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Local anesthetics Flashcards

1
Q

General intent of local anesthetics

A
  1. Produce local or regional effects

2. Avoid systemic effects

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2
Q

Mechanism of action of local anesthetics

A
  • Inhibit voltage gated Na channels
  • Bind to inactivated state
  • Prevents neural cells from generating action potentials in response to slight depolarization
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3
Q

Phasic or use dependent block

A

Affinity for activated > resting

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4
Q

What impacts dissociation from Na channels?

A
  • Smaller molecules dissociate from Na channel more rapidly

- Extreme lipophilicity (bupivicaine) favors continued binding and increases duration of action

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5
Q

What happens when you increase lipophilicity?

A
  1. Favors entry of local anesthetics into molecule
  2. Increasing potency
  3. Slower onset (slower to leave nerve membrane for intracellular fluid)
  4. Delays absorption into systemic circulation
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6
Q

How do substitutions change lipophilicity?

A

More substitutions = more lipophilic

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7
Q

Ester local anesthetics

A
  • Shorter duration of action
  • Benzocaine
  • Chloroprocaine
  • Cocaine
  • Procaine
  • Tetracaine
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8
Q

Amides local anesthetics

A
  • Longer duration of action
  • Bupivicaine
  • Lidocaine
  • Prilocaine
  • Ropivacaine
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9
Q

Absorption of local anesthetics

A

Administer close to target nerve tissue

Smallest volume and dose

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10
Q

Factors that effect absorption

A

Drug molecule size
% ionized
Lipid solubility
serum/tissue protein binding

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11
Q

How does pH and pKa effect local anesthetics?

A
  • Neutral form readily crosses phospholipid cell membrane, but most local anesthetics are weak bases and have a pKa > physiologic pH
  • 50% of molecules are cations are physiologic pH when administered
  • pKa partially determines speed of onset
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12
Q

Onset time of procaine and tetracaine

A

Slow

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13
Q

Onset time of bupivacaine and ropivacaine

A

Moderate

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14
Q

Onset time of chloroprocaine, lidocaine, etidocaine, and mepivacaine

A

Fast

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15
Q

How does pH and pKa change with administration of local anesthetics?

A
  • Neutral to pass through the membrane
  • Lipophilic to penetrate the membrane
  • Ionized to bind to Na channel
  • Inside cell non-ionized to ionized equilibrium
  • lower pH of intracellular fluid shifts towards ionized
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16
Q

Characteristics of local anesthetics with epi

A
  • Acidic pH
  • 100% ionized
  • Accelerates onset
  • Vasoconstricts to prevent redistribution away from nerve fibers
  • Prolongs duration of action and reduce peak serum concentrations
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17
Q

Highest to lower peak concentrations for vascularity

A

IV > tracheal > intercostal > caudal > paracervical > epidural > brachial plexus > subarachnoid/sciatic/femoral > subcutaneous

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18
Q

Duration of procaine, chloroprocaine

A

Short due to low protein binding and lipid solubility

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19
Q

Duration of lidocaine and mepivacaine

A

Moderate

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20
Q

Duration of tetracaine, etidocaine, bupivicaine, and ropivacaine

A

Long

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21
Q

Metabolism of esters

A
  • Hydrolyzed by plasma esterases (except cocaine is metabolized by liver)
  • occurs within minutes
  • Metabolized to inactive metabolites
  • para-aminobenzoic acid metabolite can cause allergic reactions
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22
Q

Metabolism of amids

A
  • Hepatic CYP450 enzymes
  • Longer elimination half life
  • Increased risk for accumulation of unmetabolized drug and system toxicity
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23
Q

Can cause methemiglobinemia, should be avoided in labor and delivery, patients with limited cardiopulmonary reserve, and endoscopies

A

Prilocaine, bupivacaine and sometimes lidocaine

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24
Q

Treatment for methemiglobinemia

A

Methylene blue
Reduces methemiglobin to hemoglobin
Short duration of effects
Normalizes within 20- 60 minutes

25
Q

How is potency increased?

A

More large alkyl groups to parent molecule = more potent = more lipid soluble

26
Q

What impacts the minimum concentration that will block nerve conduction?

A

Fiber size (smaller is more sensitive), type, myelination (myelinated is more sensitive)
pH (acidic pH antagonizes block)
Frequency of nerve stimulation
Electrolyte concentration (dec K+ and inc Ca++ antagonize block)

27
Q

A minimum of _ nodes must be blocked to prevent AP propagation

28
Q

Implies nerves with higher baseline firing rates will demonstrate a larger blockade compared with lower firing rates

A

Phasic block

29
Q

True/false: sensory nerves fire at a higher rate than motor

30
Q

Exceeds sensory block during spinal and epidural anesthesia

A

Sympathetic block

31
Q

Exceeds motor block during spinal and epidural anesthesia

A

Sensory block

32
Q

Associated with sharp, fast pain

A

Adelta fibers

33
Q

Associated with burning or slow pain

34
Q

More susceptible fibers to local anesthetic

A

Adelta fibers

35
Q

LA with selectivity for sensory nerves over motor during onset and offset

A

Bupivacaine and ropivacaine

36
Q

Route of administration of LA

A
  1. Topical
  2. Injection in vicinity
  3. Major nerve trunks
  4. Epidural or spinal
37
Q

