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JJ > Equine Sedation and Anaesthesia > Flashcards

Equine Sedation and Anaesthesia Flashcards

1
Q

what should be done when preparing horses for sedation?

A 
check passport
assess signalment and temperament
assess cardio and respiratory systems
establish duration of sedation required and anticipated pain level
consider facilities and handlers
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2
Q

why must a horses passport be checked before sedation?

A

due to their food production status to ensure that there is a hold placed on them if they are given specific drugs

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3
Q

do horses need to have food withheld before sedation?

A

no

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4
Q

should horses have food withheld after sedation?

A

restriction until they are adequately recovered

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5
Q

why is a calm, quiet environment required when sedating horses?

A

to enable drugs to take effect properly and so that sedation works as expected

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6
Q

with what type of sedation is a quiet environment key?

A

alpha - 2 agonists as they compete with adrenaline at receptors

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7
Q

how should you approach sedation of horses?

A 
calm, quiet environment
schedule enough time
be aware of safety issues
prepare all equipment
ensure it is a positive interaction
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8
Q

why is it crucial that horses interaction with veterinary personnel is positive?

A

can easily become needle shy which poses a problem for any further veterinary treatment

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9
Q

what is acepromazine a derivative of?

A

phenothiazine

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10
Q

what level of sedation is offered by acepromazine?

A

mild

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11
Q

what is acepromazine used for in horses?

A

only takes the edge off so used for mild procedures or premed for GA

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12
Q

what is the speed of onset of acepromazine?

A

slow onset for IM and IV - 30 mins

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13
Q

how long is the duration of action of acepromazine?

A

4-6 hours

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14
Q

what is the key side effect of acepromazine?

A

vasodilation

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15
Q

why is acepromazine problematic in breeding stallions?

A

can cause priapism

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16
Q

why should acepromazine be avoided in shocked or hypovolaemic patients?

A

cause alpha adrenergic blockade which prevents contraction of smooth muscles so leads to vasodilation

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17
Q

what are the main types of sedatives used in horses?

A

alpha-2 adrenoreceptor agonists

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18
Q

what are the effects of alpha-2 adrenoreceptoragonists?

A 
sedation
muscle relaxation
analgesia
cardiovascular effects
hypoinsulinaemia
decreased GI motility
sweating
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19
Q

what area of the brain is targeted by alpha2-adrenoreceptors?

A

pons (locus ceruleus)

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20
Q

where do alpha2-adrenoreceptor agonists have their analgesic effect?

A

dorsal horn of spinal cord

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21
Q

what are the cardiovascular effects of alpha2-adrenoreceptor agonists?

A

bradycardia
second degree AV block
initial hypertension then hypotension

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22
Q

what is the sign of adequate sedation with alpha2-adrenoreceptor agonists in horses?

A

5 point stance
ataxia
swaying

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23
Q

what receptors do alpha2-adrenoreceptor agonists bind to?

A

not totally alpha 2 specific, will also bind to alpha 1

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24
Q

how long do alpha2-adrenoreceptor agonists take to achieve full effect?

A

2-5 mins

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25
Q

what is the most specific alpha2-adrenoreceptor agonist?

A

romifidine

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26
Q

what is the least specific alpha2-adrenoreceptor agonist?

A

Xylazine

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27
Q

what is the fastest acting alpha2-adrenoreceptor agonist?

A

xylazine

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28
Q

what is the slowest acting alpha2-adrenoreceptor agonist?

A

romifidine

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29
Q

what is the alpha2-adrenoreceptor agonist that causes the most ataxia?

A

xylazine

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30
Q

what is the alpha2-adrenoreceptor agonist that causes the least ataxia?

A

romifidine

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31
Q

what alpha2-adrenoreceptor agonist has the shortest action?

A

xylazine

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32
Q

what alpha2-adrenoreceptor agonist has the longest action?

A

romifidine

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33
Q

how are alpha2-adrenoreceptor agonists administered?

