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MDENT110 > Local anaesthetic > Flashcards

Local anaesthetic Flashcards

1
Q

What is analgesia?

A

Medication that relieves pain only

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2
Q

What is anaesthetic?

A

Medication that relieves all sensation

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3
Q

What is Local Anaesthetic?

A

loss of sensation in a circumscribed areas of the body by a depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves.

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4
Q

What is local anaesthetic used for?

A 
Controlling operative pain
Control post-operative pain
Controlling operative haemorrhage
Diagnosis of pain 
Relief of orofacial pain – topical and injection
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5
Q

What are the contents of a local anaesthetic cartridge?

A

Anaesthetic
Vasoconstrictor
Vehicle (Ringers solution)
Reducing agent – sodium metabisulphite (prevents oxidation of adrenaline)
Fungicide (thymol)
Preservative (most preservative free today)

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6
Q

What general formula do all weak bases have?

A

Aromatic group – intermediate chain – amino terminal

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7
Q

What are the properties of each part of a weak base?

A

Aromatic ring - is lipophilic (dissolves in lipid sheath around the nerve)

Intermediate chain - esters (older because gave allergies) or amides

Amino terminal - hydrophilic so is soluble and can transfer through interstitial fluids

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8
Q

What were the disadvantages of the older LA’s having esters for aromatic and intermediate groups?

A

made them unstable in solution, not autoclavable and antigenic/allergies

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9
Q

What are the advantages of the new LA’s having amides for the aromatic and intermediate groups?

A

more stable, autoclavable and rarely antigenic

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10
Q

What are Lidocaine, Prilocaine, Mapivacaine, Articaine and Bupivocaine classified as and what is their duration?

A

All amides

All intermediate duration but Bupivocaine is long acting

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11
Q

What are procaine and benzocaine classified as?

A

Ester and procaine is short acting

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12
Q

What are local anaesthetics classified as chemically?

A

Weak organic bases

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13
Q

What are local anaesthetics in solution?

A

Uncharged free base or positively charged

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14
Q

What can the uncharged molecules of LA do?

A

Able to penetrate the membrane

more uncharged molecules = faster penetration

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15
Q

What do the charged form of LA bind to?

A

Specific receptors

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16
Q

What is the drug dispensed as for administration?

A

As a salt usually hydrochloride - makes them soluble in the water

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17
Q

What is the formula for pH and ionisation?

A

Log (ionised (water soluble)/ unionised (lipid soluble) = pKa - pH - henderson hasselbach equation

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18
Q

What happens at a lower pH?

A

Less of the LA solution will be non ionised i.e. infection

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19
Q

Why does LA have to be non charged?

A

The LA binding site is inside the nerve so molecules need to be able to pass the epineurium, perineurium and endoneurium

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20
Q

What does it re-equilibriate into once the LA is inside the nerve cell?

A

Mixed charged and non-charged forms.

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21
Q

Which form binds to the specific receptors inside the cell? - blocks sodium channels

A

The charged form of the LA

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22
Q

What can the non-specific form of LA cause (more about the shape of the molecule)?

A

The lipophilic portion of the molecule (aromatic ring) may cause swelling of the membrane which blocks the sodium channels (non-specific theory)

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23
Q

What does the LA actually do to the nerve cell?

A

Blocks its voltage gated sodium channels so initially increases threshold for excitation and then blocks conduction of action potentials

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24
Q

Which type of nerve fibres are affected first and last by LA?

A

First - small (pain and temp)

Last - large (motor, proprioceptive)

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25
Q

What does LA do to the blood vessel walls?

A

Blocks sympathetic vasoconstrictors so causes dilation

direct effect on the smooth muscle is variable depending on which LA is used (cocaine constricts, lidocaine dilates)

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26
Q

How do the esters in LA get broken down?

A

Esterases in blood and liver turn into benzoic acids and alcohol which are excreted in the urine

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27
Q

Why was there a change to amide LA and less ester LA?

A

1:2800 population lack certain enzymes to break down the esters but okay with the amids

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28
Q

How do amides in LA get broken down?

