Drugs for Induction

Question 1

How can Induction drugs be delivered?

Answer 1

IM
IV
Sub-cut
Inhaled
Across mucous membranes

Question 2

Ideal pharmacodynamic/kinetic properties of an induction agent

Answer 2

Causes hypnosis and amnesia
Rapid onset
Rapid metabolism
Minimal cardiovascular/respiratory suppression
No hypersensitivity reactions
Nontoxic, nonmutagenic, noncarcinogenic
No neurological side effects
Analgesic
Antiemetic
Ability to continuously monitor delivery

Question 3

Ideal Physiochemical properties of an induction agent

Answer 3

Water soluble
Stable formulation, nonpyrogenic
Nonirritant
Painless on IV injection
Small volume required
Inexpensive and easy to prepare
Antimicropial preparation

Question 4

How do anaesthetics work?

Answer 4

Pharmacological agents that target specific CNS receptors
Modulate remote brain areas and interfere with synaptic transmission
Generalised depression of CNS including:
○ Amnesia
○ Loss of consciousness (hypnosis)
○ Immobility
○ Analgesia
○ Suppression of autonomic reflexes

Question 5

How is propofol administered?

Answer 5

IV
Licensing in small animals

Question 6

Pharmacokinetics of Propofol

Answer 6

○ Poor oral bioavailability
○ Not soluble in water - must be made up as an emulsion
○ Highly protein bound
○ Metabolised by liver
○ Eliminated by kidneys

Question 7

Pharmacodynamics of Propofol

Answer 7

○ Interacts with GABA-A receptor to disrupt flow Cl- ions through the receptor channel, inhibiting neuronal depolarisation

Question 8

Propofol effects on cardiovascular system

Answer 8

Cardiovascular depression
Haemodynamic effects are largely result of sympathetic depression
Stable cardiac output
Decreased heart rate (blunted baroreceptor reflex)
Decreased MAP, SVR, CVP
□ Mean arterial pressure
□ Systemic vascular resistance
□ Central venous pressure

Question 9

Propofol effects on respiratory system

Answer 9

Respiratory depression
Apnoea common - be quick to intubate

Question 10

Uses of propofol

Answer 10

Small animals
Titrate to effect - give slowly and wait for effects to manifest - slow over 60s
Pre-meds should reduce required dose
Stable for TIVA or CRI (Total IV Anaesthesia or Constant Rate Infusions)

Question 11

How is Alfaxalone administered?

Answer 11

IV or IM
Clear colourless neuroactive steroid

Question 12

Pharmacokinetics of Alfaxalone

Answer 12

○ Good bioavailability
○ Soluble in water
○ 30-50% protein bound
Less than propofol
○ Metabolised:
Liver
Lungs
Kidney
○ Eliminated by kidneys and bile (small %)

Question 13

Pharmacodynamics of Alfaxalone

Answer 13

○ Interacts with GABA-A receptor to disrupt flow Cl- ions through the receptor channel, inhibiting neuronal depolarisation
○ Decreased CMRO2
Rate of oxygen consumption by the brain

Question 14

Propofol effects on Cardiovascular system

Answer 14

Haemodynamic effects minimal
Stable cardiac output
Stable heart rate
○ Haemodynamic effects minimal
Stable MAP, SVR, CVP

Question 15

Propofol effects on Respiratory system

Answer 15

Apnoea much less common than with propofol

Question 16

Uses of Alfaxalone

Answer 16

Licensed in small animals and rabbits
Titrate to effect
Give slowly and wit for effects to manifest
Reduce doses by premedication
Give slowly IV over 60s
Lack of premed can result in agitated recovery
Best to use premeds
Suitable for TIVA (CRI or top ups)
Total intravenous anaesthesia

Question 17

How is Ketamine administered?

Answer 17

IM
IV
Oral
(very versatile)
Schedule 2 drugs - keep locked and record in book

Question 18

Pharmacokinetics of Ketamine

Answer 18

○ Good bioavailability
○ Soluble in water (more lipid soluble)
○ 12% protein bound - less than propofol and alfaxalone
○ Metabolised in liver to norketamine
○ Eliminated by kidneys

Question 19

Pharmacodynamics of Ketamine

Answer 19

○ NMDA antagonist
○ Dissociative anesthesia
Significant muscle tone
Open and central eyes
○ Increased CMRO2 (opposite of propofol and alfaxalone)

Question 20

Effects of Ketamine on cardiovascular system

Answer 20

Haemodynamic effects minimal
Stable cardiac output
Increased heart rate
Increased MAP, SVR, CVP

Question 21

Uses of Ketamine

Answer 21

Licensed in almost all species
Poor muscle relaxation so combine with other drugs
Alpha-2 agonists
Benzodiazepines
Sometimes opioids
Component of the feline ‘triple’ or ‘’quad’ IM protocols
Only analgesic induction agent
Take care with young animals

Question 22

Volatile agent examples

Answer 22

Isoflurane - Licensed in dogs, cats, horses
Sevoflurane - Licensed in dogs and cats

Question 23

Pharmacokinetics of volatile agents

Answer 23

○ Absorption via lungs
○ Solubility in tissues/blood varies
▪ Partition coefficient
○ Distribution via blood to brain
○ Minimally metabolised
○ Elimination via lungs

Question 24

Pharmacodynamics of volatile agents

Answer 24

○ Speed of induction of anaesthesia when using IV drug is proportional to cardiac output
○ Speed of induction of anaesthesia when using inhalation is INVERSELY proportional to cardiac output
▪ Due to negative effects of cardiac output on alveolar partial pressure

Question 25

Effects of volatile agents on cardiopulmonary system

Answer 25

Very depressive on cardiac and lung function
Reduced cardiac output
Reduced heart rate
Reduced MAP, SVR, CVP