Anaesthetic Drugs Flashcards
Do anaesthetics work in the same way?
No - is no universal mechanism. Different anaesthetics work in different ways.
What is the triad of anaesthesia?
The use of drugs to produce amnesia, analgesia and akinesia - which in turn lightens the load of amnesia (anaesthetic) drugs that need to be given to the patient.
What is the medical term for unconsciousness?
Anaesthesia
What is the medical term for muscle relaxation?
Akinesia
What is the medical term for pain relief?
Analgesia
Do we know how anaesthetic drugs work?
No
Name four potential sites that anaesthetic drugs are thought to target in the body.
Cerebral cortex
Thalamus
Reticular activating system
Spinal cord
Which receptors do we think anaesthetic drugs potentially have an impact upon?
GABA & glutamate receptors
Voltage-gated ion channels
Glycine & serotonin receptors
What do anaesthetic agents do to excitable tissues?
Suppress them to varying degrees
What type of solubility do anaesthetic drugs need to have?
Need to be lipid soluble
What is the name of the correlation between lipid soluble drugs and potency?
Meyer-Overton correlation
What does the Meyer-Overton correlation say?
The more lipid-soluble a drug the more potent it is.
Name three inhaled anaesthetic drugs
Sevoflurane
Isoflurane
Desflurane
What are propofol, thiopentone, etomidate & ketamine used for?
IV anaesthetic drugs
Which is the main IV anaesthetic drug used?
Propofol
What is balanced anaesthesia?
Using the triad of drugs (analgesia, akinesia & anaesthetics) meaning that you dont have to use too much of one drug and therefore kill the patient.
Why is it important that anaesthetic drugs are lipid soluble?
It means that they can cross the BBB
What chemical family are inhaled anaesthetics from?
Halogenated ethers
What are the advantages to propofol as a drug?
Easy to administer
Doesnt harm the vein
Lipid soluble
Rapidly perfuses the brain & relaxes the larynx
Antiemetic & Antiepileptic
Can maintain anaesthestia with infusion or repeated bolus
Does not accumulate
Rapidly metabolised by the liver
What are the disadvantages to propofol as a drug?
Can cause pain on injection & abnormal movements
Can cause hypotension
Is an infection risk due to the lipid it is stored in
How does propofol wear off and allow P to wake up?
It is redistributed into the tissues - this allows P to wake up.
Ps DO NOT wake up because it is metabolised.
Where is propofol redistributed to?
Less perfused tissues - such as muscle. However fat levels of the drug remain low because fat is very poorly perfused
What is the name of the effect that is used in vaporiser bottles?
Plenum effect
Name three types of inhalational anaesthetics
Halogenated ethers
Nitrous oxide
Xenon
How are inhalational anaesthetics administered?
Through specific vaporisers which heat up the drug to its specific boiling point and vaporise it.
What is the theoretical maximum inspired concentration?
70-80%
What happens to the patient initially when using a halogenated ether? What is this termed?
Analgesia
Excitement (may fight the mask)
then Surgical anaesthesia
Termed etherisation
What are the risks of using inhaled anaesthetics?
Post-op nausea & vomiting (PONV)
If irritation - can make gas induction difficult (e.g. coughing)
Emergence phenomena - awaking during operation but being unable to move
Why is it important that the ideal inhalational agent is not metabolised?
Because to metabolise it runs an increased risk of acute hepatitis
What do muscle relaxants do?
Block neuromuscular junction receptors and stop muscles from working - thereby causing paralysis and cessation of breathing
Who should be given muscle relaxants?
Unconscious patients only
Why do we use muscle relaxants?
- To assist with intubation
- To facilitate surgery or ventilation
What are the two classes of muscle relaxants?
Depolarising and non-depolarising
How do depolarising muscle relaxants work?
Depolarising muscle relaxants bind to the ACh receptor on the post-synaptic membrane. They cause initial depolarisation of this membrane, and then as they do not release - this means the post-synaptic receptor is blocked and cannot be stimulated again.
Name one depolarising neuromuscular blocking agent (NMBA).
Succinylcholine
How rapid is succinycholine in its action?
Binds rapidly
Half-life of about 2 mins
Wears off in around 5 mins
What is succinylcholine metabolised by?
Plasma cholinesterase
What are the negatives to using succinylcholine?
Has multiple side effects
- Fasciculations
- Anaphylaxis
- K+
- Cholinesterase abnormality…
- Causes fasciculations which can cause post-op pain for the patient
- Higher rate of anaphylaxis
- Can increase levels of K+ in the blood
- If P has abnormality and doesnt produce cholinesterase - means P can remain paralysed for a few hours (rare)
How do non-depolarising NMBAs work compared to depolarising ones?
Non-depolarising compounds bind to the post-synaptic receptors competitively but DO NOT cause depolarisation of the post-synaptic membrane
What type of compounds are used as non-depolarising agents?
Quaternary ammonium compounds
How do non-depolarising agents vary in speed from depolarising agents?
Non-depolarising agents have slower onset and offset times
Name one non-depolarising agent used.
Rocuronium
(aslo - vecuronium, pancuronium, benzylisoquinolinium and atracurium)
What are NMBAs used for?
Intubation
Surgery
Ventilation
ECT
Transfer of patients
Lethal injection
Do we usually reverse depolarising agents?
Usually not - as effects wear off quickly.
However if there is prolonged paralysis due to cholinesterase deficiency then yes - may need to reverse
Which drug do we commonly use to reverse non-depolarising agents?
Neostigmine
How does neostigmine work?
Binds to acetylcholinesterase - thus preventing the breakdown of ACh in the cleft
Which drug is used for reversal of NMBAs but is very expensive?
Sugammadex
How does botulinum work?
Prevents vesicles containing ACh from binding to the membrane - therefore preventing the release of ACh into the synaptic cleft
What is Botulinum used for?
Relief of muscle spasms and contractions
Neuropathic pain
Aesthetic uses
