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Advanced Pharm > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

Local anesthetics definition

A

Drugs that reversible block conduction of electrical impulses along nerve fibers

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2
Q

Schwann cells

A

Support and insulate each axon

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3
Q

What type of cells surround each axon

A

Schwann cells

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4
Q

Unmyelinated nerves and Schwann cells

A

Small nerves, single Swann cells cover several axons

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5
Q

Myelinated nerves and Schwann cells

A

Larger nerve, Schwann cell covers only one axon and has several concentric layers of myelin

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6
Q

nodes of ranvier

A

Periodic segments between Schwann cells along the axon that do not contain myelin

There are VGNa channels in these segments and are the primary site of LA action - action potentials jump from nerve to nerve aka saltatory conduction

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7
Q

What is saltatory conduction

A

APs jump from nerve to nerve via nodes of ranvier

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8
Q

How many nodes must LAs inhibit VGNa channels in to block impulses

A

Three successive nerves

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9
Q

What are bundles of axons called

A

Fasiculi

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10
Q

What are the layers of the connective tissue that cover fasciculi

A

There are 3
Endoneurium - thin, delicate collagen that embeds the axon in the fascicule
Perineurium - consists of layers of flattened cells that binds groups of fascicules together
Epineurium - surrounds the perineurium and is composed of connective issue that holds fascicles together to form a peripheral nerve

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11
Q

Falyar’s explanation of the neuriums

A

The endoneuriums surround individual axons

The perineurium binds fasicicles together

The epineurium holds all of those bundles of fascicles together to form a peripheral nerve

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12
Q

RMP of axon

A

-70mV to -90mV

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13
Q

What physiologic mechanisms help create RMP

A

Na-K pump in axolemma

Intracellular K ratio of 30:1

Membrane impermeable to other ions

Excess of negatively charged ions in axoplasm

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14
Q

Nernst equation

A

Expresses the charge created by K+ concentration gradient

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15
Q

What charge puts VGNa into active states (end of depol)

A

20mV

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16
Q

What restores RMP

A

NA - K pump

3 Na’s leave for each 2 K’s that enter

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17
Q

LA mechanism of action

A

Bind to VGNa channels preferentially to those in open, inactive states

They also block K, Ca, and GPCRs to a lesser extent

This blocks transmission of nerve impulses

They DO NOT alter the RMP or threshold potential

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18
Q

Modulated receptor hypothesis of LA action

A

Preference to attach during active or inactive states

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19
Q

Frequency dependent blockade

A

Resting nerve is less sensitive to LA than one repeatedly stimulated

AKA = use-dependent or phasic block

“Works better when its doing something”

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20
Q

Are LAs acids or bases? And describe the mechanism of how they enter the cell

A

All LAs are weak bases

Unionized (unprotonated) base form of the LA diffuses through cell membrane and then becomes re-ionized once inside cell and is able to attach to the inner portion of the VGNa channel

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21
Q

Which type of nerves to LAs preferentially bind to

A

Smaller, unmyelinated nerves

Aka larger, myelinated nerves are harder to block

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22
Q

Differential blockade order?

A

Preganglionic (think sympathetic nerves) are blocked first, followed by small C fibers and small A fibers

= loss of pain and temp

Touch and proprioception can still be present

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23
Q

Type A - Alpha fiber characteristics

A

Proprioception, motor
Diameter = 6-22 um
Heavy myelination
Last to be blocked

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24
Q

Type A beta fiber characteristics

A

Touch, pressure
Diameter 6-22 um
Heavy myelination
Intermediate time to block

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25
Q

Type A gamma fibers

A

Muscle tone
Diameter 3-6 um
Heavy myelination
Intermediate time to block

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26
Q

Type A delta fibers

A

Pain, cold temp, touch
Diameter 1-5 um
Heavy myelination
Intermediate time to block

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27
Q

Type B fiber characteristics

A

Preganglionic autonomic vasomotor
Diameter <3 um
Light myelination
Blocked early

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28
Q

Type C sympathetic fiber characteristics

A

Postganglionic vasomotor
Diameter 0.3-1.3um
No myelin
Blocked early

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29
Q

Type C dorsal root fiber characteristics

A

Pain, warm and cold temp, touch
Diameter 0.4-1.2 um
No myelin
Blocked early

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30
Q

Halsted

A

Recognized LA as a potential for regional and spinal anesthesia

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31
Q

Koller

A

Introduced cocaine as the first LA in 1884

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32
Q

LA used for neural blockade structure

A

3 characteristics

Unsaturated aromatic ring (lipophillic)
Tertiary amine (hydrophilic)
Ester or abide linkage that binds the aromatic ring to the carbon group (this is how we designate class)
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33
Q

List the amides

A

Look for the i!!!