A

They are mainly broken down in the liver, oxidised and some conjugated with glucuronic acid and all are excreted via urine so need to take care if severe liver disease

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29
Q

What is the half life of lidocaine?

A

90 minutes

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30
Q

Why is the breakdown of articaine different even though it is in amide?

A

It initially undergoes breakdown by esterases in the plasma, and has half life of 20 minutes so rapidly broken down

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31
Q

What are the ideal characteristics of an LA?

A

Produce complete local analgesia without damaging nerve or other local tissues.
Rapid onset with predictable and appropriate duration.
Isotonic.
Non-toxic systemically.
Readily soluble and stable in solution (adequate shelf-life – usually 2-2½ years).
Sterilizable (esters not autoclavable).
Non-addictive (not cocaine!).

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32
Q

Why is a vasoconstrictor added to the LA?

A

It delays removal of LA from site (constriction of blood vessels that would take the LA away) but also causes more rapid onset of the anaesthesia so don’t have to wait as long, and also reduces operative bleeding due to the constriction, also prolongs and enhances effects of LA

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33
Q

What is the difference in analgesia time with and without adrenaline added?

A

Without - 5-20 mins, soft tissues 1 hour

with - 30-60 mins, soft tissues 3 hours

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34
Q

What are the disadvantages of adrenaline in the LA?

A

Prolonged soft tissue anaesthesia

potential systemic effects with intravascular injection - heart arrythmias (just 2 cartridges can have this effect)

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35
Q

What systemic effects can the adrenaline in the LA have?

A 
Blood pressure - vasodilation of muscles
vasoconstriction of skin
slight reduction in diastolic BP
increase in rate and force of cardiac contractions
increase in glucose
reduced potassium
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36
Q

Which vasoconstrictor can have effects on the uterus?

A

Felypressin (octapressin) - beware pregnancy

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37
Q

What can noradrenaline cause?

A

Increase in BP, can lead to CVA (stroke)

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38
Q

What reducing agent is used in the LA and why?

A

Sodium metabisulphate to prevent oxidisation of vasoconstrictors (brown discolouration

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39
Q

Why is Ringer’s solution used?

A

To make the LA isotonic

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40
Q

Which LA is highly affective as a surface anaesthetic, is an ester and long acting but not routinely used?

A

Amethocaine

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41
Q

Which is the most widely used LA?

A

Lidocaine 2%

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42
Q

What is the maximum dose of lidocaine in an adult?

A

4.4mg/kg (approx 7 cartridges)

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43
Q

Which LA is similar to lidocaine?

A

Mepivacaine

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44
Q

Which LA is approx 2x longer acting than lidocaine?

A

Bupivacaine - very long acting, used for majory surgery or short term relief for trigeminal neuralgia

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45
Q

Which LA is used if avoiding adrenaline?

A

Prilocaine - rapid onset, good penetration

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46
Q

Which LA is not yet in routine used and may cause increased incidence of nerve damage? and avoided for nerve blocks

A

Articaine

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47
Q

Which LA was recently launched in the UK and not in routine use?

A

Ropivacaine

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48
Q

What is the dose in mg/ml in 2% lidocaine?

A

20mg/ml

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49
Q

How much LA may a 65kg man have?

A
  1. 4mg/kg and there is 20mg/ml
    65x4. 4 = 286mg

286/20 = 14.3ml

cartridges have 2.2ml in them

14.3/2.2ml = 6.5 cartridges

easy way = 1/10 cartridge per kg of weight

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50
Q

When is LA contraindicated?

A

Unmanageable patients
injections into acute infections (regional blocks ok)
possible risk of bleeding with LA block in haemophilia or other bleeding disorders
allergy (rare)

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51
Q

What types of LA exist?

A

Surface
infiltrations - between mucosa and periosteum
regional blocks

52
Q

What type of cartridges are there?

A

Breech and side-loading

53
Q

how many ml is the typical cartridge?

A

2.2ml

54
Q

What types of aspirating syringes are there?

