Equine Sedation and Anaesthesia in the Field.

Question 1

How to prepare for the sedation of a horse.

Answer 1

• Check passport!
• Check guidance on BEVA.
• Check NOAH Compendium for drug withdrawal periods.
• Assess signalment and temperament.
• Assess CV and resp. system.
• Establish duration of sedation required and anticipated pain level.
• Consider facilities incl. handlers.
• No need to withhold food beforehand but generally do restrict after sedation.

Question 2

Approach to the sedation of the animal.

Answer 2

• Calm and quiet environment.
• Schedule enough time and be patient.
• Be aware of safety aspects.
• Prepare all equipment.
• Positive interaction.

Question 3

1. What is ACP?
2. Level of sedation?
3. Onset of action?
4. Duration of action?
5. Effect on BP?
6. Why recommended not to be used on breeding stallions?

Answer 3

1. Acepromazine. A phenothiazine derivative.
2. Mild.
3. Slow onset (30 min to peak effect).
4. Long (4-6hrs).
5. Reduces BP – vasodilation.
6. Risk of priapism and subsequent damage to penis.

Question 4

a2-adrenoreceptor agonists…
1. Action in what area of brain?
2. Effect on muscles?
3. Analgesia by what area of spinal cord?
4. CV effects?
5. Endocrine effect?
6. GI effect?

Answer 4

1. Locus ceruleus (pons).
2. Relaxation. (some degree of ataxia).
3. Dorsal horn.
4. Bradycardia and secondary AV block. Initial rise in BP (triggers bradycardia) then BP falls again while bradycardia remains. CO can be dropped by up to 50%.
5. Alter insulin responses and cause hypoinsulinaemia. Also induce sweating.
6. Decreased motility.

Question 5

1. What are the 3 licensed a2-adrenoreceptor agonist for use in horses?
2. Order of receptor binding of these when compared to a1.
3. Put them in order of their duration of action.
4. Which causes the most ataxia?
5. Which causes the least ataxia?
6. Which has the best visceral analgesic properties?
7. Time to peak effect for all?
8. What drug type is given alongside the a2-adrenoreceptor agonist?

Answer 5

1. Xylazine, detomidine, romifidine.
2. Xylazine – 160:1.
   detomidine – 260:1.
   romifidine – 340:1.
3. xylazine, detomidine, romifidine (up to 20-30 mins).
4. Xylazine.
5. Romifidine.
6. Xylazine.
7. 3-5 mins.
8. Opioids.

Question 6

1. Why do we give opioids alongside a2-adrenoreceptor agonists?
2. Which opioids have UK marketing authorisations?

Answer 6

1. Has a synergistic effect on analgesia.
   Increases sedation and ataxia.
   May make the horse less likely to kick.
2. Butorphanol, buprenorphine, pethidine.

Question 7

1. Specific marketing authorisation for pethidine – practical considerations.
2. What opioids must be justified via cascade?

Answer 7

1. Management of spasmotic pain and colic – High volume required and stings on IM administration.
2. Morphine and methadone.

Question 8

1. What is remote IM injection.
2. What drugs are best to use for remote IM injection?

Answer 8

1. IM injection w/ tubing between needle and syringe to allow distance between horse and vet and allow horse ability to move away while injecting. Useful in unhandled horses.
2. detomidine 20-60micrograms/kg.
   butorphanol 50micrograms/kg.
   ACP 50micrograms/kg.

Question 8

Use of oral sedatives.

Answer 8

Must be prescribed for an individual horse each time of use following a clinical exam by a vet surgeon.
Make arrangements for safe disposal of unused product.
Wear impervious gloves when handling the product.
BEVA position statement on Domosedan Gel (detomidine) available on BEVA website.

Question 9

Informed owner consent in use of sedation by paraprofessionals.

Answer 9

Paraprofessional = farriers and equine dental technicians.
Establish proposed procedures.
Warn owner regarding risks and define limits of responsibility.
Advise client that it is preferable for the vet to be present throughout period of sedation.
Advise client regarding legal aspects of performing invasive vet surgery.
Ensure advice provided verbally and in writing.

