Large Animal Complications in Anaesthesia Flashcards
When do most fatalities occur during anaesthesia in horses?
Recovery period (60%)
(50% within first 3 hours of disconnect from anaesthetic machine)
What is the mortality risk of anaesthetic in horses?
1% (1/100)
What causes anaesthetic fatalities in horses?
MOST PROBLEMS OCCUR DURING MAINTENANCE BUT DON’T PRESENT UNTIL RECOVERY
Intra-operative cardiac arrest
○ Due to increased catecholamines
○ Associated with halothane use - mostly replaced by isoflurane
Post-anaesthetic Myopathy (PAM)
○ Muscle weakness due to dysfunction of muscle fibre
Fractures in recovery
○ Could be due to myopathy
Neuropathies and spinal cord malacia
○ Results in euthanasia
Respiratory obstruction
What are the risk factors associated with equine anaesthesia
ASA category
○ Co-morbidities
○ Cardiac health
Age
○ Increased prevalence of other co-morbidities
Surgery type and position
Duration
Time of day - OOH provision
○ Fewer complications in working hours?
○ Fatigue of surgeons
Agents used
○ Halothane - increases catecholamine release
○ IV vs inhalational
Affects BP and hypoxic vasoconstriction reflex
Recovery quality
○ Box design and technique
What are the common problems in anaesthesia of horses?
Hypotension
Hypoxaemia
Hypercapnia
Poor positioning
How does Hypotension cause a problem in recovery?
Low blood pressure
Significantly increased risk of developing myopathies
□ Reduced blood/oxygen supply to muscles - anaerobic respiration/damage
How does Hypoxaemia cause a problem in recovery?
Low oxygen in blood
Same principle as hypotension
Reduced oxygen supply to muscles - anaerobic respiration/damage
How does hypercapnia cause a problem in recovery?
High CO2 in blood
Changes in blood pH
Can affect cellular metabolism
How does poor positioning cause a problem in recovery?
Increased pressure on specific muscle groups
□ Triceps myopathy or neuropathy
□ Haven’t pulled leg forward enough so weight has been put into triceps muscle
What is Post-operative Myopathy?
Muscle weakness due to dysfunction of muscle fibre
Caused by intraoperative malposition and hypotension
Weight of horse on muscles
Reduced perfusion pressure to muscle
Occurs when a horse wakes up
Painful and difficult to manage
Prevention:
Reduce inhalational requirements
IV anaesthesia
Inotropes
○ Weight of horse on muscles
○ Reduced perfusion pressure to muscle
○ Pay attention to fluid balance/therapy
What is Post-operative Neuropathy?
Caused by pressure on a nerve and hypotension
Occurs when horse wakes up
○ Knuckling
○ Facial nerve paralysis - dentals or head collar not removed
Common in lateral recumbency
Prevention:
○ Extend forelimb to reduce weight on triceps muscle
Less painful than myopathy, eventually recover
What is Spinal Cord Malacia?
When the spinal cord begins to soften
Unknown cause
FATAL
Occurs when horse recovers
Classic ‘dog sitting’ position
○ Lost function of hindlimbs
Not related to duration of anaesthesia
Often in heavy breed or young horses
What causes eye problems?
Usually due to lateral recumbency
Prevention:
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○ Must protect lowermost eye with padding
Lubrication for eye
