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Local + Opioids > Local > Flashcards

Local Flashcards

1
Q

What is saltatory conduction?

A

Electrical current skipping the nodes of Ranvier along the myelin sheath.

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2
Q

What is conduction velocity? What increases conduction?

A

How fast an axon transmits the action potential

Myelination and a larger fiber diameter

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3
Q

Nerve Fiber Chart

A
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4
Q

What is the minimum effective concentration?

A

A unit of measurement that quantifies the required concentration of local anesthetic. Analogous to ED50 for IV drugs and MAC for volatiles

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5
Q

Do fibers that are more easily blocked have higher or lower Cm?

A

Lower Cm

Fibers with a high Cm are more resistant to blockade

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6
Q

What reduces Cm?

A

Higher tissue pH or high frequency nerve stimulation

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7
Q

Order the speed of onset of nerve fibers from first to last.

A
  1. B fibers
  2. C fibers
  3. Small diameter A fibers
  4. Large diameter A fibers
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8
Q

What is the mechanism of action for local anesthetics?

A

Reversibly bind to the alpha subunit on the inside of the voltage gated sodium channels. Plugs the channel and reduces sodium conductance.

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9
Q

What is the resting state of sodium channels?

A

Resting state -70mV

Channel is closed and able to be opened

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10
Q

What is the active state of Na channels?

A

Active State -70 to +35 mV

Channel is open

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11
Q

What is the inactive state of Na channels?

A

Inactive State +35 to -70mV

Channel is closed and unable to be open

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12
Q

What is the use-dependent or phasic blockade?

A

The more often the nerve is depolarized (used), the faster the nerve will become blocked

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13
Q

When can local anesthetics not bind to Na channels?

A

In their resting state

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14
Q

Do local anesthetics affect;

A. Resting membrane potential
B. Threshold potential
C. Action potential

A

C. Action potential

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15
Q

Characteristics of Local Anesthetics in the Vial?

A

-Weak bases
-Packaged as hydrochloride salts
-Solutions have a low pH to guard against precipitation

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16
Q

How do vasoconstrictors affect Local anesthetics?

A

Prolongs the duration of action

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17
Q

How does increased blood flow affect local anesthetics?

A

Reduces duration and increases plasma concentration

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18
Q

Characteristics of ester type locals

A

Have one “i”

-Metabolized by pseudocholinesterase.

-A deficiency in pseudocholinesterase could increase the duration of action

-Low allergic potential(reacts to PABA)

-HAS cross sensitivity in the same class

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19
Q

Characteristics of amid locals

A

Has two “i’s” in the name

Metabolized by P450 enzyme

Very rare allergic potential

No cross sensitivity

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20
Q

Are there cross sensitivities between esters and amides?

A

No

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21
Q

What are the three parts of a local?

A

Benzene ring which allows it to be lipophilic

Intermediate chain which allows determines its class and allergic potential

Tertiary amine which makes it hydrophilic, accepts the proton and makes the molecule a weak base

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22
Q

What is the primary variable for the onset of action? Secondary?

A
  1. pKa
  2. Dose and concentration
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23
Q

What is the primary variable for the potency? Secondary?

A
  1. Lipid solubility
  2. Intrinsic vasodilating effect
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24
Q

What is the primary variable for the duration of action Secondary?

A
  1. Protein binding
  2. -Lipids solubility
    -Intrinsic vasodilating effect
    -Vasoconstrictors
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25
Q

How does the local act when the pKa is closer to the pH of the blood?

A

A larger fraction will exist as the lipid-soluble, uncharged base. More molecules with diffuse across and have a faster onset of action

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26
Q

How is lipid solubility increased?

A

With an alkyl group substitution on the amide group and benzene ring.

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27
Q

Do agents that are more lipophilic have longer or shorter durations of action?

A

Longer

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28
Q

How do lower concentrations of local affect the vascular smooth muscle?

A

Cause vasoconstriction by inhibiting nitric oxide

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29
Q

How do higher concentrations of local affect the vascular smooth muscle?

A

Vasoconstriction

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30
Q

What locals do not have intrinsic vasodilating activity?

A

Chloroprocaine and ropivacaine

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31
Q

How do drugs with a greater degree of intrinsic vasodilating effects affect the rate of vascular uptake? Example?

A

Lidocaine

Undergo faster rate of vascular uptake which prevents some of the medication from accessing the nerve

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32
Q

How does cocaine work?

A

Inhabits NE reuptake and always causes vasoconstriction

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33
Q

What will prolong the duration of action of locals?

A

-Increased protein binding

-Higher lipid solubility

-Vasoconstriction

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34
Q

What is the pKa of a drug?

