Local Anesthetics

P. Orzylowski6/03/2014

Naturally occurring

• Tetrodotoxin• Saxitoxin• Menthol• Eugenol (cloves)

• Reversible local anesthesia• Decrease rate of depolarization/repolarization

of the excitable neural membrane

• Pain• Others• Paralysis

MOA

• 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

• 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

• Epinephrine• Inc intensity• Dec systemic absorption

• Opiods• Steroids – dexa increases duration by 50%

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

• 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)

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

• Bind @ systole, dissociate on diastole• Dissociates slowly incomplete recovery

• L-carnitine def = increased susceptibility

• Methemoglobinemia• Metabolite of prilocaine o-toluidine

• Myotoxicity• Dysregulation of intracellular Ca concentrion

• Allergies

Uses

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

Prophylaxis

1) Aspiration2) Fractionated doses3) Slow injection

Treatment

• Mostly supportive• Stop LA• Supplemental oxygen• Ventilatory support and intubation if

necessary• Treat dysrhythmias

cardioversion/amiodarone• Lipid Rescue

Lipid Rescue

• Weinberg 1998• Published 2006 • Still relatively limited literature

• Removes anesthetic from sight of action

• 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

Questions?