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Pharmacology Exam 4 > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

What are the clinical applications of local anesthetics?

A

anesthesia, analgesia, acute and chronic pain management, decreased perioperative stress, increased perioperative outcomes, treat cardiac dysrhythmias, anti-inflammatory

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2
Q

Do axons go uni or multidirectionally?

A

action potentials propagate along the axon unidirectionally

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3
Q

How is an action potential conducted in a myelinated axon?

A

AP is conducted only at the nodes of Ranvier, skips the distance between adjacent nodes (salutatory conduction)

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4
Q

Is salutatory conduction faster or slower?

A

faster, 3 nodes of ranvier need to be blocked

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5
Q

How do LAs work?

A

reversibly bind to voltage-gated sodium channels in the nerve’s axon. block the Na channel, no entrance of na into cell=no depolarization. block propagation of AP down axon.

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6
Q

Do LAs affect the resting membrane potential?

A

no, don’t affect TP either.

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7
Q

What do LAs block?

A

Na channels, can also block voltage dependent K channels, L-type Ca channels, some-g-protein coupled receptors

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8
Q

What is the reason for the inflammatory modulating action of LAs?

A

blocking of L-type Ca channel and some g-protein coupled receptors

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9
Q

Which states do LA preferentially bind to?

A

preferably bind to activated and inactivated state

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10
Q

Do action potentials reach the threshold potential if LA are onboard?

A

no, TP never attained so can’t depolarize.

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11
Q

What is the order in which fibers are blocked?

A

B fibers, C fibers, A delta, A gamma, A beta, A alpha

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12
Q

What are the smallest fibers?

A

C-fibers, smallest are most sensitive and unmyelinated

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13
Q

What is the clinical order of loss of function?

A

1 pain, 2 temp 3 touch 4 proprioception 5 skeletal muscle tone

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14
Q

What nerves are blocked first?

A

sensory and sympathetic nerves because they are smaller. motor are blocked later because they are larger

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15
Q

What is Minimum Effective Concentration (Cm)?

A

like ED50 or MAC, minimum concentration of LA needed to produce a conduction block of an impulse

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16
Q

T/F Cm is the same for all types of nerve fibers.

A

False. Cm can be different for different nerve fibers, larger fibers need higher concentrations.

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17
Q

What does increasing the tissue pH do to Cm? And what about decreasing pH?

A

increased tissue pH decreases Cm, decreased tissue pH increases Cm

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18
Q

What does the absorption of LA depend on?

A

injection site, dose, tissue BF (increased BF=decreased DOA because more disbursement), physiochemical properties of LA, metabolism, Addition of vasoconstrictor.

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19
Q

Absorption of tissues from highest to lowest BF:

A

I Think I Can Please Everyone But Susie & Sally: IV, Tracheal, Intercostal, Caudal, Paracervical, Epidural, Brachial plexus, Subarachnoid, Subq

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20
Q

Describe the distribution of LAs.

A

site of injection determines BF, BF determines systemic absorption, systemic absorption determines brain, skeletal muscle, heart

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21
Q

Where can you inject highest LA doses?

A

subQ tissue because there is less BF.

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22
Q

How are esters biotransformed/eliminated?

A

plasma esterases then renal excretion

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23
Q

How are amides biotransformed/eliminated?

A

hepatic enzymes then renal excretion

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24
Q

What is the onset of a LA related to?

A

pKa. LAs are weak bases so when pKa lower, more nonionized form at a physiologic pH. When pKa is closer to pH of blood more molecules are lipid soluble/uncharged and able to diffuse through so onset faster.

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25
Q

What are secondary factors that affect onset?

A

dose, concentration (except choroprocaine)

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26
Q

T/F lower tissue pH=poor penetration and less effective block.

A

True.

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27
Q

How does LAST increase CNS toxicity?

A

causes respiratory depression which in turn produces hypoxia and acidosis. This increases the ionized fraction in the central circulation and decreases the ability to cross the BBB to leave the brain.

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28
Q

How can you increase onset of action from slightly acidic packaged LAs?

A

packaged LAs are slightly acidic to stabilize, increased concentration of ionized/water soluble form. Add Sodium bicarb to LA mixture which will increase pH solution, increasing conc of nonionized lipid soluble portion. This causes more rapid onset of action.

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29
Q

Which type of block is it most effective to add sodium bicarb?

A

most effective in epidural blocks, least in PNB

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30
Q

What is potency of LA related to?

