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Local Anesthetics Flashcards

1
Q

Define transduction

A

the process by which tissue damaging stimuli activate nerve endings

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2
Q

What are the free nerve endings that are stimulated in response to pain?

A

nociceptors

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3
Q

What are nociceptors stimulated by?

A
  • mechanical impulses
  • thermal impulses
  • chemical impulses
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4
Q

Define transmission

A

relay of functions by which message is carried from site of tissue injury to brain regions underlying perception

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5
Q

Describe the nerves fibers of nociceptors

A

A(delta): fast; large diamter, thinly myelinated, evoked by sharp, intense, stinging, cold, temporary localized pain
C: slow, small diameter, unmyelinated, evoked by aching, dull, burning poorly localized pain
A(beta): thickly myelinated, cutaneous mechanoreceptors, free nerve ending that responds to light touch and bending of hairs

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6
Q

Which fibers are going to be most sensitive to a blocking agent?

A

C&raquo_space;» A

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7
Q

What are the voltage-gated NA+ channels associated with pain transmission?

A

Nav1.1, Nav1.6, Nav1.7, Nav1.8, Nav1.9

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8
Q

Define a local anesthetic

A

drug that produces a state of local anesthesia by reversibly blocking the nerve conductances that transmit the feeling of pain from point of administration to the brain

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9
Q

What allows a local anesthetic to inactivate the Na+ channels?

A
  • they are lipophilic which allows them to pass through the membrane
  • after passing thru the membrane, they become hydrophilic and binds the Na+ channels – prolonging the inactivation state
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10
Q

What is the order of loss of for local anesthetics?

A

pain – temperature – touch – pressure

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11
Q

How can local anesthetics block nerve conduction?

A

1) inhibit influx of Na+ through VGSC – impaired AP
2) decrease nerve membrane permeability to sodium
- -both of these increase threshold for excitation

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12
Q

What are the ester local anesthetics?

A

procaine
tetracaine
benzocaine
chloroprocaine

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13
Q

What are the amide local anesthetics?

A

lidocaine
mepiracaine
bupivacaine
ropivacaine

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14
Q

Ester link is more prone to ________; esters usually have a _________ DOA

A

hydrolysis; shorter

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15
Q

Local anesthetics are _____________, available as salts to ____________

A

weak acids; increase solubility and stability

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16
Q

What determines the rate of onset and termination of action?

A

absorption to nerves

  • correlated with relative lipid solubility of uncharged form
  • reduced pH = reduced diffusion = reduced effectiveness (inflamed tissue)
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17
Q

An increase in molecular weight of R-1 and R-2 groups will do what?

A

increase potency and toxicity

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18
Q

Duration of action increases with what?

A

protein binding

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19
Q

An increase in lipid solubility leads to a ______ in potency

20
Q

Order the Lidocaine, bupivacaine, mepivacaine, and tetracaine from highest potency to least

A

tetracaine
bupivacaine
lidocaine
mepivacaine

21
Q

__________ pKa = faster time of onset

A

decreasing (getting closer to environmental pH for a given environment)

22
Q

Higher concentration = ______ speed of onset

23
Q

Great alkalization with NaHCO3 = ________ time of onset

24
Q

What are the DOA, potency, indications, and adverse effects of procaine?

A

DOA: short – 30-60 min
Potency: 1 (low)
Indications: dental procedures
ADR: hypersensitivity, cardiotoxicity

