Local Anesthetics Flashcards

1
Q

What is the aim of LAs?

A

Induce local analgesia, meaning local insensitivity to pain

Reduces pain and distress, an effective but safer alternative to GA

Relieves non-surgical pain and diagnoses chronic pain conditions

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2
Q

What do LAs do?

A

Cause loss of nociception by blocking afferent activity in PNS and CNS

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3
Q

What are the techniques of LA administration?

A

Topical
Plexus block
Spinal block
IV via Bier block
Trigger points

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4
Q

What are the adverse effects of LAs?

A

Localized prolonged anesthesia or paresthesia due to infection, hematoma, excessive fluid pressure in a confined cavity and severing of nerves and support tissue

Systemic reactions like depressed CNS syndrome, allergic reactions, vasovagal episodes, cyanosis etc due to injection into a highly vascularized area or accidentally into a BV

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5
Q

Name the amide group LAs

A

Lidocaine
Mepivacaine
Bupivacaine
Etidocaine
Prilocaine

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6
Q

Name the ester group LAs

A

Cocaine
Procaine
Chloroprocaine
Tetracaine

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7
Q

Difference between ester and amide LAs?

A

Ester link more prone to hydrolysis, therefore shorter duration of action

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8
Q

Charged vs uncharged LAs?

A

LAs are weak bases, dissociating more in acidic environments

Charged form is most active
Uncharged form penetrates lipid membranes

Therefore less effective when injected into acidic tissue
Inject together with sodium bicarbonate to hasten onset

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9
Q

Effects of PK on LA onset?

A

LAs are injected directly around target nerves, so absorption and distribution do not affect onset much

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10
Q

Effects of PK on LA offset?

A

Determined by systemic absorption, entering BV and distributing to cause concentration around nerves to drop and dropping to below MEC

Determined by dosage, site of injection, tissue binding strength, use of vasoconstrictors and drug properties

Metabolism and excretion differ between ester and amide LAs, where ester types are rapidly hydrolysed in blood, whereas amide types are metabolised in the liver by CYP450

Therefore, amide type metabolism and excretion is lowered in patients with liver disease, reduced hepatic blood flow, and CYP450 inhibition/competition

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10
Q

Effects of PK on LA offset?

A

Determined by systemic absorption, entering BV and distributing to cause concentration around nerves to drop and dropping to below MEC

Determined by dosage, site of injection, tissue binding strength, use of vasoconstrictors and drug properties

Metabolism and excretion differ between ester and amide LAs, where ester types are rapidly hydrolysed in blood, whereas amide types are metabolised in the liver by CYP450

Therefore, amide type metabolism and excretion is lowered in patients with liver disease, reduced hepatic blood flow, and CYP450 inhibition/competition

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11
Q

How do LAs work?

A

They stop the action potential depolarization process by inhibiting sodium ion influx through sodium channels, prolonging repolarization and reducing depolarization

LAs are voltage and time dependent, preferably blocking nerve cells firing rapidly, and therefore LAs are more selective for pain fibers than motor fibers

Has side effects in CNS and heart

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12
Q

What kind of nerves are LAs preferential towards?

A

Rapidly depolarizing nerves

Smaller, typically unmyelinated nerve fibers

Nerve fibers on the periphery of nerve bundles

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13
Q

How do the durations of LAs differ from drug to drug?

A

Short acting: Procaine
Medium acting: Lidocaine
Long acting: Bupivacaine

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14
Q

How can the LA effect be prolonged?

A

Increasing dose

Adding vasoconstrictor

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15
Q

How can LA onset be accelerated?

A

Sodium bicarbonate

Choosing LA with rapid penetration of skin

16
Q

LA toxicity effects?

A

Direct neurotoxicity due to high concentrations in close proximity to spinal cord or nerve trunks

CNS effects: sleepiness, lightheadedness, visual/auditory disturbances, restlessness, circumoral/tongue numbness with a metallic taste, nystagmus and muscle twitching, seizures and coma

CVS: depress myocardial contractility, arteriolar dilation, hypotension, arrhythmia

Allergic reactions: especially due to ester types