Local anaesthetics Flashcards Preview

Yr2 Control - Term 2 and 3 > Local anaesthetics > Flashcards

Flashcards in Local anaesthetics Deck (68):
1

What is general anaesthesia?

Total loss of sensation.

2

What is local anaesthesia?

Absence of sensation in a specific part of the body.

3

What are the main methods of local anaesthesia?

PHARMACOLOGICAL
-reversible (LAs)
-irreversible (ethanol, surgery, etc)
NON-PHARMACOLOGICAL
-cold
-pressure
-hypoxia

4

What is a local anaesthetic?

A drug that:
-REVERSIBLY prevents nerve transmission
-to REGION applied
-WITHOUT affecting consciousness

5

Where along an axon does a local anaesthetic work?

Anywhere along the axon.
-3 neuron chain

6

What is the mechanism of action of local anaesthetics?

Block voltage-gated Na channels >> no depolarisation/AP.

7

Where do local anaesthetics bind to Na channels?

Inside cells - has to cross membrane.

8

What state are local anaesthetics in when they cross the membrane and bind to Na channels?

NON-IONISED when they cross cell membrane
IONISED when they bind to Na channels

9

What are individual nerve fibres surrounded by?

Endoneurium.

10

What are nerve bundles surrounded by?

Perineurium.

11

What is the outermost layer surrounding nerve fascicles called?

Epineurium.

12

What are the layers surrounding nerves? (3)

ENDONEURIUM - surrounds individual nerve fibres
PERINEURIUM - surrounds nerve bundles
EPINEURIUM - outermost, surrounds fascicles

13

Which part of the nerve are local anaesthetics injected into?

Injected into the area around nerves, not into the nerve.

14

What layers must local anaesthetics pass through to enter the nerve?

-EPINEURIUM
-then PERINEURIUM
-then ENDONEURIUM
>> NERVE

-causes delayed numbness

15

What are the main types of local anaesthetics?

-TOPICAL (skin/eyes)
-LOCAL INFILTRATION (skin incisions)
-NERVE BLOCK (around nerve)
-EPIDURAL BLOCK (around spinal cord)

16

What are the ideal characteristics of local anaesthetics? (4)

-Reversible
-Quick onset
-Good therapeutic index
-Suitable duration

17

What is therapeutic index?

ED50/LD50.
-ratio of amount of therapeutic agent that causes therapeutic effect to amount that causes harm

18

Are local anaesthetics ever injected into nerves for quick action?

No.

19

Do local anaesthetics produce reversible conduction block?

Yes.

20

What was used as the first local anaesthetic?

Cocaine.
-Freud noticed numbness around lips
-Koller introduced it

21

What is the general structure of local anaesthetics? (3)

Aromatic residue + intermediate chain + substituted amino chain.

22

What are the 2 types of local anaesthetics based on structure?

-Esters
-Amides

23

What are the structural differences between esters and amides?

Esters; -COO-
Amides; -HN-CO-

24

What is the difference between the naming of ester and amide local anaesthetics?

AMIDES - 'i' before -caine
-e.g. Lidocaine

ESTERS - no 'i' before -caine
-e.g. Cocaine

25

Is prilocaine an ester or an amide?

Amide.
-'i' before -caine

26

Did Sigmund Freud first used cocaine clinically?

No.
-Koller did

27

What are the different characteristics between local anaesthetics?

-Onset of action
-Duration of action
-Potency
-Differential blockade

28

What is the effect if pKa (anaesthetic) = pH (body)?

Ionised and non-ionised forms of LAs are equal.
>> quicker onset

29

What is the effect if pKa > pH?

Ionised form > unionised form.
- delayed onset

30

What is the pH of the body?

7.4
-local anaesthetics with similar pKa work more effectively

31

What is the pH of pus, and what effect does this have?

~6.9
-local anaesthetics don't work as well when inflammation is present

32

Which one would have a quicker onset; procaine or bupivacaine?

Procaine (pKa = 7.7).
-pKa of bupivacaine = 8.1

33

Do local anaesthetics with the same pKa have the same clinical onset?

