Anaesthesia of Equine and Exotics Flashcards
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)
What is the dose of ketamine for induction in a horse?
2-2.5mg/kg IV
What is the main difference in induction drug giving in horses vs small animals?
Given as bolus and not ‘to effect’
What drugs for induction of a horse require restraint induction techniques?
Guaiphenesin as produces weakness and ataxia first
Do horses require intubation?
They maintian their airways well and do not require intubation for short procedures in the field. But o2 should be supplemented.
Why do we need to be careful with a GGE infusion in horses?
Prolonged infusion can lead to accumulation of GGE leading to weakness and ataxia on recovery which is not helpful for a horse trying to stand!
Describe intubation in a horse?
Lateral recumbency. Head and neck in straight line. Mouth gag needed. Horses can go into laryngospasm. Look for condensation then advance.
What kind of intubation can be used for some oral procedures?
Nasal Endotracheal intubation usuall a smaller tube ventramedially guided.
Describe how depth of anaesthesia is assessed in horses
Eye position- tend to rotate forward instead of ventrally and dont move as much.
Palpebral reflex - run finger over eyelashes
Nystagmus - may been seen when light.
Swallow reflex will be maintained if using ketamine
Where do the ECG leads go on a horse?
Red jugular, Yellow sternum behind heart and green on thorax
Where can an arterial catheter be placed on a horse?
Facial artery
Metatarsal artery
What is commonly given when horses enter recovery?
Aplha 2s - usually remofidine as long lasting a produces little ataxia
What rate of o2 flow minumum required in horses to have an effect?
15L/min
What specific conseideration are needed for anaesthesia of a foal?
Higher fluid requirements due to water content of body higher than adults.
PDA patent for 7 days, blood flow diverted to pulmonary circualtion
Prone to ulceration of GI tract and stomach e.g. when stressed.
Why is corneal damage more common in smaller animals
Same with dogs/cats - reduced tear production and no blink to distribute. But also they usually have a mask and this can cause trauma if postioned over the eyes. Inhalational induction gas flow can dry the corneas also.
Why are smaller animals more prone to heat loss?
Higher SA to volume ratio
Small mammals have a higher metabolic rate than cats and dogs which means they use more ___ + _____?
Glucose and Oxygen
(easier for them to become hypoglycaemic or hypoxaemic)
Why is EMLA useful in small animals?
Desensitises the skin before IV placement and also causes some local vasodilation.
What is the recommended volume limit for IM injections?
0.2mls/kg per site
What are the recommended guides for SC volumes in rabbits, rats and mice?
1ml/kg per site in rabbits
5mls/kg per site rats
10mls/kg/site in mice
What is the risk of sc fluids in chinchillas?
Fur slip
- sheds a lump of hair in response to being held in a stressful situation
What is the most common bone used for IO injections?
Tibia
What temperature should warmed fluids be?
40C
Describe how you would induce an animal using a gas chamber?
Place animal in chamber
Start o2 flow
Put vaporiser on 1%, watch for 3-4 breaths to ensure no breath-holding
Increase the percentage by 1% and repeat until the vapouriser is set at maximum
O2 flow should aim to fill the chamber in a minute so the size will determine the FGF
Check the depth by tilting chamber and seeing if mammal corrects position. Once lost, move onto mask.
Try to flush o2 through before opening.
What reflexes can we assess depth in small mammals?
Righting Reflex
Withdrawl reflexes
Resp and CVS
Why sometimes do the capnograoh read lower than the true value?
When using higher flow rates and patient has low tidal volume. Sample contains some fresh gas as well.
What temperature should we recover small animals such as hamsters at?
26-30C ambient. Care with drying out mm
SHould we starve ferrets pre-op?
We can as they are used to intermittent feeding
Ferrets are induced ovulators. What does this mean?
They require copulation to end oestrus. If they dont mate, they have a prolonged oestrus period. The continuous presence of oestrogen can lead to bone marrow suppression and anaemia, with reduction in platelets increasing bleeding.
What disease are ferrets prone to?
Adrenal disease
What respiratory disease are rabbits prone to?
Pasteurella
What is the main concern when GA/ reccovering a rabbit?
Ileus - gut stasis - contributed by stress, pain, drugs
What should be careful about with posisiotning of rabbits?
Large volume of guts so table should be tilted
Why is some rabbits response to atropine reduced?
Some possess atropinase enzyme
What precaution must be taken prior to GA in guinea pigs?
Withold food for 2-3h because store food in pharygeal pouches. Dont vomit but may leak green fluid from pharyngeal
What ventilation pattern will be seen in all GPs under GA?
Paradoxical breathing. Can use atropine in their pre-med to reduce secretions nd dilate airways
What anaesthetic considerations for hamsters?
Care with produding eyes
Self mutilation after ketamine IM
What care needs to be taken with gerbils and degus?
Gentle handing to prevent tail slip - loss of hair or skin on tail
List some general signs of pain in small animals
- general unkept look(lack of grooming)
- RR changes
- reduced appetite
- tooth grinding
- inactivity and swings between this and really active periods
Describe some painful faces in small animals
- orbital tightening
- Rabbit ears pulled back and closer; rats and mice ears further apart and pulled down
-more tension in the whiskers - changes in nose. Rabbits pulled down, buldge in mice, flattens in rats
- rats and rabbits flatten cheeks ; mice buldge cheeks
What are the maximum volumes of lidocaine and bupivicaine in small animals
4 mg/kg lidocaine
1.5mg/kg bupivicaine
What is a major challenge with anaesthetising ruminants? And what can we do to alleviate issues?
