Principles of Anesthetics

1. Principles of Anesthetics Bucky Boaz, ARNP-C

2. Background • Carl Koller • 1884 • Freud colleague • Eye surgery

3. Background • William Halsted • 1885 • Local injection of cocaine for surgery • Nerve block

4. 1884 Hall – Dentistry 1884 Zenfel – Ear 1890 Ritsert – Benzocaine 1905 Einhorn and Braun – Procaine 1930 Chlorprocaine 1941 Nils Lofgren Synthesized Xylocaine Changed to lidocaine Background

5. Physiochemical Properties Aromatic Segment Hydrophilic Segment Intermediate Chain Amino-ester Amino-amine “Esters” “Amines”

6. Physiochemical Properties • Amino-esters (“Esters”) • Older class of drugs • Derivatives of PABA (p-aminobenzoic acid) • Hydrolyzed by serum cholinesterase • Examples • Procaine (Novocaine) • Cocaine • Tetracaine • Benzocaine

7. Physiochemical Properties • Amino-amines (“Amines”) • Newer class of drugs • Derivatives of aniline • Hepatic degradation • Examples • Lidocaine • Bupivocaine (Marcaine, Sensoricaine, Polocaine) • Mepivocaine (Carbocaine) • Etidocaine • Prilocaine

8. Physiologic Basis • Prevention of sodium influx across the nerve membrane • Sufficient anesthetic present prevents firing threshold from being obtained • Prevents action potential from forming • No action potential, no impulse, therefore conduction blockade • End result is local anesthesia

9. Mechanism of Action Lipid solubility Vasodilatation Tissue pH Concentration of drug Protein binding Vasodilatation Mode of administration Presence of vasoconstrictor Duration Potency Onset Inherent pKa Myelination Interspersed tissue Dosage of drug

10. Ideal Anesthetic • Immediate onset • Reversible • Appropriate duration • No permanent damage • No tissue irritation / pain • Wide therapeutic range • Effective regardless of application

11. Topical Anesthesia

12. Intact Skin • Epidermis • Avascular layer measuring 0.12 to 0.7 mm • Barrier to diffusion of topicals • Dermis • Support structure • Contains blood vessels and nerve endings • Anesthetic’s targeted site of action

13. Agents • Lidocaine Cream • EMLA • Ethyl Chloride

14. Uses • Intact skin procedures • Venopuncture • Punch biopsies • Lumbar puncture

15. Lidocaine Cream • 30% lidocaine cream • Saturated on gauze pad adherent to an elastic patch • 45 minutes minimum application time • ½ hour anesthetic duration = 2 hour application • Effective and safe, but not practical

16. EMLA (Eutectic Mixture of Local Anesthetics) • 2.5% lidocaine and 2.5% prilocaine • 1-hour application time • Maximum dose at 2-3 hours • Depth of anesthesia correlated to duration of application • Duration of 1-2 hours after removal • Hypersensitivity and systemic toxicity rare

17. Ethyl Chloride (C2H5CL) • Not an anesthetic, but a vapocoolant • Immediate anesthesia, but limited duration • Spray for 3 to 7 seconds • Used for injections and lancing small abscesses or boils • Not used for punch biopsies

18. Mucous Membranes • Nose, mouth, throat, tracheobronchial tree, esophagus, and genitourinary tract

19. Agents • Tetracaine • Lidocaine • Cocaine • Benzocaine

20. Tetracaine • Effective and potent agent • Long duration of action • Downside = high toxicity • Maximum adult dose of 50mg

21. Lidocaine • 2% solution • Swished inside the mouth then expectorated • 5% liquid • Applied with a swab • 5% ointment • Applied with a sterile gauze pad

22. Lidocaine • Indicated for painful, irritated, or inflamed mucous membranes of the mouth • 2% good for aph-thous stomatitis and as adjunct before infraoral nerve block • 5% ointment good for reducing pain during oral injection

23. Lidocaine • Precautions • Impaired swallowing • Numbness of the tongue • Expectorate excess to avoid toxicity

24. Cocaine • Topical preparations available in 4% and 10% solutions and viscous formulations • Safe dose of 200mg (2 to 3 mg/kg) • Apply for 5-6 minutes • Works by vasoconstriction • Coronary vasoconstriction with 2mg/kg applied to the nasal mucosa

25. Benzocaine • Available in 14% to 20% liquid, gel, or spray • Used to relieve pain in canker sores, cold sores, other minor inflammation • Very short duration and more allergenic • Can be used prior to infraoral nerve block

26. Ophthalmic Anesthetics

27. Agents • Proparacaine • Tetracaine

28. Proparacaine • 0.5% solution • Indicated for removal of superficial foreign body • 1 to 2 drops before procedure • Onset within 30 seconds • Duration 15 minutes • Have patient avoid touching eye

