Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Chapter 10 Local Anesthetics

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetics  History of Local Anesthetics  Local anesthetics are derivatives of cocaine which is a derivative of the coca leaf 2

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Desirable Properties of Local Anesthetics  Potent  Reversible  Absence of local and systemic reactions  Absence of allergic reactions  Rapid onset and satisfactory duration  Adequate tissue penetration  Low cost  Stability in solution 3

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Site and Mechanism of Action  Local anesthetics are divided into 2 chemical groups; esters and amides.  Esters have a higher rate of allergic reaction.  Local anesthetics slows or blocks depolarization by reducing Na permeability into the nerve cytoplasm, thus inhibiting the flow of K out of the cell.  Nerve impulse travels from node to node. Local anesthetics effectively block nerve impulse travel. 4

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Ionization Factors  Local anesthetics are weak bases occurring equilibrated between their 2 forms, the fat soluble, free base and water-soluble hydrochloride salt.  The portion of drug in each form is determined by the pKa of the local anesthetic and the pH of the environment.  Once injected into local tissue, the amount of local anesthetic in the free base form increases and allows for greater tissue penetration.  If there is an infection or inflammation, the free base form decreases and less drug penetrates the tissue.  Other factors that can affect tissue penetration include inflammation, vasodilation, and dilution by fluid. 5

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetics  Absorption  Absorption of local anesthetics is dependent on the route of injection.  Once injected, the rate of absorption is dependent on tissue vascularity.  Tissue vascularity is a function of inflammation, vasodilating properties of the local anesthetic, presence of heat, or the use of massage.  Systemic absorption of the local anesthetic is reduced with the addition of a vasoconstrictor. 6

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetics  Distribution  The local anesthetic becomes partially bound to plasma and red blood cells.  The unbound drug freely diffuses to other tissue including the CNS and across the placenta.  Distribution allows absorption to occur in 3 phases.  The drug occurs at highly vascular tissues in the lungs and kidneys  It appears in less vascular muscle and fat  The drug is metabolized 7

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetics  Metabolism and Excretion  Primarily inactivated in the liver  Excretion in urine 2-5% of active drug form  Articaine is removed faster than the other amides 8

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetics  Pharmacologic Effects  The main pharmacologic effect of the local anesthetic is to reversibly block peripheral nerve conduction.  Local anesthetics also have a direct effect on the cardiac muscle by blocking cardiac Na channels and depressing abnormal cardiac pacemaker activity, excitability, and conduction. 9

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetics  Adverse Reactions  Adverse reactions and toxicity of local anesthetics are directly related to drug plasma levels.  The factors that influence toxicity include: Drug itself Drug itself Concentration Concentration Route of administration Route of administration Rate of injection Rate of injection Vascularity Vascularity Patient’s weight Patient’s weight Rate of metabolism and excretion Rate of metabolism and excretion 10

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetics  Adverse Effects  Both CNS stimulation and depression can occur.  Local anesthetics can produce myocardial depression and cardiac arrest with peripheral vasodilation.  Local effects include physical injury caused by poor injection technique.  Malignant hyperthermia only occurs in those persons with the inherited autosomal dominant gene. It is not related to amide local anesthetic use.  The incidence of allergic reactions to amide local anesthetics is very low. 11

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Composition of Local Anesthetics  Local anesthetic solutions are also made up of the following:  Vasoconstrictor that delays local anesthetic absorption, reduces systemic toxicity, and prolongs the duration of action.  Antioxidant that delays the oxidation of epinephrine. Some are used to prolong shelf-life.  Sodium hydroxide adjusts the pH of the solution to between 6 and 7.  Sodium chloride makes the injectable solution isotonic. 12

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetic Agents  Several different amide local anesthetics are available for use.  Choice of local anesthetic should be based upon onset of action, duration of local anesthesia required and side effects.  Presence or absence of a vasoconstrictor. This is of particular importance if the patient has hypertension. 13

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Local Anesthetic Agents AnestheticpKaOnsetDuration (with epi) (min) Max Dose (with epi) (mg/kg) Procaine9.1Slow Lidocaine7.9Rapid Bupivacaine8.1Slow Prilocaine7.9Medium Articaine7.8Rapid

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Vasoconstrictors  Benefits of Local Anesthetics  Suppress systemic absorption of anesthetic agent  Increase duration and intensify block  Localize hemostasis  Reduce toxicity  Act on alpha and beta receptors in body tissues, causing the constriction of blood vessels 15

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Vasoconstrictors  Contraindications  Heart attack in the last 6 months  Uncontrolled high blood pressure  Daily angina  Tricyclic antidepressants  Uncontrolled hyperthyroidism  Uncontrolled arrhythmias 16

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Vasoconstrictors  Dental Concerns  Vasoconstrictors increase the length of anesthetic effect which increases the chance of accidental patient self- mutilation.  In small quantities, epinephrine acts as a vasodilator thus having the potential to increase post-op bleeding.  Patients with cardiovascular disease, who can receive a vasoconstrictor, should receive the lowest dose possible by means of the best injection technique.  Adverse Reactions  Ischemia  Prolonged pain, numbness or paresthesia  Feelings of nervousness or fast heart rate 17

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Topical Anesthetics  Several different topical anesthetics are available for use.  Choice should be based upon onset, duration of action, and allergenic potential.  The patient should be instructed to avoid eating for 1 hour after application so that the gag reflex can become fully functional. 18

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Topical Anesthetics 19

Mosby items and derived items © 2007 by Mosby, Inc., an affiliate of Elsevier Inc. Topical Anesthetics 20