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Anesthesia MM/TL > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

What is the resting potential of a neuron?

A

Negative 60-70

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2
Q

What does Na-K ATPase pump do?

A

Pumps 3 Na ions out for every 2 K, maintaining a negative intracellular environment

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3
Q

What ion are neurons leaky to?

A

Potassium

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4
Q

What ion does depolarization of a neuron ?

A

Voltage gated sodium channels

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5
Q

Where do local anesthetics bind?

A

The alpha subunit preventing activation and thus sodium influx

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6
Q

What happens as more local anesthetic is used?

A

The sodium channel becomes unable to conduct sodium ions and the threshold for propagation goes up

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7
Q

Why is a local anesthetic block termed “use dependent”?

A

Because the local anesthetics have a higher affinity for open or inactivated channels so the fraction of Na channels with bound local anesthetic increased with frequent depolarization

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8
Q

What other receptors may local anesthetics block?

A

Calcium
Potassium
Trpv

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9
Q

Which has a higher sensitivity to the local anesthetic- smaller or larger diameter axons?

A

Smaller

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10
Q

Which has a higher sensitivity to the local anesthetic- myelinated or unmyelinated axons?

A

Myelinated

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11
Q

What is the order of sensitivity of the neurons?

A

Autonomic > sensory > motor

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12
Q

Which neurons are unmyelinated?

A

C dorsal root (pain, temperature) and C sympathetic fibers

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13
Q

What is the structure of local anesthetics?

A

Aromatic benzene ring and a tertiary amine bound by an ester or amide

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14
Q

Are local anesthetics weak acids or weak bases?

A

Weak bases with a positive charge at the tertiary amine are physiologic ph

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15
Q

What does potency of a local anesthetic correlate with?

A

Octanol solubility

Increased by adding alkyl groups

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16
Q

What does acidity due to a block?

A

Antagonism

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17
Q

What does hypokalemia do to a block?

A

Antagonism

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18
Q

What does hypercalcemia due to a block?

A

Antagonism

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19
Q

What is pka?

A

The pKa is the ph at which the fraction of ionized and nonionized drug is equal

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20
Q

What form of local anesthetic will have a more rapid onset?

A

Nonionized because it permeates the epineurium more rapidly

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21
Q

Which form more avidly binds the Na channel?

A

The charged cation

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22
Q

What are the commercial forms of local anesthetics?

A

Hydrochloride salts with ph of 6-7

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23
Q

Why are solutions with epinephrine more acidic (ph 4-5)

A

Because epinephrine is unstable in alkaline environment

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24
Q

What does addition of sodium bicarbonate cause?

A

Speeds the onset of block and improves the quality due to more free base availability

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25
Q

What does duration of action depend on?

A

Lipid solubility and potency

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26
Q

What has a longer duration of action - lipid soluble or insoluble?

A

Soluble because they diffuse more slowly from the lipid rich environment to the aqueous bloodstream

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27
Q

What binds local anesthetics in the blood?

A

Alpha 1- acid glycoprotein

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28
Q

Which sites of injection absorb the fastest?

A

Tracheal > intercostal > paracervical> epidural > brachial plexus > sciatic > subcutaneous

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29
Q

Which organs are responsible for initial uptake of local anesthetic?

A

Brain, lung, liver, kidney, heart because these are the highly perfused organs

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30
Q

What is the alpha stage?

A

The initial uptake

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31
Q

What is the beta stage?

A

The slower redistribution to moderately perfused tissues (muscle, gut)

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32
Q

What tissue provides the greatest reservoir for distribution of local?

A

Muscle

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33
Q

How are esters metabolized?

A

By pseudocholinesterase then metabolites are excreted in the urine

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34
Q

What do procaine and benzocaine get metabolized to?

A

PABA - can cause anaphylaxis

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35
Q

What lacks esterases?

A

CSF

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36
Q

How do intrathecal blocks get terminated?

A

By redistribution into the bloodstream

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37
Q

What are the ester local anesthetics?

A

Cocaine
Procaine
Benzocaine
Tetracaine

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38
Q

How are amides metabolized?

A

By P459

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39
Q

Which amides are metabolized fastest?

A

Prilocaine > lidocaine> mepivacaine > ropivacaine > bupivacaine

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40
Q

What will decrease the metabolism of amides?

A

Cirrhosis

Decreased liver blood flow: CHF, H2 blockers, Bb

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41
Q

What does prilocaine cause?

A

Methemoglobinemia because it is metabolized to o-toluidine

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42
Q

What other local anesthetic causes methemoglobinemia

A

Benzocaine

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43
Q

How do you treat methemoglobinemia

A

1-2 mg/kg of methylene blue of 1% solution over 5 minutes

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44
Q

Are the toxic effects of local anesthetics additive or synergistic?