Lidocaine
Mepivicaine
Prilocaine
Bupivicaine
Ropivacaine
Articaine
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34
Q

List the esters

A 
Procaine
Chloroprocaine
Tetracaine
Cocaine
Benzocaine
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35
Q

Ester LA metabolism

A

catalyzed by plasma and tissue cholinesterases via hydrolysis, rapidly occurs throughout body

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36
Q

Amide LA metabolism

A

Hepatic metab by CYP1A2 and CYP3A4 and thus a significant blood level may develop with rapid absorption

Severe hepatic disease can prolong metab of these drugs and increase risk for toxicity

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37
Q

Which of the classes of LAs have higher allergic potential

A

Esters because they break down into PABA (para aminobenzoic acid) which is an allergen

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38
Q

What is the longest acting ester LA

A

Tetracaine

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39
Q

Which of the LA classes are more lipophillic

A

Amides

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40
Q

Which of the LA classes are more protein bound

A

Amides

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41
Q

Minimum effective concentration

A

Cm

The minimum concentration of LA necessary to produce conduction blockade of a nerve impulse

Analogous to MAC

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42
Q

Cm of motor fibers in comparison to sensory fibers

A

Motor fibers are twice that of sensory fibers

Aka sensory anesthesia may not always be accompanied by paralysis

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43
Q

Do you need more or less LA for intathecal vs epidural anesthesia

A

You need less

***For epidural you give higher volume of a lesser concentration

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44
Q

What type of nerve fiber is most readily blocked

A

Pre-ganglionic B fibers

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45
Q

How can you increase onset of LA

A

Give more

46
Q

How is the effect of LA terminated

A

Systemic absorption

Places that are more highly vascularized will last for less time

47
Q

What increases risk of toxicity of LA

A

Faster absorption aka highly vascularized area

48
Q

Good falyar tip for injecting local

A

Only inject 5ml at a time and aspirate before you inject

49
Q

If an LA is more lipid soluble, what other characteristics would you expect

A

Increased protein binding
Increased potency
Longer duration of action
Tendency for severe cardiac toxicity

50
Q

What plasma proteins do LAs bind to?

A

Alpha1-acid glycoproteins

To a lesser extent - albumin

51
Q

Basic drugs become more ionized in what type of solution

A

A solution where pH is less than pKa

52
Q

Do drugs with a pKa closer to physiologic pH have a faster or slower onset

A

Faster

53
Q

Physiochem properties of Procaine

A 
Pka: 8.9
% ion @ pH 7.4: 97
% protein bound: 6
Onset: slow
DoA: 60-90
54
Q

Onset and doa of chloroprocaine

A

This one doesn’t intuitively make sense but falyar said its due to the high concentration you give he also said it has a similar profile to procaine but he didn’t list the numbers

Onset: fast
DoA: 30-60

55
Q

Physiochem props of tetracaine

A 
Pka: 8.5
% ion @ pH 7.4: 93
% protein bound: 94
Onset: slow
DoA:180-600 min
56
Q

Physiochem props of lidocaine

A 
Pka: 7.9
% ion @ pH 7.4: 76
% protein bound: 64
Onset: fast
DoA: 90-120min
57
Q

Onset and doa of mepivicaine

A

Onset: fast
DoA: 120-240 min

58
Q

Onset and doa of ropivicaine

A

Onset: slow
DoA: 180-600 Min

59
Q

Physiochem props of bupivacaine

A 
Pka: 8.1
% ion @ pH 7.4: 83
% protein bound: 95
Onset: slow
DoA: 180-600 mins
60
Q

Vasomotor action of LAs and exceptions

A

LA causes relaxation of smooth muscle

Exceptions = lidocaine, ropivacaine, cocaine

Relaxation = vasodilation = decreased doa and increased plasma concentration aka potential toxicity

61
Q

Rank the uptake of LAs based on regional technique from highest to lowest

A 
IV
Tracheal
Caudal
Paracervical
Epidural 
Brachial
Sciatic 
Subq
62
Q

Why do we add epi to LA

A

It’s a vasoconstrictor that decreases rate of vascular absorption

Increased duration and potency of block
Decreased risk of systemic toxicity

63
Q

Sodium bicarbonate with LAs

A

Raises pH of LA solution resulting in more drug in the non-ionized state

May result in less pain on injection

Limitation: precipitation can occur

64
Q

When LA is being distributed, where does it go first

A

Brain, heart, lungs receive most initially

Risk for toxicity

Then muscle and it receives most

65
Q

How does renal dysfunction affect LAs

A

Affects clearance but far less than hepatic failure

But it will affect protein binding

66
Q

Changes in pregnancy

A

Mechanical - reduction in epidural spaces

Hormonal - progesterone levels affect LA sensitivity

67
Q

Local anesthetic systemic toxicity (LAST)