Ruminants have a large ‘tank’ stomach that has bacterial flora digesting the food. They commonly regurge their food and re-chew it. Under GA they are prone to aspiration, and build up of gas in stomach due to lack of burping.
We can stave them for longer period pre-op 12-18 or even 24 hours. Water witheld for 12 hours.
They usually hypoventilate under GA but maintain BP well due to low compliance and tidal volumes.
Due to Bull’s thick skin, where would IV access be gained?
Auricular vein in ear.
What is tympany
Build up of gas in abdomen of ruminants. May need to be drained via stomach tube or needle into abdomen to release pressure.
What type of stomachs to camelids have? E.g. alpacas and llamas
Tripartite
Where is the best vein access in a typical pig?
Ear
What are the difficulties when intubating pigs?
- narrow gape - hard to visualise
- laryngospasm
- S-shaped bend in larynx
-Blind-ending pharyngeal diverticulum which ETT may enter
What is the only licesnsedsedative for pigs in the uk?
Azaperone (Stresnil)
What is a major concern in anaesthetising a pig?
Heat Loss
What are the main differences of the larynx in birds compared to mammals?
- no epiglottis
- much simpler
- not responsible for vocalisaiton
What are the main differences of the trachea in birds compared to mammals?
- complete tracheal rings
- some have tracheal sacs or extra loops of trachea
- variation in separation of trachea into 2 in species
What are the main differences of the lower respiratory system in birds compared to mammals?
- do not have a diaphragm
- rely on keel/rib bones to inhale (if you restrict their movement the bird cannot breathe)
- the syrinx is reposible for vocalisaiton and is located at the trachea’s bifurcation
- Bronchi divide into parabronchi (instead of alveoli) which are the main gas exchange area.
What are the main differences of inhlation and exhalation, and gas exchange in birds compared to mammals?
- the parabronchi tubes are rigid and do not extend.
- one-way system in birds. Blood flows in the opposite direction for efficient collection of oxygen.
- inhalation is also active as is mammals, but expiration is also active in birds as push air out.
- Air drawn in is stored in sacs and then pushed through the tubules
- Large abdominal air sacs are easy for us to compress!
What contributes to how light a birds skeleton is?
Air sacs are attached tot eh skeleton - called pneumatic bones.
Care with IO injections!
What is different about avian blood cells in comparison to mammals?
They are nucleated with an ovoid shape (may interfere with SPO2 readings!)
Describe the avian heart and conduction
4 chambers same as mammals
- valves in the heart can close more tightly due to electrical connections.
The ECG can therefore look different - with a predominant negative S wave.
Where can we gain IV access in a bird?
Jugular vein
Wing vein
Dorsal metatarsal vein in large leg species
IO (but not wing!)
What specific narrow then wide -at- top ETTs can eb used for birds?
Cole Tubes
What parameters can we use under GA to assess depth of a bird?
HR
RR
Jaw tone
Corneal reflex
Muscle tone in wing
Pinchin toe
(eyes will not move)
What is the minimum BP under GA for a bird?
90mmHg
What is the analgesic drug of choice in birds and why?
Butorphanol due to greater density of kappa-receptors found in brains of pigeons. Butophanol is a kappa agonist
0.05-2mg/kg IM
What pain relief has been shown to be effective in parrots and ducks?
Tramadol
What is the maximum lidocaine dose in birds?
3mg/kg
What is the main difference between reptiles and mammals?
Reptiles are poikilothermic (cold blooded) i.e. totally dependant on its surroundings for body heat.
The ambient temperature will therefore affect HR etc and also drug biotransformation. Their metabolism is much slower.
Describe the respiratory system in a snake
Left lung is vestigial or absent.
No diaphragm
episodic breathing i.e. periods of RR and then nothing
Incomplete tracheal rings
Slow circulation times
Tubular structure passes into mouth
Describe the respiratory system in a Chelonian
Short trachea, quickly divides into bronchi
Complete tracheal rings
Bronchi enter ediculi (little flat chambers)
No distendibility of lungs
Rely on muscle movement to breathe - see legs moving in and out with RR
Uusually need ventilation under GA due to muscle relaxation
Describe the respiratory system in a Lizard
Incomplete tracheal rings
simple or multi-chamber lungs
Active inspiration and expiration
What differences are there in teh reptilian CVS in comparison to mammals?
- nucleated red blood cells, more oval
- generally heart has 3 chambers (2 atria, one ventricle)
- some blood goes back where it came from etc so capnography not accurate for PaCo2. Controlled by para/sympathetic nervous control.
- Renal portal system means a proportion of blood from rear will go directly through kidneys before circulating the body.
What vein access can be had in reptiles?
Jugular in tortoises, ventral tail vein in lizards and snakes.
IO also useful.
What are teh starvation periods for reptiles?
Snakes 48hrs prior up to 1 week for larger species
Chelonia and lizards 24hours as rarely regurgitate.
List how we can monitor depth in reptiles
Righting reflex in snakes
Limp limbs (muscle relaxation)
Jaw tone
Corneal reflex in chelonians
Tongue withdrawal in snakes
What is maintenance fluid therapy in reptiles?
20-25mls/kg/day
What are the signs of pain in reptiles
- altered locomotion
-anorexia
-immobility - behavioural changes
What is the frequency of administration in reptiles of: butorphanol, buprenorphine, morphine IM and tramadol oral. ?
Butorphanol BID
Buprenorphine SID
Morphine BID
Tramadol Every 4 days
What is the maximum local anaesthesia doses in reptiles?
Lidocaine 3mg/kg
Bupivicaine 2mg/kg
