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AAN2 > Class 6 Local Anesthetics > Flashcards

Class 6 Local Anesthetics Flashcards

1
Q

What do local anesthetics do?

A

produce reversible conduction blockade of impulses along the central and peripheral nerve pathways

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2
Q

What portion of the chemical structure of a local anesthetic is lipophilic? Hydrophilic?

A
  • Benzene Ring = Lipophilic

- Quaternary Amine = Hydrophilic

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3
Q

How are the chemical structures of Amides and Esters different?

A 
Ester = -CO-
Amide = -NHC-
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4
Q

What inactivates amides?

A

-P450 (hepatic metabolism)

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5
Q

What metabolize Esters?

A

-hydrolysis by plasma cholinestesterase

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6
Q

What form of the the local anesthetic can cross the lipid membrane and gain access to the cell?

A

-Un-ionized (neutral)

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7
Q

What form of the local anesthetic blocks the Na channel?

A

-Ionized form

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8
Q

What is the left and right enentiomers called?

A
  • Left = Sinister (S)

- Right = Rectus (R)

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9
Q

What does a racemic enantiomer mean?

A

-Equal number of S (sinister/Left) and R (Rectus/Right) enantiomers

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10
Q

What are the pure isomers?

A

-Substance containing only one type of enantiomer (Only S or only R)

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11
Q

What are two examples of pure isomers?

A

-Ropivacaine and Levobupivacaine

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12
Q

What is the benefit of S (sinister/Left) enantiomers?

A

-Less neuro and cardio toxic

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13
Q

Explain how LAs work?

A

-Inhibit Na ion passage through Na channels

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14
Q

What 3 things will LAs do?

A
  • Slow rate of depolarization
  • Will not allow threshold to be met
  • No action potential propagated
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15
Q

What 2 things do LAs not alter?

A
  • Resting membrane potential

- Threshold potential

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16
Q

What sodium channel subunit do LAs bind to?

A

-Alpha

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17
Q

Na receptors need to be in what state in order for LAs to bind to it

A

-Inactivated or open state

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18
Q

Do LAs bind to internal or external part of Na channel?

A

-Both (but internal thought to be most important)

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19
Q

T/F LAs binding to Na channel is a strong bond.

A

False (weak)

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20
Q

What nerves get a faster blockade, frequently used or rarely used and why?

A

-Nerve must be in an open state to be affected by LA, thus the more it is open the more LA can work

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21
Q

What factors increase the concentration minimum (Cm) need for adequate blockade?

A

-Larger diameter nerves need more LA to produce effect

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22
Q

What factors decrease concentration minimum (Cm) needed for adequate blockade?

A
  • Higher frequency

- Higher pH

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23
Q

How does Cm differ from sensory block to motor block?

A

-Twice the Cm is needed for a motor block compared to sensory

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24
Q

How does Cm differ from spinal to epidural?

A

-Same concentration, just more amount needed for epidural

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25
Q

How many nodes of Ranvier need to be blocked to achieve effect?

A

-at least 2, preferably 3

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26
Q

What order are the different nerve types blocked?

A
  • B
  • C & A delta
  • A gamma
  • A Beta
  • A Alpha
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27
Q

In terms of what the nerves do, what order are they blocked?

A

(ATP-TP-MVP)

  • Autonomic
  • Temp
  • Pain
  • Touch
  • Pressure
  • Motor
  • Vibration
  • Proprioception
28
Q

What Pks would have the fasts onset?

A

-Those closest to physiologic pH

29
Q

What does adding bicarb to LAs do?

A

-Faster onset by bring pH closer to Pk.

30
Q

What type of LAs are more widely distributed throughout the body? Why?

A

-Amides (Ester are broken done by pseudocholinesterase found in the blood, no chance to get to muscle and fat)

31
Q

What order of distribution are LAs absorbed?

A

-Lungs → highly perfused (heart, brain) → Low perfused (muscle, fat)

32
Q

Why is LAs such a concern for a fetus?

A

-Fetus has lower pH, which means more LA will be ionized once in the fetus and be unable to cross back to maternal circulation

33
Q

LA potency is related to what?

A

-Lipid solubility

34
Q

LA speed of onset is related to what?

A
  • State of ionization (un-ionized)

- Lipid solubility

35
Q

LA duration of action is related to what?

A
  • Protein binding (greater the protein binding = greater the duration)
  • Lipid solubility
36
Q

What is the fastest cleared amide? Slowest? Intermediate?