A

Most commonly occurs from an inadvertent intravacular injection

  • initial blocking of inhibitory neurons thought to cause seizures
  • blocking of cardiac ion channel = Brady or vib if severe

Presents rapidly

  • agitation, tinnitus, circumoral numbness, blurred vision, metallic taste in mouth
  • then muscle twitching, unconsciousness, seizures
  • if levels are very high = seizures and respiratory arrest

Incident rate is 0.4 per 10,000
-most commonly seen in epidural, axillary, interscalene blocks

68
Q

How to prevent LAST

A

Test dosing
Incremental injection with aspiration
Use of pharmacologic markers
Ultrasound

69
Q

treatment of LAST

A

Prompt recognition

Airway management

  • suppress seizure: benzo and succ
  • prevent hypoxia and acidosis

Lipid emulsion therapy

Vasopressors

  • epinephrine < 1mg/kg
  • no vasopressin
70
Q

Lipid emulsion dosing

A

Lipid emulsion 20% - precise volume and flow rate are not crucial

Pt > 70kg

  • bolus 100 ml rapid over 2-3 minutes
  • gtt 200-250ml over 15-20 minutes

Pt < 70 kg

  • bolus 1.5 ml/kg rapid over 2-3 min
  • gtt 0.25 ml/kg/min (ideal body weight)

Re-bolus once or twice at the same dose and double infusion rate if patient remains unstable

DOSE LIMIT = 12 ml/kg

Be aware that total volume of lipid emulsion can approach 1 L in a prolonged resuscitation (>30min)

71
Q

Lipid emulsion therapy moa

A

Capture local anesthetic in blood (lipid sink)
Increased fatty acid uptake by mitochondria
Interference of Na channel binding
Promotion of calcium entry
Accelerated shunting

72
Q

Max dose of lidocaine

A

In mg/kg

No epi: 4
Epi: 7

73
Q

Max dose of mepivacaine

A

In mg/kg

No epi: 4
Epi: 7

74
Q

Max dose of bupivacine

A

In mg/kg

No epi: 3
Epi: n/a

75
Q

max dose of ropivacaine

A

In mg/kg

No epi: 3
Epi: N/A

76
Q

Max dose of procaine

A

In mg/kg

No epi: 12
Epi: N/A

77
Q

Max dose of chloroprocaine

A

In mg/kg

No epi: 11
Epi: 14

78
Q

Max dose of prilocaine

A

In mg/kg

No epi: 7
Epi: 8.5

79
Q

Max dose of tetracaine

A

In mg/kg

No epi: 3
Epi: n/a

80
Q

Amide related allergies

A

Related to preservative

Paraben, methylparaben, metabisulfite

81
Q

Methemglobinemia

A

A conduction of high concentration of methemoglobin in blood

Ferris form of hgb converted to ferric form

Reduced oxygen carrying capacity - hypoxemia not responsive to therapy

82
Q

Which LAs can cause methemoglobinemia

A

Benzocaine - rise in cases since 2006 r/t otc spray mostly involving infants <2

Prilocaine - d/t one of its metabolites o-toluidine

  • dosing should not exceed 2.5mg/kg
  • should be avoided in children under 6, pregnancy, pts taking other oxidizing drugs
83
Q

Treatment of methemoglobinemia

A

Methylene blue 1-2 mg/kg over 3-10 minutes

High levels may require transfusion or dialysis

84
Q

Cauda equina syndrome

A

Manifests as bowel and bladder dysfunction with lower extremity weakness and sensory impairment related to cord ischemia

  • r/f includes supernormal doses of LA
  • maldistribution of LA within intrathecal space
85
Q

Transient neurologic symptoms

A

Associated with intrathecal lidocaine

Presents as burning, aching, cramp like pain in the low back and radiating down the thighs for up to five days post op

Other risk factors include lithotomy and outpatient surgery

86
Q

When was lidocaine discovered

A

1943 by nils Lofgren in sweden

87
Q

Labor epidural test dose lidocaine concentration

A

1.5% with epi 1:200,000

88
Q

Lidocaine and the ACLS algorithm

A

Why? Depress myocardial automaticity - class IB

Dose?

