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Local Anaesthesia
Local anaesthesia is defined as a transient and completely reversible loss of sensation in a circumscribed area of the body caused by a depression of excitation in nerve endings or an inhibition of the conduction process in peripheral nerves.
Theories for mode of action of local anaesthesia:
1. Acetylcholine theory
2. Calcium displacement theory
3. Surface charge theory
4. Membrane expansion theory
5. Specific receptors theory
Mechanism of action
Properties of LA:
Absolute contraindications of LA
- Should be non irritant to the tissue to which it is applied
- Should not cause any permanent alteration of nerve structure
- Systemic toxicity should be low
- Must be effective in parenteral as well as topical application
- Time of onset should be short as possible
- Duration of action should be adequate to complete the procedure as well as comfortable recovery
- It should be stable in solution and should readily undergo biotransformation in the body
- Should be sterile or should be capable of undergoing sterilisation by heat without deterioration.
| Composition | Function |
| 2% lidocaine hydrochloride | Local anaesthetic agent |
| 1:80,000 to 1:100000 epinephrine | Vasoconstrictor prolongs the action of the local anaethetic |
| Sodium metabisulphite | Oxidising agent |
| Methyl paraben | Preservative |
| Thymol | Antifungal |
| Distilled water | Solvent |
- Myocardial infraction within 6 months
- Recent hepatitis A or hepatitis B
- Jaundice
- Local infections or sepsis
- Hypersensitivity to lidocaine
- Chronic renal failure
- Hyperthyroidism
- Atypical plasma cholinesterase
- Pregnancy- during the first trimester
- Hypertension
- Malignant hyperthermia
- Congenital methhaemoglobinaemia
