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Pharmocology > LOCAL ANESTHETICS > Flashcards

LOCAL ANESTHETICS Flashcards

1
Q

In what order do Local anesthetic block nerve transmission:

A

Autonomic blockade —> Somatic Sensory blockade —> Somatic motor blockade

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2
Q

What can you expect in an autonomic blockade?

A

Hypotension

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3
Q

What is an advantage of a somatic motor blockade?

A

Usually a downside but sometimes can be advantageous depending on the surgery.

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4
Q

How are LAs administered?

A
  1. Infiltrated around the nerve
  2. Applied topically to skin or mucous membrane
  3. Injected into blood vessel (exsanguinate first)
  4. Injected into subarachnoid/epidural space
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5
Q

What is a Bier Block?

A

Exsanguination of a limb via a tourniquet followed by injection of a large volume of local anesthetic. Tourniquet removed after surgery.

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6
Q

What does the Dorsal Nerve Roots contain?

A

Dorsal root ganglia, cell bodies of Affernt (sensory) neurons.

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7
Q

What does the Ventral NErve Root contain?

A

Efferent fibers (motor)

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8
Q

What is a myelinated nerve fiber?

A

A Schwann-cell wraps itself around the axon several times.

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9
Q

What is the myelin sheath?

A

A lipid insulated barrier that increases the speed of conduction by decreasing capacitance and resistance.

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10
Q

Where does the LA access the nerve?

A

At the Node of Ranvier.

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11
Q

How many nodes must be hit to block a nerve?

A

3 nodes.

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12
Q

Is it harder to block a large or small nerve?

A

Large motor nerve is harder to block.

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13
Q

What is an unmyelinated nerve fiber?

A

A single Schwann cell surrounds several axons.

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14
Q

What is the difference between myelinated vs unmyelinated fiber conduction?

A

Propagation of impulse is SIMILAR in both.
Unmyelinated fiber impulses travel CONTINUOUSLY.
Myelinated fiber conduction is SALTATORY (50x faster) “leaps” from node to node.

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15
Q

What are the three states of an ion channel?

A

inactivated, activated open, rested closed.

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16
Q

How do ions move across a barrier?

A

Along a concentration gradient

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17
Q

What ion is responsible for setting a resting membrane potential?

A

Potassium

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18
Q

How does conduction velocity relate to nerve fiber diameter?

A

Larger diameter leads to higher conduction velocity.

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19
Q

List fibers A, B, C in order of size

A

A>B>C

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20
Q

Describe A fibers

A

Myelinated, 1-22 microns subdivided into alpha, beta, gamma, delta.
The FASTEST conducting fiber.

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21
Q

Describe B fibers

A

Myelinated 1-3 micrometers

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22
Q

Describe C fibers

A

Unmyelinated, 0.1-2.5 micrometers. Slowest conduction.

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23
Q

Which peripheral nerve fiber is the hardest to block?

A

A-alpha (motor & proprioception), largest in size.

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24
Q

What do the A-beta nerves do?

A

Motor, touch, pressure

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25
Q

What do A-delta nerve fibers do

A

Pain, temperature, touch

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26
Q

A-gamma?

A

Motor/muscle tone.

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27
Q

What are B-fibers?

A

Pre-ganglion is autonomic

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28
Q

What do C-fibers do?

A

DULL pain, temp, touch, POST ganglion is autonomic

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29
Q

Large fibers have the highest conduction velocity and ___ (lowest/highest) threshold for excitability

A

Lowest

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30
Q

Clinically:

Sensitivity of nerve to LA is ___ (directly/inversely) related to size.

A

Inversely

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31
Q

In lab:

Large A-delta and gamma fibers are ___ (more/less) sensitive to LA than C (unmyelinated and small)

A

More

32
Q

What contributes to the differences seen in clinical and lab theories?

A

An atomic issues, variable activity in diff nerves, variable ion channel mechanisms

33
Q

What is frequency/use dependent blockade?

A

More frequently the nerve cycles through action potential, the more rapidly blockade occurs.

34
Q

What affects spread of local anesthetic?

A

LOCATION, LOCATION, LOCATION

35
Q

What is the outer surface of a peripheral nerve called?

A

Mantle (serve more proximal structures)

36
Q

What is the Core?

A

Inner surface of peripheral nerve. Serve more distal structures.

37
Q

What is the clinical sequence of local anesthesia?

A 
1 - sympathetic block - vasodilation
2 - loss of pain, temp sensation
3 - loss of proprioception
4 - loss of touch and pressure
5 - motor blockade
38
Q

How can you check if you have bilateral blockade?

A

Touch both feet. Check for warmth from both feet (sympathetic block causes dilation —> warm skin)

39
Q

How does a nerve block happen on an ion channel level?

A

Prevention of VGNa conductance by binding to these channels in an INACTIVATED-CLOSED state - physically obstruct the channel by binding to the internal H gate.

40
Q

What happens to the sodium channels once the LA has bound?

A

Stabilize the channel in an inactivated-closed state. Act as an Inverse Agonist.

41
Q

During what phases of the channel cycle can the LA access the Na channels?

A

In the “Activated-open” - just flow through open gate.

In the inactivated-closed state.

42
Q

How does lipid solubility affect onset?

A

Higher lipid solubility = faster onset = MORE POTENT = longer DOA.

43
Q

What are the classifications of Local anesthetic chemical structures?

A

Aminoamides + Aminoesters

44
Q

What does a typical molecule consist of?

A
  • Lipophilic head (aromatic ring)
  • intermediate chain with an amide (NH) or ester (COO)
  • Hydrophilic tail (tertiary amine)
45
Q

Why do we prefer Amides over Esters?

A

Esters are highly allergic

46
Q

HOw do you identify a LA as an amide?

A

“ i “ in the name before the -Caine part

47
Q

How are esters metabolized?

A

Hydrolyzed by non-specific esterases in plasma and tissues. QUICK

48
Q

How are amide metabolized?

A

In liver through biotransformation. SLOWER

49
Q

What has greater risk for toxicity? Amide or ester

A

Amides. Esters are short acting and hydralyzed very quickly = less toxicity because its harder to build up.

50
Q

How can you increase potency of a LA?

A
  • lipid solubility
  • inc length of intermediate chain
  • inc length of terminal groups on the tertiary amine and aromatic ring
  • enantiomers of a chiral drug vary
51
Q

What is Cm?

A

Minimum concentration needed to block nerve fiber.

52
Q

What influences Cm?

A
  • Nerve fiber diameter (nodes are further apart… need 3 to block)
  • motor nerve > sensory
  • tissue pH - ion trapping
  • Frequency of nerve stimulation
  • potency of particular LA
53
Q

What is Exparel Rx?

A

Extended release bupivacaine liposome injection.

54
Q

What are some things to consider with Exparel?

A

DO NOT MIX with any other local at same site.
Max dose: 266 mg or 20 ml.
May cause toxicity

55
Q

Forms of drug delivery systems

A

Liposomes
Cyclodextrins
Biopolymers

56
Q

About how long is a blockade of three nodes?

A

1cm along a myelinated fiber

57
Q

What is the benefit of using BUpivacaine?

A

Produces differential block. Sensory block with incomplete motor block.

58
Q

What is a differential nerve block?

A

Blocks pain conducting fibers without completely blocking motor fibers.

59
Q

What are the pain conducting fibers

A

A-delta, C

60
Q

What are the motor nerves?

A

A-alpha, beta, gamma

61
Q

What governs absorption of a LA?

A
  • Physiochemical characteristics
  • physical conditions at site of deposit
  • volume solt’n
  • vehicle used (epi)
  • concentration
62
Q

What are physiochemical factors afffecting LA absorption?

A

PKA, pH, lipid solubility

63
Q

What are physiologic conditions affecting LA absorption?

A
  • tissue pH (infection),
  • pCO2, Temp (cold vs hot;
  • vasoconstriction vs dilation),
  • patient characteristics (age, pregnancy)
64
Q

What is one thing that affects absorption in a specific area?

A

Vascularity!

65
Q

What has the highest rate of absorption?

A

IV

66
Q

Why is the intercostal space have such high absorption?

A

The nerve is VERY close to the artery and vein, vascular area

67
Q

What has the lowest absorption rate?

A

Subcutaneous tissue

68
Q

Which form (nonionized or ionized) binds a receptor inside the Na channel causing a blockade?

A

The Unionized diffuses across membrane & The Ionized form binds to receptor.

69
Q

How does ion trapping happen in the fetus-mother?

A

LA are weak bases, they will always favor ionization. once the unionized form enters the fetus it ionizes. The LA in the mother re-equilibriums and becomes non-ionized again —> goes into fetus —> ionizes.

70
Q

All local anesthetic are weak ___

A

Bases, pKA 7.5-9

71
Q

Why are some LA packaged in acidic formulations?

A

For stability and to preserve Epi.

72
Q

What is the idea pKA of a LA?

A

7.4

73
Q

In areas of High/normal pH, rate of LA absorption is _____ (hi/low)

A

Higher.

74
Q

At lower pH, the rate and amt of absorption of LA is ___ (hi/low)

A

Lower

75
Q

What is different about Chloroprocaine

A

It’s the exception to the rule, even though it has A LOW % unionized (2%) it has a very FAST onset… this is because it is not potent so WE give it in HIGH CONCENTRATION

Pharmocology (3 decks)

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