Local anaesthetics

Question 1

desc an AP

Answer 1

neg resting membrane potential is depol by coming AP which opens Na+ and Na+ influxes in
This repol then caused by K+ efflux
refractory period

Question 2

how do local A work

Answer 2

block vgated Na channels (nerve blocked)

block K and Ca+ - gives SE and only partial block

Question 3

LocalA are either amino-esters or amino-amides - why does this matter, and name examples of each

Answer 3

amino-esters are hydrolysed by plasma pseudo-ChE and they DONT need the liver to metab
amino esters = cocaine, procaine and benzocaine
amino-amides = lidocaine, mepivicaine and bupivicaine

Question 4

what is the pKa

Answer 4

pH is when 50% ionised and non-ionised. the closer the pKa to the pH = more non-ionised form that is present= faster action

Question 5

why do you need both ionised and non-ionised forms?

Answer 5

ionised forms cross through channels, but then they bind to the Na+ channels and block them. This stops anymore ionised form entering the cell. from this point onwards - non-ionised forms are needed to cros through the cell membrane to act

Question 6

what property increases the duration of the action of local anaesth/

Answer 6

protein binding

Question 7

what are the 2 nerve layers within the epineurium

Answer 7

mantel - peripheral motor nerves

core - sensory

Question 8

there are numerous types of nerve fibre - name easiest –> hardest?

Answer 8

B fibres = sympathetic, little myelination; blockage causes vasodil
C fibres = slow pain fibres
Ad = fast pain fibres
Ab = touch and proprioception
Aa = motor fct

Question 9

how can you help to increase duration

Answer 9

adrenaline or A2-ag to cause vasocon (and keep it there longer)

Question 10

what are the 2 form of local toxicity and describe then

Answer 10

neurotox - sedation –> seizures –> coma

cardiotox - arrythmia and cardiac arrest

Question 11

what is the least and most toxic local anaesthetics

Answer 11

mepivicaine/lido/procaine = least (max 10mg/kg)
bupivicaine = most (max 2mg/kg) - ctox+ntox at similar level!

Question 12

which LA can you use IV and why

Answer 12

lidocaine
tx - ventricular arrhythmia, systemic analgesia (crosses BBB), inc GI motility, anti-endoxaemia and anti-inflm
- decrease ICP too!

Question 13

other than toxicity what is another major risk

Answer 13

anaphylactic shock. mHb-anaemia