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Local Anesthetics Flashcards

1
Q

1884 Local anesthetics

A

cocaine introduced and used in ophthalmology and dentistry

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2
Q

Lidocaine synthesized in

A

• 1943- Lidocaine synthesized (amide)

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3
Q

First local anesthetic-

A

• Cocaine-

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4
Q

Gold standard of local anesthetics

A

Lidocaine

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5
Q

The fraction of drugs bound to proteins in plasma correlates with the

A

duration of local anesthetic activity:

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6
Q

Protein Binding from more to less

BERMeLPC

A

Bupivacaine> Etidocaine> Ropivicaine> Mepivacaine> Lidocaine> Procaine and 2-chloroprocaine

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7
Q

NO DIRECT relationship exists between

A

LA plasma protein-binding and binding to specific membrane-bound Na+ channels.

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8
Q

There is a direct correlation between

A

protein binding and lipid solubility, as there is for all drugs.

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9
Q

The MORE LIPID SOLUBLE THE DRUG, THE MORE LIKELY IT WILL

A

REMAIN IN THE LIPID-RICH ENVIRONMENT OF THE AXONAL MEMBRANE WHERE THE Na+
CHANNELS RESIDE!

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10
Q

Local anesthetics ; Water solublity

• Bases

A

• Poorly water soluble

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11
Q

LA are weak

A

Bases

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12
Q

When mixed with hydrochloric acid they

A

ionize and become water soluble (Hydrochloride)

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13
Q

Slows onset of action- LA must become

A

unionized to penetrate tissue

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14
Q

How does adding bicarbonate help LA

A

Alkalization of local anesthetic solution
• Shortens onset time
• Decreases pain on injection
• May cause precipitation of local anesthetic

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15
Q

Add NaHCO3. Will speed onset by how many minutes?

A

onset of peripheral nerve blocks & epidural blockade by 3- 5 minutes

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16
Q

Functional unit of peripheral nerves

A

Axons

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17
Q

• Extension of a centrally located neuron

A

Axon

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18
Q 
cells surround each axon and
function as support and insulation
A

Schwann cell-

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19
Q

•In unmyelinated nerves, single Schwann cells

cover

A

several axons

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20
Q

•In larger nerves the Schwann cell sheath covers ______and has several layers of lipid substance known as ________

A

covers only one axon and has several layers of a lipoid

substance known as myelin

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21
Q

• Small segments of nerve that do not contain any myelin

A

Nodes of Ranvier

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22
Q

Primary area where local anesthetics exert their action

A

Nodes of Ranvier

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23
Q

• Myelinated nerves

small vs large, impulse conduction

A
  • Larger
  • Conduct impulses faster
  • More difficult to block with local anesthetics than unmyelinated
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24
Q

How many nodes of Ranvier must be blocked to prevent nerve conduction?

A

2-3 nodes of Ranvie

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25
Q

Structures found in peripheral nerves that contain bundles of axons

A

Fasciculi

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26
Q

Components of the peripheral nerve contain 3 layers of connective tissue

A
  • Endoneurium
  • Perineurium
  • Epineurium
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27
Q

Act as barriers that local anesthetics must

penetrate in order to work

A

Layers (epineurium)

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28
Q

Resting peripheral nerves have a negative membrane potential of

A

-70 to -90 mV

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29
Q

Movement of K+ out of the cell leaves an

A

excess of negatively charged organic ions inside

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30
Q

Two opposing forces are at play(2)
• Net result is a modest movement of K+ out of the cell
Concentration gradient pushes K+

A

out of the cell while the negative charge

keeps K+ in the cell

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31
Q

This process is expressed by the

A

Nernst equation

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32
Q

• Sodium channels have 3 functional states

A

• Closed (resting)
• Open- nerve is stimulated and results in a conformational change in the proteins of the sodium channel
• Conformational change results in reversal of the membrane potential
Inactive

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33
Q

How does LA work?

