Farm animal and camelid anaesthesia Flashcards
What are some examples of surgeries do you need a GA for?
- umbilical hernia repair
- urethrostomy
- orthopaedic (not all)
- enucleation (depends on species)
Give some examples of surgeries you can use a sedation and local anaesthetic technique
- flank laparotomy
- csection
- RDA or LDA
- rumenotomy
- declaw
- dehorning
- teat surgery
- castration
List pre-anaesthetic considerations for ruminants - 8
- handling, restrain, accurate weight
- regurgitation/aspiration
- salivation
- bloat (tympany)/rumen atony
- hypotension/hypertension
- hypoventilation and hypoxaemia
- myopathy/neuropathy
- fluid and electrolyte problems
Outline regurgitation as a consequence of anaesthesia in ruminants
Can lead to aspiration pneumonia which can be fatal
- ACTIVE - light plane of anaesthesia (commonly at intubation)
- PASSIVE - deep anaesthesia (cardia relaxation)
How can you reduce the risk of regurgitation in ruminants? 6
- Reduce rumen fill (starve 18-24 hours, not if < 3 months old)
- good depth of anaesthesia when intubating
- good fitting ETT and properly blown up cuff
- position of head (fluid to drain into mouth)
- stomach tube
How does ketamine affect salivation?
- Ketamine (licensed induction agent) stimulates further production. Can lead to problems at intubation and electrolyte imbalances.
- Tx = atropine (L but never in UK food chain)
Why do you get bloat (tympany)/ rumen atony with with anaesthesia?
no eructation when anaesthetised –> reduces FRC and venous return –> continued fermentation can lead to pH shift and atony
How can you prevent bloat (tympany)/ rumen atony with anaesthesia? 2
- adequate starvation and water withholding time
- placement of a rumen tube or trochar to evacuate gas
Describe hypotension in ruminants under GA
- much less likely compared to horses
- deep planes of anaesthesia
- high xylazine doses or use of ACP (NL) implicated
- support required
What might cause hypertension in adult bulls and cattle under GA? (2 theories)
- High CO2 (due to hyperventilation, causes increased CO, when ventilated to reduce CO2, the ABP remains high)
- changeover from PS to S dominance as a result of anaesthesia
Why are ruminants more prone to airway damage during IPPV?
less fibrous connective dtissue
Why does hypoventilation and hypoxaemia occur in GA ruminants? 3
- drug induced respiratory depression
- chemoreceptor depression
- large rumen (and any bloat) –> small TV and only slightly increased RR, reduction in FRC (causes airway closure and VQ mismatch), decreased venous return (reduced CO).
Outline the likelihood of myopathy and neuropathy in ruminants under GA versus horses?
Ruminants are less prone to myopathy but neuropathy is more common.
AVOID BY: positioning, padding, ABP, oxygenation and perfusion
What sedative is used in ruminants?
ALPHA 2 AGONISTS –> sedation, anxiolysis, recumbency, analgesia, mm relaxation. Ruminants are very sensitive to these (esp. sheep and goats). Xylazine and detomidine (L-cow)
What are the side effects of alpha 2 agonists in ruminants? 7
- Pulmonary oedema - sheep and goat (xylazine)*
- reduced eructation (tympany)
- reduces swallowing (saliva in oropharynx)
- copious urine production
- osmotic diuresis
- urethral outflow issues
- oxytoxin like effect –> uterine contractions
What can be used for induction in ruminants? 2
Ketamine or thiopentone
Properties - induction with ketamine in ruminants - 4
- dissociative anaesthetis (use IV or IM)
- excellent analgesic
- mm rigidity
- laryngeal reflexes remain
Properties - induction with thipentane in ruminants - 5
- very fast acting
- no veterinary licence available
- very irritant so must go IV (extravasation –> necrosis)
- accumulation can lead to prolonged recoveries
- not in thin/debilitated animals
Are there any injectable agents for induction in ruminants?
No (but they include propofol, benzodiazepines, GCE, alphaxalone, chloral hydrate)
What is propofol good for?
Injectable induction of small ruminants as smooth induction and recovery. NOT LICENSED.
What are benzodiazepines good for?
Injectable induction. small ruminants, sedate neonates and debilitated animals well. NOT LICENSED
What is GCE good for?
Injectable induction. good centrally acting mm relaxant. NOT LICENSED
What is alfaxalone good for?
Injectable induction. used for goat disbudding. NOT LICENSED
What is chloral hydrate good for?
Injectable induction. old drug for sedation/anaesthesia. sedation acceptable, poor for GA. NOT LICENSED.
What are the 2 main ways or providing analgesia in ruminants?
- ** NSAIDs (licensed - meloxicam, flunixin, ketoprofen, carprofen, tolfenamic acid)***
- OPIODIS (NL in UK, include butorphanol, buprenorphine, morphine/methadone, pethidine)
Name 4 inhalation agents used in ruminants
- Isoflurane (licensed)
- Sevoflurane (NL)
- Desflurane (NL)
- Halothane (NL) - hepatotoxicity
How can you anaesthetise smaller ruminants?
you ca mask them down
What are your venous access options in ruminants?
- JUGULAR - deeper than horse
- TAIL VEIN - often artery is used
- CEPHALIC - small ruminants
- MILK VEIN - don’t use unless nothing left
What do you need to consider when intubating ruminants?
Laryngoscope as blind is difficult (long blade). Method is by internal palpation in adult cattle. In young cattle and small ruminants use a laryngoscope as in small animals - need a stylette to stiffen the ETT.
What can be used for local anaesthesia in ruminants?
