Drugs for Induction Flashcards
How can Induction drugs be delivered?
IM
IV
Sub-cut
Inhaled
Across mucous membranes
Ideal pharmacodynamic/kinetic properties of an induction agent
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
Ideal Physiochemical properties of an induction agent
Water soluble
Stable formulation, nonpyrogenic
Nonirritant
Painless on IV injection
Small volume required
Inexpensive and easy to prepare
Antimicropial preparation
How do anaesthetics work?
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
How is propofol administered?
IV
Licensing in small animals
Pharmacokinetics of Propofol
○ Poor oral bioavailability
○ Not soluble in water - must be made up as an emulsion
○ Highly protein bound
○ Metabolised by liver
○ Eliminated by kidneys
Pharmacodynamics of Propofol
○ Interacts with GABA-A receptor to disrupt flow Cl- ions through the receptor channel, inhibiting neuronal depolarisation
Propofol effects on cardiovascular system
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
Propofol effects on respiratory system
Respiratory depression
Apnoea common - be quick to intubate
Uses of propofol
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)
How is Alfaxalone administered?
IV or IM
Clear colourless neuroactive steroid
Pharmacokinetics of Alfaxalone
○ Good bioavailability
○ Soluble in water
○ 30-50% protein bound
Less than propofol
○ Metabolised:
Liver
Lungs
Kidney
○ Eliminated by kidneys and bile (small %)
Pharmacodynamics of Alfaxalone
○ 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
Propofol effects on Cardiovascular system
Haemodynamic effects minimal
Stable cardiac output
Stable heart rate
○ Haemodynamic effects minimal
Stable MAP, SVR, CVP
Propofol effects on Respiratory system
Apnoea much less common than with propofol
Uses of Alfaxalone
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
How is Ketamine administered?
IM
IV
Oral
(very versatile)
Schedule 2 drugs - keep locked and record in book
Pharmacokinetics of Ketamine
○ Good bioavailability
○ Soluble in water (more lipid soluble)
○ 12% protein bound - less than propofol and alfaxalone
○ Metabolised in liver to norketamine
○ Eliminated by kidneys
Pharmacodynamics of Ketamine
○ NMDA antagonist
○ Dissociative anesthesia
Significant muscle tone
Open and central eyes
○ Increased CMRO2 (opposite of propofol and alfaxalone)
Effects of Ketamine on cardiovascular system
Haemodynamic effects minimal
Stable cardiac output
Increased heart rate
Increased MAP, SVR, CVP
Uses of Ketamine
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
Volatile agent examples
Isoflurane - Licensed in dogs, cats, horses
Sevoflurane - Licensed in dogs and cats
Pharmacokinetics of volatile agents
○ Absorption via lungs
○ Solubility in tissues/blood varies
▪ Partition coefficient
○ Distribution via blood to brain
○ Minimally metabolised
○ Elimination via lungs
Pharmacodynamics of volatile agents
○ 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
Effects of volatile agents on cardiopulmonary system
Very depressive on cardiac and lung function
Reduced cardiac output
Reduced heart rate
Reduced MAP, SVR, CVP