A

lipid solubility. more lipid soluble drug=easier to diffuse through so more drug inside nerve=more molecules available to bind receptor

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31
Q

What are secondary factors affecting potency of LAs?

A

intrinsic vasodilating effects, greater vasodilating effect=faster vascular uptake and less potent

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32
Q

What is DOA of LA related to?

A

protein binding. LA are weak bases that bind to AAG with secondary albumin binding.

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33
Q

What are the 3 things that happen after injection of LA?

A

Penetrate epineurium to provide local anesthesia, Diffuse away (eliminated), Bind to tissue proteins (reservoir)

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34
Q

What are secondary factors affecting DOA of LAs?

A

lipid solubility (increased solubility=increased DOA), Intrinsic vasodilating effect (increased rate of vasc uptake=decreased DOA, addition of vasoconstrictors (increase DOA by decreasing ability to diffuse away)

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35
Q

What are the low potency, short DOA LAs?

A

procaine, chloroprocaine (Pretty Chunky can only run for short time)

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36
Q

What are intermediate potency and DOA LAs?

A

Mepivicaine, Lidocaine (MiddLe can run moderate time)

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37
Q

What are high potency, long DOA LAs?

A

Bupivacaine, Ropivacaine, Tetracaine (BERT is best, BERT can run for a long time)

38
Q

Which type of LA is more stable with less allergic reactions?

A

Amino Amides

39
Q

What are some ester local anesthetics?

A

(one i) procaine, tetracaine, chloroprocaine

40
Q

What are some amide local anesthetics?

A

(two i’s) lidocaine, mepivacaine, prilocaine, bupivacaine, ropivacaine, levobupivacaine, liposomal bupivacaine

41
Q

What ester LA is the earliest injectable LA?

A

Procaine

42
Q

What ester LA has the potential for increased nausea with spinal use?

A

procaine

43
Q

What ester LA has instability and potential for hypersensitivity reaction?

A

procaine

44
Q

What ester LA is used commonly for spinal anesthesia?

A

tetracaine

45
Q

What ester LA is more slowly metabolized than procaine and chloroprocaine?

A

tetracaine

46
Q

What ester LA is rarely used for epidurals or PNBs d/t slow onset/profound motor blockade and potential for toxicity?

A

tetracaine

47
Q

What ester LA is a popular epidural anesthetic with a short duration?

A

chloroprocaine

48
Q

What ester LA undergoes rapid hydrolysis with minimal risk to a fetus?

A

chloroprocaine

49
Q

What ester LA is often used to quickly load epidural for c-sections in crisis?

A

chloroprocaine

50
Q

What ester LA has concern from neurologic injury with high doses in intrathecal space?

A

chloroprocaine

51
Q

What amide LA is the most commonly used/most versatile?

A

lidocaine

52
Q

What amide LA has potential neurotoxicity (cauda equina syndrome)?

A

lidocaine, continuous spinal anesthesia also chloroprocaine in high doses/low pH/preservative sodium metabisulfite

53
Q

What amide LA has risk for Transient Neurologic Symptoms (TNS) via spinal route?

A

lidocaine

54
Q

How do lidocaine and mepivacaine differ?

A

mepivacaine has less vasodilation, slightly longer DOA, similar uses but ineffective as topical LA, and lower incidence of TNS

55
Q

What amide LA has a metabolite ortho-toludine?

A

prilocaine. has limited clinical acceptance

56
Q

What does ortho-toludine do?

A

convert Hgb to methemoglobin leading to methemoglobinemia

57
Q

How do you treat LA induced methemoglobinemia?

A

may spontaneously subside, can be reversed with methylene blue 1-2mg/kg over 5 min

58
Q

What amide LA has high-quality sensory anesthesia relative to motor blockade?

A

bupivacaine

59
Q

What amide LA is most commonly used LA for labor epidurals and Postop pain management?

A

bupivacaine

60
Q

What amide LA is common for PNBs and spinals?

A

bupivacaine

61
Q

What amide LA can have refractory cardiac arrest if accidental IV injection?

A

bupivacaine, 0.75% no longer recommended for epidural use

62
Q

Which amide LA do you dilute solutions to decrease concern for cardiotoxicity?

A

bupivacaine, relates to interactions with cardiac ion channels. fast in, slow out of cardiac muscle

63
Q

What amide LA is an S - enantiomer of the homolog of mepivacaine and bupivacaine?

A

ropivacaine

64
Q

How do ropivacaine and bupivacaine compare?

