L30 - local anaesthetics

Question 1

types of local anaesthetic

Answer 1

regional anaesthesia
local infiltration
topical

Question 2

regional anaesthesia

Answer 2

loss of sensation to a region or body part

Question 3

local infiltration anaesthesia

Answer 3

cuts, skin incisions

Question 4

topical anaesthesia

Answer 4

eye / skin (venepuncture)

Question 5

non-pharmalogical anaesthesia methods

Answer 5

cold (below 8-10 degrees)
pressure
hypoxia

Question 6

how does hypoxia act as an anaesthetic

Answer 6

makes the area go numb

Question 7

reversible local anaesthetic

Answer 7

loss of sensation to a localised area

after a period of time, the nerve impulse will become normal

Question 8

non-reversible local anaesthetic

Answer 8

phenol, ethanol, radio frequency, surgical

once used, nerve conduction is blocked forever (patients with chronic pain)

Question 9

LA definition

Answer 9

A drug which reversibly prevents transmission of the nerve impulse in the region which it is applied without affected consciousness

Question 10

mechanism of LA

Answer 10

At the site of injury, LA block sodium channels opening by binding to subunits from inside the membrane

• Na can no longer enter the cell
• depolarisation
• no action potentials = no pain flowing

Question 11

endoneurium

Answer 11

a layer of connective tissue surrounding nerve fibres

Question 12

fascicle

Answer 12

a bundle of nerves in the endoneurium

Question 13

perineurium

Answer 13

surrounds the fascicles

Question 14

epineurium

Answer 14

surrounds the perineurium

Question 15

where does LS bind in a Na channel

Answer 15

S6 transmembrane domain from the inside, causing closure of the channel

Question 16

how does LA travel across the membrane

Answer 16

only the unionised form can cross as it is liquid soluble (the majority is ionised)

Question 17

which form of LA binds to the sodium channel

Answer 17

only the ionised / protonated form can bind to the channel

Question 18

what determines speed of action of LA

Answer 18

% of unionised form of LA present

Question 19

what does binding of LA to sodium channel do

Answer 19

• slows the rate of AP
• increases the threshold for stimulation
• reduces rate of conduction
• eventually blocks conduction completely

Question 20

ideal LA

Answer 20

• reversible
• good therapeutic index (ratio of effective dose / legal dose)
• quick onset
• suitable duration
• no irritation even on repeated application
• no side effects
• no potential to induce allergy
• applicable by all routes
• cheap, stable, soluble

Question 21

structure of LA

Answer 21

aromatic (lipophilic part)
intermediate chain
hydrophilic substituted amino acid (protein acceptor)

Question 22

two types of LAs

Answer 22

amides

esters

Question 23

how to know if a LA is an amides

Answer 23

…i…caine

Question 24

how to know if a LA is an ester

Answer 24

…caine

Question 25

onset of action

Answer 25

depends on their ability to go into the nerve cell and cross the membrane - drug must be unionised

Question 26

pH and onset of action

Answer 26

further away the pKa of LA from the body pH (7.4), there will be fewer in unionised form = slower onset

Question 27

pH in inflammation

Answer 27

low - so LA less effective

Question 28

differential block - type of nerve fibre

Answer 28

larger fibre = slower onset

Question 29

differential block - location of nerve fibre

Answer 29

nearer the centre of the mantle = takes longer to work

Question 30

what is commonly given with a LA

Answer 30

vasoconstrictors

Question 31

action of vasoconstrictors

Answer 31

- prolong action - reduce plasma levels - greater anaesthesia or reduces dose

Question 32

when should vasoconstrictors not be used

Answer 32

not used with LAs which are supplied by end-vessels | e.g., fingers, toes, penis, ear lobe

Question 33

adrenaline

Answer 33

stimulation of alpha adrenoreceptors - constrict blood vessels

Question 34

examples of vasoconstrictors

Answer 34

- adrenaline | - felypressin (less effective than adrenaline)

Question 35

adverse effects of LAs

Answer 35

- hypersensitivity | - methaemoglobinaemia

Question 36

hypersensitivity

Answer 36

- anaphylactic reaction | - ester> than amides

Question 37

methaemoglobinaemia

Answer 37

Main toxic effect of prilocaine due to its metabolic O-toluidine, which oxidises ferrous to ferric ions

Question 38

symptoms of methaemoglobinaemia

Answer 38

cyanosis, lethargy, respiration distress which does not respond to oxygen

Question 39

dose of lidocaine

Answer 39

3mg/kg | with adrenaline: 7mg/kg

Question 40

bupivacaine / levobupivacaine

Answer 40

2mg/kg | with adrenaline: 2mg/kg

Question 41

prilocaine

Answer 41

6mg/lg | with adrenaline: 8mg/kg

Question 42

treatment of LA toxicity

Answer 42

- stop injection with LA - call for help - A: open the airway - B: give 100% oxygen and ensure adequate lung ventilation - C: confirm or establish IV access - D: control seizures - consider drawing

Question 43

treatment of LA toxicity - in circulatory arrest

Answer 43

- start cardiopulmonary resuscitation - use standard ALS protocol - give IV lipid emulsion

Question 44

how do LA diffuse in to the body

Answer 44

outside the nerves - they then diffuse through the epineurium, perineurium and endometrium to act on the Na channels on nerve axons (they are never injected into nerves)

Question 45

-COO- link

Answer 45

ester

Question 46

who initially used cocaine as a LA

Answer 46

Karl Koller

Question 47

examples of amide LAs

Answer 47

bupivacaine ropivacine prilocaine ligocaine

Question 48

what determines potency of the LA

Answer 48

lipid solubility

Question 49

duration of action in a more protein binding LA

Answer 49

More protein binding = longer the duration of action

Question 50

potency

Answer 50

dose required to produce required effect