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BDS2 BAMS Local Anesthetic > Local Anaesthetics > Flashcards

Local Anaesthetics Flashcards

1
Q

How do LA work

A

They stop nerve conduction by blocking the voltage gated sodium channels

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2
Q

What does LA work on

A

The first order afferent receptors - not the CNS but the PNS

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3
Q

What do the connective tissue barriers in the peripheral nerves act as

A

A diffusion barrier

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4
Q

What does a greater number of membrane mean for the LA

A

Will take longer to anesthetize

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5
Q

What is the general rule for weaning out

A

Nerves that will be anesthesized first will wean out first

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6
Q

What is the effect of position of the nerve in the bundle to LA

A

The further it is from the LA the longer it will take to be anaesthetised

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7
Q

What is the order of block in different fibres

A

Adelta, C, Abeta, Aalpha

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8
Q

What group do A alpha sensorial nerves belong to

A

group I

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9
Q

What group do A beta nerves belong to

A

group II

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10
Q

What group do Adelta nerves belong to

A

group III

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11
Q

What group do sensorial C nerves belong to

A

group IV

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12
Q

What is the function of A Alpha nerves

A

sensory (proprioception)

motor (skeletal muscle)

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13
Q

What is the function of A Beta nerves

A

sensory (mechanoreception)

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14
Q

What is the function of A gamma

A

Motor (muscle spindles)

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15
Q

What is the function of A delta

A

Sensory (mechanic-, thermo-, noci and chemoreceptors)

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16
Q

What is the function of C fibres

A

Sensory (noci-termo and chemoreceptors)

autonomic (post ganglionic)

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17
Q

What fibres do we want to anesthetize

A

Delta
A beta
C

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18
Q

What fibres do we not want to anaesthetise

A

autonomic

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19
Q

What is the mechanism of action of LA

A

binds to a site in the sodium channel
LA blocks the channel and prevents sodium influx
This blocks the action potential generation and propagation
Block persists so long as a sufficient number of NA channels are blocked

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20
Q

What other Na channels does LA block

A

in other excitable tissues e.g heart muscle

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21
Q

What are possible side effects of LA

A

bradycardia

hypotension

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22
Q

Do we need all sodium channels blocked

A

We don’t need to have absolutely all sodium channels blocked but enough to avoid AP reaching the maximum level

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23
Q

What are the 3 components of the organic molecule in lLA

A

aromatic region (hydrophobic)
ester or amide bond
basic amine side chain (hydrophilic)

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24
Q

How is LA presented as

A

hydrochloride (B.HCl)

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25
Q

What does the B.HCl allow

A

renders the amine base more water soluble

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26
Q

Why are LA partly dissociated

A

As they are active in the ionized form

They can cross the membrane only in the unionized form

27
Q

In what form is B.HCl pharmacologically active but non diffusible

A

B.H+

28
Q

In what form is B.HCl diffusible but not active

A

B. + H+

29
Q

What molecule binds the sodium channel

A

B.H+

30
Q

Why are small diameter axons more susceptible to LA block

A

Same concentration of LA will act better on small diameter axons because there are less sodium channels to block

31
Q

Why is a greater concentration of LA required for myelinated axons

A

NA channels and K channels are more concentrated at nodes of ranvier

32
Q

What is the safety factor

A

To block the AP the LA needs to act on several nodes of ranvier along the axon

33
Q

Why do several nodes need to be blocked

A

The local currents are strong enough to flow past the blocked region and to regenerate the AP at the nodes of ranvier

34
Q

Why is the LA base present as hydrochloride

A

to increase solubility in aqueous solution

35
Q

What is the volume of an LA cartilage in the UK

A

2.2ml

36
Q

What is the concentration for LA injections

A

2-4%

37
Q

What are other components present in LA

A

reducing agent
preservative and fungicide
+/- vasoconstrictor

38
Q

Why do we use vasoconstrictor

A

prolongs the effect so lower conc of LA required

39
Q

What is the reducing agent normally

A

sodium metabisulphide

40
Q

What are the ester LA

A

cocaine and procaine (not really used)

benzocaine

41
Q

What are the amide LAs

A 
lignocaine (lidocaine)
prilocaine
articaine
mepivacaine (not used much anymore)
Bupivacaine 
Ropivacaine (not used much anymore)
42
Q

What are most anesthetics regarding vasodilation/constriction

A

vasodilators

43
Q

What is the issue with an LA being a vasodilator

A

Increased blood flow will increase the wash out of LA

44
Q

What are the vasoconstrictors usually used in LA

A

adrenaline

felypressin (synthetic vasopressin)

45
Q

What do vasoconstrictors act on

A

receptors on vascular smooth muscle

46
Q

What are the adrenoreceptors

A

alpha receptors
B2 receptors
B1 receptors

47
Q

What do alpha receptors do

A

vasoconstrictor

48
Q

What do beta 2 receptors do

A

vasodilate

49
Q

What do beta 1 receptors do

A

in cardiac muscle increase rate and force

50
Q

Is adrenaline more effective on alpha or beta receptors

A

it is equally effective on both

51
Q

If adrenaline is given locally what is the effect

A

vasoconstrictor (action on alpha receptors)

52
Q

What is the effect of adrenaline if it is given systemically

A

it lowers the TPR (B>a)

adrenaline increases cardiac output however so overall adrenaline has no or little effect on the MABP

53
Q

What will patients often feel with LA with adrenalin

A

palpitations

54
Q

Is noradrenalin more effective on alpha or beta receptors

A

alpha

55
Q

What is the effect of noradrenalin if given locally

A

vasoconstrictor effect on the alpha receptors

56
Q

What is the effect of noradrenalin if given systemically

A

it increases TPR (a>B)
increases cardiac output
raise in MABP

57
Q

How can noradrenalin result in a fall in BP

A

paradoxical effect

58
Q

How are ester type LA broken down

A

by tissue esterase’s making their action quite brief

59
Q

How are amide type LA broken down

A

by liver amides

longer duration of action

60
Q

What are the modes of administration of LA

A 
surface application (topical)
injection 
local infiltration
regional nerve block
nerve root block ('spinal', 'epidural')
intravenous
61
Q

What are the preparations for Lignocaine

A

2% lignocaine HCl

2% lignocaine HCl + 1:80,000 adrenaline

62
Q

What are the preparations for Prilocaine

A

4% prilocaine HCl

3% Prilocaine HCl + felypressin (0.03U/ml)

63
Q

What is the x% solution equivalent to

A

X mass/volume

BDS2 BAMS Local Anesthetic (3 decks)

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