3History of local anesthesia 1500’s Accounts referring to Peruvian Indians chewing on leaves of the coco plant are found1884 Cark Koller demonstrated the usefulness of the extract from these leaves[cocaine]as a topical anesthetic for the eyes, and earned distinction as the “father of local anesthesia1884 Willium Halsted used cocaine in the first nerve block [ Inferior alveolar nerve block]. The use of cocaine for anesthesia produced several unwanted side effects including cardiac problem and addiction1885 James Corning demonstrated the use of a tourniquet to slow absorption of cocaine
4History of local anesthesia 1901 Heinrich Braun demonstrated the use of epinephrine to retard local anesthetic absorption from the site of injection1904 Alfred Einhorn introduced procaine . Epinephrine was needed to constrict the vessels in the area of administration to lengthen the duration of anesthesia. It was common to see a 1:50,000 concentration for many years1943 Nils Lofgren introduced lidocaine1947 Novocol company made the dental aspirating syringe available1959 Disposable sterile needles made available by Cook- Waite, Roehr Company
20Potency: lipid solubility Onset : pKa, concentration of local anesthetic
21(modified Henderson- Hasselbalch equation) What is pKa?pKa = pH + log[ RNH+ ][RN](modified Henderson- Hasselbalch equation)pKa is the dissociation constant, represents thepH at which the concentration of theionized base(RNH+) and the non-ionizedbase (RN) are equal.
23AnestheticpKa%RN at pH 7.4Onset [min]Mepivacaine7.6402-4Etidocaine7.733Articaine7.829Lidocaine7.925PrilocaineBupivacaine8.1185-8Procaine9.1214-18
24Example at physiologic pH (7.4) LidocaineProcainepKa7.93:1 ionized tonon-ionized8.932:1, ionized to non-ionizedonset2 to 3 minutes6 to 12 minutesif lidocaine (pKa 7.9) is administered into an area of infection (pH 4.9) resulting 1,000:1 ionized to non-ionized indicates a poorer penetration into the nerve tissue and therefore a less effective nerve block
25Quinn and Malamed (1990) and Haegerstam (1990) suggested of administer L.A. AWAY from the area of inflammation (nerve block) especially in the area of EXTENSIVE CELLULITISMalamed. Handbook of LOCAL ANESTHESIA 1990.Haegerstam, Introduction to Dental Local anesthesia 1990.
26Duration of actionDifferential sensory/ motor blockadeAdverse reaction
27Clinical use of local anesthesia Topical anesthesiaInfiltrationPeripheral nerve blockEpidural blockSpinal blockIntravenous regional anesthesia
32CC/CNS Ratioi.e. the ratio of the LA dosage required for irreversible cardiovascular collapse and the dosage that produces CNS toxicity (convulsions)the higher the CC/CNS ratio the better the safety margin
35Prevention Aspiration before injection Inject slowly Use smallest quantity of solution and lowest concentration of vasoconstrictorObserve the patient after injectionChoose another anesthetic if the patient has tendency for allergic reaction
36The signs and symptoms of allergic reaction include: generalized body rash or skin rednessitching, urticaria (hives)bronchospasm (difficulty breathing)swelling of the throatasthmaabdominal crampingirregular heartbeathypotension (low blood pressure)swelling of the face and lips (angioneurotic edema)
37Adverse reactions of commonly used local anesthetics Methemoglobinemiaassociated with prilocaine, articaine, benzocaineLocal tissue toxicity
40Adverse reactions of vasopressor drugs SignsElevated BP, HRSymptomsFearAnxietyRestlessnessThrobbing headacheTremorDizzinessPallorRespiratory difficultyPalpitations
41Contraindication for Epinephrine Blood pressure over 200 torr systolic or 115 torr diastolicUncontrolled hypertensionSevere cardiovascular disease including less than 6 months after a myocardial infarction or cerebrovascular accidentDaily episodes of angina pectoris or unstable anginaCardiac dysrhythmias despite appropriate therapyMedicated with beta blocker,monoamine oxidase inhibitor , or tricyclic antidepressant; or general anesthesia with a halogenated anesthetic like halothane
42New York Heart Association : แนะนำว่าควรใช้ epinephrine ในขนาด 3 ug. / kg. Body weight แต่ไม่ควรเกิน 0.2 mg. (200 µg)หากผู้ป่วยมีปัญหาเกี่ยวกับ โรคความดันโลหิตสูง โรคหัวใจ ให้ใช้ Epinephrine ในขนาด 40 ug และสูงสุด ไม่ควรเกิน 54 µg ต่อการฉีดยาครั้งหนึ่ง