Equine sedation and anaesthesia Flashcards
What is the main thing about equine anaesthesia?
+++ about risk management
team effort
risk procedure for ptx and staff
What are the legal aspects regarding different drugs in equine passports?
licensed agents: on a special essentials list or active substance on GB list of known MRLs, use needs to be recorded
Others: NOT to be used unless passpoty is signed as not for slaughter, permanent
Why is the risk of anaesthesia much higher in horses?
temperament/character: panic/flee causing trauma/fracture
size/strength: hard to restrain/help
weight and build
What potential problems do the weight of horses cause during anaesthesia?
large body weight squashing tissues = ischaemia
large displaceanle GI tract = colic
horizontal coursing diaphragm = ventilation and circulation compromise
obligate nasal breathers = airway obstruction
delicate limbs = trauma/fracture
What are the potential risks during each phase of anaesthesia in horses?
induction: excitement, IV mishap, trampling
maintenance: adverse effects from anaesthetic drugs and recumbency
recovery: trauma/fracture or complications induced during maintenance
How can we limit the anaesthetic risk in horses?
avoid GA, consider standing sx under sedation
keep deviations from normal small/transient
always minimise duration of anaesthesia
case selection: setting/support suitable for ptx and procedure
What are good agreed core protocols for equine sedation/premed?
alpha 2 adrenoceptor agonist +/- opioids
What are good agreed core protocols for equine induction?
ketamine + benzodiazepine
What protocols for equine anaesthesia/sedation are to never be used?
benzodiazepines for standing sedation: muscle weakness = panic
azaperone (pig sedative) causes violent excitement in horses
What are the surgical requirements for standing sedation?
cooperative stress free ptx
stand still
stock, collar, rope, head support
adequate analgesia: systemic analgesics+local on area operated
What are the drug options for sedation and analgesia during standing sedation?
acepromazine
alpha2 agonists (xylazine, detomidine, romifidine, dexmedetomidine)
opioids (butorphanol, morphine, methadone, buprenorphine)
nsaids
Which sedation and analgesia drugs are licensed for horses during standing sedation?
alpha2: xylazine, detomidine, romifidine
opioid: butorphanol
Which sedation and analgesia drugs need a not for slaughter signature during standing sedation?
methadone and buprenorphine
Which local anaesthetic block drugs are used during standing sedation?
mepivacaine, lidocaine
bupivacaine
What are the general points and limitations of equine sedation?
not an anaesthetic = can still react
all sedatives work best if animal is calm to start with
surprise arousal can occur
ensure quiet environment
give time to take effect
How responsive are horses when sedated?
can be VERY
do not pat on backside
can startle and kick
What drugs can help with touvh responsiveness in horses during sedation?
opioids
butorphanol (licensed)
morphine (6mo)/methadone
What is acepromazine?
a phenothiazine
dopamine antagonist but also alpha 1 adrenoreceptor block
limited sedative potential
slow onset long duration
What are the side effects of acepromazine?
main: vasodilation which causes hypotension, hypothermia
What are contraindications for acepromazine?
hypovolaemia, dehydration!
extreme stress/shock
+/- in foals
+/- in stallions
What is the side effect of acepromazine that is specific to male horses?
penile dysfunction/protrusion
can cause physical damage if longstanding
priapism and penile apralysis may occur
not a major problem if treated immediately
What are the alpha 2 agonists used for sedation in horses?
xylazine
detomidine (very concentrated)
romifidine (longes acting, less ataxia, less deep sedation)
dose dependent effect, reliable and profound sedation/analgesia
What are the most reliable equine sedatives?
alpha 2 agonists
What are the side effects of alpha2 agonists in horses?
ataxia, swaing (try limit dose)
CVS: periph. vasoconstriction, bradycardia
reduced GI motility: colic risk when prolonged/high doses
increased uterine tone (avoid in preg)
reduced ADH and insulin release: increased urine output and blood glucose
What is the effect of benzodiazepines as a sedative in horses?
NO appreciable sedative effect in adult horses
gives effective muscle relaxation can cause awake horses to panic
NEVER USE TO SEDATE AWAKE ADULT
useful sedative up to 2-3 week old foals
Why is the effect of benzodiazepines different in foals and adult horses?
blood brain barrier
behavioural maturity
What are the differences between ACP and alpha 2 agonists as sedatives?
