History of local anesthesia 1500’s Accounts referring to Peruvian Indians chewing on leaves of the coco plant are found 1884 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 anesthesia 1884 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 addiction 1885 James Corning demonstrated the use of a tourniquet to slow absorption of cocaine
1901 Heinrich Braun demonstrated the use of epinephrine to retard local anesthetic absorption from the site of injection 1904 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 years 1943 Nils Lofgren introduced lidocaine 1947 Novocol company made the dental aspirating syringe available 1959 Disposable sterile needles made available by Cook- Waite, Roehr Company History of local anesthesia
Potency: lipid solubility Onset : pKa, concentration of local anesthetic
What is pKa? pKa = pH + log[ RNH + ] [RN] (modified Henderson- Hasselbalch equation) pKa is the dissociation constant, represents the pH at which the concentration of the ionized base(RNH + ) and the non-ionized base (RN) are equal.
RNH + RN + H + Outside membrane RNH + RN + H + Inside membrane
Example at physiologic pH (7.4) LidocaineProcaine pKa 7.9 3:1 ionized to non-ionized 8.9 32:1, ionized to non-ionized onset 2 to 3 minutes6 to 12 minutes if 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
Quinn 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 CELLULITIS Malamed. Handbook of LOCAL ANESTHESIA 1990. Haegerstam, Introduction to Dental Local anesthesia 1990.
Duration of action Differential sensory/ motor blockade Adverse reaction
Clinical use of local anesthesia Topical anesthesia Infiltration Peripheral nerve block Epidural block Spinal block Intravenous regional anesthesia
CC/CNS Ratio i.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
Prevention Aspiration before injection Inject slowly Use smallest quantity of solution and lowest concentration of vasoconstrictor Observe the patient after injection Choose another anesthetic if the patient has tendency for allergic reaction
The signs and symptoms of allergic reaction include: generalized body rash or skin redness itching, urticaria (hives) bronchospasm (difficulty breathing) swelling of the throat asthma abdominal cramping irregular heartbeat hypotension (low blood pressure) swelling of the face and lips (angioneurotic edema)
Adverse reactions of commonly used local anesthetics Methemoglobinemia associated with prilocaine, articaine, benzocaine Local tissue toxicity
Contraindication for Epinephrine Blood pressure over 200 torr systolic or 115 torr diastolic Uncontrolled hypertension Severe cardiovascular disease including less than 6 months after a myocardial infarction or cerebrovascular accident Daily episodes of angina pectoris or unstable angina Cardiac dysrhythmias despite appropriate therapy Medicated with beta blocker,monoamine oxidase inhibitor, or tricyclic antidepressant; or general anesthesia with a halogenated anesthetic like halothane
New York Heart Association : แนะนำว่าควรใช้ epinephrine ใน ขนาด 3 ug. / kg. Body weight แต่ ไม่ควรเกิน 0.2 mg. (200 µg) หากผู้ป่วยมีปัญหาเกี่ยวกับ โรค ความดันโลหิตสูง โรคหัวใจ ให้ใช้ Epinephrine ในขนาด 40 ug และ สูงสุด ไม่ควรเกิน 54 µg ต่อการฉีดยา ครั้งหนึ่ง
วิธีคำนวณปริมาณของ Epinephrine Epinephrine ขนาด 1 : 200,000 1 gm / 200,000 ml 1,000 mg / 200,000 ml 1 mg / 200 ml 0.005 mg / 1 ml