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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

Local Anesthetics

P. Orzylowski

6/03/2014


Naturally occurring
Naturally occurring

  • Tetrodotoxin

  • Saxitoxin

  • Menthol

  • Eugenol (cloves)


Local anesthetics


Local anesthetics
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


Local anesthetics

  • 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?


Adjuvants
Adjuvants

  • Epinephrine

  • Inc intensity

  • Dec systemic absorption

  • Opiods

  • Steroids – dexa increases duration by 50%


Side effects
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


Local anesthetics

  • 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)


Local anesthetics

  • Bupivacaine has higher affinity for resting and inactive sodium channels.

  • Bind @ systole, dissociate on diastole

  • Dissociates slowly  incomplete recovery

  • L-carnitine def = increased susceptibility


Local anesthetics

  • Methemoglobinemia

  • Metabolite of prilocaineo-toluidine

  • Myotoxicity

  • Dysregulation of intracellular Ca concentrion

  • Allergies


Local anesthetics
Uses

  • Regional anesthesia

  • IV regional anesthesia (Bier’s)

  • Peripheral nerve block

  • Topical

  • Systemic?


Prophylaxis
Prophylaxis

  • Aspiration

  • Fractionated doses

  • Slow injection


Treatment
Treatment

  • Mostly supportive

  • Stop LA

  • Supplemental oxygen

  • Ventilatory support and intubation if necessary

  • Treat dysrhythmiascardioversion/amiodarone

  • Lipid Rescue


Lipid rescue
Lipid Rescue

  • Weinberg 1998

  • Published 2006

  • Still relatively limited literature

  • Removes anesthetic from sight of action


Local anesthetics