Local Anaesthesia in Dentistry Flashcards
Analgesia
Analgesia: Absenceofsensibilitytopain,particularlythereliefofpainwithoutlossofconsciousness
Anaesthesia:
Anaesthesia: Partialorcompletelossofsensation,withorwithoutlossofconsciousness,aresultofdisease,injury,oradministration ofan anaestheticagent,usuallybyinjectionor inhalation
Local anaesthesia
Local anaesthesia:
A temporary loss of sensation in one small area of the body caused by special drugs calledanaesthetics. The patient is conscious, but without feeling in the area of the body treated with the anaesthetic.
Paraesthesia
Abnormal sensation (not specifically unpleasant), spontaneous or evoked
Dysesthesia
Unpleasant abnormal sensation, spontaneous or evoked
Hypoaesthesia + hyperaesthesia
Hypoaesthesia is a reduced perception of stimulus or decreased sensation
hyperaesthesia is an increased perception of stimulus (need not be pain)
Specific receptor theory
Normally, influx of sodium ions through the voltage gated sodium channels causes nerve depolarisation and action potential propagation.
The principalmechanism of actionof a local anaesthetic is through blockage of voltage-gated sodium channels (VGSCs).
Acts by binding on specific receptors on sodium channel.
Leads to a reversible block ofactionpotential propagation i.e. reversible blocking of nerve conduction.
Specific receptor theory- LA movement across membrane
Unioinised local anaesthetic diffuse across the cell membrane as they are lipophilic. Once the LA has diffused across, it becomes ionised due to the lower intracellular pH. It is the ionised agent that binds to the sodium channel receptors and prevents action potential propagation.
Metabolism of AA and AEst
Amino amides metabolised by the liver
Amino esters metabolised by pseudocholinesterase in the blood to form para-aminobenzoic acid
- can cause an allergic reaction
Excretion of AA and AEst
Excreted via the kidneys
The reason why this is important is because if a patient presents with liver or kidney disease, further advice may need to be sought from the patient’s GP before embarking on treatment involving local anaesthetic.
Ideal Properties of Local Anaesthetic
- Specific and reversible action
- Non irritant, no permanent damage to tissues
- No allergic reaction
- No systemic toxicity
- Rapid onset of action
- Sufficient duration of action for intended procedure
- Potent (high therapeutic ratio)
- Stable in solution
- Not expensive
- Active via topically or by injection
Types of Local Anaesthetics
Esters (cocaine, procaine)
Amides (lidocaine, mepivocaine, prilocaine, bupivacaine, articaine)
- We now most commonly use the amides
Lidocaine 2% plain or with epinephrine 1:80,000 (i.e. 1:80k)
Most common, very effective
Lignospan special, Lignocaine, Xylocaine etc
Prilocaine 4% plain or 3% with felypressin
Similar to lidocaine
Citanest, Citanest with octapressin
Articaine 4% with 1:100,000 or 1:200,00 epinephrine
Better diffusion, fast onset, hydrolysed quickly, not for IDBs (never use articaine when administering an inferior dental blocks as there is a theoretical risk of haematoma).
Septonest
Mepivacaine 3% plain 2% with epinephrine
Plain, very short acting
Scandonest
Bupivacaine 0.25%,0.5%,0.75% ampoules
Slow onset but long duration – 2 hours pulpal anaesthesia
Marcaine and Sensorcaine
Types of LA in cartridge form:
a) Prilocaine 3% and octapressin 0.03 IU per ml
b) Mepivicaine 3% plain
c) Articaine 3% and 1:10k epinephrine
d) Lidocaine 2% and 1:80k epinephrine
Vasoconstrictors added to LA
Most local anaesthetics cause vasodilation, some cause vasoconstriction (e.g. bupivacaine)
Vasoconstriction = decreased blood flow
Why are vasoconstrictors added?
- lowers anaesthetic concentration in blood so decreases risk of toxicity
- increases length of action of local anaesthetic
- decreases amount of bleeding at operation site
Adrenaline/Epinephrine
Care in ischaemic heart disease, hypertensives, unstable angina
Felypressin (also prilocaine which contains Felypressin)
- Avoid in pregnancy bc may cause uterine contractions
Local Anaesthesia: Safety
For the operator +/- assistant
=Needlestick injury is main risk
- Don’t rush
- Do not re-sheath or re-use
- Use safety-plus system
- Discard of sharps appropriately
Local Anaesthesia: Safety
For the patient
- Soft tissue trauma
- Nerve trauma
- Intravascular injection (haematoma, systemic effects, ischaemia)
- always use aspirating syringe
Causes of LA administration Failure- Patient and Operator?
Operator dependent
• Choice of technique and solution
• Poor technique
Patient dependent:
- Anatomical (differences in anatomy can change the effect of LA)
- Pathological (infections and inflammation can reduce the action)
- Psychological (anxiety)
Complications: Adverse Reactions
- Psychogenic reactions – ask anxiety levels
- LA toxicity
- Allergy
- Drug interactions
Complications: Psychogenic
Key signs?
Vasovagal attack due to decreased blood to the brain resulting in full fainting Key signs: • Faint, dizzy, light headed • Slow pulse rate • Loss of consciousness • pallor and sweating • Nausea and vomiting
How to manage a vasovagal attack?
Attack due to decreased blood to the brain: • Lie flat- head down and raise legs • loosen tight clothing • Call assistance • glucose drink Then if no improvement: • Re-assess airways, breathing and circulation • Oxygen provision • Assess what else it could be
Complications: Toxicity
- Unlikely, but be wary in the older patient and those with decreased liver or renal function
- Effects on the CNS and cardiac system: Light headedness, sedation, paraesthesia, twitching
- Can lead to convulsions, loss of consciousness, respiratory depression and cardiovascular collapse
Max Safe Doses Calculation:
• Max safe dose of local anaesthetic (mg) x by the patient weight (kg)
This is then divided by the amount of local anaesthetic per cartridge
Complications: Allergy
Extremely rare
Usually due to preservatives in cartridge (e.g. sodium metabisulphite)
Historically more common in ester-type (benzocaine, cocaine procaine)
Latex allergy may be triggered by rubber bung – most LA cartridges now have latex free bung
Patient usually knows if they’ve had a bad reaction to LA (may not know which one)
Complication: Drug Interactions
Most due to vasoconstrictors
Adrenaline –
- Adrenaline may interact with drugs like beta blockers to help treat heart conditions.
- Recent myocardial infarction or coronary artery bypass graft
- Care in uncontrolled hypertension and heart problems such as arrhythmias, angina (especially if unstable)
- Care when using on patients tricyclic antidepressants, SSRIs, diuretics
Felypressin
Do not use in pregnancy (similar to oxytocin)
Complications: Adverse Events
- Broken needle (rare)
- Pain during or after
- Trismus
- Haematoma
- Blanching of areas on face
- Facial paralysis
- Prolonged impaired sensation - ID damage
- Soft tissue trauma
- Visual disturbances
Painless Local Anaesthesia?
- Use suggestion, explain, reassure throughout = build rapport and red anxieties
- Use topical anaesthetic properly
- Room temperature cartridges
- Careful needle placement
- Pressure with mirror handle, stretch tissues
- SLOW injection(controlled delivery - the wand, dentapen)