A

Where 50% of the drug is unionized and 50% is ionized

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35
Q

Do amides or esters have high pKa’s?*

A

Esters - all are greater than 8.0

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36
Q

Which local does not undergo protein binding?

A

Chloroprocaine

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37
Q

When the pKa is closer to the pH of the blood, is there a faster or slower onset?

A

Faster except for Chloroprocaine

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38
Q

What is unique about benzocaine?

A

It’s pKa is 3.5

Higher risk for methemoglobinemia (methylene blue is the treatment)

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39
Q

What factors influence the vascular uptake of locals?

A

-Site of injection
-Tissue blood flow
-Properties of the local
-Metabolism
-Addition of vasoconstrictors

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40
Q

Order from greatest to least for most vascular and highest Cp

A

-IV
-Tracheal
-Interpleural
-intercostal
-Caudal
-Epidural
-Brachial Plexus
-Femoral
-Sciatic
-Subq

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41
Q

What plasma protein to locals bind to?

A

Mainly alpha1-acid glycoprotein

but also

albumin

42
Q

How do the lungs affect locals?

A

Act as a reservoir and removes from the circulation

43
Q

How are Amides metabolized?

A

p450

44
Q

How are esters metabolized?

A

Pseudocholinesterase

45
Q

Which local is metabolized by both?

A

Cocaine

46
Q

How does dexamethasone affect the duration of action? In what block?

A

Extends the brachial plexus block

47
Q

How does experal work?

A

Aqueous droplets of bupivacaine are housed in a liposomal suspension

48
Q

How is experal dispensed?

A

133mg in 10mL
266 in 20mL

49
Q

What is the max dose of Experal?

A

266 mg

50
Q

What is experal contradicted in?

A

Paracervical block in OB patients

Epidural anesthesia

Intrathecal

Intraarticular

Pregnancy

51
Q

Can other local anesthetics be administered with Experal?

A

avoid because it can disrupt the liposomal suspension.

52
Q

When can lidocaine and experal be administrated?

A

After lidocaine, must wait 20 minutes before experal

After experal must wait for 96 hours

53
Q

Max dose for levobupivacaine ?

A

2mg/kg

150mg

54
Q

Max dose for bupivacaine ?

A

2.5mg/kg
175mg

55
Q

Max dose for bupivacaine+epi?

A

3mg/kg

200mg

56
Q

Max dose for Ropivacaine ?

A

3mg/kg

200mg

57
Q

Max dose for Lidocaine ?

A

4.5mg/kg

300mg

58
Q

Max dose for Mepivacaine ?

A

7mg/kg

400mg

59
Q

Max dose for Lidocaine + Epi ?

A

7mg/kg

600mg

60
Q

Max dose for Prilocaine ?

A

8mg/kg

<70kg 500mg
>70kg 600mg

61
Q

Max dose for Procaine ?

A

7mg/kg

350-600mg

62
Q

Max dose for Chloroprocaine ?

A

11mg/kg

800mg

63
Q

Max dose for Chloroprocaine + Epi ?

A

14mg/kg

1000mg

64
Q

What’s the most frequent symptom of toxicity ? Exception?

A

Seizure except Bupivacaine can be cardiac arrest

65
Q

What is LAST more common in?

A

Peripheral nerve blocks

66
Q

How does hypercarbia affect CNS toxicity?

A

Increases risk through increased blood flow to brain AND decreases protein binding

66
Q

Plasma concentrations for lidocaine toxicity?

A

1-5 - Analgesia

5-10 - tinnitus, restlessness, muscle twitching, numbness, blurred vision, vertigo

10-15 - Seizures, LOC

15-25 - Coma, respiratory arrest

> 25 CV collapse

67
Q

How does hyperkalemia affect CNS toxicity?

A

Increases risk - Raises resting membrane potential which makes neurons more likely to fire

68
Q

How does metabolic acidosis affect CNS toxicity?

A

Increases risk -Decreases the convulsion threshold and increases ion trapping

69
Q

How does hypocarbia affect CNS toxicity?

A

Decreases risk through decreasing cerebral blood flow

70
Q

How does hypokalemia affect CNS toxicity?

A

Decreases risk by lowering RMP, which requires a larger stimulus to depolarize the nerve

71
Q

How do CNS depressants affect CNS toxicity? What are they?

A

Decreases by raising the seizure threshold

Benzos and Barbiturates

72
Q

How locals lead to cardiovascular toxicity?

A

-Decreases automaticity, action potential duratio0n, effective refractory period

-Impairs calcium regulation

-Produces a biphasic effect on smooth muscle

73
Q

Rank the difficulty of cardiac resuscitation

A

Hardest

Bupivacaine

Levobupivacaine

Ropivacaine

Lidocaine

74
Q

What two features determine the extent of cardiotoxicity?

