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Local Anesthetics (4) Flashcards

1
Q

How many classes are there of antiarrhythmic drugs?

A

Class 1: Sodium channel blockers
Class 2: Beta blockers
Class 3: Potassium channel blockers
Class 4: CCB

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2
Q

What are the uses for local anesthetics?

A
  • Treat dysrhythmias
  • Analgesia (acute and chronic)
  • Anesthesia (ANS blockade, sensory anesthesia, skeletal muscle paralysis)
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3
Q

What was the first local anesthetic?

A

Cocaine
- Ophthalmology (1884)
- local vasoconstriction
- cerebral stimulating

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4
Q

What was the first synthetic ester?

A

Procaine (1905)

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5
Q

What was the first synthetic amide?

A

Lidocaine (1943)

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6
Q

What are all other local anesthetics compared to?

A

Lidocaine

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7
Q

What is the dose of lidocaine for initial bolus?

A

1-2 mg/kg IV over 2-4min

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8
Q

What is the dose for lidocaine gtt?

A

1-2 mg/kg/hr gtt
Terminated 12-72 hours

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9
Q

What is important to monitor when patient is getting IV lidocaine?

A

Cardiac, hepatic, renal dysfunction

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10
Q

What effects are associated with 1-5 mcg/mL of lidocaine?

A

Analgesia

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11
Q

What effects are associated with 5-10 mcg/mL of lidocaine?

A
  • Circum-oral numbness
  • Tinnitus
  • Skeletal muscle twitching
  • Systemic hypotension
  • Myocardial depression
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12
Q

What effects are associated with 10-15 mcg/mL of lidocaine?

A
  • Seizures
  • Unconsciousness
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13
Q

What effects are associated with 15-25 mcg/mL of lidocaine?

A
  • Apnea
  • Coma
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14
Q

What effects are associated with >25 mcg/mL of lidocaine?

A

Cardiovascular depression

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15
Q

What is the molecular structure of local anesthetics?

A
  • Lipophilic portion
  • Hydrocarbon chain
  • Hydrophilic portion

Bond between lipophilic portion and hydrocarbon chain

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16
Q

Which bond of LA determines whether it is an ester or amide?

A

Bond between lipophilic (1) and hydrocarbon chain (2)

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17
Q

Which part of the LA is the hydrophilic portion?

A

Amino group

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18
Q

Which part of the LA structure is the lipophilic portion?

A

Aromatic benzene ring

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19
Q
A

bond between hydrocarbon chain on the intermediate chain= middle chain

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20
Q

LA are weak ______

A

Bases

poorly soluble in water
usually add epi to make sure the local anesthetics stay longer

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21
Q

List ester local anesthetics?

A
  • Procaine
  • Chloroprocaine
  • Tetracaine
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22
Q

List amide local anesthetics:

A
  • Lidocaine
  • Prilocaine
    -Mepivacaine
  • Bupivacaine
  • Levobupivacaine
  • Ropivacaine
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23
Q

What is the purpose of sodium bisulfide added with LA?

A

Added to LAs when epi is added to prevent breakdown of the vasoconstrictor

Extends shelf life (prevents degradation to precipitate)

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24
Q

What is the purpose for adding epi to LA?

A

Prolong the duration of the LA

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25
Q

The higher the non ionized component of the LA means more lipid soluble= the higher the ________

A

potency

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26
Q

Non-ionized form help to determine LAs _________ solubility

A

Lipid

Can cross membrane easily

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27
Q

Bupivacaine is more lipid soluble so it is more ________ than lidocaine

A

POtent

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28
Q

What is the major determinant for potency?

A

Lipid solubility

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29
Q

What are 3 liposome forms of LA?

A
  • Lidocaine
  • Tetracaine
  • Bupivacaine
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30
Q

What is the function of liposomes?

A

Uploads a higher amount of LA into a molecule & have a consistent release of LA in the tissues

(like extended release capsule)

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31
Q

What is the benefit for liposomes?

A
  • Prolonged duration of action
  • Decreases toxicty
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32
Q

What is the MOA of Local anesthetics?

