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BDS2 BAMS > Local anaesthetics > Flashcards

Local anaesthetics Flashcards

1
Q

How do local anaesthetics stop nerve conduction?

A
  • By blocking the voltage-gated Na+ channels
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2
Q

What receptors does LA work on?

A
  • Works on first order afferent receptors - doesn’t touch the central nervous system
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3
Q

What are the 3 connective tissue layers of a peripheral nerve?

A
  • Epineurium (outer)
  • Perineurium
  • Endoneurium (inner)
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4
Q

Are the functions of type A-alpha nerve fibres? (2 points)

A

Sensory (proprioception)

Motor (skeletal muscle)

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5
Q

Are type A-alpha nerves myelinated or unmyelinated?

A

Myelinated

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6
Q

Which nerves do you not want LA to go near?

A

Type C fibres (autonomic (post-ganglion))

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7
Q

What type of nerve fibre is the most affected by LA?

A

A-delta fibres

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8
Q

What type of nerve fibre is the last one affected by LA?

A
  • A-alpha fibres
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9
Q

Where does LA bind to?

A

A site in Na+ channels

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10
Q

What is LA’s action on Na+ channels? (3 points)

A
  • LA blocks the channel and prevents Na+ influx
  • This blocks the AP generation and propagation
  • Block persists so long as sufficient number of Na+ channel are blocked
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11
Q

LA blocks Na+ channels in other excitable tissues e.g. the heart. What 2 effects can this have?

A

La can cause bradycardia and hypotension

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12
Q

What are the 3 organic components of LA?

A
  • Aromatic region (hydrophobic)
  • Ester or amide bond
  • Basic amine side chain (hydrophilic)
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13
Q

What happens when the base of an LA is HCl?

A

Renders the amine base more water soluble

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14
Q

Is LA active or inactive in its ionised form?

A

Active

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15
Q

Can LA ONLY cross the membrane in its ionised or un-ionised form?

A
  • Un-ionised
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16
Q

Why are small diameter axons more susceptible to LA block?

A

Due to the number of channels that are blocked - need to block proportionally (do not need to block all of the channels)

  • SO, small diameter = less channels to block
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17
Q

Where are Na+ channels and K+ channels concentrated in a myelinated axon?

A
  • At the nodes of Ranvier
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18
Q

What is meant by needing the ‘safety factor’ when injecting La to a myelinated axon?

A

If you block one NOR you might not be able to block the nerve completely as the jump is so strong it can bypass the block

  • Need to block a greater area to have an effect (to block the AP, the LA needs to act on several NOR along the axon)
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19
Q

Why is the LA base present as hydrochloride?

A

To increase the solubility in aqueous solutions

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20
Q

For dental injections what are the solutions (in %)?

A

2%-4% solutions

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21
Q

What is the reducing agent in LA?

A

Sodium metabisulphide

22
Q

Are preservative and fungiside’s included in LA preparations?

A

Yes

23
Q

Are vasoconstrictors present in LA preparations?

A

Can be +/- having vasoconstrictors

24
Q

In the UK, what sizes are the cartridges (in mls)?

A

1.8 or 2.2 mls

25
Q

What are the 2 subtypes of LA?

A
  • Esters

- Amides

26
Q

What are 3 examples of LA that are esters?

A
  • Cocaine
  • Procaine
  • Benzocaine
27
Q

What are 4 examples of LA that are amides?

A
  • Lignocaine (lidocaine)
  • Prilocaine
  • Articaine
  • Bupivacaine
28
Q

Are most LA’s vasoconstrictors or vasodilators?

A

Vasodilators - increased blood flow will increase the ‘wash-out’ of LA - this is why we may want to include a vasoconstrictor

29
Q

To increase the duration of action, LA preparations often include a vaso-constrictor. Give 2 examples of these?

A
  • Adrenaline

- Felypressin (synthetic vasopressin)

30
Q

What do vasoconstrictors act on? (3 points)

A
  • Vascular smooth muscle
  • Adrenoreceptors
  • ADH receptors (vasopressin)
31
Q

Which adrenoreceptors do vasoconstrictors act on? (3 points)

A
  • alpha receptors: vasoconstriction
  • B2 receptors: vasodilation
  • B1 receptors (cardiac muscle: Positive chronotropic effect (increase rate), positive inotropic effect (increase force))
32
Q

Is adrenaline more effective on alpha or beta receptors?

A
  • Equally effective on both
33
Q

Does adrenaline increase or decrease CO?

A

Increases

34
Q

What is adrenalines effect on mean arterial BP?

A

Overall, has little or no effect

35
Q

Is noradrenaline more effective on alpha or beta receptors?

A

More effective on alpha receptors

36
Q

Systemically, does adrenaline increase or lower total peripheral resistance?

A

Lowers

37
Q

Given locally, does adrenaline have a vasoconstrictor or vasodilator effect?

A

Vasoconstrictor

38
Q

Given locally, does noradrenaline have a vasoconstrictor or vasodilator effect?

A

Vasoconstrictor

39
Q

Systemically does noradrenaline increase or lower total peripheral resistance?

A

Increases

40
Q

Does noradrenaline increase or decrease CO?

A

Increases

41
Q

Overall, does noradrenaline raise or lower mean arterial BP?

A

Raises

  • This can result in a FALL in BP (paradoxical effect)
  • Response of the body when we have an increase in arterial BP that is not necessary for compensation and the compensation is to drive to other areas to reduce TPR
42
Q

How is LA ‘inactivated’?

A

It is ‘washed out’ from tissues by the blood supply

  • (this is what is countered by the presence of a vasoconstrictor)
43
Q

Ester types of LA are broken down by tissue esterases, what does this mean?

A

Means action of the LA is quite brief

44
Q

Amide types of LA are broken down by liver amidases. What does this cause?

A

Causes longer duration of the action of LA

45
Q

What are the different modes of administration of LA ? (6 points)

A
  • Surface application (topical)
  • Injection
  • Local infiltration
  • Regional nerve block
  • Nerve root block (spinal, epidural)
  • IV
46
Q

What are the 2 doses of Lignocaine we can use for LA?

A
  • 2% lignocain HCL

- 2% lignocaine HCL + 1:80,000 adrenaline

47
Q

What are the 2 doses of Prilocaine we can use for LA?

A
  • 4% prilocaine HCl

- 3% prilocaine HCl + felypressin (0.03U/ml )

48
Q

How can you convert LA into % solutions as %’s are still widely used in clinical practice?

A
  • x% solution = X mass/volume
    e. g. 3% Prilocaine HCl solution

3% = 3g/100ml

= 30mg/1ml

A 2ml cartridge of 3% prilocaine HCl will contain 2x30 = 60mg prilocaine HCl

49
Q

Why is adrenaline content expressed as a ratio instead of a % ?

A

Because only very small amounts of vasoconstrictor are present in LA preparations so can be confusing if it is given as a %

50
Q

What is the max dose of Lignocaine?

A

Approx. 4mg per kg of body weight

51
Q

What is the max dose of adrenaline in an LA preparation?

A

500ug (I think)

52
Q

How much adrenaline does a cartridge of LA contain?

A

27.5ug

BDS2 BAMS (57 decks)

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