A

Additive

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45
Q

Why is local anesthetic toxicity of the CNS excitatory?

A

Because they preferentially block inhibitory pathways

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46
Q

What does hyperventilating do to the seizure threshold?

A

Raises it

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47
Q

How much Propofol is needed to break a seizure?

A

0.5-2 mg/ kg

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48
Q

How much does infused lidocaine decrease the MAC by?

A

40%

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49
Q

What do IV lidocaine due to the cerebral blood flow?

A

Decreases it

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50
Q

Why don’t we use lidocaine in spinal anesthesia?

A

Side effects of dysesthesia, burning pain and aching in butt and LE
Direct neurotoxicity

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51
Q

What is the max dose of lidocaine?

A

4.5 mg/kg

7 mg/kg with Epi

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52
Q

What is this max dose of mepivacaine?

A

4.5 mg/kg

7 mg/kg with Epi

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53
Q

What is the max dose of ropivacaine

A

3 mg/kg

54
Q

What is the max dose of bupivacaine

A

3 mg/kg

55
Q

What does lidocaine due to hypoxemic drive?

A

Depresses it through the medullary respiratory center

56
Q

What is apnea due to in a high spinal?

A

Hypotension

57
Q

What does lidocaine due bronchial smooth muscle?

A

Relaxes it

58
Q

What do local anesthetics do to the heart?

A 
Depresses automaticity 
Depresses contractility and conduction
Arterial vasodilation (high doses)
Inhibit nitric oxide causing vasoconstriction (low doses)
59
Q

What happens first CNS or cardiac signs of toxicity

A

CNS

60
Q

At low doses, what is th effect of local anesthetics on the CV system?

A

Inhibition of nitric oxide and therefore vasoconstriction

61
Q

What does IV administration off bupivacaine produce?

A

Severe left ventricular depression, Vt, AV block, VF

62
Q

What are the CV effects of cocaine?

A

Decreases uptake or norepinephrine so HTN, ventricular ectopic, vasoconstriction

63
Q

What can bupivacaine intoxication be treated with?

A

1.5 ml/kg lipid solution

64
Q

Which you of locals are more likely to illicit an allergic response?

A

Esters

65
Q

What are the heme effects of local?

A

Decreases platelet aggregation and thrombosis

Increases fibrinolysis

66
Q

What are the musculoskeletal effects of locals?

A

Myotoxic

Worse with steroids or Epi

67
Q

What do local anesthetics due to nondepolarizing blocks.

A

Potentiation them

68
Q

What kind of local is dibucaine?

A

Amide

69
Q

What drugs prolong local anesthetics?

A

Clonidine
Opioid
Organophosphates
Anti-acetylcholinesterase

70
Q

How does an action potential in a neuron get terminated?

A

Inactivation of voltage gated sodium channels

Potassium efflux

71
Q

What is EMLA cream?

A

Local anesthetic applied transdermally to provide anesthesia for the skin

72
Q

What does EMLA cause?

A

Methemoglobinemia secondary to prilocaine in the formulation

73
Q

What deficiency should EMLA cream not be used in?

A

G6PD deficiency

74
Q

What other drugs cause methemoglobinemia

A 
Benzocaine
Prilocaine
Quinine
Sulfa
Dapsone
Choral hydrate
75
Q

How long should EMLA cream be applied for to get the desired effect?

A

1 hour under an occlusive dressing

76
Q

How long does anesthesia from EMLA cream last after removal?

A

1-2 hours

77
Q

What is 20% benzocaine used for?

A

Mucosa

78
Q

What is 4% cocaine used for?

A

Awake intubation so

Sinus surgery

79
Q

What is 11.8% TAC used for?

A

Wound repair

80
Q

What is LET and what is it used for?

A

Lidocaine + Epi + tetracaine

Laceration repair

81
Q

Which local anesthetic cross the placenta the least?

A

Chloroprocaine because it is rapidly metabolized by plasma cholinesterase

82
Q

How does fetal ph affect local anesthetic concentration

A

Fetal ph is lower than mom’s so you will get ion trapping and more concentration of local anesthetic in the fetus

83
Q

What is the plasma half life of chloroprocaine?

A

12 seconds

84
Q

What is the onset of action of chloroprocaine

A

6-10 minutes

85
Q

What is the duration of action of chloroprocaine

A

30-60 minutes

86
Q

What is the disadvantage of chloroprocaine?

A

Antagonistic effects on opioids and other locals

Neurotoxicity

87
Q

What are the first signs of lidocaine toxicity?

A

Numbness/tingling of lips

88
Q

What are the second set of signs of lidocaine toxicity?

A

Tinnitus

89
Q

What are the third set of signs?

A

Dizziness, lightheadedness, twitching,seizure

90
Q

What is intrathecal lidocaine known to cause?