A

IV or IM

care as absorbed across MM

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34
Q

what are the effects of opioids on horses when given with an alpha2-adrenoreceptor agonist?

A

have synergistic effect on analgesia and sedation depth
increased ataxia
possibility that animals are less likely to kick?!

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35
Q

what is the most popular opioid used in horses?

A

butorphanol

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36
Q

does butorphanol provide good analgesia to horses?

A

no so other analgesic must be given alongside

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37
Q

what is a better opioid to use in horses for it’s analgesic effect?

A

ketamine

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38
Q

what are the issues with using buprenorphine?

A

controlled drug

increased volume required so administration is more difficult

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39
Q

what is pethidine used for in horses?

A

relief of spasmodic colic, given IM only

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40
Q

can methadone be given to horses?

A

yes but on cascade as only licenced in small animals

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41
Q

when may remote IM sedation be used in horses?

A

unhandled or fractious horses

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42
Q

what combination of drugs may be given in a remote IM injection technique?

A

detomidine - 20-60 micrograms/kg
butorphanol - 50 micrograms/kg
acepromazine - 50 micrograms/kg

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43
Q

how must oral sedatives be prescribed?

A

for each individual horse for each time of use following a clinical exam by VS

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44
Q

what should be arranged when prescribing oral sedatives?

A

safe disposal of any unused product

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45
Q

what should be done when handling oral sedatives?

A

wear gloves

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46
Q

what is involved in gaining informed owner consent for sedation for paraprofessionals?

A

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

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47
Q

what is the calculated total mortality from peri-operative complications in horses?

A

1.9% died within 7 days of surgery

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48
Q

what are the top 3 factors responsible for anaesthetic death in horses?

A

cardiac arrest 33%
fracture 23%
myopathy 7%

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49
Q

what type of surgery is highly risky in horses?

A

colic

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50
Q

what are the risk factors associated with equine anaesthesia?

A 
drugs used
age of animal
duration of anaesthesia
time of surgery
operation type
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51
Q

what drug may have a protective effect against anaesthetic related death?

A

acepromazine

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52
Q

why is TIVA protective in equine anaesthesia?

A

TIVA is only safe in shorter procedures (<2 hrs)

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53
Q

is there a difference in risk between isoflurane and halothane when used in horses?

A

no difference found

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54
Q

what age of horse is associated with lowest risk of anaesthetic death?

A

2-7 years

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55
Q

what effect does time of surgery have on risk of anaesthetic death?

A

middle of the night (tend to be emergencies anyway)

towards the end of the day (4pm)

56
Q

what effect does duration of anaesthesia have on anaesthetic risk?

A

longer anesthesia = increased risk of death

57
Q

what factors should be considered when deciding whether a procedure will be carried out in the field or the theatre?

A

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

58
Q

what should be done to prepare a horse for anaesthesia?

A 
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
59
Q

should horses be starved prior to anaesthesia?

A

remove large haynet 12 hours before, leave small amount of food in stable and provide small breakfast to reduce stress

60
Q

why must any antibiotics that are going to be administered be given at least 30mins before anaesthesia?

A

as they can lead to hypotension

61
Q

why should horses have their mouth rinsed before anaesthesia?

A

prevent advancement of debris into the trachea leading to trauma

62
Q

where should an IV catheter be inserted into a horse/

A

left jugular vein

63
Q

describe the correct technique for jugular IV catheter insertion

A

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)

64
Q

what equipment is required for equine anaesthesia?

A

padded headcollar and leadrope
towel and ophthalmic equipment
drugs drawn up and labelled
ET tubes and gag

65
Q

what size ET tubes are required for an adult horse?

A

20-30mm

66
Q

what size ET tubes are required for a pony?

A

25mm

67
Q

what size ET tubes are required for a small pony?

A

20mm

68
Q

what aspects of the theatre environment must be prepared before anaesthesia?