A
  • Binds to and inactivates (Closed) inner voltage gates channels
  • inhibit passage of Na in nerve membranes
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33
Q

How do LA affect action potential?

A
  • Slows rate of depolarization
  • Does not reach threshold
  • No action potential propagated
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34
Q

What factors can affect local anesthetic blockade?

A
  • Lipid solubility or non-ionized/unionized form
  • Repetitively stimulated nerve
  • Diameter of the nerve
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35
Q

What are other target ion channels for LAs besides Na+?

A
  • Potassium channels
  • Calcium Ion Channels
  • G protein-coupled receptors
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36
Q
A

Non-ionized form

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37
Q

What is the minimum effective concentration (MEC/Cm) for LAs?

A
  • 1 cm blocked (3 nodes of ranvier)
  • Larger fibers need higher concentrations of LAs
  • Motor 2x bigger diameter than sensory
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38
Q

What fibers are the fasted in the propagation of SNS impulse?

A

Pre-ganglionic B fibers

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39
Q

Which fibers control pain/temp (touch, pressure, proprioception, and motor)?

A

Myelinated A-delta and unmeylinated C fiber

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40
Q

__________ increases sensitivity of local anesthetics

A

Pregnancy (give less)

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41
Q

Which pH of LA as the most rapid onset of action?

A

pH closest to physiologic pH

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42
Q

__________ has greater systemic absorption which makes it potency less

A

Lidocaine

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43
Q

What factors influence LA absorption?

A
  • Site of injection
  • Dosage
  • Use of Epinephrine
  • Pharmacologic characteristics of the drug
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44
Q

Which areas of the body are highly vascular and have increased absorption of LA?

A
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45
Q

Using Epi with LA counter acts which effects of LAs?

A

Vasodilatory effects (enhances/prolongs DOA Of LA)

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46
Q

What is the rate of clearance of LA dependent on?

A
  • Cardiac output
  • Protein binding
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47
Q

Which LA has the fastest clearance between Lido, Mepivacaine, and Bupivacaine?

A

Lidocaine has faster clearance than mepivacaine and bupivacaine d/t less protein binding of lidocaine

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48
Q

Higher protein bound LAs have _______ intravascular clearance

A

Slower

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49
Q

How are amide LAs metabolized?

A

Microsomal enzymes in the liver

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50
Q

Which amides LAs have rapid, intermediate, and slower metabolism?

A
  • Most rapid: Prilocaine
  • Intermediate: Lidocaine, Mepivacaine
  • Slowest: Etidocaine, Bupivacaine, Ropivacaine
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51
Q

How are Ester LAs metabolized?

A

Hydrolysis by cholinesterase enzyme in the plasma

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52
Q

What is a metabolite with metabolism of ester LAs?

A

Para-aminobenzoic acid (PABA)→ causes allergies

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53
Q

________ LAs have slower metabolism than __________ LAs

A

Amide, Ester

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54
Q

Which LAs have pulmonary first pass metabolism?

A

Lidocaine, bupivacaine (dose dependent), and prilocaine

Inactivated in the lungs

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55
Q
A

True

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56
Q
A
  • Clearance (from site of action)
  • Protein binding **
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57
Q

How are LAs eliminated and cleared?

A

Renal
- Poor water solubility= unchanged drug in urine (5%)
- PABA through urine
- Cocaine 10-12% unchanged drug

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58
Q

What are considerations of local anesthetics with pregnant patients?

A
  • Lower levels of plasma cholinesterases
  • Significant transplacental transfer with amides (fetal pH is much lower leads to ion trapping)
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59
Q

What happens when the unionized form of LA crosses from mom to fetus?

A

Unionized form enters acidic environment of fetus and turn ionized and isnt metabolized→ can cause seizures, bradycardia/asystole for the fetus

60
Q

Which LAs have significant protein binding?

61
Q

How is lidocaine metabolised?

A

Oxidative dealkylation in the liver then hydrolysis

62
Q

What is lidocaine metabolite?

