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Local Anesthetics

Local Anesthetics. P. Orzylowski 6/03/2014. Naturally occurring. Tetrodotoxin Saxitoxin Menthol Eugenol (cloves). Reversible local anesthesia Decrease rate of depolarization/ repolarization of the excitable neural membrane Pain Others Paralysis. MOA.

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Local Anesthetics

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  1. Local Anesthetics P. Orzylowski 6/03/2014

  2. Naturally occurring • Tetrodotoxin • Saxitoxin • Menthol • Eugenol (cloves)

  3. Reversible local anesthesia • Decrease rate of depolarization/repolarization of the excitable neural membrane • Pain • Others • Paralysis

  4. MOA • Inhibit Na influx via Na-specific ion channels in neuronal cell membranes • Voltage-gated Na channels • Bind intracellular portion of channel and inhibit influx • Action potential inhibited

  5. 1-2% of LA penetrated nerve fibre • Not everything equally blocked • Depends on diameter and type of nerve fibres • B>C>Adelta(temp)>Agamma(proprio)>Abeta(touch&pressure)>Aalpha(motor) • B>C?

  6. Adjuvants • Epinephrine • Inc intensity • Dec systemic absorption • Opiods • Steroids – dexa increases duration by 50%

  7. Side effects • CNS toxicity • Cross BBB • More common with certain LAs (bupi) • Inc: acidosis, Vc, epinephrine • Dec: barbiturates.benzos, dec systemic abs (epinephrine) • 3/10,000 epidural, 1/10,000 PNB

  8. Cardiotoxicity • Higher doses required • Single isomers – ropi&levo-bupi • - decreased affinity for brain and cardiac tissue • 1) less lipid-soluble (lido): • Hypotension/bradycardia/art hypoxemia • 2) more lipid-soluble (bupi): • Ventricular cardiac arrhythmias cardiovascular collapse  resistance to resus (large doses of epi)

  9. Bupivacaine has higher affinity for resting and inactive sodium channels. • Bind @ systole, dissociate on diastole • Dissociates slowly  incomplete recovery • L-carnitine def = increased susceptibility

  10. Methemoglobinemia • Metabolite of prilocaineo-toluidine • Myotoxicity • Dysregulation of intracellular Ca concentrion • Allergies

  11. Uses • Regional anesthesia • IV regional anesthesia (Bier’s) • Peripheral nerve block • Topical • Systemic?

  12. Prophylaxis • Aspiration • Fractionated doses • Slow injection

  13. Treatment • Mostly supportive • Stop LA • Supplemental oxygen • Ventilatory support and intubation if necessary • Treat dysrhythmiascardioversion/amiodarone • Lipid Rescue

  14. Lipid Rescue • Weinberg 1998 • Published 2006 • Still relatively limited literature • Removes anesthetic from sight of action

  15. 1) IV bolus 20% Lipid emulsion @ 1.5mL/kg • 2)continue infusion @ 0.25ml/kg/min after restoration of cardiac function • 3)if continues, rpt bolus and increase to 0.5mL/kg/min • Upper limit 10mL/kg over 30mins

  16. Questions?

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