Local anaesthetics Flashcards
What are local anaesthetics?
Drugs which cause a loss of sensation when applied locally by remissibly blocking conduction of APs.
What is the make up of LAs?
aromatic group with and ester or amide link to a basic side chain
Mechanism of action of LAs?
block the voltage dependant NA channels, meaning there is no upstroke of the AP even if the threshold is reached.
Why are LAs given in an alkaline solution?
Most LAs act on the internal surface of the axon/neurone membrane. Therefore LAs need to be non ionised in order to be able to cross the membrane, as LAs are weak bases, an alkaline solution will keep then non ionised
Do LAs work in an ionised or non ionised form?
Ionised LAs are more effective at blocking Na channels, inside cells is a higher pH which ionises the LAs as they enter.
What is use dependant block and why is it clinically important?
When LAs only work in high activity, with lots of Na channels open, this is good as it has less side effects and low activity neurones aren’t affected.
What nerve fibres are more sensitive and blocked more easily by LAs?
Thin and myelinated
What nerve fibres carry nociceptor impulses?
A - myelinated and
C - unmyelinated but thin
therefore both are blocked easily by LAs.
What are the 5 types of administration of LAs?
Surface - on mucosa surface Infiltration- directly into tissue Nerve block - close to nerve trunk Spinal anaesthesia - into subarachnoid space Epidural - into epidural space
Why are vasoconstrictors (adrenaline) sometimes given along with LAs?
To keep the LAs confined locally to the site of administration, this prolongs the action, and reduces the risk of toxicity
Side effects of LAs?
CNS- stimulation produces restelssness and agitation
CVS- myocardial depression and vasodilator effects (hypotension
Hypersensitivity- allergic reactions
Local damage- may occur with infiltration and spinal anaesthesia.