63
Q

What does pregnancy induced hypertension do to clearange of lidocaine?

A

Prolongs clearance

64
Q

________ disease affects metabolism and elimination of lidocaine

65
Q

What is the max infiltration dose of lidocaine?

A

300 mg OR
500 mg with epi

66
Q

What is the metabolite of prilocaine?

A

Orthotoludine

67
Q

What is the MOA of prilocaine metabolite orthotoluidine?

A

Converts Hemoglobin to Methemoglobin→Methemoglobinemia

68
Q

At what dose is there concern for methemoglobinemia with prilocaine?

A

> 600mg

S/S: cyanosis from decreased O2 carrying capacity

69
Q

What is the treatment of Methemoglobinemia?

A

TX: Methylene Blue
1 to 2 mgs/kg IV over 5 mins
Total dose not to exceed 7 to 8 mg/kg

70
Q

How does Mepivacaine differ from Lidocaine?

A
  • Longer duration of action
  • Lacks vasodilator activity
  • Prolonged elimination in fetus & newborn; no OB
71
Q

How is Bupivacaine metabolized?

A

Aromatic hydroxylation, N-dealkylation, amide hydrolysis and conjugation

72
Q

Which protein does Bupivacaine bind to and what percent it bound?

A

A1-acid glycoprotein 95%

73
Q

What is Dibucaine used for? What is the MOA?

A

Used to diagnose succs allergy

MOA: inhibits the activity of normal butyrylcholinesterase (plasma cholinesterase) by more than 70%

Metabolized in liver

74
Q

How is Ropivacaine metabolised?

75
Q

Does Ropivacaine metabolize into metabolites?

A

Can accumulate with uremic patients→Less system toxicity than Bupivacaine

76
Q

How is Chloroprocaine metabolized?

A

Plasma cholinesterase (3.5x faster)

77
Q

Hydrolysis of LA ranked fasted to slowest:

A

chloroprocaine > procaine > tetracaine

78
Q

What makes Benzocaine unique structurally from other LAs?

A

Weak acid (pK 3.5)

79
Q

What are the uses of Benzocaine?

A
  • Topical anesthesia of mucous membranes:
  • Tracheal intubation, Endoscopy, Transesophageal echocardiography (TEE), Bronchoscopy
80
Q

What is the onset, duration, and dose of Benzocaine?

A

Onset: rapid
Duration: 30 to 60 minutes
Dose: Brief spray (20%) = 200 to 300 mgs

81
Q
82
Q

How is cocaine metabolized? When patients is metabolism decreased in?

A
  • Plasma and liver cholinesterases
  • Decreased in: Parturients, Neonates, Elderly, Severe Hepatic Disease
83
Q

Cocaine is a ______ LA

84
Q

What is the peak, duration, and elimination of cocaine? Caution with which patients?

A
  • Peak: 30 to 45 mins
  • Duration: 60 minutes after peak
  • Elimination: Urine (24 to 36 hours)

Caution: Coronary vasospasm, ventricular dysrhythmias, HTN, tachycardia, CAD

85
Q

What is the function of alkalinization of LA Solution? What is the benefit?

A
  • Increase percent of lipid soluble (non ionized form) or LAs

Benefits:
Faster onset of action
Peripheral and epidural blocks by 3 to 5 mins.
Enhances the depth
Increase the spread (i.e., epidural)

86
Q

What is used to alkalinize LAs?

A

8.4$ Sodium bicarb (1mL only added to 10mL LA)

87
Q

Easy way to think of ionization with weak bases

A

Drug V= more non ionized
Drug W= more ionized

89
Q

How does mixing dexmedetomidine with LA affect things?

A

Increased duration of:
* Both motor and sensory blocks
* First analgesic request after spinal anesthesia

90
Q

Magnesium + LA =

A

Increased duration with subarachnoid block with opioids.

91
Q

Clonidine and Ketamine + LA =

A

Pediatric regionaa anesthesia prolonged duration

92
Q

Dexamethasone + LA =

A

Increased duration either IV or mixed with LA

93
Q

What happens when combining chloroprocaine and bupivacaine?

A
  • Rapid onset
  • Tachyphylaxis
94
Q

When local anesthetics are given in combination the toxic effects are ________

95
Q

Why do we use vasoconstrictors (Epi) with LAs?

A
  • Produce vasoconstriction
  • Increased neuronal uptake of LA
  • α-adrenergic effects may have some degree of analgesia
  • No effect on onset rate of LA
  • Enhanced cardiac irritability with inhaled anesthetics
  • Systemic absorption (HTN/ tachycardia?)
96
Q

How many mcg/mL are in a concentration of 1:200,000?

97
Q

Local anesthetics strengths for 0.25%, 0.5%, 1%, 2%, and 4%:

98
Q
A

Bupivacaine= 50mg total
epi= 100mcg

99
Q

What are uses for LAs?

A
  • Topical
  • Local Infiltration
  • Peripheral N. Block
  • Intravenous
  • Epidural
  • Spinal
  • Tumescent Liposuction
100
Q

Where is topical anesthesia applicable?

A
  • nose
  • mouth
  • tracheobronchial
  • esophagus
  • GU tract
101
Q

What is LA is the most effective for topical anesthesia?

A

Cocaine→ localized vasoconstriction and decreases blood loss and improves surgical visualization

102
Q

When is lidocaine used for topical anesthesia?

A
  • Surface anesthesia
  • Inhalation does not alter airways resistance
  • causes vasodilation
103
Q

Which LAs are not used for topical anesthesia?

A
  • Procaine
  • Chloroprocaine
104
Q

What is EMLA?

A

Eutectic Mixture of LA

105
Q

What is the EMLA composed of?

A

Cream 2.5% lidocaine and 2.5% prilocaine (5% total LA cream)

106
Q

How long before certain procedures do we need to apply EMLA?

A
  • skin grafting (2 hours)
  • Cautery of genital warts (10min)
  • Venipuncture, lumbar puncture (10 min)
  • Arterial cannulation (Nitroglycerine) (10 min)
  • Myringotomy (10 min)
107
Q

What are cautions with EMLA?

A
  • Caution with methemoglobinemia
  • Not recommended for skin wounds
  • Contraindicated with amide allergies
108
Q

What other preparations are available for topical cream locals?

A
  • Amethocaine (EMLA-like)
  • Tetracaine 4% Gel
  • Lidocaine 7%
  • Tetracaine 7%
109
Q

What type of LA is Epi contraindicated?

A

Intracutaneously or into tissues at end arteries
(Fingers, toes, ears, nose, and penis
vasoconstriction→ ischemia/necrosis)

110
Q

Where is extravascular placement of LA?

A

Subcutaneous injection

111
Q

How does subcutaneous LA duration change when epi is added?

A

Doubled (contraindicated in subq LA of end arteries)

112
Q

How is peripheral nerve block achieved?

A

LA injection into tissues surrounding individual peripheral nerves or nerve plexuses.

113
Q

What is the MOA of peripheral nerve blocks?

A
  • Diffusion from outer mantle to central core of nerve along a concentration gradient
  • Proximal effect first then distal
  • Proximal sensation comes back first then distal/ larger motor
114
Q

What is onset of peripheral nerve blocks?

A

Dependent on local anesthetic pK

lidocaine: 3 min
Bupivacaine: 15 min

115
Q

What is the duration of peripheral nerve blocks?

A

Depends on dose of LA (Bupivacaine with epi/fentanyl/clonidine = 12 to 18 hrs)

116
Q

What is the benefit of continuous infusion blocks?

A
  • Improved pain control
  • Less nausea
  • Greater satisfaction
117
Q

Examples of peripheral nerve blocks:

A
  • Interscalene
  • Axillary
  • Femoral
  • Sciatic
118
Q

What is another name fore IV regional anesthesia?

A

Bier block→ IV injection of LA into an extremity isolated from the rest of the systemic circulation with a tourniquet

Sensation and muscle tone dependent on tourniquet

Can use ester or amide: mostly lidocaine

119
Q

What is involved in the bier block?

A
  • IV start
  • Exsanguination
  • Double cuff
  • LA injection
  • IV D/C
120
Q

What is the sequence of neuraxial blockade?

A

1) SNS
2) Sensory
3) Motor

121
Q

Which neurons are first affected with neuraxial anesthesia?

A

Myelinated Preganglionic B fibers (fastest) (SNS)

122
Q

Which neurons are affected after myelinated preganglionic B fibers?

A

Myelinated A (medium) and B fibers (faster) THEN Unmyelinated C fibers (small)

123
Q

Neuraxial blockade is the last reference with which assessment parameter?

A

Leg movement (motor is affected last)

124
Q

How do we confirm we are in the spinal area for subarachnoid block?

A

CSF confirmation
Preganglionic fibers= principle site of action

125
Q

Sensory effect is on the _________ level of denervation

126
Q

Where is the SNS effect of spinal anesthesia block?

A

2 spinal segments above sensory

127
Q

Where is the motor effect of spinal anesthesia block?

A

2 spinal segments below sensory

128
Q
A

1) T4
2) T8

129
Q

What are most common subarachnoid block agents?

A
  • Tetracaine
  • Lidocaine
  • Bupivacaine
  • Ropivacaine
  • Levobupivacaine
130
Q

How is subarachnoid block dose calculated?

A
  • Height of patient (volume of subarachnoid space)
  • Segmental level of anesthesia desired
  • Duration of anesthesia desired
131
Q

________ is more important in subarachnoid blocks than the concentration of drug or the volume of the solution

A

Dose
(ex: 5ft= 1mL of 0.75% bupivacaine)
+ 0.1mL for every inch above (2mL total)

132
Q

What is important in determining the spread of LA for subarachnoid blocks?

A

Specific gravity of LA

Hyperbaric (LA sp. gr. > CSF) with glucose is additive

Hypobaric with distilled water as additive

133
Q

What is the most common epidural anesthetic?

A

Lidocaine: safe and good diffusion through tissue

134
Q

Why are levobupivacaine and ropivacaine not as safe for epidural anesthesia?

A

They are highly protein bound so toxic effects last a lot longer (cardiac and CNS toxicity)

135
Q

What is the onset for epidural anesthesia?

A
  • 15-30 minutes (slow diffusion/delay)
  • Great with loading dose and then intermittent boluses (usually have continuous gtt)
136
Q

When does epidural pose risk to fetus?

A

24-48 hours it can go systemic through the veins and cross placental barrier

137
Q

Will bupivacaine or lidocaine have more cross over to the fetus?

A

Lidocaine crosses more than bupivacaine (lido more rapid onset)

138
Q

_______ are acceptable as additive to both epidural and SAB

A

opioids (synergistic effect)

139
Q
140
Q

What is tumescent liposuction?

A
  • SQ infiltration of large volumes (5L of more)
  • diluted lidocaine solution (0.05-0.1%) and epi
141
Q

What is infiltration of tumescent lipsuction MOA?

A
  • Causes taut stretching and blanching of skin from the large volume of fluid and vasoconstriction
  • local anesthesia with bloodless aspirates and prolonged postoperative analgesia
142
Q

When in LA plasma peak after tumescent liposuction?

A

12-14 hours after injection

143
Q

Where is tumescent liposuction injuected?

A

Thigh, abdomen, hips, butt

144
Q

What is the recommended dose for tumescent?

A
  • Regional Anesthesia Lidocaine with Epi: 7 mg/kg
  • Highly diluted Lidocaine with Epi Tumescent: 35 to 55 mg/kg
145
Q

1 gm of SQ tumescent can absorb up to ____mg of Lidocaine

A

1 (theory)

146
Q

Weak bases=

A

pK before pH

If weak base (pk 8.0) is put in an acid ph (Blood 7.2)
8.0 – 7.2= +0.8 weak bases are ionized at acid ph

“nicely negative numbers are nonionized”

Anesthesia Pharm (A) (17 decks)

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