Local Anaesthetic Flashcards
Definition
Define Local Anaesthetic
A drug which makes nerve tissue incapable of transmitting an impulse on stimulation by blocking the nerve conduction along the nerve axon.
How does local anaesthetic work
Local anaesthetic causes a reversible block to conduction along nerve fibres by blocking the entry of sodium ions into the sodium channels within the nerve axon membrane wall therefore preventing depolarisation and the transmission of pain stimulus
Action of Local Anaesthetic
Diffusion across plasma membrane then:
1) Ionized anaesthetic binds to sodium channel
2) Sodium entry is blocked into theses channels
3) Sodium channel blockade prevents initiation of action potentials
4) Lack of initiation blocks pain sensation due to signal not being transmitted to brain
Action of Local Anaesthetic
1) Ionized anaesthetic binds to sodium channel
2) Sodium entry is blocked into theses channels
3) Sodium channel blockade prevents initiation of action potentials
4) Lack of initiation blocks pain sensation due to signal not being transmitted to brain
Nerve supply
Upper 8,7,6 - PSD - Buccal gingiva & tooth, greater palatine - palatal gingiva
Upper 5, 4 - MSD - Buccal gingiva & tooth, Greater palatine - palatal gingiva
Upper 3,2,1 - ASD - Labial gingiva, tooth, nose & lip, nasopalatine - Palatal gingiva
Lower 3,2,1 - Incisive - Labial gingiva, tooth, chin & lip, Lingual - lingual gingiva, Mental nerve - buccal gingiva
Lower 4,5 - ID block - tooth, Mental nerve - tooth/buccal gingiva, Lingual - lingual gingiva
Lower 6, 7, 8 - ID block - tooth, Long buccal - buccal gingiva, Lingual - lingual gingiva
What are Esters
Topical anaesthetic which is metabolised in blood plasma by cholinesterase, has higher incidence of allergic reaction, is less effective and is shorter acting than amides
What are Amides
Injectable anaesthetic which is metabolised via the liver (approx. 70%), has low incidence of allergic reaction, is potential for toxicity and overdose and can causes vasodilation of blood vessels
Reasons for LA usage
Controls pain, controls haemorrhage (vasoconstrictor), controls post operative pain, and can be used as a diagnostic tool
Define Analgesia & Anaesthesia
Analgesia is lack of pain
Anaesthesia is lack of sensation
Contents of an LA cartridge
- Local anaesthetic agent
- Vasoconstrictor
- Reducing agent ( antioxidant)
- Buffering agent
- Ringers solution
- Sterile water
- Preservative
- Fungicide
Local anaesthetic agent
an active agent which blocks the transfer of sodium ions across the nerve membrane and stops the transmission of pain messages.
Active LA agents are:
- Lidocaine (Xylocaine, Lignospan)
- Articaine (Septanest)
- Mepivacaine (Scandonest)
- Prilocaine (Citanest)
Vasoconstrictor
drug which decreases blood flow by constricting blood vessels, slows absorption into cardiovascular system, reduces systemic toxicity and increases duration of LA
Vasoconstrictors are:
- epinephrine/adrenaline
- felypression
- no vasoconstrictor ( Plain LA)
Reducing agent (Antioxidant)
an antioxidant, sodium metabisulphite, which prevents oxidation of adrenaline resulting in a lower pH of LA solution
Ringer Solution
the LA vehicle containing sodium chloride to give an isotonic solution and sterile water as the dilutant making it soluble
Fungicide
the fungicide, Thymol, is use to reduce fungal growth
Common LA drugs
with vasoconstrictor- Epinephrine:
- lidocaine 2% 1:80 000
- Articaine 4% 1:200 000
- Articaine 4% 1:100 000
with vasoconstrictor - Felypression:
- Prilocaine 3%
without vasoconstrictor -
- Prilocaine 4%
Lidocaine 2% with 1:80 000 Epinephrine
Gold standard, 2.2ml cartridge, 60 - 90mins pulpal anaesthesia, 3-4hrs mucosal anaesthesia
Caution: (as it increases heart rate and blood pressure):
- severe hypertension
- unstable angina
- unstable cardiac rhythm
contraindications:
- significant renal impairment
- significant liver dysfunction
- heart failure
Articaine 4% with 1: 100 000 or 1: 200 000 Epinephrine
effective as lidocaine, is an amide and ester, shorter duration, diffuses through soft and hard tissue better, metabolised in blood plasma, decreases systemic toxicity
Caution:
not to be used in pregnancy
not to be used for ID blocks (tissue necrosis)
Prilocaine 3% with Felypressin
Prilocaine 4%
3% with felypression - similar to lidocaine but not as effective, reduces ability of blood to transport oxygen
Caution: to be avoided in pregnancy as it causes uterine contractions.
contraindications:
- significant renal impairment
- significant liver dysfunction
- heart failure
4% Plain - as above, can be used on pregnant & sickle cell anaemia patients
Reasons for incomplete anaesthesia
- local anaesthetic solubility and tissue pH factors
- needle to jaw discrepancy i.e. Long-ID, Short- Infiltration
- needle deflection, prevented by ensuring bevel toward bone
- volume factors - large patient, thicker nerves
- skeletal and neuroanatomic variations
- LA or vasoconstrictor degraded
- uncooperative/overwrought patient
Ideal properties of LA agent
- Specific action only on peripheral sensory nerves
- Reversible action
- Rapid onset
- suitable duration of action
- non-irritant
- causes no permanent damage
- no systemic toxicity
- chemically stable
- non- allergenic
- non-addictive
- sterilisable
Efficacy of LA
Dependable on:
patient ( fears, phobias, past experience) patient-operator relationship supplementary management (sedation) operator technique patient anatomy (can vary)
LA Absorption
Topical - onto mucous membrane
Injection - into oral tissues
Factors of anaesthetic dosage
1) patients physical condition (kidney/liver function for metabolic and excretory competence)
2) body weight
Medically compromise indications
Epinephrine/adrenaline: - use for everyone (+ cardiac patients) large doses should be avoided in - significant cardiovascular disease & if taking beta-blockers - taking antidepressants - taking anti-hypertensives and non-potassium diuretics Avoid in: uncontrolled hyperthyroidism cocaine abusers
Felypression: - hyperthyroidism - taking antidepressants Avoid in: - patients where you want control bleeding - pregnancy
Topical Anaesthetics
maybe indicated to minimize sensation from needle insertion or very brief relief from painful mucosal lesions
Cartridge checks
Date Cloudiness Partly used Large air bubbles Pierced seal Silicone rubber stopper - leakage, bulging- frozen/expanded Cartridge chipped Contents stated clearly
Allergies reaction more likely to Ester
The ester Procaine changes to para-aminobenzoic acid (PABA)and it’s the products from this that is associated with allergic reactions