A

Self-aspirating (passive) - occurs by light pressure on the plunger and then release (springs back - shows flashback of blood) and positive aspiration (physically have to pull back to see if there is blood - o ring)

55
Q

How long are the short and long needles used?

A 
Short = 19mm
Long = 34mm
56
Q

How would you approach with the needle for a palatine injection?

A

Needle from the opposite side and at 90 degrees to the tissues, not posterior to the second molars
press on palate with the mirror to distract from pain and also increase view
inject very slowly

57
Q

Where is the commonest site for haematomas after an injection?

A

Posterior superior dental region in maxilla

58
Q

What is an intraligamentary injection?

A

Injection into the periodontal ligament

good for haemophiliacs but could be damage to PDL/pulp and decrease blood flow to tooth

59
Q

Why do you also need the charged form of LA?

A

Active and stops the local anaesthetic spreading further

60
Q

What happens to pH of the tissues when there is an infection?

A

PH becomes more acidic - shifts HH equation - get more ionised molecules than non ionised, so the LA becomes less effective in infective tissues

61
Q

What is the inferior alveolar nerve a branch of?

A

Branch of mandibular division of trigeminal nerve

62
Q

What space does the inferior alveolar nerve travel through?

A

Pterygomandibular space (gives off mylohyoid branch) and then into the mandibular foramen - mandibular canal (splits into mental and incisive)

63
Q

What does the IAN innervate?

A

Tooth pulps, periodontal ligament and gingivae of posterior mandibular teeth

64
Q

What does the incisive branch innervate?

A

tooth pulps, periodontal ligaments and gingivae of first premolar to midline

65
Q

What does the mental nerve innervate?

A

labial gingivae of canines and incisors

mucosa and skin of lower lip/chin

66
Q

What does the buccal branch innervate?

A

Buccal gingivae in the molar/premolar region of mandible

mucosa and skin of the cheek

67
Q

What does the lingual nerve supply?

A

Supplies floor of the mouth and the anterior two thirds of the tongue with somatic sensation

lingual gingivae of anterior teeth

68
Q

What does the glossopharyngeal branch innervate?

A

Posterior 1/3 of tongue in both taste and somatic sensation

mucosa over palatoglossal folds

69
Q

Where does the lingual nerve branch from?

A

Inferior alveolar nerve

70
Q

What nerve joins the lingual branch?

A

Chorda tympani from facial nerve

71
Q

What does the chorda tympani supply?

A

Taste in the anterior 2/3 of tongue - secretomotor and vasomotor

72
Q

What does the long buccal nerve pass between?

A

two heads of the lateral pterygoid, along medial side of mandibular ramus

73
Q

What nerve does the mylohyoid nerve split from?

A

IAN

74
Q

What does the mylohyoid innervate?

A

mylohyoid muscle, anterior belly of digastric and skin over chin point

75
Q

What three nerves would be anaesthetised for a first molar extraction?

A

IAN

lingual

buccal

76
Q

Why is infiltration not satisfactory for lower teeth apart from incisors?

A

thick cortical plate with few vascular channels

77
Q

What space would you put the IAN block in?

A

Pterygomandibular space central to mandibular foramen (triangle)

78
Q

What are the landmarks used in the IAN block?

A

pterygomandibular raphe
external oblique ridge - thumb at deepest concavity
angle of mandible - little finger
posterior border of mandible - other fingers
needle approaches from direction of opposite premolars

79
Q

What factors affect the position of the operator?

A

Width of ramus (further back if ramus wider)
Angle of ramus and arch
Foramen lower in children

80
Q

What would you do if you struck the bone too soon?

A

withdraw, straighten angle, advance and then return to original angle

81
Q

What would you do if you had not struck the bone by 3cm depth?

A

withdraw almost completely, readvance from over opposite molars

82
Q

What would you assume if no anaesthesia after 3-4 minutes felt?

A

Failure

83
Q

What is the indirect method of IAN block?

A

Similar entry point, but further lateral
Hit bone, straighten, advance 7mm, return to angle, i.e. stays nearer to bone
More manipulation in tissues

84
Q

How would you give the mental/incisive block?