LICENSED: procaine, benzocaine, tetracaine
NOT LICENSED: lidocaine
DOSES vary depending on toxicity. Sheep and goats are quite susceptible.
Which nerves might be blocked for local anaesthesia? 5
- Infraorbital
- mental
- cornual
- retrobullar
- Peterson’s/ Auriculopalpebral
Name 3 methods for local anaesthesia of ruminant limbs
- Peineural infiltration
- ring infiltration
- IVRA (Bier’s Block)
Name 5 methods for local anaesthesia of ruminant body
- paravertebral block (distal/proximal)
- inverted L-block
- segmental lumbar epidural block
- line block
- teat block
Name 3 methods for local anaesthesia of ruminant genitalia
- epidural
- pudendal block
- intra-testicular
What are the specific considerations for camelids (alpacas and llamas)? 8
- 3 compartment stomach (ruminate)
- prone to bloat / regurgitation/ salivation
- projectile regurgitation possible
- lingual torus
- temperamental behaviour, often placcid
- obligate nose breathers
- more prone to respiratory obstruction
- can develop C3 stomach ulcers with stress
Why is catheter placement in camelids problematic?
Has to either really high or low in neck:
HIGH - 4cm below angle of jaw
LOW - rostral to ventral process of C5 but care of carotid.
Why is it hard to differentiate camelid venous and arterial blood?
Both very red due to altitude adaptation.
Why is camelid intubation problematic?
- torus lingae and soft palate
- long narrow face
- larynx relatively far back
- sternal and positioning
What should you do with camelid (hyper)salivation? 3
- head down
- suction
- protect eyes (ulceration)
Name 2 drugs that can be used to sedate camelids.
Like ruminants.
Xylazine and benzodiazepine
Name 3 drugs that can be used to provide analgesia for camelids
- NSAIDs - flunixin
- Buprenorphine/Methadone
- Nerve blocks/epidural
Name 2 drugs used for induction in camelids
- ketamine
- propofol
Name 2 drugs used for maintenance in camelids
- isolfurane
- sevoflurane
Outline recovery for camelids
ideally in sternal recumbency - allow head to rotate down for drainage from time to time. should eructate. don’t remove ETT until can remain like this - keep cuff INFLATED to protect airway. extubate with cuff inflated, suction prior to extubation. recovery is usually quite quick.
What are the main problems when anaesthetising pigs - 8
- IV access difficult so go IM first
- thick fat layer so long needles
- handling difficult and prone to stress
- very strong and potentially dangerous
- can vomit so starve for at least 6 hours, water from pre-medication onwards
- difficult to intubate
- prone to temperature fluctuation (hypothermia) and sunburn
- susceptible to Malignant Hyperthermia (MH)
What drug is usually used to sedate pigs?
- **Azaperone (Buytrophenone) - licensed for this. cheap and effective, can cause penile prolapse in boars. Wait minimum 20 minutes for sedation to take affect.
- Other NL options include: alpha 2s, acepromazine and benzodiazepines
How can analgesia be provided to pigs?
Licensed NSAIDs - flunixin, ketoprofen and meloxicam
What drugs are usually used to perform induction in pigs?
- ** Ketamine or thipentone (both licensed).***
- Ketamine - give after sedation, may need top up
- Thiopentone - after sedation, IV only
- OTHERS - etomidate, alphaxalone, propofol, mask
How can anaesthesia be maintained in pigs?
- ** Isoflurane (licensed) ***
- Also sevoflurane or desflurane (neither are licensed)
Where should you give an IM injection in the pig?
Neck (poorer meat mm here)
Which veins can you use for IV access in the pig?
- ear (whens sedated or restrained)
- limb (when asleep)
- jugular (blind or cut down)
- tail
- epigastric
Why is ET intubation difficult in pigs? How do you do it?
WHY DIFFICULT: small cricothyroid junction, marked laryngeal reflexes (LA spray?)
HOW: need small tubes with stylette, visual method with laryngoscope, small pigs to be kept in sternal recumbency, (down then up) technique due to shape of laryngotracheal gunction
What does MH stand for?
Malignant Hyperthermia or Malignant Hyperpyrexia (MH or MHP) in pigs.
What causes MH?
MH = an autosomal dominant gene implicated Also RYR1 (ryanodine receptor gene) implicated. Overall effect of a fault in the RYR1 gene is decreased activation threshold and much increased deactivation threshold to calcium --> clinical signs (ATP depletion (Ca pumps) --> mm rigidity) and temperatures of 42 degrees +
What agents can cause MH to trigger with an often fatal consequence? 3
Halothane or other inhalant agents, caffeine or suxamethonium
Treatment - MH in pigs - 11
- Remove drug (causing the MH)
- Treat the hyperthermia:
- active cooling
- maintain IV fluids to minimise renal insult (myoglobinuria)
- remove trigger (totally clean circuit, ideally non-rebreathing)
- ventilate to reduce CO2
- (bicarbonate to reduce acidosis)
- (monitor K+ to avoid hyperkalaemia - damaged mm)
- Dantrolene (drug that reduces Ca release, prophylactic use better)
- don’t use inhalants or depolarising neuromuscular blockade
- can test for it
What are the adverse effects of dantrolene (used to treat MH in pigs)? 4
- mm weakness
- sedation
- hepatitis (occasional)
- arrhythmias
What are the main differences with ruminants in terms of monitoring? 3
- ruminant eyes tend to roll down with deepening anaesthesia towards a surgical plane rotating back to a central position when centrally deep
- alpacas may still retain a blink reflex and may also chew or swallow
- pigs may retain a laryngeal reflex until a deeper plane of anaesthesia.