Question 10

Anaesthesia risks in horses.

Answer 10

Total mortality from peri-op complications.
Non-colic complications.
Colic.
Cardiac arrest.
Fracture.
Myopathy.

Question 11

Risk factors of equine anaesthesia.

Answer 11

• Drugs – use of ACP in healthy horses is thought to reduce the risk of GA.
  Use of ACP in hypotensive horses is thought to increase risks.
  – Risk reduced if using TIVA (but can only be used for short anaesthesia (max 90-120 mins).
  – No difference in risk w/ isoflurane vs halothane.
• Extremes of age pose a risk. – 2-7 yrs has lowest risk.
• Duration of anaesthesia is key. – need to be organised and prepared and efficient. Need to keep length of anaesthesia to <2hrs or risk of myopathy increases X10.
• Time of surgery affects risk – overnight higher risk.
• Operation type – e.g. ex lap higher risk than other electives.

Question 12

Deciding factors for the location of the procedure – field vs theatre.

Answer 12

• Temperament of horse e.g. for loading.
• Procedure to be performed e.g. level of sterility needed.
• Duration of procedure (only up to 90 mins in the field).
• Facilities available.

Question 13

Preparation of the horse for anaesthesia.

Answer 13

• Full PE and obtain informed consent.
• Remove hay 12hrs before anaesthesia (controversial – some prefer to just reduce volume).
• Groom to remove mud and remove shoes.
• Weigh / use weigh tape.
• Antibiotics at least 30 mins before anaesthesia as can cause hypotension.
• Rinse mouth to reduce risk of aspiration.
• Tetanus antitoxin if required and check vaccination status.

Question 14

1. Where would an IV catheter be placed?
2. Aseptic technique?
3. Analgesia to do so?
4. Place of raising.
5. What is used to secure the IV in place?

Answer 14

1. Left jugular vein.
2. Clip site, scrub w/ chlorhexidine and apply surgical spirit, wear sterile gloves.
3. Intradermal bleb of mepivacaine (LA).
4. Close to point of insertion so does not take too long to fill.
5. Secure w/ sutures/glue/both.

Question 15

Equine anaesthesia equipment.

Answer 15

• ET tubes and gag – 28-30mm adult horse, 25mm pony, 20mm small pony.
• Padded head collar and lead rope.
• Ophthalmic lubricant.
• Drugs drawn up and labelled.
• Anaesthetic machine.
• Table in correct position.
• Monitoring incl. ECG and invasive BP.

Question 16

Anaesthetic drugs.

Answer 16

• ACP – 30 mins before anaesthesia.
• a2-agonist sedation (xylazine, detomidine, romifidine) and wait 5 mins for…
• Induction (give calculated dose as fast as you can).
  – ketamine/diazepam.
  – thiopental (becoming difficult to source).
  – +/- GGE (in some specialist practices).

Question 17

Handling for anaesthetic induction.

Answer 17

• Ensure “five point stance” (4 legs planted and head lowered) and quiet environment.
• Free fall induction – 1-2 handlers at horse’s head, guiding the horse to recumbency.
• Tilt table.
• Gate for restraint.

Question 18

ET intubation.

Answer 18

• Head and neck extended.
• “Blind” technique – x visualise larynx.
• Usually place oral tube but is possible to intubate via nares (nasotracheal).

Question 19

1. What is GGE?
2. Can GGE be used alone in anaesthesia?
3. Haematological risk?
4. GGE route of administration.

Answer 19

1. Guaiphenesin – muscle relaxant that acts centrally.
   Works at internuncial neurones of the spinal cord, brainstem and subcortical area of the brain.
2. No. No analgesia / anaesthetic properties – must be used in conjunction w/ other drugs.
3. Haemolysis >10%.
4. IV only – tissue damage if perivascular.

Question 20

1. What combo of drugs could be used for TIVA and for how long.
2. What gaseous anaesthetic agent can be used?
   – Advantages.
   – Disadvantages.

Answer 20

1. GGE, ketamine and a2-agonist for 1-2hrs max.
2. Isoflurane (sevoflurane not licensed but can be used).
   – Rapid recovery (often sedate horse for recovery).
   – Hypotension and respiratory depression.

