Local anesthetics Drug produce reversible conduction block of neural impulses transmission of autonomic, sensory and motor neural impulses

History The natives of Peru have chewed the leaves of the indigenous plant “Erythroxylon coca” the source of cocaine, to induce a feeling of well-being Koller used cocaine for the eye in 1884 Halsted used cocaine as nerve block First synthetic local-- procaine in 1905 Lidocaine synthesized in 1943

Mechanism of action is by reversibly blocking sodium channels to prevent depolarization Structure Linear molecules that have a lipophilic and hydrophilic end (ionizable) low pH-- more in ionized state and unable to cross membrane adding sodium bicarb-- more in non-ionized state

Two groups: esters and amides esters metabolized by plasma cholinesterase amides metabolized by cytochrome p-450

Clinical uses Local anesthetics Nerve block (brachial plexus block, wrist block, ankle block----etc.) Local infiltration Ointment, spray, lotion, lozenges, EMLA Regional block (spinal, epidural, caudal) Intravenous regional block (Bier’s block)

Lidocaine uses: Prevent or treat cardiac ventricular dysrhythmias Attenuate presser responses associated with intubation of the trachea Prevent or treat increases in intracranial pressure as are often associated with intubation of the trachea Minimize coughing during intubation or extubation of the trachea

Addition of epinephrine to local anesthetic solutions Epinephrine 1:200000 or 5μg/ml Advantage: Limits systemic absorption Prolongs the duration of local anesthetics by keeping them in contact with nerve fibers Decreasing the possibility of systemic toxicity cause the rate of metabolism will match the rate of absorption As test in epidural regional anesthesia

Addition of epinephrine to local anesthetics is not recommended in: Unstable angina pectoris Cardiac dysrhythmias Uncontrolled hypertension Uteroplacental insufficiency Peripheral nerve block anesthesia in areas that may lack collateral blood flow (digits, penis) Intravenous regional anesthesia

Local Anesthetic Toxicity Central nervous system Side effects Local Anesthetic Toxicity Central nervous system initially-- lightheadedness, circumoral numbness, dizziness, tinnitus, visual change later-- drowsiness, disorientation, slurred speech, loss of consciousness, convulsions finally-- respiratory depression

Cardiovascular myocardial depression and vasodilation-- hypotension and circulatory collapse specially with bupivacaine 2. Allergic reactions-- rare (less than 1%) preservatives or metabolites of esters rash, bronchospasm

Prevention and Treatment of Toxicity Primarily from intravascular injection or excessive dose – anticipation or from absorption from tissue injection sites aspirate often with slow injection ask about CNS toxicity have monitoring available prepare with resuscitative equipment, CNS-depressant drugs, cardiovascular drugs ABC’s

All cases Seizures Hypotension Dysrthymia Assure adequate ventilation Administer supplemental oxygen Seizures Diazepam Hypotension Trendelenburg position (head down legs up) IV fluid bolus (isotonic saline or Ringer lactate) Vasopressor (dopamine) Dysrthymia accordingly

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