Local anaesthetic Flashcards
What is analgesia?
Medication that relieves pain only
What is anaesthetic?
Medication that relieves all sensation
What is Local Anaesthetic?
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.
What is local anaesthetic used for?
Controlling operative pain Control post-operative pain Controlling operative haemorrhage Diagnosis of pain Relief of orofacial pain – topical and injection
What are the contents of a local anaesthetic cartridge?
Anaesthetic
Vasoconstrictor
Vehicle (Ringers solution)
Reducing agent – sodium metabisulphite (prevents oxidation of adrenaline)
Fungicide (thymol)
Preservative (most preservative free today)
What general formula do all weak bases have?
Aromatic group – intermediate chain – amino terminal
What are the properties of each part of a weak base?
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
What were the disadvantages of the older LA’s having esters for aromatic and intermediate groups?
made them unstable in solution, not autoclavable and antigenic/allergies
What are the advantages of the new LA’s having amides for the aromatic and intermediate groups?
more stable, autoclavable and rarely antigenic
What are Lidocaine, Prilocaine, Mapivacaine, Articaine and Bupivocaine classified as and what is their duration?
All amides
All intermediate duration but Bupivocaine is long acting
What are procaine and benzocaine classified as?
Ester and procaine is short acting
What are local anaesthetics classified as chemically?
Weak organic bases
What are local anaesthetics in solution?
Uncharged free base or positively charged
What can the uncharged molecules of LA do?
Able to penetrate the membrane
more uncharged molecules = faster penetration
What do the charged form of LA bind to?
Specific receptors
What is the drug dispensed as for administration?
As a salt usually hydrochloride - makes them soluble in the water
What is the formula for pH and ionisation?
Log (ionised (water soluble)/ unionised (lipid soluble) = pKa - pH - henderson hasselbach equation
What happens at a lower pH?
Less of the LA solution will be non ionised i.e. infection
Why does LA have to be non charged?
The LA binding site is inside the nerve so molecules need to be able to pass the epineurium, perineurium and endoneurium
What does it re-equilibriate into once the LA is inside the nerve cell?
Mixed charged and non-charged forms.
Which form binds to the specific receptors inside the cell? - blocks sodium channels
The charged form of the LA
What can the non-specific form of LA cause (more about the shape of the molecule)?
The lipophilic portion of the molecule (aromatic ring) may cause swelling of the membrane which blocks the sodium channels (non-specific theory)
What does the LA actually do to the nerve cell?
Blocks its voltage gated sodium channels so initially increases threshold for excitation and then blocks conduction of action potentials
Which type of nerve fibres are affected first and last by LA?
First - small (pain and temp)
Last - large (motor, proprioceptive)
What does LA do to the blood vessel walls?
Blocks sympathetic vasoconstrictors so causes dilation
direct effect on the smooth muscle is variable depending on which LA is used (cocaine constricts, lidocaine dilates)
How do the esters in LA get broken down?
Esterases in blood and liver turn into benzoic acids and alcohol which are excreted in the urine
Why was there a change to amide LA and less ester LA?
1:2800 population lack certain enzymes to break down the esters but okay with the amids
How do amides in LA get broken down?
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
What is the half life of lidocaine?
90 minutes
Why is the breakdown of articaine different even though it is in amide?
It initially undergoes breakdown by esterases in the plasma, and has half life of 20 minutes so rapidly broken down
What are the ideal characteristics of an LA?
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!).
Why is a vasoconstrictor added to the LA?
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
What is the difference in analgesia time with and without adrenaline added?
Without - 5-20 mins, soft tissues 1 hour
with - 30-60 mins, soft tissues 3 hours
What are the disadvantages of adrenaline in the LA?
Prolonged soft tissue anaesthesia
potential systemic effects with intravascular injection - heart arrythmias (just 2 cartridges can have this effect)
What systemic effects can the adrenaline in the LA have?
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
Which vasoconstrictor can have effects on the uterus?
Felypressin (octapressin) - beware pregnancy
What can noradrenaline cause?
Increase in BP, can lead to CVA (stroke)
What reducing agent is used in the LA and why?
Sodium metabisulphate to prevent oxidisation of vasoconstrictors (brown discolouration
Why is Ringer’s solution used?
To make the LA isotonic
Which LA is highly affective as a surface anaesthetic, is an ester and long acting but not routinely used?
Amethocaine
Which is the most widely used LA?
Lidocaine 2%
What is the maximum dose of lidocaine in an adult?
4.4mg/kg (approx 7 cartridges)
Which LA is similar to lidocaine?
