Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

BDS2 BAMS > Local Anaesthetics > Flashcards

Local Anaesthetics Flashcards

1
Q

basics of how LA work

A

stop nerve conduction by blocking the voltage-gated Na+ channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what part of the nervous system do LAs work on

A

peripheral nervous system (doen’t touch CNS)

work on first order afferent receptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what do the connective tissue layers in peripheral nerves act as

A

diffusion barriers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what factor determines which nerve will be affect by LA first , when they are in similar proximity to the LA

A

number of membranes that are barriers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is the general rule for anaesthetising and weaning out

A

in general anaesthetised first, tends to be weaned out first

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what type of molecule can cross connective tissue nerve membranes

A

lipophillic

aromatic ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

how can the lipophilic characteristics of LA influence how they perform

A

adheres, penetrates the membrane easier, like to be around fat - take longer to leave, will work in certain areas longer

fat allows to stay in nerve for longer

Cannot be too great affinity as can stay in fat and not reach nerve

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the order of blockage by LA in different nerve fibres

A

A delta
C
A beta
A alpha

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how can we assess whether a nerve fibres have been blocked or not

A

different nerve fibres have different functions so can assess if worked effectively

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

myelination status of A alpha

A

myelinated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

myelination status of A beta

A

myelinated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

myelination status of A gamma

A

myelinated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

myelination status of A delta

A

myelinated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

myelination status of C fibres

A

unmyelinated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

function of A alpha fibres

A

sensory (proprioception)

motor (skeletal muscle)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

function of A beta fibres

A

sensory (mechanoreceptors)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

function of A gamma fibres

A

motor (muscle spindles)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

function of A delta fibres

A

sensory (mechano-, themo-, noci- and chemoreceptor)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

function of C fibres

A

sensory (noci-, thermo- and chemoreceptors)

autonomic (post ganglionic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

what function of C nerve fibres do you not want to anaesthetise

A

autonomic (post ganglionic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

mechanism of LA action

A

LA binds to a site in the Na+ channel

LA blocks the channel and prevents Na+ influx
- This blocks action potential generation and propagation

Block persists so long as a sufficient number of Na+ channels are blocked

  • Enough blocked but not necessarily all
  • Enough to avoid AP reaching maximum level

Local anaesthetics block Na+ channels in other excitable tissue, e.g. heart muscle
- LA can cause bradycardia and hypotension
Distressing for pt
- could faint

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what group of nerve fibres are you aiming to anaethetise

A

A beta (3rd in order)

sensory (mechanoreceptors)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what class of molecule is LA

A

organic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what are the 3 basic components of LA

A

aromatic ring (hydrophobic)

