Systemic Effects of Local Anesthetics

• Systemic effects of local anesthetics (LA) are explored

Absorption and Metabolism

• LA agents are not readily absorbed through intact skin
• Absorption occurs when applied to mucous membranes or injected into tissues, entering the bloodstream
• Distribution involves dilution throughout the body
• The body metabolizes and eliminates LA agents

Systemic Actions of LA

• LA causes a reversible blockage of conduction in nerve endings and nerve trunks
• They induce direct relaxation of smooth muscle
• Myocardial depression occurs via decreased conduction rate, decreased force of contraction, and decreased electrical excitability
• Depression of the central nervous system, initial signs are excitatory

LA Absorption and Circulation

• Absorption of local anaesthetics will cause the action of the LA to wear off
• LA systemic absorption can lead to toxicity
• The rate of systemic absorption depends on the anaesthetic agent and its concentration, the vascularity of the tissues, the presence or absence of a vasoconstrictor, and whether there was an accidental intravascular injection

Metabolism and Elimination

• Metabolism and elimination depend on patient physiology
• Most frequently used LA agents are metabolized in the liver into inactive metabolites; articaine is also metabolized in plasma
• The metabolites are then excreted in the urine
• Reduced liver and/or kidney function may warrant a lower LA dosage for patient safety

Signs of Systemic Toxicity

• Systemic toxicity is rare in dentistry, but signs include:
• Perioral tingling and numbness of lips
• Visual and hearing disturbances (e.g., tinnitus)
• Mood changes such as irritability, agitation, anxiety, and restlessness
• Light-headedness/dizziness
• Increased depth and rate of respiration
• Drowsiness
• Coma and convulsions
• Respiratory arrest
• Cardiac arrest

Reducing Systemic Toxicity

• Aspirate to avoid intravascular injection
• Inject slowly
• Use safe doses of the agents
• Choose less toxic drugs, such as 3% prilocaine with felypressin
• Use vasoconstrictors

Maximum Safe Dose Parameters

• Lidocaine 2% has a max dose of 4.4 mg/kg. For adults (70kg) the Max number of 2.2ml cartridges is 6.8 and for children (20kg) it is 2.0
• Prilocaine 3% has a max dose of 5.0 mg/kg. For adults (70kg) the Max number of 2.2ml cartridges is 6.0 and for children (20kg) it is 1.8
• Mepivacaine 3% has a max dose of 4.4 mg/kg. For adults (70kg) the Max number of 2.2ml cartridges is 4.5 and for children (20kg) it is 1.3
• Articaine 4% has a max dose of 7.0 mg/kg. For adults (70kg) the Max number of 2.2ml cartridges is 5.0 and for children (20kg) it is 1.5

Contraindications and Cautions of LA Agents

• Lidocaine: Contraindication includes hypersensitivity which is very rare, caution when using Betablockers e.g. propanolol
• Prilocaine: Contraindication includes hypersensitivity which is very rare, caution when using Sulphonamides and Betablockers
• Mepivacaine: Contraindication includes Hypersensitivity, very rare and in children under the age of 4, Caution if pregnant or breastfeeding and with Betablockers
• Articaine: Contraindications are hypersensitivity, patients under 4 years of age, and deficiency in plasma cholinesterase. Caution is advised during pregnancy (use only if the benefit outweighs the risk), when breastfeeding (avoid for 48 hours after administration), when using Beta-blockers, and with ID blocks due to the risk of post-op paraesthesia
• Epinephrine/Adrenaline: Contraindication is cocaine use within the last 24 hours, cautions are required with tricyclic antidepressants, mono-amine oxidase inhibitors, beta-blockers, calcium-channel blockers, diuretics, cardiac conditions, hypertension, and circulatory problems (including previous strokes)
• Felypressin: Contraindicated in late stages of pregnancy due to the risk of inducing labor and is similar to oxytocin

Cautions to Consider

• Limit to 2 x 2.2ml cartridges per day
• In renal failure/dialysis or liver failure limit to 1 cartridge per day and may need to liaise with patient’s physician to decide a safe dose

Equipment

• Cartridges with local anaesthetic
• Plunger (handle)
• Safety plus needles come in:
  • Extra short- 30G 10mm
  • Short-30G 25mm
  • Long- 27G 35mm
• Bevel indicator
• Traditional LA system

Explore the systemic effects of local anesthetics (LA), including absorption, metabolism, and distribution throughout the body. Learn about how LA causes reversible blockage of conduction in nerve endings and nerve trunks and induces direct relaxation of smooth muscle. Understand how absorption of local anaesthetics will cause the action of the LA to wear off.