29. Tetracaine • 0.5% solution • Onset, duration, and potency similar to proparacaine • Burning sensation worse and longer

30. Lacerations

31. TAC • TAC (tetracaine-adrenalin-cocaine) • Used to anesthetize lacerations in children • Wounds < 5cm • Vasoconstrictor • More effective on face and scalp

32. TAC • Advantages • Disadvantages

33. Agents and Effectiveness • 0.5% tetracaine, 1:2000 epinephrine (adrenalin), and 11.8% cocaine • Epinephrine 1:2000, cocaine 11.8% • Tetracaine 0.25%, epi 1:4000, cocaine 5.9% • Tetracaine 1.0%, epi 1:4000, cocaine 4% • Lidocaine 4.0%, epi 1:1000, tetracaine 0.5% • Gel by adding 0.15g methylcellulose to 1.5ml of epi and cocaine solution

34. Application • Fill wound with TAC solution • After 3 minutes, instill saturated gauze or cotton into wound • Leave in place 15-20 minutes • SAFE dose maximum • Full strength TAC 0.09 ml/kg • Tetracaine 50mg, cocaine 150-300mg

35. Adverse Reactions • Can lead to systemic toxicity from mucosal application • Gel form reduces runoff • Ischemic complications

36. Precautions • Avoid in: • CAD • Uncontrolled HTN • Seizures • PVD • Risk of Toxicity

37. Infiltration Anesthesia • Injection of anesthetic agent directly into tissue

38. Indications • Excision of skin lesions • Incision of abscess • Suturing of wounds

39. Advantages & Disadvantages • Advantages • Quick and safe • Provides hemostasis • Disadvantages • Large dose for small area • Distorts wounds

40. Choice of Agent • Lidocaine 0.5 to 1.0% • Procaine 0.5% to 1.0% • Bupivacaine 0.25%

41. Agent Concentration(%) Maximum Dose Onset (min) Duration Adult (mg) Pediatric (mg/kg) Procaine 0.5-1.0 500 (600) 7.0 (9) 2-5 15-45 min Lidocaine 0.5-1.0 300 (500) 4.5 (7) 2-5 1-2 hr Bupivacaine 0.25 175 (225) 2.0 (3) 2-5 4-8 hr Choice of Agent

42. Choice of Agent • Prolong duration by adding: • Epinephrine • Sodium bicarbonate • Both • Use bupivicaine

43. Advantages Disadvantages 1. Prolongs duration 1. Impairs host defenses--increases infection * 2. Provides hemostasis 2. Delays wound healing * 3. Slows absorption:  Decreases agent toxicity potential  Allows increased dose 3. Do not use for:  Areas supplied by end arteries  Patients"sensitive" to catecholamines 4. Increases level of blockade 4. Toxicity--catecholamine reaction * Based on laboratory studies.    For example, in patients taking MAO inhibitors. Epinephrine Use

44. Injection Technique • Bicarbonate • Reduces pain of injection • Mechanism unclear • 1 cc 8.4 % bicarb : 9 cc lidocaine • “Neut” 4.2 % bicarb (1cc:4cc) • Precipitates in bupivicaine • Shelf life : 1 wk (unref), 2 wks (refr) Bartfield JM, et al: Buffered lidocaine as a local anesthetic: An investigation of shelf life. Ann Emerg Med 21:24, 1992.

45. Lidocaine Bupivacaine Advantage Onset 2-5 min 2-5 min Equal Effectiveness (equianesthetic dose) Excellent Excellent Equal Duration 1-2 hr 4-6 hr B Infection potential No No Equal Administration pain Less More L Maximum volume --plain lidocaine Less More B Maximum volume--epinephrine Less More B Toxic potential Less cardiotoxic; equal CNS More cardiotoxic; equal CNS L Comparison of 1% Lidocaine (L) and 0.25% Bupivacaine (B)--Infiltration Anesthesia

46. Injection Technique • Lowest concentration effective • Prep wound first if possible • Smallest needle available (27g) • Use wound margin • Subdermal injection • Insert, then inject

47. Injection • Injection should be subdermal • Bury the hub and inject as you withdraw • Through wound edge

48. Injection Technique • Warming • No change in efficacy • Less pain of injection • Probably synergistic with buffering Brogan GX, et al: Comparison of plain, warmed and buffered lidocaine in wound repair. Ann Emerg Med; Aug. 1995.

49. Complications • Effects on wounds • Systemic toxic reactions • Catecholamine reaction • Allergic reactions

50. Effect on Wounds • Wound healing • Wound strength • Avoid in poor healing wounds • Help prevent keloids • Wound infection • Local injuries