Anesthesia 5th year, 9th lecture (Dr. Aamir)

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The lecture has been given on Mar. 29th, 2011 by Dr. Aamir.

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Anesthesia 5th year, 9th lecture (Dr. Aamir)

  1. 1. Local anesthetics Drug produce reversible conduction block of neural impulses transmission of autonomic, sensory and motor neural impulses
  2. 2. History <ul><li>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 </li></ul><ul><li>Koller used cocaine for the eye in 1884 </li></ul><ul><li>Halsted used cocaine as nerve block </li></ul><ul><li>First synthetic local-- procaine in 1905 </li></ul><ul><li>Lidocaine synthesized in 1943 </li></ul>
  3. 3. Local anesthetic Esters Cocaine Procaine Tetracaine Amides Lidocaine Bupivacaine Prilocaine
  4. 4. Mechanism of action is by reversibly blocking sodium channels to prevent depolarization <ul><li>Structure </li></ul><ul><li>Linear molecules that have a lipophilic and hydrophilic end (ionizable) </li></ul><ul><ul><li>low pH-- more in ionized state and unable to cross membrane </li></ul></ul><ul><ul><li>adding sodium bicarb-- more in non-ionized state </li></ul></ul>
  5. 5. <ul><li>Two groups: esters and amides </li></ul><ul><ul><li>esters metabolized by plasma cholinesterase </li></ul></ul><ul><ul><li>amides metabolized by cytochrome p-450 </li></ul></ul>
  6. 6. Clinical uses <ul><li>Local anesthetics </li></ul><ul><li>Nerve block (brachial plexus block, wrist block, ankle block----etc.) </li></ul><ul><li>Local infiltration </li></ul><ul><li>Ointment, spray, lotion, lozenges, EMLA </li></ul><ul><li>Regional block (spinal, epidural, caudal) </li></ul><ul><li>Intravenous regional block (Bier’s block) </li></ul>
  7. 7. <ul><li>Lidocaine uses: </li></ul><ul><li>Prevent or treat cardiac ventricular dysrhythmias </li></ul><ul><li>Attenuate presser responses associated with intubation of the trachea </li></ul><ul><li>Prevent or treat increases in intracranial pressure as are often associated with intubation of the trachea </li></ul><ul><li>Minimize coughing during intubation or extubation of the trachea </li></ul>
  8. 8. Addition of epinephrine to local anesthetic solutions <ul><li>Epinephrine 1:200000 or 5 μ g/ml </li></ul><ul><li>Advantage: </li></ul><ul><li>Limits systemic absorption </li></ul><ul><li>Prolongs the duration of local anesthetics by keeping them in contact with nerve fibers </li></ul><ul><li>Decreasing the possibility of systemic toxicity cause the rate of metabolism will match the rate of absorption </li></ul><ul><li>As test in epidural regional anesthesia </li></ul>
  9. 9. <ul><li>Addition of epinephrine to local anesthetics is not recommended in: </li></ul><ul><li>Unstable angina pectoris </li></ul><ul><li>Cardiac dysrhythmias </li></ul><ul><li>Uncontrolled hypertension </li></ul><ul><li>Uteroplacental insufficiency </li></ul><ul><li>Peripheral nerve block anesthesia in areas that may lack collateral blood flow (digits, penis) </li></ul><ul><li>Intravenous regional anesthesia </li></ul>
  10. 10. <ul><li>Side effects </li></ul><ul><li>Local Anesthetic Toxicity </li></ul><ul><li>Central nervous system </li></ul><ul><ul><li>initially-- lightheadedness, circumoral numbness, dizziness, tinnitus, visual change </li></ul></ul><ul><ul><li>later-- drowsiness, disorientation, slurred speech, loss of consciousness, convulsions </li></ul></ul><ul><ul><li>finally-- respiratory depression </li></ul></ul>
  11. 11. <ul><li>Cardiovascular </li></ul><ul><ul><li>myocardial depression and vasodilation-- hypotension and circulatory collapse specially with bupivacaine </li></ul></ul><ul><ul><li>2. Allergic reactions -- rare (less than 1%) </li></ul></ul><ul><ul><li>preservatives or metabolites of esters </li></ul></ul><ul><ul><li>rash, bronchospasm </li></ul></ul>
  12. 13. Prevention and Treatment of Toxicity <ul><li>Primarily from intravascular injection or excessive dose – anticipation or from absorption from tissue injection sites </li></ul><ul><ul><li>aspirate often with slow injection </li></ul></ul><ul><ul><li>ask about CNS toxicity </li></ul></ul><ul><ul><li>have monitoring available </li></ul></ul><ul><ul><li>prepare with resuscitative equipment, CNS-depressant drugs, cardiovascular drugs </li></ul></ul><ul><ul><li>ABC’s </li></ul></ul>
  13. 14. <ul><li>All cases </li></ul><ul><li>Assure adequate ventilation </li></ul><ul><li>Administer supplemental oxygen </li></ul><ul><li>Seizures </li></ul><ul><li>Diazepam </li></ul><ul><li>Hypotension </li></ul><ul><li>Trendelenburg position (head down legs up) </li></ul><ul><li>IV fluid bolus (isotonic saline or Ringer lactate) </li></ul><ul><li>Vasopressor (dopamine) </li></ul><ul><li>Dysrthymia </li></ul><ul><li>accordingly </li></ul>
  14. 15. <ul><li>Thank you </li></ul>

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