Local Anaesthetics Flashcards
What are the uses of local anaesthetics?
When loss of consciousness is neither necessary or desirable
Adjunct to surgery
Postoperative analgesia
For major surgery with sedation
What link is found in procaine and lidocaine?
Procaine- Ester
Lidocaine- Amide
Which anaesthetics are more unstable and less commonly used?
Esters
What local anaesthetics have an amide link?
Lidocaine
Prilocaine
Bupivacaine
Articaine
What local anaesthetics have an ester link?
Tetracaine
Chloroprocaine
Benzocaine
What is the duration and onset of lidocaine?
Medium acting
Rapid onset
What is the duration and onset of prilocaine
Medium acting
No vasodilation
What is the duration and onset of bupivacaine/ levobupivacaine?
Long acting
Short onset
What is the duration and onset of articaine?
Short acting
Rapid onset
What is the duration and onset of tetracaine?
Long acting
V. slow onset
What is the duration and onset of chloroprocaine?
Medium acting
What is the duration and onset of benzocaine?
Atypical mechanism of action
How do local anaesthetics work?
Reversibly blocking voltage-gated sodium channels
What happens If you block a voltage-gated sodium channel?
It stabilises excitable membranes
Prevents membranes from being depolarised
What is the order of loss in nerves?
Pain
Temperature
Proprioception
Skeletal muscle tone
What factors affect the probability of a local anaesthetic being blocked?
Diameter of the diameter of the fibre- smaller nerves blocked more easily
Myelination status- myelinated fibres blocked ore easily
Length of nerve
Length of time exposed to drug
Concentration of drug
Why are myelinated fibres more easily blocked?
Smaller number of sodium channels as they are only present at the nodes of Ranvier
Where do LA act?
They can only act inside the cell when ionised
What problem arises id the LA is ionised?
It cannot base through the membrane
Describe the use-dependent pathway
Drug enters through membrane
Becomes ionised by absorbing a proton
Blocks sodium channel
What us the use-dependent pathway dependent on?
Transmission of signal so the channels are being opened
What mechanism does Benzocaine have?
Pass through membrane
Becomes ionised
So hydrophobic it can pass straight into the channel and block it
What is pKa?
pH at which 50% of the drug is ionised
What is pKa of most LA?
8-9