A

1-1.5ml L/A deposited at mental foramen – diffuses into mandibular canal to block incisive nerve

Usually between apices of premolars – radiograph helpful if available

Mouth partly closed – for retraction

Palpate foramen if possible (often not)
Not always successful

85
Q

When would you anaesthetise the long buccal nerve?

A

molar/premolar extractions and buccal surgery

86
Q

Where would you give the long buccal anaesthesia?

A

Quarter of cartridge over external oblique ridge, disto-buccal to third molar (after IA and lingual block)

Infiltration immediately disto-buccal to surgical site

87
Q

Why may there be a failure to obtain anaesthesia?

A

Agitated patient

faulty technique

anatomical variations - zygomatic buttress over first molar roots, or alternative pathways of pulpal fibres

local infection - pH changes, reduced lipophilic component

88
Q

Why might pain be experienced during the injection?

A

Tissues not taut
Excessive pressure in tight tissues
Subperiosteal injection
Solution cold – use at room temperature
Wrong solution – never refill LA cartridges
Penetration of nerve – ‘electric shock’

89
Q

Why are articaine and prilocaine not usually given as an IAN block?

A

prolonged (usually partial) impairment of sensation

recovery dependent upon degree of injury, usually <3 months.

90
Q

What should you always check first on the cartridge before using it?

A

Expiry date

91
Q

What do you do if your needle breaks?

A

Remove immediately with artery forceps

If not possible, refer to oral surgeon for removal under G/A (or may move in tissues, cause pain, trismus and worry)

Radiographs at 2 angles + ? localising needles
Keep all details and hub of needle in notes

92
Q

Why may the face become paralysed after injection?

A

L/A within parotid
May be partial or complete, resolves after L/A wears off
Protect eye if lids affected

93
Q

Why may sight be affected from the injection?

A

very rare but due to intravascular LA to eye/orbit or diffusion from maxillary injection site

recovery after LA wears off

94
Q

Why may a haematoma occur?

A

Injection into vessel by accident

worst in posteriorsuperior dental region

results in swelling and bruising and possible trismus if in medial pterygoid (IA block)

treatment - pressure, resolves slowly, exercises

95
Q

Why may blanching occur at a distant site?

A

Due to intra-arterial vasoconstrictor or effect of needle on vessel – may last up to half-hour, reassure

96
Q

What condition can prilocaine cause?

A

methaemoglobinaemia (reduces RBC oxygen carrying capacity

97
Q

What systemic effects can adrenaline have?

A

Inappropriately high, toxic levels would lead to anxiety, trembling, headache, palpitations, sweating, dizziness (very similar to vaso-vagal syncope

98
Q

How can you prevent toxic effects from LA?

A

Aspiration
Slow injection
Dose limitation – should have no problems with correct doses

99
Q

What is the treatment for toxicity from LA?

A 
Stop dental treatment
Call for medical assistance
Protect the patient from injury
Monitor vital signs
Provide basic life support
100
Q

What is the maximum dose for prilocaine 3 and 4% and articaine 4%?

A

Prilocaine - 6mg/kg

Articaine - 7mg/kg

101
Q

What would you use in the case of unstable angine, recent MI or refractory arrythmias?

A

adrenaline best avoided

use prilocaine, or lidocaine/mepvicaine

102
Q

Why are cartridges limited to two in patients taking non-potassium sparing diuretics?

A

adrenaline exacerbates decrease in circulating potassium

103
Q

How many cartridges can patients on anti-parkinson drugs have?

A

the drugs entacapone and tolcapone affect the metabolism of adrenaline

104
Q

What medications would cause you to reduce the number of LA cartridges used?

A 
Calcium channel blockers
anti-parkinson drugs
general anaesthesia 
recreational drugs
beta-blocks
tricyclic antidepessants
non-potassium sparing diuretics
105
Q

What is the effect of beta-blockers on LA?

A

increase the toxicity by reducing hepatic blood flow and inhibiting liver enzymes; may also lead to unopposed increase in systemic BP by adrenaline

106
Q

Why should Bupivacaine abnd felypressin be avoided in pregnancy?

