Week 3: Local Anesthetics

Goal of local anesthesia

block afferent neural transmission along peripheral nerve so that procedure is painless, reversible

when administering local anesthesia near SC,

transmission are blocked that level and below

list the 3 order of nerve fiber loss with local anesthesia

1) loss of sympathetic fiber function, loss of pinprick sensation and temp, loss of motor

advantages of local anesthesia

rapid recovery, lack systemic residual effects (no confusion), doesnt interfere with cardio/pulm/renal function, good for childbirth

disadvantages of local anesthesia

time required to establish effect, may be insufficient/incomplete (switch to general)

local anesthetics naming

-caine

choosing a local anesthetic

depends on procedure, operative site, type of regional anesthesia desired (have similar make up tho)

main example of local anesthetic

lidocaine, can be used with iontophoresis or with IV for cardiac arrhythmias

mechanism of action

inhibit opening of sodium channels so the neuron cant depolarize, no signal is sent

where should the drug remain

at site of administration, losses effect if in systemic

what is often coadministered to prevent washout from target area

vasoconstricting agent (epinephrine)

metabolism of local anesthetic

liver and blood stream (hydrolyzing by hepativ enzymes and enzymes in plasma)

local anesthetic excretion

kidneys via polar metabolites

topical use

directly to surface, sympathetic relief to minor irritations/injury (burn), reduce pain before minor procedures (circumcisions)

transdermal use

patches, can be enhanced by electrical current (iontophoresis)

3 main uses for iontophoresis

anesthetize area before treatment, treating MSk, before derm treatments

target tissues for transdermal

tendon, bursae, soft tissue

how long can you leave a lidocain transdermal patch on for for temporary pain relief

up to 8 hrs, no more than 12

lidocain transdermal patch reactions

blisters, bruising, burning, depigmentation, pruritis, irritation, erythema, edema, abnormal sensation

lidocain transdermal patch peak plasma time

11 hrs

lidocain transdermal patch rehab concerns

remove if irritating, heat can cause increased absorption

peripheral nerve block

drug injection close to nerve trunk so transmission along peripheral nn is interipted (can be used in single, large, nerve plexus)

continuous nerve block

catheter left implanted near nerve, after surgery to optimize pain relief

purpose of central nerve blockage

chronic pain, obstetric procedures, alternative to general anesthesia of lumbar surgery or LE arthroplasties

for central nerve blockade where are injections given

epidural space, spinal block, intrathecal block

sympathetic blockade

selective interruption fo sympathetic efferent discharge to disrupt outgoing sympathetic signals

sympathetic blockade is used in

CRPS, due to their increased sympathetic discharge to a limb causing severe pain/dysfunction

adverse effects of local anesthetics

bradycardia, dizziness, headache, hypotension, nausea, vomiting, paresthesia, pain, rigors/fever

Local anesthetic systemic toxicity (LAST)

disrupts excitability of CNS and cardiac tissues (brain stimulation followed by CNS depression-impaired respirations

decreased cardiac excitation, hr, force of contraction)

CNS toxicity signs

ringing of ears, agitation, restlessness, decreased sensation in tongue and mouth

cardiac toxicity signs

bradycardia, ecg changes, fatigue, dizziness

rehab concerns for local anesthetics

avoid heat on patches, if getting injections for CRPS to therapy after them

rehab concern after peripheral nerve block

lack sensation and motor control, be careful when mobilizing

rehab concern after central nerve blockae

sensation may be diminished below level of administration (may affect motor and sensation)