A

table in correct position
anaesthetic machine ready
monitoring equipment ready including ECG and invasive BP

69
Q

when is acepromazine given during anaesthesia?

A

20-30 mins before induction in normovolaemic patients

70
Q

where is alpha2-agonist sedation given during anaesthesia?

A

in induction box

71
Q

what alpha-2 agonist is preferable in abdominal pain patients requiring anaesthesia?

A

xylozine as it has best analgesic effects

72
Q

what is vital about the induction area?

A

should be quiet to ensure full effectiveness of drugs

73
Q

what drugs may be used to induce anaesthesia in horses?

A

ketamine/diazepam
thiopental
+/- GGE

74
Q

what state should the horse be in before induction of anaesthesia is attempted?

A

profound sedation (5 mins post alpha2 agonist) - 5 point stance

75
Q

what methods can be used to manage the horse as it goes down following induction?

A

free fall - handler supports head
tilt table
gate/padded stall

76
Q

how should intubation be performed in horses?

A

head and neck extended
blind technique
usually oral

77
Q

when may nasotracheal intubation be performed in horses?

A

if access to the mouth/airway is required during surgery

78
Q

when may GGE be used?

A

during induction/maintenance of equine anaesthesia

79
Q

what is GGE?

A

centrally acting muscle relaxant

80
Q

what neurons does GGE act at?

A

internuncial neurones of spinal cord, brainstem and subcortical areas of the brain

81
Q

does GGE have any anaesthetic/analgesic properties?

A

no - only used in combinatio with other drugs

82
Q

via what route can GGE be given?

A

IV only as causes tissue damage if given perivascularly

83
Q

how can anaesthesia of horses be maintained?

A

TIVA
sevoflurane (not licenced)
isoflurane

84
Q

what combination of drugs can be used for TIVA of horses?

A

GGE, ketamine and alpha2-agonist

85
Q

what are the impacts of isoflurane on horses cardiovascular and pulmonary systems?

A

respiratory depression

hypotension

86
Q

why is the rapid recovery from anaesthesia not ideal in horses?

A

they need to recover slowly to reduce the risk of injury when they attempt to stand or injury to any handlers

87
Q

how long can TIVA be used for?

A

1-2 hours max

88
Q

what should be available at all times during equine anaesthesia?

A

syringe of induction agent to top up anaesthesia fast if depth is too light

89
Q

what types of analgesia should be given to horses?

A 
NSAIDs most common
opioids - reduced analgesic effect
alpha-2 agonists
ketamine
local anaesthetics wherever possible
90
Q

what horses should receive fluid therapy?

A

all on inhalational maintenance

91
Q

what type of fluid should be used in anaesthetised horses?

A

Hartmann’s

92
Q

do NSAIDs have similar renal effects in horses as in small animals?

A

effects during dehydration are not as bad in horses

93
Q

how should anaesthetic depth of horses be monitored?

A 
respiratory rate and pattern
eye position and nystagmus
palpebral reflex / anal reflex
muscle tone
movement
blood pressure
heart rate (not a very good indicator)
94
Q

when is respiratory rate and pattern a good indicator of anaesthetic depth?

A

during IV maintenance as those on gas maintenance are often ventilated

95
Q

where should the eye be positioned if equine anaesthetic depth is adequate?

A

medially

96
Q

what does nystagmus indicate in the anesthetised horse?

A

lightening anaesthesia

97
Q

what should the palpebral reflex be like in the anaesthetised horse?

A

sluggish but not absent

98
Q

what can muscle tone tell us about the depth of equine anaesthesia?

A

neck muscles will stand out when anaesthetic is too light

99
Q

what monitoring devices that is not always used on small animals are essential on horses?

A

ECG

direct blood pressure monitoring

100
Q

where should the ECG leads be placed on the horse?

A

red lead - neck
yellow lead - sternum
green/black lead - ribs

101
Q

what arrhythmia is common in horses undergoing anaesthetic?

A

2nd degree AV block

102
Q

what blood pressure should horses be maintained at?

