principles of local anaesthesia

Question 1

structure of LA’s+ types, therefore examples

Answer 1

have an aromatic region, an amino side chain, which are connected by either an ESTER or an AMIDE bond, thus there are 2 types of LA’s (ester= cocaine, amide=lidocaine)

Question 2

main MOA and what it doesn’t do

Answer 2

HYDROPHILIC pathway- UNIONISED (B) LA goes INSIDE neurone, and then once inside becomes IONISED (BH+), and then binds to the voltage-gated Na+ channel, which MUST be open= inhibition o AP (NOT RMP ie doesn’t cause hyperpolarisation like GABA)

Question 3

use dependency of hydrophilic pathway and thus selectivity significance

Answer 3

neurones that are more active are more effectively blocked, as the Na+ channels are open for longer- thus they effect small diameter/unmyelinated fibres ie C fibres, so SELECTIVE for nociceptors

Question 4

other less important MOA with example

Answer 4

HYDROPHOBIC pathway- lipid soluble LA’s eg BENZOCAINE dissolve in membrane ie don’t go inside neurone, become ionised like before, and block Na+ channels from within the membrane

Question 5

are LA’s weak bases or weak acids, thus significance with infection

Answer 5

weak bases, thus infected tissue difficult to anaesthatise, as the tissue is acidic

Question 6

types of administration-

Answer 6

SENISI: surface anaesthesia INFILRATION anaesthesia , INTRAVENOUS regional anaesthesia , NERVE block anaesthesia, spinal anaesthesia , and epidural anaesthesia

Question 7

surface anaesthesia- how it’s done, issue

Answer 7

SPRAY onto mucosal surface eg mouth: may cause systemic toxicity at high conc as may get into blood

Question 8

infiltration anaesthesia- use, what given with

Answer 8

into tissue for MINOR surgery, given with adrenaline to keep it local, as causes vasconstriction= logner DOA in that area

Question 9

intravenous regional anaesthesia- use, and how to use it

Answer 9

for LIMB surgery, DISTAL to a pressure cuff to keep it local, otherwise= systemic toxicity

Question 10

nerve block anaesthesia- pro and con

Answer 10

close to nerves, low dose sufficient but slow onset)

Question 11

spinal anaesthesia vs epidural- uses, dosage+ BP

Answer 11

for pelvic/lower limb surgery: low doses needed but may lower BP: uses same as spinal, but also childbirth: needs high dose, but less effect on BP

Question 12

pharmacokinetics of lidocaine (amide) vs cocaine (ester)- absorption, PP binding, metabolism, and half life

Answer 12

absorption similar, both have good plasma protein binding but cocaine more bound, metabolism by hepatic dealkylation vs hepatic AND plasma esterases, and amide half life greater (as more stable)

Question 13

side effects of lidocaine and reasons

Answer 13

effects on CNS and CVS: lidocaine causes PARADOXICAL CNS stimulation ie restlessness, and myocardial depression + vasodilation+ low BP (due to Na+ blockade)

Question 14

side effects of cocaine and reason

Answer 14

both CNS and CVS again- causes euphoria of CNS, and increases CO/vasoconstriction/high BP due to cocaine SNS actions