Premedication

Question 1

Why do we premedicate before induction of anaesthesia?

Answer 1

• Decrease stress and risk of injury to both animal and staff.
• Produce balanced anaesthesia to reduce dose of induction agents and reduce dose of maintenance agents.
• Analgesia (preventative).
• Smooth recovery.
• Reduce side effects of anaesthetic drugs (by reduced dose or counteracting drugs administered).

Question 2

List the classes of drugs used for premedication for dogs, cats and rabbits.

Answer 2

Phenothiazines.
a2 agonists.
Benzodiazepines.
Butyrophenones.
Opioids.

Question 3

1. Are phenothiazines sedative?
   Are they analgesic?
2. Are a2 agonists sedative?
   Are they analgesic?
3. Are benzodiazepines sedative?
   Are they analgesic?
4. Are butyrophenones sedative?
   Are they analgesic?
5. Are opioids sedative?
   Are they analgesic?

Answer 3

1. Yes.
   No.
2. Yes.
   Yes.
3. Yes.
   No.
4. Yes.
   No.
5. Some are (spp dependent).
   Yes.

Question 4

Sedative action of…
1. Phenothiazines.
2. a2 agonists.
3. Benzodiazepines.
4. Butyrophenones.

Answer 4

1. Dopamine receptor antagonist in the CNS.
2. a2 adrenergic receptor agonist in the CNS.
3. Enhance the effect of gamma-aminobutyric acid (GABA) at the GABA-A receptor.
4. Dopamine receptor antagonist in the CNS and also interferes w/ GABA, norepinephrine, and serotonin-mediated neuronal activity.

Question 5

1. What is the licensed phenothiazine vet product? And what spp is it licensed for?
2. What a2 agonists are most commonly used in vet med? What a2 agonists are also used in vet med? – What spp are these licensed for?
3. What benzodiazepines are licensed for vet use? – What spp are these licensed for?
4. What butyrophenone product is licensed for vet use and what spp is it licensed for?

Answer 5

1. Acepromazine (ACP). Dogs and cats.
2. Dexmedetomidine and medetomidine. Romifidine and xylazine. – All licensed for dogs and cats.
3. Diazepam and midazolam. – Diazepam for dogs and cats and midazolam for horses.
4. Fluanisone – only available in a combination product w/ fentanyl (Hypmorm). Licensed for rabbits.

Question 6

Routes of administration for premedication.

Answer 6

IV, IM, SC, OTM (oral transmucosal).

Question 7

1. Advantage of IV administration.
2. Disadvantage of IV administration.
3. Advantage of IM administration.
4. Disadvantage of IM administration.
5. Advantage of SC administration.
6. Disadvantage of SC administration.
7. Advantage of OTM administration.
8. Disadvantage of OTM administration.

Answer 7

1. Rapid onset pf action w/ predictable effect.
2. Requires restraint and/or IV catheter placement before anaesthesia.
3. Fairly rapid onset of action w/ predictable effect.
4. Painful.
5. Easier to do than IV or IM.
6. Not all drugs can be absorbed by this route. Can be unpredictable. Slower onset of action.
7. Would not use this route routinely but can be useful in special cases.
8. Not all drugs are absorbed by this route. Can be unpredictable. Slower onset of action.

Question 8

1. Key clinical effects of ACP?
2. Use of ACP?
3. What is ACP often used in combination with?

Answer 8

1. Sedation and anxiolysis.
2. Premedication and sedation for procedure in dogs and cats in the UK. Also used for premedication in rabbits but not licensed.
3. Opioids.

Question 9

1. What is the effect of ACP dependent on?
2. Effects improved by what?
3. Route of administration in cats and rabbits – advantages?
4. Dose as premedication vs dose as a sedative alone.

Answer 9

1. Dose, up to a plateau dose.
2. Use in combination with opioid.
   And/or leaving animal in a quiet environment for 30-40 mins.
3. SC – Non-irritant and efficacious.
4. Lower for premed than for sedative alone.

Question 10

Other physiological effects of ACP.

