Injectable Anaesthetics Flashcards
Why are injectable anaesthetics used mostly?
- For induction prior to inhalational anaesthesia
- As a sole agent for short procedures
- Supplement inhalational agents and deepen anaesthesia
- Suppress CNS stimulation in certain conditions e.g. poisoning
What are the advantages and disadvantages of IV catheter?
- Reduces risk of extravascular injection
- Rapid IV access for emergencies
- Rapid deepening of anaesthesia
- Administration of fluids
- Vein damage
- Sepsis risk
What is TIVA?
Total Intravenous Anaesthesia
- using injectables instead of any gaseous agents
- ideally, using a CRI or syringe driver
- still need o2 supply and good airway
When does unconsciousness occur?
When a critical concentration of the drug is reached in the brain
What does the route of administration of injectable anaesthetics affect?
- speed of onset of anaesthesia
- anaesthetic duration
- its peak effect
When does consciousness return?
When less well-perfused organs e.g. skeletal muscle, will start to take up the drug and results in lower plasma levels. This drop in plasma concentration of drug triggers the drug to move from the brain into the plasma. This causes the brain level to fall below critical level and consciousness returns
What affects the duration of action of an injectable anaesthetic?
- Redistribution - How fast the drug moves from the brain to the less well-perfused areas. This depends on cardiac output and the mass of tissues available
- Metabolism
How are injectable anaesthetic drugs rid from the body?
Metabolised in the liver, converted from lipid to water-soluble molecules which are then excreted in bile or urine.
What drug is metabolised very fast and therefore causes a very quick wake-up?
Propofol
What animals are highly lipid-soluble barbiturates contraindicated in?
Any animals with renal, hepatic or cardiovascular disease. Not suitable for shocked patients due to reduced blood flow to fat and increased cardia and cerebral blood flow.
What drug is used for euthanasia?
Pentobarbitone
Describe Propofol’s characteristics
- Phenol anaesthetic
- Safer, more rapidly metabolised and better recovery than thiopentone
- Rapid loss of consciousness
- rapid recovery
- useful in TIVA techniques
What are the advantages of Propofol?
- Non-irritant peri-vascular
- rapid metabolism and recovery
- free from hangover if single dose given
- non-cumulative
What are the disadvantages of Propofol?
- May cause apnoea if injected too fast
- May cause hypotension & occasional bradycardia
- may cause twitches and excitable recoveries (if used on own)
- May have mild pain on injection (can be reduced by cooling the solution)
Describe the storage of Propofol?
- Do not freeze
- Store below 25C
- Once opened, bin. Or use Propoflo Plus (28 days)
- Protect from light
Describe the characteristics of Alfaxalone
- Steroid-based anaesthetic
- Suitable for dogs, cats and rabbits
What are the advantages of Alfaxalone?
- Smooth and rapid induction
- Smooth and rapid recovery
- not painful to inject
What are the disadvantages of Alfaxalone?
- Rapidly metabolised so need an adequate pre-med. Also causes a rapid recovery so need a dark and quiet room for recovery
How should alfaxalone be stored?
- Protect from light
- Room temp
- Dispose immediately or after 28 days if a multi dose vial
What different routes can Ketamine be given via?
- IV, IM (painful), SC, IP and also may be absorbed sublingually (good for aggressive dogs)
Describe the characteristics of Ketamine
- Dissociative anaesthetic (does not cause complete loss of consciousness)
- Sympathetic nervous system stimulant - increases HR
- May be used alone in cats but MUST be combined with other drugs in dogs (e.g. alpha 2 to produce GA)
What are the advantages of Ketamine?
- Protective airway reflexes maintained
- Analgesic properties - somatic
What are the disadvantages of Ketamine?
- Challenge to monitor - eyes remain open, pupils dilated
- Muscle relaxation poor
- Risk of corneal drying
- Stings IM
- Need slow reversal of other drugs to avoid leaving on ketamine only
Describe the storage of Ketamine
Schedule 2 CD
- must be stored in a locked cupboard and a register of use kept