A

Cauda equina syndrome due to demyelination from pooling in this area

91
Q

What are the risk factors of transient neurologic syndrome?

A 
Lidocaine use
Lithotomy position
Early ambulation after surgery
Needle trauma
Same day surgery
92
Q

What is transient neurologic syndrome?

A

Pain in legs, butt that develops within 24 hours of lidocaine spinal. Resolves spontaneously in 1-3 days

93
Q

What is a Bier block?

A

It is IV local anesthetic used with 2 tourniquettes: a distal and proximal. The extremity is exsanguinated with an Esmarch bandage and then proximal cuff inflated. If the patient experience pain, the distal cuff is inflated and proximal deflated.
It lasts up to 90 minutes

94
Q

How does a Bier block work?

A

Tourniquettes cause ischemia which provides some anesthesia and analgesia
Local diffuses into the vaso nervora and extravascularly to cutaneous branches in the skin

95
Q

What determines the spread of spinal anesthesia?

A

Baricity of the drug, drug concentration, patient position

96
Q

What does not determine the spread of spinal anesthesia?

A

Drug volume

97
Q

What is baricity?

A

The density of a drug compared to the specific gravity of CSF

98
Q

How is a solution made hyperbaric?

A

Adding glucose

99
Q

How is a solution made hypobaric?

A

By adding water

100
Q

How is a solution made isobaric?

A

By mixing 1:1 with CSF

101
Q

What does drug volume affect in spinal anesthesia?

A

The level of blockade

102
Q

When can a neuraxial catheter be removed with BID dosing of heparin?

A

Anytime

103
Q

When can a neuraxial catheter be removed if a patient is on a heparin drip?

A

2-4 hours after the drip is stopped

104
Q

When can an epidural be placed in someone taking Lovenox (1 mg/kg bid), Dalteparin, or Tinzaparin?

A

24 hours later

105
Q

When can you restart lovenox after placing a catheter?

A

2 hours after

106
Q

What happens when you mix sodium bicarb with ropivacaine or bupivacaine?

A

Precipitation and therefore decreased effectiveness and drug availability

107
Q

Why is sodium bicarb added to local anesthetics?

A

It increases the ph of the solution to increase the amount of nonionized drug thereby increasing the onset time.
It also decreases pain on injection

108
Q

What is post spinal back ache?

A

Happens within 7 days of spinal. Will go away on its own.

Treated conservatively with APAP

109
Q

Which regional block has the highest blood levels of local after blocking?

A

Intercostal

Then caudal, epidural, brachial, IV, lower extremity

110
Q

What is the adductor canal block?

A

Block of the femoral nerve under the sartorius to provide anesthesia to medial aspect of lower leg and distal femur

111
Q

How much bupivacaine can you give with Epi?

A

2.5 mg/kg, not to exceed 225 mg

112
Q

How much chloroprocaine can you give?

A

11 mg/kg

113
Q

How much chloroprocaine with Epi can you give?

A

14 mg/kg

114
Q

What’s the duration of action of lidocaine?

A

30-60 minutes

115
Q

What’s the duration of action of lidocaine with Epi?

A

120-360 minutes

116
Q

What’s the duration of bupivacaine?

A

120-140 minutes

117
Q

What’s the duration of mepivacaine?

A

45-90 minutes

118
Q

What’s the max dose of mepivacaine?

A

7 mg/kg

119
Q

What determines potency?

A

Lipid solubility

120
Q

What determines onset?

A

Pka/ph

121
Q

What determines duration of action?

A 
Protein binding 
(Highly - remain bound for longer so last longer)
122
Q

What does BICEPSS stand for?

A 
The order of site that absorbs the most local anesthetic
b- blood (IV)
I- intercostal
c- caudal
E- epidural 
P- plexus (brachial)
S- sciatic
S- subq
123
Q

Which nerves are affected first?

A

Small, myelinated fibers (B fibers)

Autonomic> sensory> motor

124
Q

What do A-delta and C fibers feel?

A

Pain and temperature

125
Q

What do A-beta fibers feel?

A

Touch

126
Q

What are B fibers?

A

Preganglionic sympathetic nerve fibers

127
Q

What are the most resistant fibers to local?

A

C fibers

128
Q

Why is bupivacaine more cardio toxic?

A

It has higher affinity for resting and inactivated sodium channels in the myocardium

129
Q

How do you treat LAST?

A

Intra lipid bolus of 1.5 mg/kg
Then infusion of 0.25 ml/kg/min (increase to 0.5 if persistent hypotension)

Get CPB team, avoid vasopressin CCBs and BBs, lower Epi dosing

130
Q

What is the preferred treatment for ventricular arrhythmias in the setting of LAST?

A

Amiodarone

Anesthesia MM/TL (36 decks)

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