Mepivacaine
Which LA is approx 2x longer acting than lidocaine?
Bupivacaine - very long acting, used for majory surgery or short term relief for trigeminal neuralgia
Which LA is used if avoiding adrenaline?
Prilocaine - rapid onset, good penetration
Which LA is not yet in routine used and may cause increased incidence of nerve damage? and avoided for nerve blocks
Articaine
Which LA was recently launched in the UK and not in routine use?
Ropivacaine
What is the dose in mg/ml in 2% lidocaine?
20mg/ml
How much LA may a 65kg man have?
- 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
When is LA contraindicated?
Unmanageable patients
injections into acute infections (regional blocks ok)
possible risk of bleeding with LA block in haemophilia or other bleeding disorders
allergy (rare)
What types of LA exist?
Surface
infiltrations - between mucosa and periosteum
regional blocks
What type of cartridges are there?
Breech and side-loading
how many ml is the typical cartridge?
2.2ml
What types of aspirating syringes are there?
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)
How long are the short and long needles used?
Short = 19mm Long = 34mm
How would you approach with the needle for a palatine injection?
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
Where is the commonest site for haematomas after an injection?
Posterior superior dental region in maxilla
What is an intraligamentary injection?
Injection into the periodontal ligament
good for haemophiliacs but could be damage to PDL/pulp and decrease blood flow to tooth
Why do you also need the charged form of LA?
Active and stops the local anaesthetic spreading further
What happens to pH of the tissues when there is an infection?
PH becomes more acidic - shifts HH equation - get more ionised molecules than non ionised, so the LA becomes less effective in infective tissues
What is the inferior alveolar nerve a branch of?
Branch of mandibular division of trigeminal nerve
What space does the inferior alveolar nerve travel through?
Pterygomandibular space (gives off mylohyoid branch) and then into the mandibular foramen - mandibular canal (splits into mental and incisive)
What does the IAN innervate?
Tooth pulps, periodontal ligament and gingivae of posterior mandibular teeth
What does the incisive branch innervate?
tooth pulps, periodontal ligaments and gingivae of first premolar to midline
What does the mental nerve innervate?
labial gingivae of canines and incisors
mucosa and skin of lower lip/chin
What does the buccal branch innervate?
Buccal gingivae in the molar/premolar region of mandible
mucosa and skin of the cheek
What does the lingual nerve supply?
Supplies floor of the mouth and the anterior two thirds of the tongue with somatic sensation
lingual gingivae of anterior teeth
What does the glossopharyngeal branch innervate?
Posterior 1/3 of tongue in both taste and somatic sensation
mucosa over palatoglossal folds
Where does the lingual nerve branch from?
Inferior alveolar nerve
What nerve joins the lingual branch?
Chorda tympani from facial nerve
What does the chorda tympani supply?
Taste in the anterior 2/3 of tongue - secretomotor and vasomotor
What does the long buccal nerve pass between?
two heads of the lateral pterygoid, along medial side of mandibular ramus
What nerve does the mylohyoid nerve split from?
IAN
What does the mylohyoid innervate?
mylohyoid muscle, anterior belly of digastric and skin over chin point
What three nerves would be anaesthetised for a first molar extraction?
IAN
lingual
buccal
Why is infiltration not satisfactory for lower teeth apart from incisors?
thick cortical plate with few vascular channels
What space would you put the IAN block in?
Pterygomandibular space central to mandibular foramen (triangle)
What are the landmarks used in the IAN block?
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
What factors affect the position of the operator?
Width of ramus (further back if ramus wider)
Angle of ramus and arch
Foramen lower in children
What would you do if you struck the bone too soon?
withdraw, straighten angle, advance and then return to original angle
What would you do if you had not struck the bone by 3cm depth?
withdraw almost completely, readvance from over opposite molars
What would you assume if no anaesthesia after 3-4 minutes felt?
Failure
What is the indirect method of IAN block?
Similar entry point, but further lateral
Hit bone, straighten, advance 7mm, return to angle, i.e. stays nearer to bone
More manipulation in tissues
How would you give the mental/incisive block?
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
When would you anaesthetise the long buccal nerve?
molar/premolar extractions and buccal surgery
Where would you give the long buccal anaesthesia?
Quarter of cartridge over external oblique ridge, disto-buccal to third molar (after IA and lingual block)
Infiltration immediately disto-buccal to surgical site
Why may there be a failure to obtain anaesthesia?
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
Why might pain be experienced during the injection?