ester or amide bond

basic amide side chain (hydrophilic)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
what is evidence that the amine base in more water soluble than the chloride?
the LA is presented as a hydrochloride (B.HCl)
26
what is the active form of LA
B.H+ partially dissociated
27
what is the diffusible form of LA
B (inactive) cannot cross membrane in active B.H+ form
28
what form of LA renders and block sodium channels in nerve
B.H+
29
how many B.H+ active molecules are needed to deactivate each sodium channel
one per channel
30
why are small diameter axons more susceptible to LA block
more channels are blocked proportionally - less number of total channels
31
what is the distribution of sodium channels like in myelinated nerves
greater concentration at nodes of Ranvier | - more channels to block
32
is anaethetism by LA a linear process
no
33
what is the 'safety factor' of myelinated nerves
The local currents are strong enough to flow past the blocked region, and to regenerate the AP at the next node of Ranvier - Block one node of ranvier - Not able to block nerve or that axon - Can bypass that LA block Need to block a greater area Need to dissolve to greater extent to anaesthetised axons that are myelinated To block the AP, the LA needs to act on several nodes of Ranvier along the axon
34
what must the LA do in order to be effective on a myelinated nerve
Need to dissolve to greater extent to anaesthetised axons that are myelinated To block the AP, the LA needs to act on several nodes of Ranvier along the axon
35
what is the role of the LA base present as hydrochloride in LA preparations
needed to increase solubility in aqueous solutions
36
what is the % range for dental preparations of LA
2-4%
37
what is the cartridge volume for dentistry LA use in UK
1.8 or 2.2ml
38
what is a common reducing agent in LA
sodium metabisulphide
39
4 basic constituents of LA preparations for dental use
LA base as hydrochloride reducing agent (sodium metabisulphide) preservative(s) and fungicide and/or vasoconstrictor
40
what is the role of vasoconstrictor in LA preparations
prolong effect of aesthetic - More time in certain area - less LA volume needed thus - Reduce clearance - Reduce need for larger volume
41
2 disadvantages of adding a vasoconstrictor
increase HR Reduces the blood flow - needed in certain treatments - Periodontal treatment - recreate healthy tissue (flap - stick gingiva from other area over) Need to consider if affected by vasoconstrictor - Tissue may not survive
42
what is the more likely cause of pt being allergic to LA
they are allergic to brand of LA Preservative and reducing agent (preservative vary brand to brand, reducing less so) E.g. Latex glaze on plug - common allergy
43
what should you do if you recognise that a pt is having an allergic reaction to a LA
note the product and manufacturer both need to be ID to work out true cause of reaction - rare to react to lidocaine
44
2 families of LA
esters amides
45
3 ester LAs
benzocaine (cocaine) (procaine)
46
use of benzocaine
ester LA Topical anaesthetic reduce pain but sting Taste unpleasant Varies between clinicians whether to use - Technique can reduce need for topical
47
use of cocaine as LA
ester LA good topical LA hard to use
48
use of procaine as LA
ester LA has toxic effects
49
6 amide LAs
ligocaine (lidocaine) prilocaine articaine bupivacaine (mepivacaine) (ropivacaine)
50
what is a commonly used LA
ligocaine (lidocaine) amide LA
51
common action of LA on circulation
most LAs are vasodilators
52
what is the effect of increased blood flow on the action of LA
increase 'wash-out'
53
what can be added to LA to increase their duration of action
a vasoconstrictor e.g. adrenaline, felypressin (synthetic vasopressin, for prilocaine)
54
what do vasoconstrictors act on
receptors in vascular smooth muscle ``` adrenoreceptors - alpha - beta 2 - beta 1 ADH receptors ```
55
in general what is the effect of vasoconstrictors
heart rate and force increased
56
alpha adrenoreceptor vasoconstrictor effect
vasoconstriction
57
beta 2 adrenoreceptor vasoconstrictor effect
vasodilation
58
beta 1 adrenoreceptor vasoconstrictor effect
on cardiac muscle - positive chronotropic effect (increase rate) - positive inotropic effect (increase force)
59
effect of adrenaline as a vasoconstrictor
Adrenaline is equally effective on alpha and beta receptors equal effect - not preferential Given locally, it has a vasoconstrictor effect (action on alpha receptors) Systemically, it lowers TPR (beta > alpha - works on beta-2 more than alpha) increases Cardiac Output Overall, adrenaline has little or no effect on mean arterial BP - More force and flow and less peripheral resistance increase in HR and force gives feelings of palpitations
60
effect of noradrenaline as a vasoconstrictor
More effective on alpha than beta receptors Given locally, it has a vasoconstrictor effect (alpha receptors) Systemically, it increases TPR (alpha > beta) - Effect lesser on beta - So increase in arterial BP increases Cardiac Output Overall, NA raises mean arterial BP - can cause a FALL of BP –Response of body when have increase in BP us not necessary or physiological - Drive blood flow to other areas - Reduce peripheral resistance Can overshoot if go too high can cause fall in BP (overshoot)
61
what is a possible side effect of noradrenaline as a vasoconstrictor
Overall, NA raises mean arterial BP - can cause a FALL of BP –Response of body when have increase in BP us not necessary or physiological - Drive blood flow to other areas - Reduce peripheral resistance Can overshoot if go too high can cause fall in BP (overshoot)
62
what process occurs to inactivate LA
Washout’ from tissues by blood supply Countered by presence of vasoconstrictor agent
63
how are ester LAs broken down
by tissue esterases
64
in general what is the duration of action of ester LAs
action is quite brief | topical anaesthetic
65
how are amide LAs broken down
by liver amidases
66
in general what is the duration of action of amide LAs
longer duration of action
67
6 modes of LA administration
Surface application (‘topical’) Injection Local infiltration Regional nerve block Nerve root block (‘spinal’, ‘epidural’) Intravenous
68
why is it important to ask about pt liver medical history
amide LAs are broken down by liver amidases re-evaluate how to use LA as process of removal is effected
69
what type of nerve blocks do dentists use
local nerve blocks - ID nerve block rare to use root nerve blocks (maxillofacial)
70
2 common drugs used for LA preparations in dentistry
ligocaine prilocaine
71
common LA dental preparation of ligocaine
2% ligocaine HCl 2% ligocaine HCl and 1:80,000 adrenaline
72
common LA dental preparation of prilocaine
4% prilocaine HCl | 3% prilocaine HCl + felypressin (0.03Uml)
73
why would there need to be a higher concentration of prilocaine in LA preparation without a vasoconstrictor
reduced clearance with vasoconstrictor hence lesser volume required
74
% solution =
X mass/volume e.g. 3% Prilocaine HCl solution - 3% = 3g / 100ml - = 30mg / 1ml A 2ml cartridge of 3% prilocaine HCl will contain 2 x 30 = 60mg prilocaine HCl In clinic 2.2 calculate
75
1ml=
1g
76
how are vasoconstrictors volumes given for LAs
very small volumes are present content is expressed as a ratio: e. g. 1:80,000 - 1 part of adrenaline in 80,000 parts of liquid
77
maximum dose of ligocaine
4mg per kg body weight Reach max dose of LA first before adrenaline - But symptoms tend to be more associated with adrenaline Although bradycardia is serious
78
maximum dose adrenaline
500 micrograms (ug) Cartridge contains 27.5 ug adrenaline - If this entire amount was injected into 5 litres of blood then 5ug/l Plasma levels of adrenaline following dental injections increase with amount injected - Increase in force and speed of heat The plasma levels following ‘normal’ injections are within the physiological range (up to 0.5 ug /litre) * - Not inject BV – entering blood stream Maximum physiological levels (intense exercise) can reach 0.5 ug /litre Reach max dose of LA first before adrenaline - But symptoms tend to be more associated with adrenaline Although bradycardia is serious

BDS2 BAMS (54 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions