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Pharmacology > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

What is the goal of LA administration?

A

Goal is to reduce the sensation of pain from a painful stimuli.

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2
Q

Do LA produce reversible or irreversible conduction block?

A

Reversible.

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3
Q

Which two anatomical qualities of a nerve have the greatest effect on the conduction speed?

A

The size and the degree of mylenation.

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4
Q

The ability for a LA to produce conduction blockage is dependent on two things:

A
  1. Physiochemical properties of the local anesthetic.

2. Anatomy of the nerve being blocked

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5
Q

Where are the nodes of Ranvier located?

A

The space between myelin sheaths.

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6
Q

What is saltatory conduction?

A

Electrical conduction the produces a jumping action along a nerve.
Named by the metal/non-metal reaction which is often called a salt (saltatory)

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7
Q

Do mylenated or unmylenated nerves produce a “jumping” effect of nerve impulse conduction?

A

Mylenated

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8
Q

What is faster for nerve conduction- a pushing mechanism for action potential or jumping mechanism?

A

Jumping via mylenated nerve fibers.

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9
Q

Nerve fibers are classified into three groups: what are they?

A

A
B
C

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10
Q

A Fibers are broken down into 4 sub-groups: what are they?

A

Alpha
Beta
Gamma
Delta

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11
Q

Which A fiber sub-group conducts mostly pain and temperature sensation?

A

A-Delta fibers (and A Beta Fibers)

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12
Q

Which A fiber sub-group conducts mostly touch and motor function?

A

A-Alpha fibers

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13
Q

What is proprioception?

A

Touch sensation

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14
Q

What type of fibers are autonomic nerves?

A

B Fibers

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15
Q

Between A, B, and C fibers, which conduct the fastest?

A

A>B>C

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16
Q

Which type of pain impulse is conducted by C-Fibers?

A

Slow, chronic, dull, aching type of pain.

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17
Q

Which type of fibers are the only ones that are not mylenated?

A

C-Fibers

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18
Q

Which A-fiber subgroup conducts mostly muscle spindles and reflex?

A

A-Gamma

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19
Q

Higher or lower dosages of LA produce different responses. What are they?

A

Lower dose=Autonomic fibers.
Moderate doses=Sensory (heat, cold, pressure, pain)
Higher dose= Motor

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20
Q

MOA of all LA

A

Reversibly block sodium channels

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21
Q

Where are the receptors located that LA act on?

A

Intracellular side of the nerve cell membrane.

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22
Q

What physiochemical property effects how well a LA enters the nerve fiber?

A

It’s level of lipophilicity.

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23
Q

What is required of the LA to bind to the receptor?

A

Ionization

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24
Q

How does a LA become ionized inside the nerve cell?

A

It is more acidic inside the nerve cell. For stability, the LA becomes more acidic by kicking off hydrogen once inside the nerve cell. This causes it to be able to bind to the receptor

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25
Q

What condition can cause the LA to have no or little effect?

A

In the presence of local infection, LA has difficulty working because the body tissues it is injected into is more acidic. This means it never gets to enter the nerve cell (Where the receptors are located).

26
Q

What three chemical characteristics do all LA have?

A
  1. An unsaturated aromatic ring system.
  2. An intermediate carbon group.
  3. A tertiary amine
27
Q

What does the unsaturated aromatic ring system provide of the LA?

A

Big Lipophilic body

28
Q

What are the two major differences between ester and amide linkages of LA?

A
  1. Rate/Type of metabolism.

2. Allergic potential/side effects

29
Q

Which of these is ester and which are amides?.
Procaine, chloroprocaine, etidocaine, bupivacaine, cocaine, mepivacaine, lidocaine, etidocaine, tetracaine, ropivacaine, levobupivacaine

A

Esters:
Procaine, chloroprocaine, tetracaine, cocaine.
Amides:
Lidocaine, mepivacaine, prilocaine, bupivacaine, levobupivacaine, ropivacaine, etidocaine.

30
Q

An LA that is more lipophilic, does it have a longer duration or shorter duration of effect?

A

Longer duration of effect

31
Q

Does an area of higher vascularity have shorter or longer duration of effect?

A

Shorter

32
Q

What does the addition of epinephrine provide for LA administration?

A

Can cause roughly a 25% increase in duration of action by constricting blood vessels.
It also decrease possible toxic side effects

33
Q

Why would you see less toxic side effects with epinephrine additive in LA?

A

It is being released into the blood stream more slowly and steadily.

34
Q

What is the only LA that provides vasoconstriction?

A

Cocaine

35
Q

What should you do if a patient was allergic to a LA?

A

Ask them which LA was used and use a different type (ester vs amide)

36
Q

Which two LAs are associated with increased allergic reaction related to PABA metabolite?

A

Procaine and benzocaine

37
Q

What is the metabolite associated with allergic reaction?

A

PABA- p-aminobenzoic acid

38
Q

How are amides metabolized?

A

Via liver P450 enzymes

39
Q

How are esters metabolized?

A

Via pseudocholinesterases (found in blood)

40
Q

What patient diagnosis could increase risk of toxicity of amide LA?

A

Liver dysfunction or failure

41
Q

Metabolite of prilocaine and benzocaine convert hemoglobin to what?

A

Methemoglobin

42
Q

How does methemoglobinemia do in the body?

A

It converts Fe3+ to Fe2+ which limits its ability to bind to O2.

43
Q

What is the treatment for methemaglobinemia?

A

IV Methylene blue

44
Q

What patient population has increased clinical significance of methemoglobinemia compared to a healthy patient?

A

Severely anemic.

Heart failure

45
Q

What three things can be added to LAs during administration to increase safety, quality, intensity, and duration and rate of onset of anesthesia?

A

Opioids- pain management capabilities.
Sodium bicarbonate- for injecting into more acidic environment.
Epinephrine- longer duration, better receptor binding.

46
Q

What is LAST?

A

Local Anesthetic Systemic Toxicity

47
Q

What are the two main reasons for LAST?

A
  1. Inadvertant intravascular injection.

2. Administration of excessive dose

48
Q

CV effects of LAST?

A

Initially with lesser toxic levels you will see HTN and tachycardia.
With higher toxic levels, bradycardia and eventuall asystole.

49
Q

CNS effects of LAST

A

Initially patient talks incoherently or is confused. Higher toxicity can be seizures.

50
Q

Why do all LAs depress myocardial automaticity?

A

Because they are Sodium Channel Blockers

51
Q

Which LA has highest incidence of cardiovascular toxicity?

A

Bupivacaine

52
Q

What is the main treatment LA toxicity?

A

Lipid Rescue.

53
Q

What is the recommended dose/administration of Lipid Rescue?

A

Recommended 20% intralipid administration.

54
Q

What is Transient Neurologic Symptoms (TNS)?

A

13% incidence with lidocaine.
It is not permanent (up to 10 days).
Characterized by tingling, burning, aching in lower extremities and buttocks.

55
Q

Which has higher prevalence of allergic reactions? Esters or Amides?

A

Esters

56
Q

What does EMLA stand for?

A

Eutectic Mixture of Local Anesthetics

57
Q

How long does it take for satisfactory dermal analgesia to occur with EMLA?

A

Approx 1 hour

58
Q

What is the onset of most injectable LAs?

A

Under 15mins

59
Q

Overdosage of Cocaine is treated how?

A

Administration of both Beta Blocker and Alpha Blocker

60
Q

What is the fastest type of all the nerve fibers?

A

A-Alpha

61
Q

What is the second fastest of all the nerve fibers?

A

A-Beta

Pharmacology (9 decks)

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