ACP: not licensed for food producing
ALPA: licensed IV
ACP: long duration of action, 20-30 min onset
ALPHA: shorter depending on drug, 2 min onset
ACP: limited sedative depth
ALPHA: dose dependent reliable deep sedation
ACP: limited ataxia
ALPHA: ataxia, dose dependent
ACP: not analgesic
ALPHA: analgesic
Why are opioids avoided in horses and what are the workarounds?
risk of reduced GI motility, colic
risk of central excitation, box walking/locomotor stimulation
prudent peri-operative use at common dosages avoids these risks
laxative diet/mineral oil prophylaxis if prolonged systemic use
What are the main uses of opioids in horses?
excellent peri operative analgesic
improve acp/alpha 2 based sedation
localised prolonged pain relied
When are NSAIDs given in horses?
excellent for post op pain
often given pre op in heathy horse
should always be inclused unless contra-indicated
What are potential side effects of nsaids in horses?
all rarer
GI toxicity (ulceration)
renal toxicity
What are the different local anaesthetics in horses and their particularities?
mepivacaine: less swelling than lido, longer acting (2.5h)
bupivacaine: longest duration (6-8h)
What is the typical protocol for standing sx in horses?
may give ACP in stables 1h prior
alpha2agonist + opioid IV
NSAID
LA block of area
maintain steady sedation alpha2 agonist
What is an essential thing to know post sedation?
no eating until well awake
~2hr oesophageal obstruction risk
What is a side effect of butorphanol and when should we avoid it?
muzzle twitches
prefer mu agonist for head surgery or CT
What are the pre GA steps in horses?
risk assessment owner consult
exam: temperament, behviour, GE, auscultation, lameness, jug veins
fasting/starrving? short (under 4h) if at all
remove shoes: avoid damage to rubber floors and avoid soft tissue trauma
What is the aim of induction in horses?
achieve unconsciousness and recumbency
What is used as drugs for induction in horses?
ketamine + muscle relaxant used universally
usually midazolam or diazepam IV
Why is propofol impractical in horses?
poor quality induction
not licensed
imprcatical vs volume
What is the typical ASA1-2 pre med in horses?
In stable:
ACP IV/IM 30min-1h before
low dose of alpha 2 IV just before
in theatre:
sedate with alpha 2 agonist
opioid, nsaids if not already
What are the effects of ketamine as an induction agent in horses?
dissociative anaesthetic: eyes open, can still blink and swallow
CVS: sympathomimetic, vasoconstriction and HR increase
Resp: irreg pattern but maintain minute volume
motor: no muscle relaxation
sensory: good somatic analgesia
How do we control/restrain horses during induction?
people or swing gate
horse squeezed to go down along passes wall
head restrained to go down with hind end first
OR free fall in field/padded box
What are the types of maintenance for GA?
total iV anaesthesia (TIVA)
inhalation
partial IV anaesthesia (PIVA)
When is it best to use IV anaesthesia?
GA under 1h or drugs can accumulate
short procedures in healthy and not too heavy animals
What is a good example of protocol for a field castration?
alpha2 agonist +/- butorphanol
ketmaine +/- benzodiazepine induction = 10-15min GA
LA in testicle
What is a triple drip?
often combo of guaifenesin, alpha 2 agonist, ketamine
or midazolam, alpha2 agonist and ketamine
to maintain field anaesthesia
How do we position horse on the operating table?
everything padded
limbs in neutral relaxed position
no sharp edges
raise head-end of table to reduce nasal oedema
protect and lubricate eyes
What are the volatile anaesthetic agents used in equine anaesthesia?
isoflurane: licensed
sevoflurane: 6mo
What are the side effects of the volatile anaesthetic agents on horses?
resp depression: reduced RR and tidal volume (may require IPPV to correct)
hypotension: vasodilatation, myocardial depression (may require positive inotrope dobutamine to correct)
What are the common intra operative problems during inhalation anaesthesia?
hypotension
hypercapnia
hypoxaemia
What are the main causes of hypotension during anaesthesia?
vasodilation (drugs, endotoxin effects, shock)
low CO: low HR, low contractility, low venous return (drugs, endotoxins, inhalants, position, hypovolaemia)
What can poor tissue blood flow during anaesthesia cause?
can lead to hypoxic damage which may only show during recovery
How can we prevent/treat hypotension during anaesthesia?
moditor direct BP
treat hypovolaemia before GA
avoid ACP
How can we treat hypotension if MAP is under 70mmHg in horse anaesthesia?
reduce inhalant agent % = less vasodilation
improve CO
give fluids + infuse beta 1 agonist dobutamine
if no response: other sympathomimetics including vaspressors
What is hypercapnia?
elevated arterial CO2 due to reduced alvolar minute leading to CO2 retention, can develop resp acidosis
How do we treat hypercapnia under 60mmHg during equine anaesthesia?
ventilate IPPV
What is the main cause of hypoxaemia during equine anaesthesia?
compression atelectasis creating so called V/Q mismatch
How can we treat hypoxaemia in equine anaesthesia?
tell surgeon to speed up
give FiO2 (100% O2)
recruitment manoevre and applying positive end expiratory pressure
tilt table 7 degrees head up
bronchodilator (salbutamol) via ETT
What is the main goal of anaesthesia recovery in horses?
slow but good quality!
What are problems seen during or after recovery?
trauma: fractures, lameness…
Resp obstruction
pulonary oedema
neuropraxi and neuropathy
myopathu
myelopathy/myelomalacia
What is PA neuropathy?
nerve paralysis
usually neuropraxia: transient deficit, not painful
What is PA myopathy?
ischaemia reperfusion injury
inadequate oxygen delivery to muscles during GA
very painful
