Local Anaesthesia Flashcards
What do local anaesthetic (LA) agents do?
They reversibly block the transmission of peripheral nerve impulses.
What are examples of physical factors that can cause reversible nerve block?
Pressure and cold.
What was the first local anaesthetic, and when was it discovered?
Cocaine, discovered in 1860 from Erythroxylum coca.
Who demonstrated the first LA action of cocaine, and when?
Koller in 1864.
Why is cocaine’s use as an LA limited?
Due to allergic reactions.
When was procaine first synthesised?
Procaine was synthesised in 1904.
Which LA was synthesised in 1943?
Lidocaine.
List the LAs synthesised from 1957 to 2000.
Mepivacaine (1957), prilocaine (1960), bupivacaine (1963), ropivacaine (1997), levobupivacaine (2000).
What types of LAs are popular in North America?
Ester LAs (e.g., cocaine, procaine, chloroprocaine).
What limits the use of ester LAs in North America?
Due to potential allergic reactions.
How are LAs classified based on their physical structure?
Based on ester and amide structures.
What type of linkage do ester and amide LAs have?
Esters have an ester linkage, and amides have an amide linkage.
List examples of ester LAs.
Cocaine, procaine, amethocaine, chloroprocaine.
List examples of amide LAs.
Lidocaine, mepivacaine, prilocaine, bupivacaine, ropivacaine, levobupivacaine.
How are LAs classified based on potency and duration of action?
Based on their potency and duration of action.
What LAs have a short duration of action and low potency?
Procaine and chloroprocaine.
Which LAs have intermediate potency and duration?
Lidocaine, mepivacaine, prilocaine, cocaine.
Name LAs with long duration of action and high potency.
Bupivacaine, tetracaine, etidocaine.
How do ester LAs differ from amide LAs in terms of stability?
Esters hydrolyse spontaneously and can be heat-sterilised once; amides are more stable.
What factors increase the duration of action of LAs?
Lipid solubility, protein binding affinity, and type of nerve fibre.
What factors influence the potency of LAs?
Lipid solubility.
How is the rate of onset of LA action determined?
By the pKa of the LA; lower pKa leads to faster onset.
What factors affect the pharmacokinetics of LAs?
Absorption kinetics, distribution, dosage, injection site, and physiological factors.
Which factors influence the absorption kinetics of LAs?
Physicochemical properties, dosage, injection route, vasoconstrictors, and pathophysiological factors.
How does pregnancy affect the pharmacokinetics of LAs?
It increases the segmental spread of epidurals.
How does the site of injection affect the rate of LA absorption?
It is influenced by the rate of blood flow to different nerves and tissues.
What happens if the IVRA tourniquet is released prematurely?
It causes rapid entry of a large dose into circulation.
How are ester LAs metabolised?
They undergo hydrolysis by plasma cholinesterase.
How are amide LAs metabolised?
They are metabolised in the liver, with prilocaine undergoing some extra-hepatic metabolism.
What is the function of additives to LAs?
To adjust pH, tonicity, baricity, and for pharmacologic reasons.
