LA revisited

Question 1

define LA

Answer 1

any technique to render part of the body insensitive to pain without affecting consciousness

Question 2

describe simple events of nerve cell firing/ ion channels

Answer 2

at rest: -70mV

depolarisation: voltage gated Na+ channels open –> +40mV
repolarisation: voltage gated K+ channels open –>-90mV

Question 3

how does LA work

Answer 3

reversibly blocks nerve conduction by blocking Na channels by membrane expansion (10%)

Question 4

how does this change in inflammation 3

Answer 4

• acidic environment –> LA ionises early, cannot cross neural membrane
• vasodilation –> LA transported away from site in blood
• hyperstimulated nerves –> more LA needed

Question 5

draw structure of LA

Answer 5

• aromatic ring (lipophilic- inside cells)
• intermediate linkage (ester/ amide)
• terminal amine (hydrophilic- between cells)

Question 6

what LA is both an amide and ester

Answer 6

articaine

Question 7

name 5 amides

Answer 7

articaine
lidocaine
prilocaine
mepivacaine
bupivacaine

Question 8

name 4 esters

Answer 8

articaine
procaine
TOPICALS: amethocaine, benzocaine

Question 9

breakdown of

a. amides
b. esters

Answer 9

a. amides: liver

b. esters: plasma cholinesterases

Question 10

what type of LA is allergy more common

Answer 10

ester

Question 11

2 forms of LA molecule

Answer 11

unionised lipophilic form: R3N

ionised hydrophilic form: R3NH+

Question 12

type of structure and pKa

Answer 12

weak base, pKa 7.7 (lidocaine)

Question 13

TABLE OF LAs

dosage rule of lidocaine

Answer 13

1 cartridge per 10kg of pt

Question 14

which LA is less effective

Answer 14

prilocaine

Question 15

which LA is contraindicated in pregnant women and why

Answer 15

prilocaine

analogue of oxytocin –> uterine contractions

Question 16

3 options of LA of inf alveolar n

Answer 16

• IDB (direct/ indirect)
• Gow gates (higher up, risk of hitting max artery)
• akinosi (closed mouth, gd for trismus eg in swelling)

Question 17

IDB landmarks

Answer 17

finger: posterior border of mandible
thumb: coronoid notch
pterygomandibular raphe
35mm needle 1cm above occlusal plane from contralateral premolar region

Question 18

site and best LA for long buccal

Answer 18

posterolateral to last standing molar

articaine best

Question 19

reasons for failure of LA:

a. operator dependent 3
b. pt dependent 3

Answer 19

a. operator dependent 3:poor technique, not enough, wrong LA agent
b. pt dependent 3: anatomical (variations, accessory nerves), inflammation, psychological (eg anxiety)

Question 20

what is intra-ligamentary injection and when to use it

Answer 20

LA in to periodontal ligament
use for mandibular molars w short needle
post op discomfort

Question 21

10 immediate complications of LA

Answer 21

• pain (too fast injection or under mucoperiosteum)
• faint
• skin blanching (w intra arterial injection, only lasts 10 mins)
• self-inflicted trauma (ID blocks, kids)
• tachycardia (IV )
• facial paralysis (hit VII)
• allergy (rare)
• needle breakage
• toxicity (excitable then depressed)
• electric shock sensation (hit a nerve. include in notes, can have long lasting effects)

Question 22

6 delayed complications of LA

Answer 22

• haematoma
• trismus
• infection
• persistent anaesthesia/ paresthesia (w articaine)
• tissue necrosis (palatal injections- less connective tissue)
• post anaesthetic lesion (HSV, recurrent apthae)

Question 23

how to avoid complications 6

Answer 23

-gd medical history
-aspirate
-inject slowly
2% lidocaine 2.2ml=10kg
avoid regional blocks
monitor pt

Question 24

how common is nerve damage after IDB

Answer 24

1:500 000