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’
Why are articaine and prilocaine not usually given as an IAN block?
prolonged (usually partial) impairment of sensation
recovery dependent upon degree of injury, usually <3 months.
What should you always check first on the cartridge before using it?
Expiry date
What do you do if your needle breaks?
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
Why may the face become paralysed after injection?
L/A within parotid
May be partial or complete, resolves after L/A wears off
Protect eye if lids affected
Why may sight be affected from the injection?
very rare but due to intravascular LA to eye/orbit or diffusion from maxillary injection site
recovery after LA wears off
Why may a haematoma occur?
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
Why may blanching occur at a distant site?
Due to intra-arterial vasoconstrictor or effect of needle on vessel – may last up to half-hour, reassure
What condition can prilocaine cause?
methaemoglobinaemia (reduces RBC oxygen carrying capacity
What systemic effects can adrenaline have?
Inappropriately high, toxic levels would lead to anxiety, trembling, headache, palpitations, sweating, dizziness (very similar to vaso-vagal syncope
How can you prevent toxic effects from LA?
Aspiration
Slow injection
Dose limitation – should have no problems with correct doses
What is the treatment for toxicity from LA?
Stop dental treatment Call for medical assistance Protect the patient from injury Monitor vital signs Provide basic life support
What is the maximum dose for prilocaine 3 and 4% and articaine 4%?
Prilocaine - 6mg/kg
Articaine - 7mg/kg
What would you use in the case of unstable angine, recent MI or refractory arrythmias?
adrenaline best avoided
use prilocaine, or lidocaine/mepvicaine
Why are cartridges limited to two in patients taking non-potassium sparing diuretics?
adrenaline exacerbates decrease in circulating potassium
How many cartridges can patients on anti-parkinson drugs have?
the drugs entacapone and tolcapone affect the metabolism of adrenaline
What medications would cause you to reduce the number of LA cartridges used?
Calcium channel blockers anti-parkinson drugs general anaesthesia recreational drugs beta-blocks tricyclic antidepessants non-potassium sparing diuretics
What is the effect of beta-blockers on LA?
increase the toxicity by reducing hepatic blood flow and inhibiting liver enzymes; may also lead to unopposed increase in systemic BP by adrenaline
Why should Bupivacaine abnd felypressin be avoided in pregnancy?
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
What should you avoid in a bleeding diatheses?
IAN block
What type of injection should you avoid if there is a susceptibility to endocarditis?
intraligamentary injections
Why should a cartridge with an air bubble never be used?
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
Which LA is very good at penetrating mandibular bone?
Articaine 4%
This may be especially important in patients with bleeding problems (such as haemophiliacs) where you may wish to avoid a mandibular block
What problems have been reported with Articaine 4% as a nerve block?
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
Why may it be safer for a child to have general anaesthetic?
Unco-operative
multiple extractions
difficult procedure/invasive
too young to co-operate
What are possible contra indications for LA in children?
lidocaine - known hypersenstivity, acute porphyria (porphyrins build up in the body, own body attacks), heart block
adrenaline - cardiac arrhythmias, hyperthroidism
prilocaine - known allergy
What are possible contra indications for LA in children?
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
What topicals are used for children?
Xylonor gel (5% lidocaine) Benzocaine gel (20%) EMLA cream - skin
What concentration is the lidocaine and prilocaine and articaine used?
2% (20mg/ml) lidocaine with 1:80000 adrenaline
prilocaine -
4% articaine with 1:100000 or 1:200000 adrenaline (septanest)
What is the maximum dose for articaine in children?
5mg/kg
What are the advantages of safety plus vs traditional syringe?
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
What types of behaviour managements are used for children?
verbal and non verbal communication TLC tell show do positive reinforcement control distraction relaxation
What types of communication techniques are used with children?
-
What is systemic desensitisation?
control
trust
relaxation
What is systemic desensitisation?
control
trust
relaxation
visit 1 - explain and teach relaxation techniques
visit 2 - needle uncovered …..
What are the differences in anatomy in children?
bone is less dense
mouth is smaller
mandibular foramen/IAN foramen is slightly lower - at level of the lower occusal plane
What are the 4 types of LA injections given to children?
buccal
intrapapillary mesial and distal injection
palatal injfection
What equation gives appropriateness of infiltration over ID block in the mandible for a patient?
Age + tooth number < 10 = okay for infiltration
rule of 10 for lidocaine
rule of 12 for articaine <12
Reasons for LA failure?
acute infection
incorrect site - muscle,vein, dense buccal bone
insufficient amount
abnormal nerve supply - anastomosis from aberrant or normal nerve fibres
patient immaturity