A

ropivacaine has less cardiotoxic effects and greater vasoconstriction, also has lower lipid solubility/less potent than bupivacaine

65
Q

What amide LA has a less pronounced motor block but preferentially blocks C fibers which can produce a greater differential block?

A

ropivacaine

66
Q

True/false. Ropivacaine is expensive.

A

True

67
Q

Which amide LA is an s - enantiomer of bupivacaine?

A

levobupivacaine

68
Q

What is the advantage of levobupivacaine over bupivacaine?

A

less cardiotoxic, no advantage in regards to differential block.

69
Q

When do bupivacaine and levobupivacaine have a clinical advantage?

A

restricted to situations where relatively high doses of anesthetic are administered.

70
Q

How is liposomal bupivacaine delivered?

A

infiltration only, delivered by diffusion.

71
Q

What is the dose, onset, and DOA of exparel?

A

10-20ml vial of 1.33% bupivacaine, max dose 266mg
onset 15 min-2h
doa up to 72h

72
Q

True/false. You can administer other LA after exparel.

A

False. no bup for 96h, if you must, you can give lido first…wait 20 min…then exparel

73
Q

What are the adverse effects of LAs?

A

allergic reactions, direct neurotoxicity, intraneural injections, Transient Neurologic Syndrome (TNS), Methemoglobinemia, LAST

74
Q

Which type of LA is most likely to have an allergic reaction?

A

esters because they are metabolized to paraminobenzoic acid which is a known allergenic compound

75
Q

Is there cross reactivity between esters and amides?

A

no

76
Q

What happens in cauda equina syndrome (CES)?

A

Bowel/bladder dysfunction with bilateral LE weakness and sensory impairment of varying degrees.

77
Q

What causes cauda equina syndrome?

A

supranormal doses of intrathecal LA or maldistribution of LA spread within intrathecal space

78
Q

Describe TNS.

A

back and LE pain for up to 5 days PO, burning, aching, cramp-like, and radiating pain in anterior and posterior thighs–radiate to LEs

79
Q

What can cause TNS?

A

spinal lidocaine or surgical positioning

80
Q

How can you treat TNS?

A

supportive care and NSAIDs when possible

81
Q

How does methemoglobinemia happen?

A

ferrous Hgb oxidized to ferric form, oxidized Hgb with reduced oxygen carrying capacity so curve shifts left

82
Q

What are the common causes of methemoglobinemia?

A

benzocaine, procaine, dapsone, and nitrites

83
Q

How do you treat methemoglobinemia?

A

methylene blue 1-2mg/kg over 3-10 min, greater than 50% give 2mg/kg initially, greater than 70% may require transfusion or dialysis

84
Q

What are the clinical clues of methemoglobinemia in anesthetized patients?

A

hypoxia not improving with increased FiO2, abnormal color of blood, appropriate paO2 on blood gas but low pulse ox sat, new onset cyanosis or hypoxia after ingestion of agent with oxidative properties

85
Q

What causes LAST?

A

high systemic blood levels of LA d/t inadvertent IV injection of LA, absorption of large amounts of LA, continuous infusion and accumulation of drug and metabolites over many days

86
Q

What does LAST cause?

A

depression of voltage-gated sodium, potassium, and calcium channels in excitable tissues of CNS and cardiac system, depression of inhibitory CNS neurons–>seizures, decreased cardiac contractility/arrhythmias

87
Q

What are some symptoms of LAST?

A

numbness of tongue, dizziness, tinnitus, visual problems, muscle cramps, seizures, decreased consciousness, coma, resp arrest.

88
Q

How do you treat LAST?

A

stop injecting LA, consider lipid emulsion therapy, alert bypass team, ventilate with 100%, avoid hyperventilation, control seizures with benzos, avoid large propofol doses, treat hypotension and bradycardia

89
Q

What are the doses for lipid emulsion therapy for LAST?

A

> 70KG patient: bolus 100mL of lipid emulsion 20% rapidly over 2-3 min then infusion 200-250 mL over 15-20 min. may rebolus once or twice at same dose and double infusion rate…dose max 12mL/kg

90
Q

How does each affect the DOA of LAs:

epi, opioids, dexamethasone, clonidine, dexmedetomidine?

A

epi increase DOA, opioids increase DOA and analgesia, dexamethasone increase DOA, clonidine increase DOA and anesthesia, dexmedetomidine increase DOA and anesthesia

Pharmacology Exam 4 (7 decks)

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