Not necessarily.
-other factors involved
-e.g. diffusion rate

34

How does protein binding affect duration of action?

More protein binding >> longer duration of action.

35

Which of the following local anaesthetics has the most protein binding, and therefore the longest duration?
-lignocaine, procaine, bupivacaine

Bupivacaine - 95%

Lignocaine - 65%
Procaine - 5%

36

What affects the level of protein binding in local anaesthetics?

The length of the intermediate chain joining aromatic and amine groups.

37

What is potency?

The dose required to produce the desired effect.

38

What does potency depend on?

Lipid solubility.

39

What is the effect of an increased lipid solubility?

More lipid soluble drugs penetrates the cell membrane >> smaller dose required.
-more potent

40

What is differential block?

Nerve fibres with different functions have different sensitivities to local anaesthetics.

41

What does differential block depend on?

-Type of nerve fibre
-Location of nerve fibre (outside/inside mantle)

42

What's the effect of a larger nerve fibre?

Larger nerve fibre >> slower onset.

43

What order is sensory function generally lost in?

-Temperature
-Pain
-Touch/deep pressure
-Motor function

44

What type of sensation is lost first?

'First pain' (Ao fibres)
-then 'second pain' (C fibres)

45

What type of drug is often used with local anaesthetics?

Vasoconstrictors.

46

What are the advantages of using vasoconstrictors with local anaesthetics? (4)

-Prolong action
-Reduce plasma levels
-Reduced does
-Reduced operative haemorrhage

47

What are the disadvantages of using vasoconstrictors with local anaesthetics?

Not used on end-vessels as >> hypoxia.
-e.g. fingers, penis, ear lobule

48

Give 2 examples of vasoconstrictors.

-Adrenaline
-Felypressin

49

How does adrenaline cause vasoconstriction?

Stimulates alpha-adrenoreceptors.

50

How much adrenaline is needed for dental LA and peripheral nerve blocks?

Dental - 1:80,000
Peripheral - 1:200,000

51

What is felypressin an analogue of?

Vasopressin.

52

What are the main differences between adrenaline and felypressin?

-Adrenaline is a more effective vasoconstrictor
-Adrenaline stimulate cardiac B1 receptors, felypressin has no effect on the heart

53

What affect the onset of action of local anaesthetics?

pKa of local anaesthetics.

54

Does adrenaline decrease the safe dose of local anaesthetics?

No.

55

What are the main adverse effects of local anaesthetics? (2)

-Hypersensitivity (allergy)
-Methaemoglobinaemia

56

What sort of allergic response can local anaesthetics cause?

Anaphylactic reaction.
-skin rash >> shock

57

What type of local anaesthetic are allergic reactions more common in?

Esters.
-rare with amides

58

Which local anaesthetic causes methaemoglobinaemia?

Prilocaine.
-due to metabolite 0-toluidine

59

What is the effect of O-toluidine?

Oxidises ferrous to ferric ions.

60

What are the main symptoms of methaemoglobinaemia?

-Cyanosis
-Lethargy
-Respiratory distress

61

What is the treatment of methaemoglobinaemia?

IV methylene blue.
-doesn't respond to O2

62

What sort of toxicity to local anaesthetics occurs first; neuro or cardiac?

Neuro.
-convulsions occur before cardiac arrest

63

How is local anaesthetic toxicity treated?

-Stop injecting
-Call for help
-Airways
-Breathing (100% O2)
-Circulation (IV access)
-Control seizures
-Consider taking blood for analysis

64

What drugs are used to control the seizures? (3)

-Benzodiazepine
-Thiopental
-Propofol

65

What may be the initial presenting symptom of local anaesthetic toxicity?

Tinnitus
Lightheadedness
Tongue numbness

66

What is the toxic does of lidocaine with and without adrenaline?

3 mg/kg.
-with adrenaline; 7 mg/kg

67

What is the toxic does of bupivacaine/levobupivacaine with and without adrenaline?

2 mg/kg.
-with adrenaline; 2 mg/kg

68

What is the toxic does of prilocaine with and without adrenaline?

6 mg/kg.
-with adrenaline; 8 mg/kg