1. Local anesthetics

2. Objectives Recall how an action potential is generated and propagated Classify local anesthtics Describe the machanism of action, pharmacokinetics and toxic effects of local anesthetics Describe the different techniqes of use of LA Describe the risks and benefits of using vasoconstrictors with LA

3. Overview Local anesthetics produce a transient and reversible loss of sensation (analgesia) in a circumscribed region of the body without loss of consciousness. Normally, the process is completely reversible.

5. ANESTHETICS

6. Local anesthetics - esters or amides –a lipophilic aromatic group –to a hydrophilic, ionizable amine. Most are weak bases

7. Classification of LA Esters Benzocaine Procaine/Procaine Proparacaine

8. Classification of LA Amide Bupivacaine Levobupivacaine Lidocaine/LignocaineLidocaineLignocaine Mepivacaine

9. Ionized

10. Local anesthetics gain access to the inner axonal membrane by 1.traversing sodium channels while they are more often in an open configuration 2.passage directly through the plasma membrane

12. Block inititation and propagation of action potential

14. Sympathetic block (vasodilatation) Loss of pain and temperature sensation Loss of proprioception Loss of touch and pressure sensation Loss of motor function Sequence of clinical anesthesia

15. Potency = lipid solubility Higher solubility = can use a lower concentration and reduce potential for toxicity Anesthetic Potency

16. DURATION OF ACTION Duration = protein binding Bupivacaine 95% Lidocaine 65%

17. Pharmacokinetics Effective within 5 min Duration of action – 1-1.5 h Activity is Ph dependent Increased action in acidic ph

19. CLEARANCE ESTERS hydrolysis via cholinesterase AMIDES metabolism via hepatic enzymes

20. LA Infiltration anesthesia Regional anesthesia Surface anesthesia

21. LA Infiltration anesthesia Regional anesthesia Surface anesthesia

22. Gegional anaesthesia Nerve block Intravenous Extradural Intrathecal block/ spinal anaesthesia

23. Nerve block Inject a drug around the nerve Anaesthetise a region

24. Intravenous 0.5-1% lidocaine without adrenaline

25. Extradural/epidural Thoracic, lumbar, sacral Act on nerve roots No hypotention

27. Spinal anesthesia Sympathetic nerve block hypotension

28. LA Infiltration anesthesia Regional anesthesia Surface anesthesia

29. On intact skin – eutectic mixture of bases of prilocaine (EMLA) Slow absorption

31. Prolongation of action Add vasoconstrictor – adrenaline Can use a larger dose Not to – fingers, toes, nose, penis

33. Adverse effects LA’s cause some vasodilatation at site LA toxicity related to rate of absorption via blood flow

34. Systemic Toxicity Blockage of voltaged-gated Na channel affects action potential propagation throughout the body Potential is present for systemic toxicity

35. Effects of local anesthetics Excitation – anxiety, agitation, restlessness Convulsions Reduced myocardial contractility Vasodilatation