Anaesthesia of Equine and Exotics Flashcards
(98 cards)
What is the anaesthesia triad?
Unconsciousness
Analgesia
Muscle relaxation
What is the risk of death during GA ina guinea pig and in a hamster, and in a budgy and other birds?
GP: 1 in 26
Hamster: 1 in 27
Budgie: 1 in 6
Birds: 1 in 41
What is allometric scaling?
Dose requirements dont remain proportionately the same with size change. Smaller animals need larger doses per kg.
What are our main concerns when anaesthetising a horse?
- Neuropraxis - limb or facial
- Gut stasis/ileus (dont need to withold food as horses dont vomit)
- Fit horses swing depth of GA and prone to hypotension. Usually horses are ‘let down’ from peak fitness for 7-10 days.
- Recovery injuries (#s of long bones or spine are fatal)
- Ocular injuries ( hitting off surface or scratching cornea)
- Myopathies (muscle injury , myoglobin in blood, and then urine. Care with positioning, use fluid to flush myoglobins, and keep GA less than 2 hours))
- Myelopathy (damage to the spinal cord- from dorsal).
- Hypoxaemia prone during GA. Ventilation-perfusion mismatch common in lateral recumbency (the circulating blood is not fully oxygenated).
What does teh hypoxic pulmonary vasocontriction reflex do?
It shuts down poorly ventilated parts of the lung and directs blood to well-ventilated areas to avoid ventilation perfusion mismatch. This is reduced during anaesthesia.
How many ribs does a horse have?
18
What drugs are normally used in horses?
ACP often as a pre-med IM IV as calming.
Alpha 2s e.g. xyalzine, romifidine, detomidine.
Guaiphenesin (GG) - muscle relaxant should not be used alone
Ketamine - induction and injectable maintenance.
Thiopental - very fast onset of action, good if a 600lg horse wakes up.
Benzodiazepines e.g. diazepam and midazolam
Inhalants - isoflurane and better recovery with sevo (off license)
NSAIDs
Opiods - can cause restlessness e.g. box walking. E.g. buprenorphine, morphine, torb, pethidine.
Tetanus anti-toxin
Hypertonic Saline
Dobutamine - increases contracility and CO (good for treating hypotension in horses as hard to overdose)
ACP has been reported to cause priapism in horses… what is this?
A continous erect penis. (ACP is often avoided in breeding stallions)
Out of the alpha 2 agonists used in horses: xyalzine, romifidine and detomidine. Which have the best and worst:
- analgesia
-onset
-duration
-muscle ataxia
- muscle relaxation
- xyalzine best analgesia; romifidine worst.
- xyalzine quickest; romifidine slowest.
- xyalzine shortest DOA; romifidine longest
- xyalzine most muscle ataxia and relaxation, romifidine least.
Detomidine is in the middle for all of the categories.
What are the main differences when using isoflurane in horses compared to small animals?
Horses have marked respiratory depression with iso - 4bpm. Leads to notable hypercapnia. Ventilators often needed.
Describe the characteristics of pethidine for use in a horse
- licensed UK
- full mu agonsit opiod
- duration of action only approx 1 hour.
- large volume IM injection
What is the dose of morphine for a horse and duration of action ?
0.1-0.2mg/kg IV and 4 hours of action
Describe the use of buprenorphine in horses?
Licensed UK
Slow onset of action, even IV
Long duration of action 6-8 hours
Gut motility side effects
Dose 6-10mcg/kg
Why is hypertonic saline of use in horses?
Great GA risk and hard to get enough fluid into them as such large volumes required. A bolus in a horse might be 50-60 litres! It is importnat to follow hypertonic saline with crystalloids.
What technique is often used instead of ‘sedation’ or GA in horses?
Standing chemical restraint (SCR) or standing surgical anaesthesia (SSA)
What risks to we need to be aware of for SCR in horses?
- Head position (congestion of blood in a drooped head can lead to airflow issues in the obligate nasal breathers)
- Stocks (ensure head and neck not pressing onto gate and impeding blood flow in carotid arteries causing fainting)
- Noise and touch - horses are sensitive to noise under sedation, also if you touch the horse it may jump or kick.
- ensure effective desensitisation before starting!
What should be checked on the horse prior to GA?
Shoes. Any loose shoes can cause damage as can be sharp and damage contralateral limb. Can remove shoes, tape or bandage feet.
Wash the horses mouth out incase food in there.
What are the sites used for IV cannulation in a horse?
Jugular vein- either up or down facing
What are the pros and cons of an upward jugular cannula vs a downwards one?
Upwards is technically easier to palce, but its against blood flow and more turbulent (thereofre more likely to cause thrombophlebitis). If the cap dislodges blood will clot and flow will cease.
Downwards is harder to place but with blood flow and less turbulant.If the cap dislodges air can get into the vein causing an embolus.
Why is jugular flow so important in horses?
They solely rely on the jugular to drain the head, if blocked causes swelling.
What is the dose of ACP in horses?
0.02-0.03mg/kg not exceeding 0.05mg/kg
What IV premeds are commonly used in horses?
no more than 100ug/kg romifidine or 20ug/kg detomidine.
Usually alongside an opiod e.g. butorphanol or morphine.
What IM premeds are commonly used in horses?
Alpha 2, ACP and an opiod commonly.
Need about 3 x dose of alpha 2 than IV
What are the methods of induction in horses?
- Induction gate (padded walls, restrict movement, then can be opened once sternal -> lateral)
- Wall hold ( using people to hold against wall)
- Freefall (guided by handler)