  • 1-1.5 mg/kg IV/IO
  • 0.5-0.75 mg/kg (refractory)
  • 3 mg/kg total
  • 1-4 mg/min or 30-50 mcg/kg/min (maintenance infusion)
89
Q

EMLA cream

A

Eutetic mix of LA

1:1 lidocaine:prilocaine

Don’t give

  • mucous membranes
  • broken skin
  • infants < 1 month
  • hx methemoglobinemia
90
Q

Why give lidocaine during induction

A

Decrease pain of prop
Attenuate CV response to intubation
Attenuate increase in ICP in patients with decreased compliance

Dose on ideal body weight

91
Q

Lidocaine and pain of propofol

A

20 mg lidocaine in 10 mL with venous occlusion for 60 seconds

92
Q

Attenuation of SNS with lidocaine

A

1.5 mg/kg IV administration 1-3 minutes prior to laryngoscopy

93
Q

Topical lidocaine (trachea)

A

Decreases emergence phenomenon aka coughing, sore throat, dysphonia

LTA - administer 30 minutes prior to extubation for best effect

Jelly

Fill cuff with low-dose alkalized lidocaine (40mg) - seeps out over time - need 60 min minutes to achieve desired effect (add bicarbonate to increase non-ionized fraction)

Or just more IV at end of case

94
Q

Technique for adding alkalized lidocaine to the ETT tube

A 
Achieve correct pressure using air
Remove and record amount of air required
Add 2ml lidocaine
Add 1-2ml sodium bicarbonate 
Add saline to match cuff volume

USE MANOMETER

Case has to last at least an hour

95
Q

Airway block

A

Nebulized lidocaine =.4% lidocaine applied directly to oropharynx

Transtracheal block - 4% lidocaine injected through the cricothyroid membrane

Higher risk of aspiration because pt cannot tell if they are even swallowing or not

96
Q

Lidocaine infusions

A

Used as part of multimodal analgesia

Bolus: 1.5 mg/kg bolus dose
Infusion: 2mg/kg/hr

Shown to reduce post op pain and speed up return of bowel function in open and laparoscopic procedures

Decreased pain and improve outcomes in prostatectomy, thoracic, and spine procedures

Accumulation is a concern so monitor patients

97
Q

Cochrane’s review on lidocaine infusion

A

Quality of evidence is limited

Benefits uncertain

98
Q

Bier block

A

IV regional anesthesia

Indicated for short procedures

25-50ml of 0.5% lidocaine injected into an IV distal to a tourniquet

Onset time 5-10 minutes

Tourniquet pain at 20 minutes

99
Q

Plasma concentration of lidocaine 1-5 ug/ml effects

A

Analgesia

100
Q

Plasma concentration of lidocaine 5-10 ug/ml effects

A 
Circumoral numbness
Tinnitus
Skeletal muscle twitching
Systemic hypotension
Myocardial depression
101
Q

Plasma concentration of lidocaine 10-15ug/ml effect

A

Seizures unconsciousness

102
Q

Plasma concentration of lidocaine 15-25ug/ml effect

A

Apnea coma

103
Q

Plasma concentration of lidocaine >25ug/ml effect

A

CV depression

104
Q

Liposomal local anesthetics: exparel

A

Injected directly into surgical site shown to reduce opioid requirements for up to 72 hours

Bupivacaine combined with liposomal agent depofoam

Lipid membranes separate chambers of bupivicaine in a honeycomb structure

105
Q

Administration of exparel

A

Single dose infiltration only

Admin with a 25g or larger bore needle

Not to exceed 266mg (20ml 1.3% undiluted drug)
- dilute up to 0.89 mg/ml (1:14 by vol)

Invert vial multiple times to re-suspend particles

Inject slowly via infiltration into surgical site with frequent aspiration

Do not admin if its not white

You will need some sort of adjunct to deliver with it because it is going to take a while to start
working - but don’t mix with lidocaine because it will break down the liposome

If you do mix it, use within 4 hours

106
Q

Exparel what not to do

A

Don’t

  • mix with non-bupivacaine LAs
  • use for OB cervical blockade
  • give to patients under a8
  • use for epidural/intrathecal
  • use for peripheral nerve block
  • administer if vial has been frozen or exposed to high temp

Do
- use caution for patients with hepatic disease

107
Q

Adverse effects of exparel

A

> 10% N/V

<10% dizzy, tachycardia, HA, somnolence, bradycardia, hypoesthesia, lethargy

108
Q

Cocaine

A

The original LA and the only one that is naturally occurring

109
Q

How does cocaine cause SNS stimulation

A

Blocks monoamine transporter in the adrenergic system which blocks reuptake of catecholamines to cause vasoconstriction

110
Q

Cocaine use

A

Primarily used for topical anesthesia of nose and throat

111
Q

Max dose cocaine

A

5ml of 5% solution

112
Q

When should cocaine be used cautiously

A

Use cautiously with other epi containing solutions, MAOi’s, tricyclics

Advanced Pharm (11 decks)

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