Local anesthesia

# LOCAL ANESTHESIA

* DEFINITION :-

       It is defined as reversible loss of sensation in circumscribed area of body caused by

       depression of excitation in nerve endings and inhibition of conduction process in

       peripheral nerves.

* COMPOSITION:-

     1.  2% lignocaine with hydrochloric acid

             - act as local anesthetic agent

     2. 1:80000 to 1:100000 epinephrine

            - act as vase constrictor

     3. Sodium meta bisulphite

           - as an oxidizing agent

     4. Methyl paraben

           - as preservative

     5. Thymol

           - as an anti fungal agent

     6. Distilled water

           - as a solvent

* CLASSIFICATION:-

    A. BASED ON CHEMICAL STRUCTURE

     1.ESTERS

      a. Bezoic acid esters

       - benzocaine

       - butacaine

       - cocaine

       - tetracaine

      b. Paraamino benzoic acid esters

      - chloroprocaine

      - propoxycain

      - procaine

    2. AMIDES

      - lignocaine

      - bupivacaine

      - mepivacaine

      - prilocaine

    3.QUINOLONE

       - centbucridine

   B. ACCORDING TO DURATION OF ACTION:-

    1. ULTRASHORT (10-15)

        - Lignocaine

        - mepivacaine

        - prilocaine

    2.SHORT (45-90)

        - Procaine

        - Chloroprocaine

    3.INTERMEDIATE (60-90)

        - Lignocaine

        - prilocaine

        - Mepivacaine

    4. LONG (>90)

        - Bupivacaine

        - tetracaine

C. BASED ON MODE OF ADMINISTRATION :-

    1.INJECTABLE

       a. Low potency, short duration

          - Procaine

          - Chloroprocaine

       b. Intermediate potency and duration

          - Lidocaine

          - Prilocaine

       C. High potency, long duration

          - tetracaine

          - Bupivacaine

          - Dibucaine

    2. SURFACE ANAESTHETIC

        a. Soluble

          - cocaine

          - lidocaine

          - tetracaine

        b. Insoluble

          - benzocaine

* PROPERTIES:-

 1. Not irritating to the tissue.

 2. Should not cause any permanent alteration To the nerve structure.

 3. Systemic toxicity should be low.

 4. Should effective whether it injected or Applied topically.

 5. Time of onset of anesthesia should as short as possible.

 6. Duration of action must be long enough to Complete the procedure.

 7. Should be stable in solution and easily biotransformed.

 8. Should not cause an allergic reaction.

 9. Should be sterile or capable of being sterilized by heat.

* MECHANISM OF ACTION OF LOCAL

   ANESTHESIA :-

 1.Displacement of Ca ion from receptor site

 2.Binding of local anesthetic molecule to  this receptor site

 3.Blockade of the Na channel

 4.Decrease in Na conductance

 5.Depression of rate of electrical depolarization

 6.Failure to achieve threshold potential level

 7.Lack of development of propagated action potential

 8.Conduction blockade

* CONTRAINDICATIONS :-

A. ABSOLUTE

 - Myocardial infarction

 - Recent hepatitis A or B

 - Jaundice

 - Local infection or sepsis

 - Hypersensitivity to lidocaine

B. RELATIVE :-

 - Chronic renal failure

 - Hyperthyroidism

 - Pregnancy - 1st trimester

 - Hypertension

 - Malignant hyperthermia