Answer 10

• Peripheral vasodilation.
• Potential to decrease BP – esp animals w/ CVS disease or shock.
• Managed by administration of fluids.
• Has an ant-arrhythmic action – advantage.
• Vasodilation also causes fall in body temperature – issue w/ high body SA to weight ratio (smaller patients).
• Minimal effects on respiration.
• No analgesia so another reason to combine w/ opioids.

Question 11

1. ACP time to clinical effect after IV administration?
2. ACP time to clinical effect after IM administration?
3. ACP duration of action?
   – Where is ACP metabolised?
4. Oral bioavailability?

Answer 11

1. 10-15 mins.
2. 30-40 mins.
3. 4-6hrs (long). – In the liver so action more prolonged in animals with liver disease.
4. Poor. But there are oral tablets for anxiolysis in dogs and cats so could use for premed in selected cases.

Question 12

1. Key clinical effects of a2 agonists?
2. What should be used for accurate dosing and why?
3. What does level of sedation and analgesia depend on?
4. What can happen if a2 agonists are combined with other sedative / analgesics.
5. What is a big advantage of using a2 agonists?

Answer 12

1. Sedation, analgesia, muscle relaxation.
2. Use body SA rather than weight as drugs are potent.
3. Dose.
4. Additive or synergistic effects.
5. Reversible using the specific antagonist = atipamezole.

Question 13

Other physiological effects of a2 agonists…
1. CVS.
2. Respiratory.
3. GI.
4. Behaviour.

Answer 13

1. Bradycardia, reduced CO and second-degree AV block. BP rises initially then falls either back to normal or hypotension.
2. Variable between spp and individuals within spp. Some seen to have respiratory depression but not all. – often see rate decrease but no overall effect on minute volume or blood gases.
3. Can be emetic in dogs and cats.
   Can depress GI activity and has been reported to cause bloat in ruminants and GI stasis in dogs (possibly avoid in deep-chested dog breeds prone to GDV).
4. Temporary behaviour and personality changes in dogs and cats (like other sedatives incl. ACP, opioids and diazepam).

Question 14

….
1. Endocrine.
2. Renal.
3. Reproductive.

Answer 14

1. Reduced secretion of insulin by pancreas so may see a transient hyperglycaemia – Not harmful to animal but may cause confusion if blood samples taken in this period.
2. Increased urine production by a decrease in secretion of vasopressin. Need to catheterise bladder in some animals receiving a2 agonist by CRI.
3. Complex effects on uterine contractility. Depends on dose and concentration =s of oestrogen and progesterone therefore avoid in near term animals due to risk of abortion.

Question 15

1. a2 agonist time to clinical effect after IV administration?
   2 How long after IM administration do the effects peak?
2. Duration of action of a2 agonists?
3. Reversal drug for a2 agonists.
4. Where a2 agonists metabolised?

Answer 15

1. 5 mins.
2. 15 mins.
3. 2-3hrs.
4. Atipamezole.
5. Liver so action more prolonged in animals w/ liver disease.

Question 16

Key clinical effects of benzodiazepines?

Answer 16

Minor tranquilisers, muscle relaxation, anticonvulsant.

Question 17

1. What animals are benzodiazepines not used for and why?
2. How can sedation with benzodiazepines be improved?
3. What are benzodiazepines often administered as?
4. Benefit of benzodiazepines having minimal effects on CVS and respiratory system?

Answer 17

1. Healthy animals, as sedation can be unreliable and the drugs can cause excitement when administered alone.
2. By using them in combination with opioid, ketamine or a2 agonists.
3. Adjuncts to anaesthetic induction agents for co-induction.
4. Good choice for unhealthy patients.

Question 18

Other physiological effects of benzodiazepines…
1. CVS.
2. Respiratory.
3. Musculoskeletal system.

Answer 18

1. Minimal CVS depression so commonly administered to patients w/ CVS disease.
2. Mild dose-dependent respiratory depression.
3. • Potentiates GABA ergic mediated muscle relaxation of inhibitory neurons at the level of the spinal cord.
     - So often administered with drugs that do not provide muscle relaxation e.g. ketamine.