A

Local anesthetics produce their effects by blocking the

sodium channels

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34
Q

Local anesthetics have a greater affinity for Na+

channels that are in the

A

open or inactive state

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35
Q

For LA to exert their actions they must

A

First penetrate the cell membrane before they produce these effects

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36
Q

For LA to exert their actions they must First penetrate the cell membrane before they produce these effects
This interaction is most likely the mechanism of
action of the drug _______which can only exist
in the uncharged form

A

benzocaine

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37
Q

What is the CM

A
  • Lowest concentration of a drug that is needed for blocking impulse propagation
  • Analogous to MAC
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38
Q

Variables that affect Cm: Increase Cm

A

Increased nerve fiber diameter
Increased myelination
Greater distance between nodes of Ranvier

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39
Q

Variables that affect Cm: DEcrease Cm

A

Increased tissue pH
High frequency of nerve stimulator
Pregnancy
Elevated temperature

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40
Q

• Three groups of nerve fibers

A 
• A
• Alpha
• Beta
• Gamma
• Delta
B
C
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41
Q

• Most myelinated

A

• A-alpha

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42
Q

Fastest conduction velocity (60-120 m/s)

A

A-ALPHA

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43
Q

Responsible for skeletal muscle tone, reflexes

A

A-GAMMA

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44
Q

Responsible for pain, temperature & touch

A

A-Delta

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45
Q

Last blocked by local anesthetics

A

A-Alpha

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46
Q

Slowest conduction (0.5-2.3 m/s)

A

C-Fibers

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47
Q

Second fibers to be blocked along with A-delta fiber

A

C fibers

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48
Q

First then second blocked

A

B fibers

A-delta and C fibers

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49
Q

Conducts pain, temperature, touch, postganglionic sympathetic neurons

A

C fibers

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50
Q

Only UNMYELINATED fibers

A

C fibers

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51
Q

• Constitute preganglionic autonomic nerves

A

B Fibers

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52
Q

Proprioception, touch, pressure

A

A-Beta

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53
Q

• Largest 15-20 microns

A

A-alpha

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54
Q

• Motor and proprioception are the last to be blocked

A

(A-alpha, beta andGamma)

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55
Q

is currently the best example of a differential block

A

Bupivicaine

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56
Q

Epidural Bupivicaine 0.125%

A

blocks autonomics, partial pain, temperature but not touch, proprioception or motor function

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57
Q

Epidural Bupivicaine 0.25% blocks

A

autonomics, pain and temperature but not touch, proprioception and moto

58
Q

Epidural Bupivicaine 0.5% blocks

A

autonomics, pain, temperature, touch

and proprioception & motor

59
Q

Blocking order

B-DcGBA

A

Blocking order
• First– B, Autonomics
• Second– A- delta, fast pain temp; C, slow pain autonomics
• Third– A-gamma, muscle tone, motor
• Fourth– A-beta, Sensory- touch, pressure
• Fifth– A-alpha, Motor, skeletal muscle

60
Q

Fast pain and temp

61
Q

muscle tone, motor

62
Q

Sensory- touch, pressure

63
Q

Motor, skeletal muscle

64
Q

slow pain autonomics

65
Q

throbbing pain & temperature

A

• C fibers-

66
Q

Sympathetic and parasympathetic preganglionic neurons are B fibers

67
Q

Myelinated nerves conduct action potentials ____________than unmyelinated nerves

A

faster than

68
Q

Larger diameter nerves conduct______than smaller diameter nerves

A

faster than

69
Q

• Local anesthetics have 3 characteristic segments

A
  • Aromatic ring (lipophilic portion)
  • Intermediate carbon group ( ester or amide)
  • Tertiary amine (hydrophilic group)
70
Q

Either an ester or an amide linkage bind the

A

aromatic ring to the tertiary amine

71
Q

Linkage characterizes the drug as either an

A

Ester

Amide

72
Q

• Esters are hydrolyzed by

A

plasma cholinesterase and to a lesser extent in the liver

73
Q

• Paraaminobenzoic acid (PABA) is a metabolite

A

hydrolysis

74
Q

Is a metabolite of hydrolysis responsible for the

higher incidence of allergic reactions in esters

A

Paraaminobenzoic acid (PABA)