Question 21

Analgesia for equine procedures.

Answer 21

• Always give NSAIDs before anaesthesia if possible (less predisposed to renal dysfunction than SA patients).
• Can use opioids but not commonly used.
• a2-agonists and ketamine provide some analgesia.
• LA mainstay for analgesia in horses.

Question 22

Supportive treatments in anaesthesia.

Answer 22

IVFT w/ Hartmanns.
Need to monitor blood loss during procedure.

Question 23

Monitoring depth of anaesthesia in horses.

Answer 23

• RR and pattern.
• Eye position (eyes should be crossed at adequate anaesthetic depth. Either too light or too deep if eyes central), nystagmus (too light).
• Sluggish palpebral reflex / anal reflex.
• Muscle tone.
• Movement – always have “top-up” IV agent ready.
• Invasive BP.
• HR is not a good indicator as remains fairly consistent regardless of depth.

Question 24

Monitoring equipment in equine anaesthesia.

Answer 24

• ECG – red (neck), yellow (sternum), black (ribs).
• 2nd Degree AV block common initially.
• Direct arterial BP.

Question 25

BP during equine anaesthesia.

Answer 25

• CO sig. decreased during anaesthesia.
• Hypotension common.
• Maintain MAP >60mmHg (70mmHg) for muscle perfusion.
• Use of positive inotropes e.g. Dobutamine / ephedrine.
• Check anaesthesia depth.
• IV fluids.

Question 26

Horse respiratory function.

Answer 26

Breathe poorly when recumbent.
- Ventilation perfusion mismatch.
– Hypoxaemia.
– Not responsive to IPPV.
– Large amount dead space.
– Inhaled salbutamol.
- Hypoventilation – hypercapnia (often need to be mechanically ventilated under anaesthesia).

Question 27

Recovery from anaesthesia.

Answer 27

• Quiet environment.
• Towel over eyes.
• Supplement O2 .
• Remove ET tube when respiratory effort increases.
• May recover w/ oral / nasal tube in place.
• Sedate.
• Ensure analgesia adequate.
• Catheterise bladder.
• Assist recovery.
  – Manual.
  – Ropes.
  – Sling.
• Pool recovery.

Question 28

1. When can post-anaesthetic myopathy occur?
2. What causes it?
3. Signs of post-anaesthetic myopathy.

Answer 28

1. In the recovery period.
2. Damage to muscles during anaesthesia.
3. Lame and unable to stand.
   Distress.
   Muscles hard, swollen and painful on palpation.
   Myoglobinuria.
   Elevated muscle enzymes – CK.

Question 29

Prevention of post-anaesthetic myopathy.

Answer 29

• Careful positioning. Padded surfaces.
• “Let down” fit horses (take out of training).
• Minimise anaesthesia time.
• Maintain MAP >60mmHg.
• “Light” depth of anaesthesia.
• Avoid hypoxia.

Question 30

Treatment of post-anaesthetic myopathy.

Answer 30

• Analgesia w/ NSAIDs and opioids.
• Sedation w/ ACP as vasodilation beneficial.
• Fluid therapy to preserve renal function.
• Nursing care.

Question 31

Pressure on what nerves commonly cause neuropathies in equine anaesthesia?

Answer 31

Radial nerve.
Facial nerve (from headcollar so headcollar often removed).
Brachial plexus.
Femoral nerve.
Not usually painful, just causes loss of function.

Question 32

1. What is spinal cord malacia?
2. Aetiology.
3. Most commonly affecting…
4. Signs?
5. Outcome?

Answer 32

1. Where spinal cord becomes degenerate and necrotic.
2. Unknown.
3. Heavy horses.
4. “Dog-sit”, unable to stand.
   Compete HL paralysis w/ no sensory perception.
5. Fatal, requiring euthanasia.

Question 33

Fractures during equine anaesthesia.

Answer 33

Due to…
Trauma during anaesthesia induction/recovery.
Pre-existing fracture/injury.
Often associated w/ myopathy.