Question 19

1. Why should benzodiazepines be administer slowly by IV?
2. Plasma half-life for diazepam vs midazolam.
3. Where are benzodiazepines metabolised?
4. What is the reason for a more prolonged effect of diazepam?
5. What happens if midazolam given by CRI?
6. Bioavailable?
7. Rare reported effect on cats after diazepam administered?

Answer 19

1. As it rapidly crosses BBB.
2. Diazepam shorter than midazolam.
3. Liver.
4. The metabolites of diazepam are active.
5. No significant accumulation.
6. Is bioavailable when given intranasally but not licensed in vet spp by this route.
7. Liver failure.

Question 20

1. Specific reversal agent for benzodiazepines?
2. How does it work?
3. Why is it rarely used in vet med?

Answer 20

1. Flumazenil.
2. Is a competitive antagonist of BDZ w/ high affinity for the BDZ binding site.
3. Expensive and not licensed.

Question 21

1. In what spp is butyrophenone product Fluanisone licensed for use?
2. What is the one other vet licensed butyrophenone drug and what spp is it licensed for?

Answer 21

1. Rabbits, rats, mice, guinea pigs.
2. Azaperone. Pigs.

Question 22

1. Used alone, what effect does the fentanyl/fluanisone combination provide?
2. Duration of sedation/immobilisation with fentanyl/fluanisone combination.
3. Consequence of administration alone?
   – What is it beneficial to be administered alongside?
4. Duration of good surgical anaesthesia with addition of drug above?
5. Respiratory effects of fentanyl / fluanisone?
6. How can fentanyl/fluanisone be reversed?

Answer 22

1. Surgical anaesthesia for minor surgery / diagnostic techniques.
2. 30-60 mins.
3. Poor muscle relaxation – midazolam.
4. 20-40 mins. (with good muscle relaxation).
5. Moderate-severe respiratory depression.
6. By administration of naloxone/butorphanol/buprenorphine.

Question 23

ASA categorisations and how they will influence anaesthesia…
1. 1. Normal and healthy animal.
2. 2. Animal with mild systemic disease.
3. 3. Animal with severe systemic disease.
4. 4. Animal with severe systemic disease that is a constant threat to life.
5. 5. A moribund animal who is not expected to survive w/o the operation.

Answer 23

1. Standard protocols should apply w/ routine monitoring.
2. Standard protocols should apply w/ routine monitoring.
3. Thorough stabilisation should be performed before anaesthesia attempted, IV, fluid therapy and airway protection strongly advised.
4. As for 3. Owners should be fully briefed as to additional anaesthetic risk. Doses for CPR should be calculated and the first dose drawn up.
5. As for 4.

Question 24

Premed protocols by ASA grade…
1. Dogs and cats at grade 1 and 2.
2. Rabbits at grade 1 and 2.
3. Dogs at grade 3.
4. Cats at grade 3.
5. Rabbits at grade 3.

Answer 24

1. ACP + opioid OR a2 agonist + opioid.
2. ACP + opioid OR a2 agonist + opioid OR Fentanyl / Fluanisone (Hypnorm) alone or w/ benzodiazepine (e.g. midazolam).
3. ACP + opioid OR benzodiazepines + opioid.
4. Benzodiazepines (midazolam) + ketamine.
5. Benzodiazepines + opioid.

Question 25

…
1. All grade 4 and 5 animals.

Answer 25

1. Benzodiazepines + opioid OR benzodiazepines + ketamine OR opioid alone OR no premed at all but then need higher dose of induction.

Question 26

How do we care for our sedated or premedicated patient?

Answer 26

• Quiet environment.
• Observe ideally continuously w/ eyes, ears and nose.
• Think ABC (airway, breathing, circulation).
• Monitor TPR and MMs.
• Pulse oximeter.
• Recording of obs.

Question 27

What could go wrong with the sedated or premedicated patient?

Answer 27

• Excitement/excessive sedation.
• Airway obstruction (vomit inhalation, anatomical).
• CVS effects up to and including cardiac arrest.
• Patient cannot compensate for an existing condition / hidden condition exposed.
• Something odd develops (e.g. gastric dilation).