Injectable anaesthetic agents Flashcards
Name 4 injectable agents and what they are used for
- Propofol
- Alfaxalone
- Ketamine
- Etomidate
What is the use of Total Intra Venous Anaesthesia?
- Use of injectable agents to induce and maintain anaesthesia
- Intermittent boluses
- Constant rate infusion
What is partial Intravenous anaesthesia?
- co-administration of injectable and inhalational anaesthetics to maintain anaesthesia
- creates a balanced anaesthesia
What is the function of propofol?
- Hypnotic alkyl phenol
- lipid water macroemulsion
- licensed in dogs and cats
- concentration 1%
What are the indications of propofol?
- induction and maintenance of anaesthesia
- status epilepticus
- fish and reptile anaesthesia
What is preservatiive free propofol?
- Supports bacterial growth
- Discard at the end of the day
- Constant rate infusion
What is preservative based propofol?
- PropoFlo Plus
- benzyl alcohol preservative
- induction and short-term maintenance
- last 28 days
- no CRI
What are the key factors surrounding propofol?
- IV administration
- Highly protein bound to albumin and RBC
- highly lipid soluble -> rapid onset of action
- equilibration between the CNS and plasma
- Induction and recovery -> usually smooth and excitement free
- Extrapyramidal signs
What is the propofol method of action?
- Hypnotic agent and GABA enhancer
1. Binds to the B subunits of the GABA receptor
2. Prolonged opening of Cl- channels
3. Hyperpolarisation of the post-synaptic neurons
4. inhibits NMDA receptors
How does propofol work in cats?
- Slower hepatic metabolism
- Feline Hb is prone to oxidative injury by repeated daily administration
What is alfaxalone?
- synthetic neuroactive steroid
- Insoluble in water
- Preservatives- last 28 days
- licensed in dogs, cats and rabbits
- concentration = 10mg/ml
What are the indications for alfaxalone?
Induction & maintenance of anaesthesia
* Sedation (not licensed) * Suitable for immersion anaesthesia in amphibians, reptiles & fish
What is the mechanism of action for alfaxalone?
- Enhanced inhibitory effect on GABA
- high dose is a GABA agonist
How might you dose alfaxalone?
IV, IM, SC administration (occasional pain on injection)
* Rapid induction: 30-60’ (IV)
* Dose premedicated animal: 1-2 mg/Kg (to effect)
* IM sedation/anaesthesia (7-10’)
* Alpha 2 agonist, opioids, ACP, midazolam: ↓ induction dose
How does the alfaxalone induction work?
Induction usually smooth without excitement
* Recovery quality ~ to propofol
* Prolonged recoveries if long infusions
* Excitable recovery (Paddling, rigidity, vocalisation possible, especially if used alone)
* Rapid metabolism (hepatic)
What is ketamine?
Phencyclidine derivative
* Licensed: Dog, cat, horse, cattle, sheep, goat, pig, rabbits…
* Used also for exotic & wildlife anaesthesia
* IV, IM, SC, transmucosal absorption
* Aqueous solution: Acidic PH: pain on IM injection
* 10% solution (most commonly used)
What are the indications for ketamine?
Induction ( + other agent(s) to provide myorelaxation)
* Analgesia
* Sedation ( aggressive/ painful patients
How might ketamine be administered?
Can be administered as a bolus, CRI
* Sedation: 0.5-3 mg/kg IM
* Induction dose: * ~ 2.5 up to 5 mg/Kg (higher dose for exotics)
* Rapid onset IV (60-90’’)
* Pain (CRI 10-20 mcg/kg/min intra-op, 2-5 mcg/kg/min post-op)
* HepaƟc metabolism → acƟve metabolite: Norketamine
* Ketamine & Norketamine excreted unchanged (urine) in : careful if renal dx * Dog, horse: Norketamine further metabolised (inactive compounds), urinary + biliary
excretion
What is the ketamine mechanism of action?
- Interacts with many differet receptors
- non-competitive NMDA receptor antagonist
- pain, memory, learning, processing and modulation of neural activity
What is ketamine used for?
Chronic pain/ central sensitisation
What is etomidate?
- Imidazole derivative
- not licensed for animals in the UK
What are the indications for etomidate?
Induction (with premed +/- co-induction) * 1-3 mg/Kg IV
What is etomidate used for?
Rapid induction & recovery (poor quality)
* Metabolism (hepatic & plasma estereses)
* Inactive metabolites excreted in urine, bile, faeces
What is co-induction/ what is the purpose of co-induction?
Administration of two or > drugs together for induction of anaesthesia
* Drug synergism
* Dose sparing effect (< side effects)
* Cost sparing
* Improve cardiovascular stability
* Helpful properties of the non-induction agents (i.e. muscle relaxation, analgesia,
cough response to intubation
How might you obtain central myorelaxation?
Depress internuncial transmission at spinal cord & brainstem
How might you obtain peripheral myorelaxation?
Action at neuromuscular junction (acetylcholine receptors)