A
  • Fastest = Prilocaine
  • Intermediate = Lidocaine
  • Slowest = Bupivacaine & Ropivicaine
37
Q

What is the fastest cleared ester? Slowest? Intermediate?

A
  • Fastest = Chlorprocaine
  • Intermediate = Procaine
  • Slow = Tetracaine
38
Q

How is cocaine metabolized?

A

-Liver

39
Q

What metabolite of LAs causes the majority of allergic reactions?

A

-PABA

40
Q

What common local injection site contains little to no cholinesterase enzyme?

A

CSF

41
Q

What things inhibit plasma cholinesterase?

A
  • Deficiency
  • Liver disease
  • ↑ BUN
  • Partuients
  • Chemo
42
Q

What can be used as an additive to LA to vasoconstrict the vessels around the nerves?

A

-Epi (found to be superior), phenylepherine, NorEpi

43
Q

What does addition of epi to LA do? Not do?

A
  • Limit absorption
  • Maintain concentration around nerves
  • Decrease toxicity
  • Can prolong lido by 1/3
  • Does not effect onset
44
Q

Which 2 local anesthetics have no vasodilator activity?

A
  • Cocaine

- Ropivicaine

45
Q

What are the 2 types of respiratory depression associated spinal and epidural opioid administration?

A

Early (fentanyl) and late (duramorph)

46
Q

What is clonidine? What does it do for neuraxial anesthesia?

A
  • Preservative free alpha-2 agonist

- Lengthens duration of action. (will last longer)

47
Q

Why would neostigmine be added to LA?

A

-Anticholinesterase will prolong ester duration

48
Q

What has a higher pH premixed Lido w/ Epi, or Plain Lido? What will work faster Lido w/ Epi or plain Lido w/ epi wash?

A
  • Lido plain pH = 6.5,
  • Lido w/ Epi pH = 4.5
  • Lido w/ epi wash will have faster onset
49
Q

Why are esters more prone to allergic reaction?

A

-Metabolite (PABA)

50
Q

What LA preservative is responsible for some allergic reactions?

A

-Methylparaben

51
Q

Is there a cross sensitivity between ester and amides?

A

No

52
Q

What are the signs of a real allergy to LA?

A
  • Rash
  • Uticaria
  • Laryngeal edema
  • Can be w/ or w/o hypotension and bronchospasm
53
Q

Describe the effects of plasma lidocaine levels?

A 
1-5 = Analgesia
5-10 = Circumoral numbness, tinitus, muscle twitch, hypotension, myocardial depression
10-15 = Seizures/Unconsciousness
15-25 = apnea/coma
>25 = CV depression
54
Q

How do you treat LA induced seizures?

A
  • O2

- Benzos

55
Q

Marcaine/bupivicaine toxicity is unique in what way?

A

Cardio Toxic effects long before other effects

56
Q

Name the blood flow to tissues from fastest to slowest

A

In time I can please everyone but Susie and Sally

  • IV
  • Tracheal
  • Intercostal
  • Caudal
  • Paracervical
  • Epidural
  • Brachial Plexus
  • Subarachnoid
  • SubQ
57
Q

What are transient neurologic symptoms? What drug is most commonly associated with it?

A
  • Pain in lower back, but and thighs

- Lidocaine

58
Q

What is cauda equina syndrome? What drug?

A
  • Injury across lumbosacral plexus that can cause bowel and bladder problems and paraplegia
  • Lidocaine
59
Q

What is spinal artery syndrome?

A

-Lower extremity paresis and sensory deficit

60
Q

Cardiotoxicity r/t LA can cause what effect? Why?

A

-Profound hypotension from vascular smooth muscle relaxation and direct myocardial depression

61
Q

How do you treat LA toxicity?

A
  • Airway management (100% O2)
  • Seizure suppression (Benzos, no propofol)
  • Manage arrhythmias
  • Lipid Emulsion therapy
62
Q

What 4 LAs can cause methemoglobinemia? What is the treatment?

A
  • Prilo, Benzo, Ceta and Lidocaine

- Methylene blue

63
Q

What are the low potency, short duration of action LAs?

A
  • Procaine

- Chloprocaine

64
Q

What is the intermediate potency/duration LAs?

A

-Lidocaine

65
Q

What are the 3 high potency / long duration LAs?

A
  • Bupivicaine
  • Ropivicaine
  • Tetracaine

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