Analgesics and General Anaesthetics for Exotics

What are good rules to apply when determining whether you should use analgesics in exotics?

1. Would this lesion or procedure be painful to any species?

2. Is this lesion or procedure damaging to tissues in any species?

3. Is the animal displaying abnormal behavioural responses?

What happens to CV system if painful?

Increased HR, increased BP, peripheral vasoconstriction, increased CO (workload) → heart under more strain → impaired CV function & arryhthmias

What happens to respiratory system if painful?

Increased RR, decreased ventilation, hypoxia, hypercapnia, acidosis, increasd risk of atelectasis/pneumonia

What happens to GI system if painful?

Increased interstinal secretions, anorexia, reduced GI motility, nausea/V+, risk of GI ulceration from increased gastric acid production

What happens to urinary system if painful?

Reduced renal blood flow, urinary retention, altered hormone levels (increased ADH)

What happens to metabolic/endocrine system if painful?

Increased metabolic rate & glucose consumption, increased catabolism (muscle breakdown), increased cortisol levels, hyperglycaemia

What happens to immune system if painful?

Immune suppression, delayed wound healing, risk of sepsis

What happens to nervous system if painful?

Hyperalgesia (sensitivity to pain), perception threshold altered, behavioural changes

What can we use to assess pain in exotics?

Grimace scales.

Give at least 2 examples of things that are observed in the grimace scale for rats mica and rabbits

• Oribital tightening

• Nose bulge

• Cheek bulge

• Ear position

• Whisker change

How does the fact that reptiles are exothermic affect drugs?

• Affects pharmacodynamics and pharmacokinetics when body temperature varies (due to variation in metabolism)

What analgesics are used in exotic species?

• Local anaesthetics

• Opioids

• Non-steroidal anti-inflammatories (NSAIDs)

• Alpha2 agonists

• Neurokinin-1 receptor antagonists

• NMDA receptor antagonists

give pre-empively —> more effective

What condition is required for safe administration of analgesics in reptiles?

Animal must be within their optimal temperature zone.

What is the general mechanism of action of local anaesthetics?

Block ion channels to prevent generation and conduction of pain impulses.

What local anaesthetic is used for birds, reptiles rabbits and rodents?

Lidocaine or bupivicane (bupivicane longer acting but dangerous in birds)

When may local anaesthetics become toxic?

If rate of absorption exceeds rate of administration.

What is the general mechanism of action of opioids used as analgesics for exotics?

Block pain centrally by binding to μ-, κ- or δ-opioid receptors (agonists).

What type of opioid is best for small mammals?

Mu agonists.

What type of opioid is best for birds?

Kappa agonist.

What opioid drug is best for small mammals? What type is it?

Morphine —> mu agonist.

Buprenorphine —> partial mu agonist unsure on kappa activity (effective in SA)

What opioid drug is best for birds? What type is it?

Butorphanol —> weak mu agonist but strong kappa agonist.

Buprenorphine —> Partial mu agonist unsure on kappa activity (may be effective in birds)

What is the general mechanism of action of NSAIDs?

Inhibit cylcooxygensase (COX) in arachidonic acid pathway (precursor to prostaglandin production). Preferably COX2 which causes anti-inflammatory effects.

What NSAIDs can be used for small mammals, birds and reptiles? What COX do they inhibit?

• Ketoprofen —> potent COX-1 inhibitor

• Carprofen —> weak inhibitor of COX1 / wide safety margin

• Meloxicam —> COX-2 inhibitor

What is the mechanism of action of alpha-2-agonists?

Sedative, analgesic (through decrease in neurotransmitter release), anxiolytic & muscle relaxant

What is the most common alpha-2-agonist used in exotic species?

Medetomidine (often in combo with other drugs)

Which neurokinin-1 receptor antagonist is used in exotics?

Maropitant

Which NMDA receptor antagonist is used in exotics?

Ketamine

Why is the use of glucocorticoids not supported and sustained?

Have severe adverse effects so not recommended for use in birds and reptiles.

(can be used in ferrets, use with extreme caution in other species due to immunosuppressive effects)

What is anaesthesia?

Loss of sensation.

What are the effects of anaesthesia?

Loss of consciousness, analgesia and muscle relaxation.

What are the routes of administration for induction agents for exotics?

Inhalational, IV, IM.

What are the routes of administration for maintenance for exotics?

Via respiratory system —> face mask & endotracheal tube.

Is fasting prior to GA recommended for exotics? Why?

No, as susceptible to hyperglycaemia.

Can fast ferrets (can vomit) for short amount of time (fast gut transit time so don’t fast for longer than 4hrs)

What type of ET tube is preferred for exotics? Why is it preferred?

Uncuffed, better as ensures a patent airway (better oxygenation than using face mask)

What exotic species should be intubated?

Birds, small mammals and reptiles.

What is required to be administered with ET tubes in small mammals?

Prone to laryngospasm so use local anaesthetic spray.

What induction agent is used for most exotics? How and what to consider?

4-5% isofluorane (or sevoflurane) via mask.

Rabbits may breath-hold esp. with ISO (can become hypoxic) —> use sevoflurane if available to avoid breath holding

Pre-med recommended if using mask induction (or induce with injectable agent)

Give at least 2 injectable induction agents used for exotics

• Propofol

• Ketamine combinations

• Alfaxalone

• Fentanyl/fluanisone

What injectable induction agent is best for small mammals?

Ketamine combinations (ket + meddetomidine or ket + midazolam in ferrets)

Alfaxolone for rabbits/rodents

What injectable induction agent is best for birds?

Ketamine combinations

Pre-med with midazolam + butorphanol when inducing using inhalant

What injectable induction agents won’t work for birds?

Propofol and alfaxalone.

What injectable induction agent is best for reptiles?

Propofol, alfaxalone, ketamine combinations.

What breathing system should be used for exotics?

Mapleson E / F and Bain.

What maintenance agent is safe for all exotics? Which is safer?

Isofluorane.

Sevoflurane safer but considerably more expensive than ISO

Why do all reptiles require IPPV?

Spontaneous breathing ceases under GA.

What recumbency is IPPV required for in birds? Why?

Dorsal recumbency due to weight of pectorals / abdominal contents.

What recumbency under GA is safest for birds?

Lateral.