Adverse neurological effects of local anesthetics

A
  1. tongue paresthesia
  2. dizziness
  3. blurred vision
  4. restlessness/agitation
  5. seizures
  6. dysesthesia
  7. burning pain
  8. Aching in lower extremities/buttock
38
Q

Adverse respiratory effects of local anesthetics

A
  1. depressed hypoxic drive
  2. apnea from phrenic and intercostal nerve paralysis
  3. Depressed medullary respiratory center
  4. apnea after “high” spinal or epidural hypotension
39
Q

Adverse cardio effects of local anesthetics

A
  1. suppressed phase 4 depolarization
  2. slowed conduction velocity
  3. depressed contractility
  4. vasodilation (except with cocaine)
  5. tachycardia or HTN in awake pts
  6. arrhythmias
40
Q

What is Local Anesthetic Severe Toxicity (LAST)?

A
  • most commonly seizures
  • 1/3 begins with CNS and progresses to CVS features
  • Typically occurs immediately following LA injection
41
Q

LAST risk factors

A
  1. Drugs
  2. Patient age (neonates, infants, elderly)
  3. Pregnancy
42
Q

CC/CNS ration

A

drug dose required to cause catastrophic cardiovascular collapse to the drug dose required to produce seizures

  1. low ratio = more cardiotoxic (bupivacaine)
  2. High ratio = greater safety margin to recognize early onset CNS issues before cardiac collapes (lidocaine, mepivacaine)
43
Q

Treatment of LAST

A

Lipid emulsion 20% IV early,
100ml bolus over 2-3 minutes followed by 200-250 ml over 15-20 min
Rebolus up to 2 additional times

44
Q

May lead to prolonged action/slower systemic absorption in LAST

A

Vasoactive drugs; ropivacaine, levobupivacaine

45
Q

May lead to more rapid systemic absorption

A

Bupivacaine; vasodilating

46
Q

How much should you reduce the LA dose in neonates and infants

A

15% <4 months of age

47
Q

How much should you reduce the LA dose in elderly?

48
Q

Why are women in labor at risk for LAST?

A
  • reduced alpha 1 acid glycoprotein
  • Increased CO
  • Rapid absorption, high Cmax
49
Q

Benzocaine: techniques, available concentrations, max dose, typical duration

A

Technique- topical
Available concentration-20%
Max dose-N/A
Typical duration-N/A

50
Q

Chloroprocaine techniques, available concentrations, max dose, typical duration

A

Technique- epidural, infiltration, peripheral nerve block, spinal
Available concentration- 1, 2, 3%
Max dose-12 mg/kg, 600 mg
Typical duration-short due to rapid metabolism
rapid onset

51
Q

Cocaine: techniques, available concentrations, max dose, typical duration

A

Technique: topical, ENT
Available concentration: 4, 10%
Max dose: 3mg/kg
Typical duration: NA

52
Q

Procaine (Novocain): techniques, available concentrations, max dose, typical duration

A 
Technique: spinal, local infiltration
Available concentration: 1, 2, 10%
Max dose: 12 mg/kg, 500mg
Typical duration: short
slow onset
53
Q

Tetracaine (amethocaine) techniques, available concentrations, max dose, typical duration

A

Technique: spinal, topical (eye)
Available concentration: 0.2, 0.3, 0.5, 1, 2%
Max dose 3mg/kg, 100mg topical
Typical duration: long as far as esters go
Slow onset

54
Q

Bupivacaine: techniques, available concentrations, max dose, typical duration

A

Technique: epidural, spinal, infiltrations, peripheral nerve block (sensory>motor **cardiotoxic)
Available concentration: 0.25, 0.5, 0.75%
Max dose: 3mg/kg, 175 mg
Typical duration: long
Slow onset

55
Q

Lidocaine: techniques, available concentrations, max dose, typical duration

A

Technique: epidural, spinal, infiltration, peripheral nerve block, IV, regional, topical
Available concentration: 0.5, 1, 1.5, 2, 4, 5%
Max dose: 4.5 mg/kg (7 mg/kg with epi), 300 mg
Typical duration: medium
Rapid onset

56
Q

Mepivacaine: techniques, available concentrations, max dose, typical duration

A

Technique: epidural, infiltration, peripheral nerve block, spinal
Available concentration: 1, 1.5, 2, 3%
Max dose: 4.5 mg/kg (7 mg/kg with epi), 300 mg
Typical duration: medium
Slow onset

57
Q

Prilocaine: techniques, available concentrations, max dose, typical duration

A 
Technique: EMLA (topical), epidural, IV, regional (outside US)
Available concentration: 0.5, 2, 3, 4%
Max dose: 8 mg/kg, 400 mg
Typical duration: medium
Slow onset
58
Q

Ropivacaine: techniques, available concentrations, max dose, typical duration

A

Technique: epidural, spinal, infiltration, peripheral nerve block
Available concentration: 0.2, 0.5 0.75, 1%
Max dose: 3mg/kg, 200mg
Typical duration: long
Slow onset

Pharmacology-J (3 decks)

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