A

-Affinity for the voltage gated sodium channel

-Rate of dissociation from the receptor during diastole

75
Q

What should be avoided with cocaine?

A

MAOI

TCA’s

Sympathomimetic drugs

76
Q

How should cocaine toxicity be treated?

A

Vasodilator like nitro

or

Mixed beta blocker

77
Q

Cocaine dosage?

A

1.5mg-3.0mg/kg

Max 200

78
Q

How to prevent LAST?

A

Incremental dosage with periodic aspiration

79
Q

How is LAST treated?

A

-100% FiO2
Hypoxia and acidosis will worsen

-Treat with a benzo, not propofol

-Avoid Epi or use less than 1mcg/kg
-Avoid vasopressin
-Avoid beta and CCB

-GIVE amiodarone

-Lipid emulsion

-Bypass

80
Q

How to administer Lipid emulsion?

A

-20%

-Continue infusion for 15 minutes after stabilization

Max dose 12ml/Kg

Safe in pregnancy

Watch for pancreatitis

81
Q

Lipid emulsion dosing?

A

-Over 70kg

Bolus 100mL over 2 min

Infusion 250mL over 20 min

Repeat dose

-Under 70kg
Bolus 1.5mL of LBW over 2 min

Infusion .25mL/kg/min

Repeat dose

82
Q

Tumescent Anesthesia - what is given?

A

During liposuction a solution of sodium chloride, lidocaine, bicarb, and epi is given into the adipose tissue

83
Q

Tumescent Anesthesia - quick facts

A

Max dose is 55mg/kg

General Anesthesia is recommended for >2L is injected

-Watch for fluid overload

84
Q

What is the normal iron molecule on hemoglobin?

What is it on Methemoglobin?

A

Ferrous (Fe +2)

Oxidized to Ferric (Fe+3)

85
Q

How does Methemoglobin decrease the oxygen carrying capacity?

A
  1. Methemoglobin can’t bind oxygen molecules

2.It shifts the dissociation curve to the left which produces anemia

86
Q

What wavelength does Hgb absorb infrared wavelength at?

A

Equally at 660nm and 940 nm

This results in a low SpO2 reading at 85%

87
Q

What is required to diagnose methemoglobinemia ?

A

A co-oximeter

88
Q

What causes methemoglobinemia ?

A

Benzocaine
Cetacaine (Contains benzocaine)
Prilocaine
EMLA (Prilocaine and Lidocaine)

Nitroprusside
Nitroglycerin
Sulfonamides
Phenytoin

89
Q

How does methemoglobinemia present?

A

Hypoxia
Cyanosis
Tachycardia
Tachypnea
Chocolate colored blood
Coma
Mental status changes

90
Q

How is methemoglobinemia treated?

A

Methylene Blue

1-2mg/kg over minutes with a max dose of 7mg/kg

The metabolite (leucomethylene blue) of methylene blue functions as an electron donor which reduces methemoglobin back to hemoglobin

91
Q

What deficiency is does not possess methemoglobin reductase? Treatment?

A

Glucose-6-phosphate

Blood transfusion

Fetal Hgb is also low in methemoglobin reductase

92
Q

What is 5% EMLA cream? When is it used?

How long till it achieves analgesia? Max effect?

A

50/50 2.5% lidocaine and 2.5% prilocaine

Arterial or Venous IV, lumbar puncture, myringotomy

1 hour, max effect after 2-3 hours

93
Q

What is unique about EMLA cream?

A

-Lower melting point which facilitates absorption
-Can use nitro to hasten absorption
-Cover with Tegaderm
-Has to be on intact skin

94
Q

Contraindications with EMLA cream?

A

It’s metabolized to o-toluidine which oxidizes Hgb into methemoglobin. Infants and small children are at increased odds for toxicity

95
Q

EMLA dosage chart

A
96
Q

What drugs prolong duration of action of locals?

A

Epi - vasoconstriction (does better with intermediate locals)

Dexamethasone - Glucocorticoid activity on the steroid receptor

Dextran - Due to low molecular weight

Cocaine

97
Q

What block does dexamethasone increase the best? What percentage?

A

Brachial Plexus

50%

98
Q

What drugs provide supplemental analgesia ?

A

Clonidine (100mcg to the solution)

Epi through alpha 2

Opioids except chloroprocaine

99
Q

Which local reduces the effectiveness of opioids?

A

Chloroprocaine

100
Q

What drugs shorten onset time?

A

Sodium bicarb - 1mL of 8.4%

101
Q

What drug improves diffusion through tissues?

A

Hyaluronidase

Great in Opthalmic blocks

Potential for allergies

Local + Opioids (3 decks)

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