75
Q

• Amides are metabolized in the

76
Q

Greater chance to accumulate and cause systemic toxicity

77
Q

• Allergic reactions are rare-

A

Allergic are rade with AMIDE< due

to preservative methylparaben-structure similar to PABA

78
Q

ph of esters range

79
Q

pH of amide range

A

Close to pH(7.4) 7.6-8.1

80
Q

Distribution of local anesthetics

A
  • Dependent on blood flow

* High initial uptake by lung

81
Q

Distriubution of LA: _________is a major factor

A

Redistribution

82
Q

LA Ultimately eliminated via

A
  • Metabolism

* Excretion

83
Q

Amide vs esters: which tend to be more widely distributed

84
Q

• Determined by Lipid solubility

85
Q

Duration of Action

•Determined by

A

Protein binding –more important

86
Q

Potency vs protein binding which is more important

A

Protein binding

87
Q

Most important determinant of onset of action of LA

A

Ionization

88
Q

Drugs with lower pKa (Amides)

A

Less ionized at physiological pH

Shorter onset of action

89
Q

Decreased tissue pH=

A

more ionized local

90
Q

Patients at high risk of poor quality anesthetic effect

A

Renal failure

Septic pt with metabolic acidosis

91
Q

*Chloroprocaine is the exception to the rule. The fast onsetof chloroprocaine may be due to the

A

high concentration that

is injected .

92
Q
  • Interventions to affect onset and duration

* Carbonation

A
  • theoretically improve the onset & intensity

of block

93
Q

• Sodium bicarbonate may reduce the

A

latency of onset and increase the duration of action

94
Q

• Results in more of the drug in the unionized state

A

Adding sodium bicarbonate

95
Q

Major limitation of bicarbonate

A

MAY FORM PRECIPITATE

96
Q

Dextran may

A

increase the duration of action

97
Q

All local anesthetics except 2 produce relaxation of vascular smooth muscle

A

except Mepivacaine & Cocaine

98
Q

LA injection•Results in an______ in blood flow to the area where drug is applied and causes (2)

A

increase
• Decrease in duration of action
• Increased potential of systemic toxicity

99
Q

Degree of VASODILATION From more to least

A

Lidocaine > procaine > Mepivacaine (none)

Bupivacaine = Etidocaine

100
Q

No vasodilation with this LA

A

Mepivacaine

101
Q

• Effects on systemic toxicity is dependent on

A
  • Total dose given
  • Concentration
  • Volume administered
102
Q

Area where the local anesthetic is applied also determines

A

the speed and

extent of systemic absorption/ toxicity

103
Q

Most to least absorption
IvTIcCauPac
EpiBraSubaSciFemSub

A

Intravenous > Tracheal > Intercostal > Caudal > Paracervical > Epidural >
Brachial Plexus > Subarachnoid/Sciatic/Femoral > Subcutaneous

104
Q

Addition of a vasoconstrictor, such as epinephrine, to the local anesthetic can

A

reduce the rate of systemic absorption

105
Q

Action of Epinephrine

A

Helps increase the concentration of drug at the site

of action, which results in a longer, more intense block and less systemic toxicity

106
Q

Epinephrine prolongs the duration of action for local infiltration, peripheral nerve block and epidural administration of

A

Procaine
Mepivacaine
lidocaine

107
Q

Epinephrine prolongs the duration of action for local infiltration & peripheral nerve blocks, but no significant effects with epidural

A

Prilocaine
Bupivicaine
Etidocaine

108
Q

Epinephrine has been proven to be the most effective agent usual concentration is

A

1:200,000 or 5 mcg/ml

109
Q

Esters are Hydrolyzed by in

A

pseudocholinesterase
• Plasma- primary route
• Red blood cells
• Liver

110
Q

Metabolite of hydrolysis responsible for allergic reactions associated with esters

A

PABA- para amino benzoic acid

111
Q

_____________ is the most toxic ester

A

Tetracaine

112
Q

leading to prolonged spinal action To terminate must diffuse out of the CS

A

No spinal cholinesterase’s

113
Q

Rate of Hydrolysis

A

• Chloroprocaine > Procaine > Tetracaine

114
Q

Plasma T ½ of both Procaine & Chloroprocaine is less

A

than

1 minute

115
Q

Factors that effect plasma cholinesterase

• Saturated

A

• Drugs that are inhibited or metabolized by plasma cholinesterase, like succinylcholine,
could reduce the metabolism of ester LA’s

