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

Local anaesthetics Flashcards

1
Q

What is general anaesthesia?

A

Total loss of sensation.

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2
Q

What is local anaesthesia?

A

Absence of sensation in a specific part of the body.

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3
Q

What are the main methods of local anaesthesia?

A 
PHARMACOLOGICAL
-reversible (LAs) 
-irreversible (ethanol, surgery, etc)
NON-PHARMACOLOGICAL
-cold
-pressure
-hypoxia
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4
Q

What is a local anaesthetic?

A

A drug that:

  • REVERSIBLY prevents nerve transmission
  • to REGION applied
  • WITHOUT affecting consciousness
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5
Q

Where along an axon does a local anaesthetic work?

A

Anywhere along the axon.

-3 neuron chain

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6
Q

What is the mechanism of action of local anaesthetics?

A

Block voltage-gated Na channels&raquo_space; no depolarisation/AP.

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7
Q

Where do local anaesthetics bind to Na channels?

A

Inside cells - has to cross membrane.

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8
Q

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

A

NON-IONISED when they cross cell membrane

IONISED when they bind to Na channels

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9
Q

What are individual nerve fibres surrounded by?

A

Endoneurium.

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10
Q

What are nerve bundles surrounded by?

A

Perineurium.

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11
Q

What is the outermost layer surrounding nerve fascicles called?

A

Epineurium.

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12
Q

What are the layers surrounding nerves? (3)

A

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

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13
Q

Which part of the nerve are local anaesthetics injected into?

A

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

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14
Q

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

A

-EPINEURIUM
-then PERINEURIUM
-then ENDONEURIUM
» NERVE

-causes delayed numbness

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15
Q

What are the main types of local anaesthetics?

A
  • TOPICAL (skin/eyes)
  • LOCAL INFILTRATION (skin incisions)
  • NERVE BLOCK (around nerve)
  • EPIDURAL BLOCK (around spinal cord)
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16
Q

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

A
  • Reversible
  • Quick onset
  • Good therapeutic index
  • Suitable duration
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17
Q

What is therapeutic index?

A

ED50/LD50.

-ratio of amount of therapeutic agent that causes therapeutic effect to amount that causes harm

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18
Q

Are local anaesthetics ever injected into nerves for quick action?

A

No.

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19
Q

Do local anaesthetics produce reversible conduction block?

A

Yes.

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20
Q

What was used as the first local anaesthetic?

A

Cocaine.

  • Freud noticed numbness around lips
  • Koller introduced it
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21
Q

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

A

Aromatic residue + intermediate chain + substituted amino chain.

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22
Q

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

A
  • Esters

- Amides

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23
Q

What are the structural differences between esters and amides?

A

Esters; -COO-

Amides; -HN-CO-

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24
Q

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

A

AMIDES - ‘i’ before -caine
-e.g. Lidocaine

ESTERS - no ‘i’ before -caine
-e.g. Cocaine

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25
Q

Is prilocaine an ester or an amide?

A

Amide.

-‘i’ before -caine

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26
Q

Did Sigmund Freud first used cocaine clinically?

A

No.

-Koller did

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27
Q

What are the different characteristics between local anaesthetics?

A
  • Onset of action
  • Duration of action
  • Potency
  • Differential blockade
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28
Q

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

A

Ionised and non-ionised forms of LAs are equal.

|&raquo_space; quicker onset

29
Q

What is the effect if pKa > pH?

A

Ionised form > unionised form.

- delayed onset

30
Q

What is the pH of the body?

A
  1. 4

- local anaesthetics with similar pKa work more effectively

31
Q

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

A

~6.9

-local anaesthetics don’t work as well when inflammation is present

32
Q

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

A

Procaine (pKa = 7.7).

-pKa of bupivacaine = 8.1

33
Q

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

A

Not necessarily.

  • other factors involved
  • e.g. diffusion rate
34
Q

How does protein binding affect duration of action?

A

More protein binding&raquo_space; longer duration of action.

35
Q

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

A

Bupivacaine - 95%

Lignocaine - 65%
Procaine - 5%

36
Q

What affects the level of protein binding in local anaesthetics?

A

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

37
Q

What is potency?

A

The dose required to produce the desired effect.

38
Q

What does potency depend on?

A

Lipid solubility.

39
Q

What is the effect of an increased lipid solubility?

A

More lipid soluble drugs penetrates the cell membrane&raquo_space; smaller dose required.
-more potent

40
Q

What is differential block?

A

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

41
Q

What does differential block depend on?

A
  • Type of nerve fibre

- Location of nerve fibre (outside/inside mantle)

42
Q

What’s the effect of a larger nerve fibre?

A

Larger nerve fibre&raquo_space; slower onset.

43
Q

What order is sensory function generally lost in?

A
  • Temperature
  • Pain
  • Touch/deep pressure
  • Motor function
44
Q

What type of sensation is lost first?

A

‘First pain’ (Ao fibres)

-then ‘second pain’ (C fibres)

45
Q

What type of drug is often used with local anaesthetics?

A

Vasoconstrictors.

46
Q

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

A
  • Prolong action
  • Reduce plasma levels
  • Reduced does
  • Reduced operative haemorrhage
47
Q

What are the disadvantages of using vasoconstrictors with local anaesthetics?

A

Not used on end-vessels as&raquo_space; hypoxia.

-e.g. fingers, penis, ear lobule

48
Q

Give 2 examples of vasoconstrictors.

A
  • Adrenaline

- Felypressin

49
Q

How does adrenaline cause vasoconstriction?

A

Stimulates alpha-adrenoreceptors.

50
Q

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

A

Dental - 1:80,000

Peripheral - 1:200,000

51
Q

What is felypressin an analogue of?

A

Vasopressin.

52
Q

What are the main differences between adrenaline and felypressin?

A
  • Adrenaline is a more effective vasoconstrictor

- Adrenaline stimulate cardiac B1 receptors, felypressin has no effect on the heart

53
Q

What affect the onset of action of local anaesthetics?

A

pKa of local anaesthetics.

54
Q

Does adrenaline decrease the safe dose of local anaesthetics?

55
Q

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

A
  • Hypersensitivity (allergy)

- Methaemoglobinaemia

56
Q

What sort of allergic response can local anaesthetics cause?

A

Anaphylactic reaction.

-skin rash&raquo_space; shock

57
Q

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

A

Esters.

-rare with amides

58
Q

Which local anaesthetic causes methaemoglobinaemia?

A

Prilocaine.

-due to metabolite 0-toluidine

59
Q

What is the effect of O-toluidine?

A

Oxidises ferrous to ferric ions.

60
Q

What are the main symptoms of methaemoglobinaemia?

A
  • Cyanosis
  • Lethargy
  • Respiratory distress
61
Q

What is the treatment of methaemoglobinaemia?

A

IV methylene blue.

-doesn’t respond to O2

62
Q

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

A

Neuro.

-convulsions occur before cardiac arrest

63
Q

How is local anaesthetic toxicity treated?

A
  • Stop injecting
  • Call for help
  • Airways
  • Breathing (100% O2)
  • Circulation (IV access)
  • Control seizures
  • Consider taking blood for analysis
64
Q

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

A
  • Benzodiazepine
  • Thiopental
  • Propofol
65
Q

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

A

Tinnitus
Lightheadedness
Tongue numbness

66
Q

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

A

3 mg/kg.

-with adrenaline; 7 mg/kg

67
Q

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

A

2 mg/kg.

-with adrenaline; 2 mg/kg

68
Q

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

A

6 mg/kg.

-with adrenaline; 8 mg/kg

Yr2 Control - Term 2 and 3 (17 decks)

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