A

MAP: 60 mmHg

103
Q

by how much may cardiac output reduce during equine anaesthesia?

A

up to 50%

104
Q

what post op complication in horses is associated with low BP?

A

EPAM

105
Q

what can be used if a horses blood pressure falls too low during anaesthesia?

A

dobutamine / ephedrine

106
Q

what can be done if BP is falling too low?

A

check the depth of anaesthesia

107
Q

what are common issues with respiratory function in anaesthetised horses?

A

ventilation perfusion mismatch

hypoventilation

108
Q

what can hypoventilation lead to?

A

hypercapnia

109
Q

what should be done prior to recovery with horses maintained on gas?

A

given a small dose of sedation (alpha-2 agonist) to slow recovery

110
Q

where should horses be recovered?

A

quiet environment with a towel over their eyes

111
Q

what should horses have supplemented during recovery?

A

O2

112
Q

when should horses ET tube be removed?

A

when respiratory effort increases - don’t wait for swallowing as equine laryngeal reflexes are slow and may even be standing before swallow returns

113
Q

what may horses recover with in place?

A

oral /nasal tube

114
Q

how should a horse be recovered from anaesthesia?

A

sedate
ensure analgesia is adequate
catheterise bladder

115
Q

why is catherisation of the bladder useful in recovering horses?

A

reduces stimulation so they don’t try to stand as fast

116
Q

what types of assisted recovery are available for horses?

A

manual (H and S!)
ropes
sling

117
Q

what is a complication associated with equine surgery?

A

equine post-anaesthetic myopathy

118
Q

when are symptoms of EPAM seen?

A

during the recovery period

119
Q

what causes EPAM?

A

damaged gained to muscles under compression during anaesthesia

120
Q

what are the signs of EPAM?

A 
lame (hobbling to unable to stand)
distressed horse
muscles hard, swollen or painful on palpation
myoglobinuria
elevated muscle enzymes - CK
121
Q

what muscles are usually affected by EPAM when horses have been positioned in lateral recumbancy?

A

triceps

122
Q

what muscles are usually affected by EPAM when horses have been positioned in dorsal recumbancy?

A

gluteal

123
Q

how can EPAM be prevented?

A 
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
124
Q

how should equine limbs be positioned during anaesthesia?

A

neutral - not tied or flexed / extended

horse in lateral recumbancy should look like he would standing. Dependant forelimb should be pulled forwards

125
Q

how can EPAM be treated?

A 
depends on severity
analgesia - NSAIDs / opioids
sedation - ACP (vasodilation beneficial)
fluid therapy to preserve renal function
good nursing care
126
Q

when should euthanasia be considered in horses with EPAM?

A

if they are unable to stand

127
Q

why do neuropathies occur?

A

due to prolonged pressure on a nerve

128
Q

what are the nerves most vulnerable to neuropathies during equine anaesthesia?

A

radial nerve
facial nerve
brachial plexus
femoral nerve

129
Q

are neuropathies painful?

A

not usually just result in loss of function

130
Q

what is the recovery time of neuropathy linked to?

A

the degree of nerve damage

131
Q

what causes spinal cord malacia?

A

unknown aetiology

132
Q

when is spinal cord malacia often seen?

A

short anaesthetics in dorsal recumbancy

heavy horses - although seen in ponies

133
Q

what are the signs of spinal cord malacia?

A

‘dog sit’
unable to stand
complete hindlimb paralysis with no sensory perception

134
Q

what is the prognosis of a horse with spinal cord malacia?

A

it is fatal

135
Q

when may fractures occur in the horse undergoing surgery?

A

trauma durig induction or recovery
pre-existing fracture or injury
often associated with myopathy

136
Q

why does myopathy increase the risk of post op fractures?

A

due to lameness and muscle weakness caused which reduces horses coordination

137
Q

how can a post op fracture be diagnosed?

A

challenging - consider if severely lame or unable to stand

JJ (33 decks)

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