116
Q

Liver disease severe enough to reduce the amount of
cholinesterase
More prone to toxicity
Exception-

A

Procaine, Chloroprocaine toxicity unlikely in pt

with liver disease

117
Q

Amide Metabolism primarily ______, affected by
•
•
Liver disease and CHF can affect the metabolism of amide LA’s
Greater chance to accumulate & cause systemic toxicity
Allergic reaction is
If occurs, most likely due to

A

in liver
Hepatic enzyme activity
• Hepatic blood flow

Rare
preservatives in preparation

118
Q

Rate of metabolism Greatest to slowest

PELMeB

A

Prilocaine > Etidocaine > Lidocaine > Mepivacaine > Bupivacaine

119
Q

Primary factors affecting rate of clearance of amide local anesthetics

A

Hepatic enzyme activity & hepatic blood flow

120
Q

Clearance is independent of

A

potency, lipid solubility, protein binding

& chemical structure

121
Q

• Sequence of LA CNS toxicity •

A
  1. Circumoral numbness •
  2. lightheadedness •
  3. Tinnitus •
  4. Visual Disturbances •
  5. Slurring of Speech •
  6. Muscle twitching •
  7. Unconsciousness •
  8. Grand mal seizures •
  9. Coma •
  10. Apnea
122
Q

LidocaineToxic Manifestations
• Plasma concentration Effect
• 1-5 mcg/ml
•

123
Q

LidocaineToxic Manifestations

• Plasma concentration Effect• 5-10 mcg/ml

A 
Circumoral/tongue numbness
Tinnitus
Systemic hypotension
Muscle twitching
Myocardial depression
124
Q

LidocaineToxic Manifestations

• Plasma concentration Effect• 10-15 mcg/ml

A

Seizures

Unconsciousness

125
Q

LidocaineToxic Manifestations

• Plasma concentration Effect 15-20 mcg/ml

A

•Apnea, Coma

126
Q

LidocaineToxic Manifestations

• Plasma concentration Effect >25 mcg/ml

A

Cardiovascular collapse

127
Q

Midazolam 5-10 minutes prior to local anesthetic injection can help prevent
Vigilance! Monitor EKG, BP, SPO2 continuously
Communicate with the patient to observe for S/S of
toxicity

A

he CNS toxicity of LA’s

128
Q

• Use agents less likely to cause toxicity (3)
produce limited systemic toxicity due
to short distribution & elimination ½ time

A

• Lidocaine, Prilocaine & chloroprocaine

129
Q

• Aspirate syringe before injection- watch for

A

blood or CSF

130
Q

syringe before injection

A

• Aspirate

131
Q

• Acid- Base status of patient

A

Respiratory & metabolic acidosis= increased risk for toxicity- causes less
protein binding and more free drug available
• Alkalosis = decreased risk

132
Q

Elevation of carbon dioxide tension causes

A

cerebral dilation which leads to more drug being delivered to the brain

133
Q

At 1st sign of toxicity have pt

A

voluntarily hyperventilate- will

decrease transfer of agent into cells

134
Q

Acute lowering of the CO2 tension may also

A

lower the seizure threshold

135
Q

CNS Toxicity Treatment

are the primary concern

A

• Seizures

136
Q

Seizure First intervention- maintain

A

patent airway and oxygenate pt

137
Q
  • If hypotension occurs and is unresponsive to conservative treatment
  • Vasopressor may be necessary
A
  • Ephedrine 15-30 mg is usually drug of choice

* Atropine 0.4 mg can be used to treat bradycardia

138
Q

CNS toxicity and seizures

Succ

A

Use of ultra short muscle relaxant such as succinylcholine can help control the convulsive state
Will not stop seizures
Will stop muscle contractions
May need immediate intubation

139
Q

Cardiovascular Toxicity

•Related to the

A

potency of the drug

140
Q

Cardiovascular Toxicity •Related to the

A

potency of the drug

141
Q

Peripheral effects of the local anesthetics are biphasic
• At lower concentrations LA’s
• Increased doses cause
•

A
  • vasoconstrict
  • increase SVR

Vasodilation
• Possible hypotension

SRNA3Regional (17 decks)

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