Local anaesthetics Flashcards
What factors affect the onset of general anaesthesia?
potency
pKa (pH)
How do general anaesthetics work?
LA is lipid soluble and crosses the membrane when it is IONISED
when it is UNIONISED it binds to the Na+ channel, blocking the voltage gated ion channel = no action potential
What are the properties of an ideal anaesthetic?
Reversible Good therapeutic index - low = good Quick onset Suitable duration No local irritation even on repeated application No side effects No potential to induce allergy Applicable by all rules Cheap Stable Soluble
What LA has the fastest onset?
Procaine
What is the criteria for a local anaesthetics?
reversibly presents transmission of nerve impulses
targets a region
doesn’t affect conciousness
What are the two classifications of local anaesthetics?
Amides - have a ‘i’ before the ‘caine’
Esters
What affects the duration of a local anaesthetic?
protein binding - more = longer duration
length of intermediate chain
What affects the ability to block neuronal conduction?
length/thickness of neuron
location of neuron within the nerve - LA must pass through epineurium, perineurium, endoneurium and outer neuron
What fibre type can be tested to check that the LA has taken effect?
proprioception - A gamma fibres
What is the function of combining vasoconstrictors with LAs?
decreases vascularity
LA stays in the same place for longer
Where should vasoconstrictors with LAs not be used?
fingers & toes penis ear lobule ala of nose can causes hypoxia
What are the adverse effects of LA?
Type I hypersensitivity reaction
Methaemoglobinaemia - oxidation of ferrous
What is the treatment for LA toxicity?
STOP
ABCD
CPR
intravenous lipid emulsion - last resort
Which LA has the longest duration?
Bupivacaine
