1. Local Anesthetic DR. ISRAA

2. Local Anesthetic A local anesthetic is an agent that interrupts pain impulses in a specific region of the body without a loss of patient consciousness. Normally, the process is completely reversible.

3. History The first local anesthetic was Cocaine which was isolated from coca leaves. It was first introduced to clinical ophthalmology as a topical ocular anesthetic. In 1884, Dr. William Stewart Halsted was the first to describe the injection of cocaine into a sensory nerve trunk to create surgical anesthesia.

4. Types of local anesthetics 1.Esters: – These include cocaine, procaine, tetracaine, and chloroprocaine. – They are hydrolyzed in plasma by pseudo- cholinesterase. – One of the by-products of metabolism is para-aminobenzoic acid, the common cause of allergic reactions seen with these agents.

5. Types of local anesthetics 2. Amides: – These include lidocaine, mepivicaine, prilocaine, bupivacaine, and etidocaine. – They are metabolized in the liver to inactive agents. – True allergic reactions are rare (especially with lidocaine)

6. Mechanism of Action Local anesthetics work to block nerve conduction by reducing the influx of sodium ions into the nerve cytoplasm. They block the sodium channel Anesthetics bind directly to the intracellular voltage-dependent sodium channels Block primarily open and inactive sodium channels, at specific sites within the channel.

7. Mechanism of Action Local anesthetics abolish sensation (and in higher concentrations, motor activity) in a limited area of the body without producing unconsciousness. The small, un-myelinated nerve fibers, that conduct impulses for pain, temperature, and autonomic activity, are most sensitive to actions of local anesthetics.

8. Order of sensory function block 1. Pain 2. Cold 3. Warmth 4. Touch 5. Deep pressure 6. Motor Recovery in reverse order

9. Factors affecting local anesthetic action 1.Effect of pH : local anesthetics are basic drugs. The charged (cationic) form binds to receptor site, uncharged form penetrates membrane, efficacy of drug can be changed by altering extracellular or intracellular pH 2.Effect of protein binding: increased binding increases duration of action 3.Effect of vasodilator activity: greater vasodilator activity = decreased potency and decreased duration of action

10. Factors affecting local anesthetic action 4.Lipid solubility: appears to be the primary determinant of intrinsic anesthetic potency. Chemical compounds which are highly lipophilic tend to penetrate the nerve membrane more easily, such that less molecules are required for conduction blockade resulting in enhanced potency.

11. Adverse effects of local anesthetics Effects attributable to the technique itself rather than to the agent used, for example needle damage to a vessel or nerve. Local and regional effects of the drug, which may be related to its anesthetic activity or a consequence of irritation or allergy. Systemic effects, most usually seen if the agent is inadvertently injected into a blood vessel in sufficient quantities.

12. Adverse effects of local anesthetics Effects of additives: – Vasoconstrictors to prolong the local effect – Hyaluronidase to promote penetration – Preservatives to prevent bacterial contamination or degradation

13. Adverse effects of local anesthetics 1.Hypersensitivity. Ester type local anesthetics are metabolized to product which can stimulate immune system This is very rare and can be prevented by using agents from amide subclass. 2.Peripheral vascular action: arteriolar dilation (except cocaine which is vaso-constrictive) 3.Hypotension 4.Methaemoglobinaemia.

14. Adverse effects of local anesthet ics 5.Central Nervous System Toxicities: Local anesthetics, if absorbed systematically in excessive amounts, can cause light headedness or sedation, restlessness, nystagmus, and convulsions which may be followed by respiratory and cardiovascular depression.

15. Adverse effects of local anesthetics 6.Cardiovascular Toxicities: Local anesthetics with exception of cocaine are vasodilators. Local anesthetics with exception of cocaine can cause brady-arrhythmia and heart block Cocaine in abuser can cause severe hypertension, MI, cerebral hemorrhage and arrhythmias.

16. Administration of Local Anesthetics 1.Infiltration Anesthesia: – Local infiltration occurs when the nerve endings in the skin and subcutaneous tissues are blocked by direct contact with a local anesthetic, which is injected into the tissue. – Infiltration Anesthesia is used primarily for surgical procedures involving a small area of tissue (for example, suturing a cut).

17. Administration of Local Anesthetics 2.Topical Block: – This technique is often used during examination procedures involving the respiratory tract, the eye etc. – For topical application, the local anesthetic is always used without epinephrine. 3.Nerve Block: – In this type of anesthesia, a local anesthetic is injected around a nerve that leads to the operative site. – Usually more concentrated forms of local anesthetic solutions are used for this type of anesthesia.

18. Administration of Local Anesthetics 4.Peridural Anesthesia. – This type of anesthesia is accomplished by injecting a local anesthetic into the Peridural space. 5.Spinal Anesthesia. – In spinal anesthesia, the local anesthetic is injected into the subarachnoid space of the spinal cord

19. Vasoconstrictors Vasoconstrictors decrease the rate of vascular absorption which allows more anesthetic to reach the nerve membrane and improves the depth of anesthesia. 1:200,000 epinephrine (adrenaline) appears to be the best vasoconstrictor.

20. GOOD LUCK