 hours max
what should be available at all times during equine anaesthesia?
syringe of induction agent to top up anaesthesia fast if depth is too light
what types of analgesia should be given to horses?
NSAIDs most common opioids - reduced analgesic effect alpha-2 agonists ketamine local anaesthetics wherever possible
what horses should receive fluid therapy?
all on inhalational maintenance
what type of fluid should be used in anaesthetised horses?
Hartmann’s
do NSAIDs have similar renal effects in horses as in small animals?
effects during dehydration are not as bad in horses
how should anaesthetic depth of horses be monitored?
respiratory rate and pattern eye position and nystagmus palpebral reflex / anal reflex muscle tone movement blood pressure heart rate (not a very good indicator)
when is respiratory rate and pattern a good indicator of anaesthetic depth?
during IV maintenance as those on gas maintenance are often ventilated
where should the eye be positioned if equine anaesthetic depth is adequate?
medially
what does nystagmus indicate in the anesthetised horse?
lightening anaesthesia
what should the palpebral reflex be like in the anaesthetised horse?
sluggish but not absent
what can muscle tone tell us about the depth of equine anaesthesia?
neck muscles will stand out when anaesthetic is too light
what monitoring devices that is not always used on small animals are essential on horses?
ECG
direct blood pressure monitoring
where should the ECG leads be placed on the horse?
red lead - neck
yellow lead - sternum
green/black lead - ribs
what arrhythmia is common in horses undergoing anaesthetic?
2nd degree AV block
what blood pressure should horses be maintained at?
MAP: 60 mmHg
by how much may cardiac output reduce during equine anaesthesia?
up to 50%
what post op complication in horses is associated with low BP?
EPAM
what can be used if a horses blood pressure falls too low during anaesthesia?
dobutamine / ephedrine
what can be done if BP is falling too low?
check the depth of anaesthesia
what are common issues with respiratory function in anaesthetised horses?
ventilation perfusion mismatch
hypoventilation
what can hypoventilation lead to?
hypercapnia
what should be done prior to recovery with horses maintained on gas?
given a small dose of sedation (alpha-2 agonist) to slow recovery
where should horses be recovered?
quiet environment with a towel over their eyes
what should horses have supplemented during recovery?
O2
when should horses ET tube be removed?
when respiratory effort increases - don’t wait for swallowing as equine laryngeal reflexes are slow and may even be standing before swallow returns
what may horses recover with in place?
oral /nasal tube
how should a horse be recovered from anaesthesia?
sedate
ensure analgesia is adequate
catheterise bladder
why is catherisation of the bladder useful in recovering horses?
reduces stimulation so they don’t try to stand as fast
what types of assisted recovery are available for horses?
manual (H and S!)
ropes
sling
what is a complication associated with equine surgery?
equine post-anaesthetic myopathy
when are symptoms of EPAM seen?
during the recovery period
what causes EPAM?
damaged gained to muscles under compression during anaesthesia
what are the signs of EPAM?
lame (hobbling to unable to stand) distressed horse muscles hard, swollen or painful on palpation myoglobinuria elevated muscle enzymes - CK
what muscles are usually affected by EPAM when horses have been positioned in lateral recumbancy?
triceps
what muscles are usually affected by EPAM when horses have been positioned in dorsal recumbancy?
gluteal
how can EPAM be prevented?
careful positioning of the horse on a padded surface fit horses should be 'let down' minimise anaesthesia time MAP >60 mmHg light anaesthetic depth avoid hypoxia
how should equine limbs be positioned during anaesthesia?
neutral - not tied or flexed / extended
horse in lateral recumbancy should look like he would standing. Dependant forelimb should be pulled forwards
how can EPAM be treated?
depends on severity analgesia - NSAIDs / opioids sedation - ACP (vasodilation beneficial) fluid therapy to preserve renal function good nursing care
when should euthanasia be considered in horses with EPAM?
if they are unable to stand
why do neuropathies occur?
due to prolonged pressure on a nerve
what are the nerves most vulnerable to neuropathies during equine anaesthesia?
radial nerve
facial nerve
brachial plexus
femoral nerve
are neuropathies painful?
not usually just result in loss of function
what is the recovery time of neuropathy linked to?
the degree of nerve damage
what causes spinal cord malacia?
unknown aetiology
when is spinal cord malacia often seen?
short anaesthetics in dorsal recumbancy
heavy horses - although seen in ponies
what are the signs of spinal cord malacia?
‘dog sit’
unable to stand
complete hindlimb paralysis with no sensory perception
what is the prognosis of a horse with spinal cord malacia?
it is fatal
when may fractures occur in the horse undergoing surgery?
trauma durig induction or recovery
pre-existing fracture or injury
often associated with myopathy
why does myopathy increase the risk of post op fractures?
due to lameness and muscle weakness caused which reduces horses coordination
how can a post op fracture be diagnosed?
challenging - consider if severely lame or unable to stand