25
What are the DOA, potency, indications, and adverse effects of Tetracaine?
DOA: long -- 60-200 min Potency: 8 (high) Indications: spinal anesthesia ADR: CNS excitation/toxicity at higher concentrations
26
What are the DOA, potency, indications, and adverse effects of Benzocaine?
DOA: very short -- 5-10 min Potency: - Indications: topical anesthesia ADR: methemoglobinemia in <2 yo
27
What are the DOA, potency, indications, and adverse effects of Chloroprocaine?
DOA: short -- 30-60 min Potency: 1 (low) Indications: spinal anesthesia ADR: CNS excitation, local neurotoxicity at higher concentrations
28
Describe the metabolism of of Ester type LAs
- rapid hydrolysis of ester linkage by plasma cholinesterase - metabolites are benign (except for PABA allergy) - atypical pseudocholinesterase - high incidence of systemic toxicity
29
Why would we not use procaine?
- requires a vasoconstrictor | - no real advantage over lidocaine
30
Describe cocaine and its mode of action and toxicity
- topical ester LA; 1st used in dentistry - MOA: vasoconstrictor; inhibits reuptake of norepinephrine into adrenergic nerve terminals; intrinsic sympathomimetic - toxicity - myocardial ischemia, myocardial infarction, arrhythmias, seizures, hypertension, mania, paranoia
31
What are the DOA, potency, indications, and adverse effects of lidocaine?
DOA: short -- <60 min Potency: 2 (int.) Indications: dental procedures, nerve block ADR: CV at high concentrations; neurotoxicity at high concentrations*, methemoglobinemia
32
What are the DOA, potency, indications, and adverse effects of Mepivacaine?
DOA: moderate -- 60-120 min Potency: 1.5 Indications: spinal anesthesia, nerve block ADR: ringing of ears, blurred vision, headache
33
What are the DOA, potency, indications, and adverse effects of Bupivacaine?
DOA: long -- 120-340 min Potency: 8 (high) Indications: spinal anesthesia ADR: CV at high concentrations, increased atrial excitability*
34
What are the DOA, potency, indications, and adverse effects of Ropivacaine?
DOA: short -- 30-60 min Potency: 8 (high) Indications: spinal anesthesia ADR: N/V, headaches
35
What is the most commonly used amide type LA?
lidocaine
36
Describe Lidocaine
- liver metabolism - successive N-de-ethylations -- glycinexylidide (GX) is more toxic than the parent compound [important when lidocaine is used as IV antiarrhythmic]
37
Describe Benzocaine
- used topically; it needs 20% or greater concenrtation to be effective as local anesthetic topically - beware of PABA or sulfonamide allergy -- safer alternative may be topical lidocaine - found in OTC lotions and ointments including dental preparations - risk of methemoglobinemia with oral use
38
What is the "Bier Block"?
- circulation to the limb is blocked and LA injected into the venous vessels distal to the occlusion - nerves that travel with blood vessels will be anesthetized - useful for surgeries <1 hr on an extremity or for chronic pain - prilocaine commonly used
39
What is the most frequent clinical use of LAs?
"Bier block"
40
Describe a peripheral nerve blockade
- deliberate interruption of signals traveling along a nerve - combination of LA (lidocaine), epinephrine (constricts blood flow), steroid (reduce inflammation), and opioid - used for femoral nerve blockade and sciatic nerve blockade --- anesthetic for leg surgeries
41
Describe neuraxial anesthesia
- pertains to local anesthesia plasced around the nerves of the CNS (spinal anesthesia) - epidural space or spinal
42
What is systemic toxicity determined by?
- local blood flow: most LAs are vasodilators except cocaine - addition of vasoconstrictor - physiochemistry of LA -- increased cardiac and CNS toxicity w/ increased lipid solubility - local pH - infection
43
What are the allergic reactions associated with LAs?
- rare (PABA or sulfonamides for a few) | - *Esters are most likely to cause an allergic reaction
44
What toxicities are associated with LAs?
- respiratory acidosis and hypoxemia - cardiovascular-arrythmias and BP - treat seizures - barbituates or benzodiazepines - intralipid (20%) by IV infusion
45
How do vasoconstrictors treat toxicities of LAs?
- decrease peak plasma concentration of LA - reduces renal and systemic toxicity - decreases blood flow -- slows removal of drug from injection site - increases DOA - no effect on potency
46
What is most commonly used as a vasoconstrictor?
epinephrine
47
What is the second most commonly used vasoconstrictor?
norepinephrine (and then other proprietary vasoconstrictors)

IMSK Exam 2 (5 decks)

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