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Anesthesia > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Define dysesthesia.

A

abnormal or unpleasant sensation to normal stimuli

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2
Q

Define hyperesthesia.

A

excessive pain response to non-noxious stimuli

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3
Q

Define hypoesthesia.

A

decreased sensitivity to stimuli (aka numbness)

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4
Q

Define anesthesia

A

the loss of sensation caused by depression of excitation or inhibition of conduction, without inducing loss of consciousness

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5
Q

Define paresthesia.

A

altered sensation (pins and needles)

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6
Q

What are the desirable qualities we want in a local anesthetic?

A

adequate duration, no permanent nerve damage, must remove sensation, low systemic toxicity, non-irritating to tissue, reversible, has short onset, stable in solution, non-allergenic, can be sterilized w/o deteriorating

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7
Q

How many millivolts does a resting membrane potential possess? What amount is the threshold for signal conduction to occur?

A

resting membrane = -70mV

threshold = -55mV

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8
Q

What are the types of nerve fibers?

A

Types A (α, β, γ, δ), B and C. Type A are myelinated, α and β can be afferent or efferent, γ is only efferent, δ only afferent. Type B are myelinated sympathetic nerves. Type C are not myelinated

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9
Q

What are the two periods of the repolarization process of the nerve membrane?

A

Absolute refractory: Na channels are shut and conduction cannot occur.
Relative refractory: Na channels can function, but large stimulus is needed to induce conduction

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10
Q

What is impulse propagation?

A

When a stimulus causes the reversal of the membrane potential at a localized site on the unmyelinated nerve, that then spreads to adjacent areas

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11
Q

What is salutatory conduction?

A

How myelinated nerves send signals: depolarization jumps from node to node by raising the membrane potential closer to -55mV in adjacent nodes, making them easier to excite.

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12
Q

Nerve membranes are freely permeable to what two ions?

A

K+ and Cl-

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13
Q

What is the sequence of events for local anesthetics?

A

LA molecule diffuses across nerve membrane, LA displaced Ca ion from Na channel, LA binds intracellularly to Na channel, Na conduction inhibited, depolarization depressed

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14
Q

How is the effect of LA different in healthy vs. unhealthy tissue?

A

In healthy tissue the pH is ~7.4 so the LA can penetrate the nerves; In unhealthy tissue the pH is acidic, so the LA cannot penetrate the nerves and remains toxic in tissue

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15
Q

What are the two general types compounds used as local anesthetics?

A

Amino esters, and amino amides

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16
Q

How does LA distribute in the tissue?

A

It accumulates in highly perfused tissue (especially muscle), can cross the blood-brain barrier and placenta

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17
Q

What metabolizes the LA compounds? (esters and amides)

A

Esters are metabolized in blood plasma by pseudocholinesterases; Amides are metabolized in liver

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18
Q

How does methemoglobinemia occur?

A

It happens if the amino amide compound cannot be properly metabolized, and accumulates in the tissue.

19
Q

How are local anesthetics excreted from the body?

A

They’re excreted in the urine via the kidneys

*renal problems raise the risk for toxicity

20
Q

Which molecular form of the LA compound can diffuse through the nerve membrane?

A

The basic form (RN) as compared to the acid/ionized form (RNH+)

21
Q

What are the five amino ester local anesthetics?

A

Benzocaine, Procain, Chloroprocaine, Cocaine, and Tetracaine

22
Q

What are the five amino amide local anesthetics?

A

Bupivacaine, Lidocaine, Articaine, Mepivocaine, and Prilocaine
*acronym B-LAMP

23
Q

Why are vasoconstrictors important?

A

They’re crucial because they cause the vessel to constrict, allowing the LA to have longer and better action on the nerve

24
Q

What are the three common vasoconstrictors added to LAs?

A

Epinephrine, Norepinephrine, and Levonordefrin

**All catecholamines, and all act on adrenergic receptors of vascular smooth muscle

25
Q

A 1:1,000 dilution of vasoconstrictor is how much per mL?

A

1g vasocon./1000mL solution = 1mg/1mL

26
Q

A 1:10,000 dilution of vasoconstrictor is how much per mL?

A

0.1mg vasoconstrictor/1mL solution

27
Q

A 1:100,000 dilution of vasoconstrictor is how much per mL?

A

0.01mg vasoconstrictor/1mL solution

28
Q

What is the volume of the average carpule of LA?

A

normally 1.8mL/carpule

*4% Articaine is 1.7mL/carp

29
Q

What mass of anesthetic is in 1 carpule of 2% Lidocaine?

A

36mg Lidocaine/carp

(20mg/mL x 1.8mL)

30
Q

What mass of anesthetic is in 1 carpule of 3% Mepivicaine?

A

54mg Mepivicaine/carp

(30mg/mL x 1.8mL)

31
Q

What mass of anesthetic is in 1 carpule of 4% Articaine?

A

68mg Articaine/carp

(40mg/mL x 1.7mL)

32
Q

What mass of anesthetic is in 1 carpule of 4% Prilocaine?

A

72mg Prilocaine/carp

(40mg/mL x 1.8mL)

33
Q

How much LA is in one carp of 5% Bupivacaine?

A

90mg Bupivacaine/carp

(50mg/mL x 1.8mL)

34
Q

What portion of your patients will exhibit “normal” or expected effects of an LA injection?

A

about 70% will have “normal” rxn to LA

35
Q

What are the characteristics of 2% Lidocaine?

A

Onset 5min; Duration 90-120min; Max Dose 2mg/lb; Max LA 300mg/appt; Max epi 0.2mg/appt, 0.04mg/appt if CV problems; used for most pts and procedures

36
Q

What are the characteristics of 3% Mepivicaine?

A

Onset 1-4min; Duration 20-40min; Max Dose 2mg/lb; Max LA 300mg/appt; don’t give to pregnant its
safe alt to 2% Lidocaine for pts w/ CV problems or HTN

37
Q

What are the characteristics of 4% Articaine?

A

Onset 1-6min; Duration 1hr; Max Dose 3.2mg/lb; Max LA 400mg/appt; Max epi same as lidocaine

  • *don’t give to pregnant or pedo pts**
  • *penetrates bone, and used if 2% Lido isn’t working**
38
Q

What are the characteristics of 4% Prilocaine plain?

A

Onset 2-3min; Duration 20min (180 if IA block); Max Dose 2.7mg/lb; Max LA 400mg/appt

  • *can cause methemoglobinemia**
  • *alt to 2% Lido but avoid in pts with blood disorder**
39
Q

What are the characteristics of 5% Bupivacaine?

A

Onset 1-17min; Duration 2-9hr; Max Dose 0.6mg/lb; Max LA 90mg/appt

  • *avoid in pts w/ CV problems**
  • *NEVER use in kids, pregnant, or severely compromised**
40
Q

What are the color bands associated with each type of LA?

A 
2% Lidocaine = red
3% Mepivicaine = bright gold
4% Articaine = dull gold
4% Prilocaine = black
5% Bupivacaine = blue
41
Q

What are other names for the five amino amide LA injections?

A 
Lidocaine = xylocaine
Mepivicaine = carbocaine
Articaine = septocaine
Prilocaine = citanest
Bupivacaine = marcaine
42
Q

What is benzocaine used for?

A

It’s used as a topical anesthetic that you can apply to injection site prior to giving the LA injection

43
Q

What is procaine used for?

A

It’s used for dilating the vessels when peripheral blood flow has been compromised by an accidental intra-arterial injection of another LA

Anesthesia (3 decks)

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