Local Anaesthetics Flashcards
What do local anaesthetics produce?
Transient + reversible loss of sensation without loss of consciousness
Are they reversible?
YES
What are some examples?
Benzocaine
Cocaine
Lidocaine
What are the different types?
Esters - eg. cocaine
Amides - eg. Lidocaine
What is their general structure?
Aromatic ring = lipophilic portion
Intermediate linkage
Terminal amine = hydrophilic portion
What does the aromatic ring allow?
Go through the membrane
What happens if the linkage is longer?
Action is longer
What is the mechanism of action?
Block Na+ channel on the intracellular side
= artificial inactivated state
= ions can’t travel
= NO generation + propagation of AP
Which fibres does they act on?
All types
BUT structure of fibres determine how long it works
Which fibre do they work longest on?
C fibres
= unmyelinated
What type of drugs are local anaesthetics?
Potent vasodilating
Describe their distribution in the body
Cross BBB
Cross placenta
Distribute to all tissues
What does it mean if they distribute to all tissues?
Should use low doses
Why would the brain, head, liver and lungs, kidneys + spleen receive high levels?
High level of perfusion
What is their duration of action dependent on?
Protein binding
What is their potency dependent on?
Lipid solubility
= higher solubility = use lower dose
What is the organ for excretion of local anaesthetics?
Kidneys
When do you need to caution with local anaesthetics?
Patients undergoing dialysis
= unable to excrete unchanged portion of esters/amides
= increasing toxicity
What is their pharmacological action?
CNS depression
At high levels what can local anaesthetics do?
Produce convulsions
What are their cardiovascular effects?
Decreased myocardial depolarisation
Decreased myocardial excitation = decreased force of contraction
Hypotension
What are their respiratory effects?
Direct relaxant of bronchial smooth muscle
Normal respiratory function unaffected unless overdose
What is the local tissue toxicity?
Skeletal muscle will heal within 2 weeks of being injected
Longer acting produce more damage - eg. Bupivacaine
What are the 6 administration sites?
Surface/topical
Local infiltration
Peripheral nerve block
Bier block
Epidural anaesthesia
Spinal anaesthesia
