Local Anaesthetic Theory - Part 1 (Student Copy) PDF

Systemic effects of LA  Absorption and metabolism of LA agents  Not easily absorbed through intact skin  When applied to mucous membranes or injected into tissues, they are absorbed into blood stream  Distribution (dilution) through the body  Metabolism and elimination  Systemic...

Systemic effects of LA  Absorption and metabolism of LA agents  Not easily absorbed through intact skin  When applied to mucous membranes or injected into tissues, they are absorbed into blood stream  Distribution (dilution) through the body  Metabolism and elimination  Systemic actions of a local anaesthetic agent Reversible blockage of conduction in nerve endings and nerve trunks  Direct relaxation of smooth muscle  Myocardial depression (↓conduction rate, ↓force of contraction, ↓electrical excitability)  Depression of the central nervous system (initial signs are excitatory) Absorption of local anaesthetic agents into the circulation This causes the action of the LA to wear off May lead to toxicity Rate of systemic absorption depends on: 1. Anaesthetic agent and its concentration (dose) 2. Vascularity of the tissues 3. Presence /absence of vasoconstrictor 4. Accidental intravascular injection Metabolism and elimination of LA  Dependent on patient physiology  Most commonly used LA agents are metabolised in the liver to make inactive metabolites (N.B articaine also metabolised in plasma)  Then excreted in the urine  Decreased liver and kidney function - may need less LA agent for safety Signs of systemic toxicity – extremely rare in dentistry Perioral signs – tingling and numbness of lips Visual and hearing disturbances e.g. tinnitus Mood changes (irritability, agitation, anxiety, restlessness) Light-headedness/dizziness Increase in depth and rate of respiration Drowsiness Coma and convulsions Respiratory arrest Cardiac arrest Reducing systematic toxicity Avoid intravascular Inject slowly Use safe doses injection (aspirate) Choose less toxic drugs Use (e.g. 3% prilocaine with vasoconstrictors felypressin) Maximum safe dose Contraindications and cautions of LA Agent Lidocaine Contraindication Hypersensitivity (very rare) Caution  Betablockers e.g. propanolol Prilocaine Contraindication Hypersensitivity (very rare) Caution  Sulphonamides  Betablockers Mepivacaine Contraindication Hypersensitivity (very rare) Children under age of 4 years Caution  Pregnancy  Breastfeeding  Betablockers Articaine Contraindication Hypersensitivity Under 4 years of age Deficiency in plasma cholinesterase Caution  Pregnancy (only use if benefit outweighs risk)  Avoid breast feeding for 48 hours after administration  Betablockers  ID block (risk of post-op paraesthesia) Epinephrine/Adrenaline Contraindication Cocaine use within last 24 hours Cautions  Tricyclic antidepressants  Mono-amine oxidase inhibitors  Betablockers  Calcium-channel blockers  Diuretics  Cardiac conditions  Hypertension  Circulatory problems (including previous strokes) Felypressin  Late stages of pregnancy - theoretical risk of inducing labour  Similar to oxytocin (natural hormone) For cautions listed above  Limit to 2 x 2.2ml cartridges per day  If renal failure/dialysis or liver failure limit to 1 cartridge per day. May need to liaise with patient’s physician as to safe dose LA Equipment Cartridges Plunger (handle) Safety plus needles 1. Extra short- 30G 10mm 2. Short- 30G 25mm 3. Long- 27G 35mm Bevel indicator Traditional LA system YOUR TURN! Summary Today we have…  Explored different LA agents used in dentistry and how they work  Outlined the systemic effects of LA agents  Identified contra-indications and cautions regarding LA delivery  Demonstrated how LA equipment is safely used Next session…  Revise oral anatomy and nerve supplies  Understand how to deliver infiltrations and inferior dental blocks Any questions? Reference List Evers, H. (1990) Introduction to Dental Local Anaesthesia. 2nd Edition. Switzerland: Mediglobe SA. Udayangan, S (2017) Difference Between Depolarization and Repolarization. Available from: https://www.differencebetween.com/difference-between-depolariza tion-and-vs-repolarization/ [Accessed 12th December 2022]. Yapp, K.E., Hopcraft, M.S. and Parahos, P., (2011) Articaine: a review of the literature, British Dental Journal volume, 210, pp. 323–329. Available from: https://www.nature.com/articles/sj.bdj.2011.240 [Accessed on 5th