A

it causes more maternal cardiac problems and foetal hypoxia in animal models

Felypressin theoretically could lead to uterine contraction and a decrease in placental blood flow

Prilocaine crosses placental barrier more readily than lignocaine

107
Q

What should you avoid in a bleeding diatheses?

A

IAN block

108
Q

What type of injection should you avoid if there is a susceptibility to endocarditis?

A

intraligamentary injections

109
Q

Why should a cartridge with an air bubble never be used?

A

Large air bubbles raise the possibility of injecting air instead of solution, which can be very dangerous (especially if injected intravascularly). Air injected into a blood vessel can cause heart failure.

more likely to be an indication of the cartridge having frozen (this forces the bung out as the water in the cartridge expands

110
Q

Which LA is very good at penetrating mandibular bone?

A

Articaine 4%

This may be especially important in patients with bleeding problems (such as haemophiliacs) where you may wish to avoid a mandibular block

111
Q

What problems have been reported with Articaine 4% as a nerve block?

A

There have been persistent reports of unexplained paraesthesia (burning, tingling, and sometimes sharp shooting pains in tissues previously anesthetized with this anesthetic) in a low percentage of patients. This effect has been noted only when articaine is used in nerve blocks such as the mandibular block

112
Q

Why may it be safer for a child to have general anaesthetic?

A

Unco-operative
multiple extractions
difficult procedure/invasive
too young to co-operate

113
Q

What are possible contra indications for LA in children?

A

lidocaine - known hypersenstivity, acute porphyria (porphyrins build up in the body, own body attacks), heart block

adrenaline - cardiac arrhythmias, hyperthroidism

prilocaine - known allergy

114
Q

What are possible contra indications for LA in children?

A

lidocaine - known hypersensitivity, acute porphyria (porphyrins build up in the body, own body attacks), heart block

adrenaline - cardiac arrhythmias, hyperthyroidism

prilocaine - known allergy
bleeding disorders - blocks contraindicated but not infiltrations
infection at injection site - consider block techniques - catch nerve higher up rather than acidic environment of LA

115
Q

What topicals are used for children?

A 
Xylonor gel (5% lidocaine)
Benzocaine gel (20%)
EMLA cream - skin
116
Q

What concentration is the lidocaine and prilocaine and articaine used?

A

2% (20mg/ml) lidocaine with 1:80000 adrenaline
prilocaine -
4% articaine with 1:100000 or 1:200000 adrenaline (septanest)

117
Q

What is the maximum dose for articaine in children?

A

5mg/kg

118
Q

What are the advantages of safety plus vs traditional syringe?

A

Sterile, single-use, aspirating syringe
no recapping necessary
bevel indicator to assist in orientating the bevel to the bone
transparent barrel to allow visualisation of aspiration

119
Q

What types of behaviour managements are used for children?

A 
verbal and non verbal communication
TLC
tell show do 
positive reinforcement
control 
distraction
relaxation
120
Q

What types of communication techniques are used with children?

A

-

121
Q

What is systemic desensitisation?

A

control
trust
relaxation

122
Q

What is systemic desensitisation?

A

control
trust
relaxation

visit 1 - explain and teach relaxation techniques
visit 2 - needle uncovered …..

123
Q

What are the differences in anatomy in children?

A

bone is less dense
mouth is smaller
mandibular foramen/IAN foramen is slightly lower - at level of the lower occusal plane

124
Q

What are the 4 types of LA injections given to children?

A

buccal
intrapapillary mesial and distal injection
palatal injfection

125
Q

What equation gives appropriateness of infiltration over ID block in the mandible for a patient?

A

Age + tooth number < 10 = okay for infiltration
rule of 10 for lidocaine

rule of 12 for articaine <12

126
Q

Reasons for LA failure?

A

acute infection
incorrect site - muscle,vein, dense buccal bone
insufficient amount
abnormal nerve supply - anastomosis from aberrant or normal nerve fibres
patient immaturity

MDENT110 (26 decks)

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