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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
How many nodes of Ranvier need to be blocked to achieve effect?
-at least 2, preferably 3
26
What order are the different nerve types blocked?
- B - C & A delta - A gamma - A Beta - A Alpha
27
In terms of what the nerves do, what order are they blocked?
(ATP-TP-MVP) - Autonomic - Temp - Pain - Touch - Pressure - Motor - Vibration - Proprioception
28
What Pks would have the fasts onset?
-Those closest to physiologic pH
29
What does adding bicarb to LAs do?
-Faster onset by bring pH closer to Pk.
30
What type of LAs are more widely distributed throughout the body? Why?
-Amides (Ester are broken done by pseudocholinesterase found in the blood, no chance to get to muscle and fat)
31
What order of distribution are LAs absorbed?
-Lungs → highly perfused (heart, brain) → Low perfused (muscle, fat)
32
Why is LAs such a concern for a fetus?
-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
LA potency is related to what?
-Lipid solubility
34
LA speed of onset is related to what?
- State of ionization (un-ionized) | - Lipid solubility
35
LA duration of action is related to what?
- Protein binding (greater the protein binding = greater the duration) - Lipid solubility
36
What is the fastest cleared amide? Slowest? Intermediate?
- Fastest = Prilocaine - Intermediate = Lidocaine - Slowest = Bupivacaine & Ropivicaine
37
What is the fastest cleared ester? Slowest? Intermediate?
- Fastest = Chlorprocaine - Intermediate = Procaine - Slow = Tetracaine
38
How is cocaine metabolized?
-Liver
39
What metabolite of LAs causes the majority of allergic reactions?
-PABA
40
What common local injection site contains little to no cholinesterase enzyme?
CSF
41
What things inhibit plasma cholinesterase?
- Deficiency - Liver disease - ↑ BUN - Partuients - Chemo
42
What can be used as an additive to LA to vasoconstrict the vessels around the nerves?
-Epi (found to be superior), phenylepherine, NorEpi
43
What does addition of epi to LA do? Not do?
- Limit absorption - Maintain concentration around nerves - Decrease toxicity - Can prolong lido by 1/3 - Does not effect onset
44
Which 2 local anesthetics have no vasodilator activity?
- Cocaine | - Ropivicaine
45
What are the 2 types of respiratory depression associated spinal and epidural opioid administration?
Early (fentanyl) and late (duramorph)
46
What is clonidine? What does it do for neuraxial anesthesia?
- Preservative free alpha-2 agonist | - Lengthens duration of action. (will last longer)
47
Why would neostigmine be added to LA?
-Anticholinesterase will prolong ester duration
48
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?
- Lido plain pH = 6.5, - Lido w/ Epi pH = 4.5 - Lido w/ epi wash will have faster onset
49
Why are esters more prone to allergic reaction?
-Metabolite (PABA)
50
What LA preservative is responsible for some allergic reactions?
-Methylparaben
51
Is there a cross sensitivity between ester and amides?
No
52
What are the signs of a real allergy to LA?
- Rash - Uticaria - Laryngeal edema - Can be w/ or w/o hypotension and bronchospasm
53
Describe the effects of plasma lidocaine levels?
``` 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
How do you treat LA induced seizures?
- O2 | - Benzos
55
Marcaine/bupivicaine toxicity is unique in what way?
Cardio Toxic effects long before other effects
56
Name the blood flow to tissues from fastest to slowest
In time I can please everyone but Susie and Sally - IV - Tracheal - Intercostal - Caudal - Paracervical - Epidural - Brachial Plexus - Subarachnoid - SubQ
57
What are transient neurologic symptoms? What drug is most commonly associated with it?
- Pain in lower back, but and thighs | - Lidocaine
58
What is cauda equina syndrome? What drug?
- Injury across lumbosacral plexus that can cause bowel and bladder problems and paraplegia - Lidocaine
59
What is spinal artery syndrome?
-Lower extremity paresis and sensory deficit
60
Cardiotoxicity r/t LA can cause what effect? Why?
-Profound hypotension from vascular smooth muscle relaxation and direct myocardial depression
61
How do you treat LA toxicity?
- Airway management (100% O2) - Seizure suppression (Benzos, no propofol) - Manage arrhythmias - Lipid Emulsion therapy
62
What 4 LAs can cause methemoglobinemia? What is the treatment?
- Prilo, Benzo, Ceta and Lidocaine | - Methylene blue
63
What are the low potency, short duration of action LAs?
- Procaine | - Chloprocaine
64
What is the intermediate potency/duration LAs?
-Lidocaine
65
What are the 3 high potency / long duration LAs?
- Bupivicaine - Ropivicaine - Tetracaine

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