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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
How does the local act when the pKa is closer to the pH of the blood?
A larger fraction will exist as the lipid-soluble, uncharged base. More molecules with diffuse across and have a faster onset of action
26
How is lipid solubility increased?
With an alkyl group substitution on the amide group and benzene ring.
27
Do agents that are more lipophilic have longer or shorter durations of action?
Longer
28
How do lower concentrations of local affect the vascular smooth muscle?
Cause vasoconstriction by inhibiting nitric oxide
29
How do higher concentrations of local affect the vascular smooth muscle?
Vasoconstriction
30
What locals do not have intrinsic vasodilating activity?
Chloroprocaine and ropivacaine
31
How do drugs with a greater degree of intrinsic vasodilating effects affect the rate of vascular uptake? Example?
Lidocaine Undergo faster rate of vascular uptake which prevents some of the medication from accessing the nerve
32
How does cocaine work?
Inhabits NE reuptake and always causes vasoconstriction
33
What will prolong the duration of action of locals?
-Increased protein binding -Higher lipid solubility -Vasoconstriction
34
What is the pKa of a drug?
Where 50% of the drug is unionized and 50% is ionized
35
Do amides or esters have high pKa's?*
Esters - all are greater than 8.0
36
Which local does not undergo protein binding?
Chloroprocaine
37
When the pKa is closer to the pH of the blood, is there a faster or slower onset?
Faster except for Chloroprocaine
38
What is unique about benzocaine?
It's pKa is 3.5 Higher risk for methemoglobinemia (methylene blue is the treatment)
39
What factors influence the vascular uptake of locals?
-Site of injection -Tissue blood flow -Properties of the local -Metabolism -Addition of vasoconstrictors
40
Order from greatest to least for most vascular and highest Cp
-IV -Tracheal -Interpleural -intercostal -Caudal -Epidural -Brachial Plexus -Femoral -Sciatic -Subq
41
What plasma protein to locals bind to?
Mainly alpha1-acid glycoprotein but also albumin
42
How do the lungs affect locals?
Act as a reservoir and removes from the circulation
43
How are Amides metabolized?
p450
44
How are esters metabolized?
Pseudocholinesterase
45
Which local is metabolized by both?
Cocaine
46
How does dexamethasone affect the duration of action? In what block?
Extends the brachial plexus block
47
How does experal work?
Aqueous droplets of bupivacaine are housed in a liposomal suspension
48
How is experal dispensed?
133mg in 10mL 266 in 20mL
49
What is the max dose of Experal?
266 mg
50
What is experal contradicted in?
Paracervical block in OB patients Epidural anesthesia Intrathecal Intraarticular Pregnancy
51
Can other local anesthetics be administered with Experal?
avoid because it can disrupt the liposomal suspension.
52
When can lidocaine and experal be administrated?
After lidocaine, must wait 20 minutes before experal After experal must wait for 96 hours
53
Max dose for levobupivacaine ?
2mg/kg 150mg
54
Max dose for bupivacaine ?
2.5mg/kg 175mg
55
Max dose for bupivacaine+epi?
3mg/kg 200mg
56
Max dose for Ropivacaine ?
3mg/kg 200mg
57
Max dose for Lidocaine ?
4.5mg/kg 300mg
58
Max dose for Mepivacaine ?
7mg/kg 400mg
59
Max dose for Lidocaine + Epi ?
7mg/kg 600mg
60
Max dose for Prilocaine ?
8mg/kg <70kg 500mg >70kg 600mg
61
Max dose for Procaine ?
7mg/kg 350-600mg
62
Max dose for Chloroprocaine ?
11mg/kg 800mg
63
Max dose for Chloroprocaine + Epi ?
14mg/kg 1000mg
64
What's the most frequent symptom of toxicity ? Exception?
Seizure except Bupivacaine can be cardiac arrest
65
What is LAST more common in?
Peripheral nerve blocks
66
How does hypercarbia affect CNS toxicity?
Increases risk through increased blood flow to brain AND decreases protein binding
66
Plasma concentrations for lidocaine toxicity?
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
How does hyperkalemia affect CNS toxicity?
Increases risk - Raises resting membrane potential which makes neurons more likely to fire
68
How does metabolic acidosis affect CNS toxicity?
Increases risk -Decreases the convulsion threshold and increases ion trapping
69
How does hypocarbia affect CNS toxicity?
Decreases risk through decreasing cerebral blood flow
70
How does hypokalemia affect CNS toxicity?
Decreases risk by lowering RMP, which requires a larger stimulus to depolarize the nerve
71
How do CNS depressants affect CNS toxicity? What are they?
Decreases by raising the seizure threshold Benzos and Barbiturates
72
How locals lead to cardiovascular toxicity?
-Decreases automaticity, action potential duratio0n, effective refractory period -Impairs calcium regulation -Produces a biphasic effect on smooth muscle
73
Rank the difficulty of cardiac resuscitation
Hardest Bupivacaine Levobupivacaine Ropivacaine Lidocaine
74
What two features determine the extent of cardiotoxicity?
-Affinity for the voltage gated sodium channel -Rate of dissociation from the receptor during diastole
75
What should be avoided with cocaine?
MAOI TCA's Sympathomimetic drugs
76
How should cocaine toxicity be treated?
Vasodilator like nitro or Mixed beta blocker
77
Cocaine dosage?
1.5mg-3.0mg/kg Max 200
78
How to prevent LAST?
Incremental dosage with periodic aspiration
79
How is LAST treated?
-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
How to administer Lipid emulsion?
-20% -Continue infusion for 15 minutes after stabilization Max dose 12ml/Kg Safe in pregnancy Watch for pancreatitis
81
Lipid emulsion dosing?
-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
Tumescent Anesthesia - what is given?
During liposuction a solution of sodium chloride, lidocaine, bicarb, and epi is given into the adipose tissue
83
Tumescent Anesthesia - quick facts
Max dose is 55mg/kg General Anesthesia is recommended for >2L is injected -Watch for fluid overload
84
What is the normal iron molecule on hemoglobin? What is it on Methemoglobin?
Ferrous (Fe +2) Oxidized to Ferric (Fe+3)
85
How does Methemoglobin decrease the oxygen carrying capacity?
1. Methemoglobin can't bind oxygen molecules 2.It shifts the dissociation curve to the left which produces anemia
86
What wavelength does Hgb absorb infrared wavelength at?
Equally at 660nm and 940 nm This results in a low SpO2 reading at 85%
87
What is required to diagnose methemoglobinemia ?
A co-oximeter
88
What causes methemoglobinemia ?
Benzocaine Cetacaine (Contains benzocaine) Prilocaine EMLA (Prilocaine and Lidocaine) Nitroprusside Nitroglycerin Sulfonamides Phenytoin
89
How does methemoglobinemia present?
Hypoxia Cyanosis Tachycardia Tachypnea Chocolate colored blood Coma Mental status changes
90
How is methemoglobinemia treated?
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
What deficiency is does not possess methemoglobin reductase? Treatment?
Glucose-6-phosphate Blood transfusion Fetal Hgb is also low in methemoglobin reductase
92
What is 5% EMLA cream? When is it used? How long till it achieves analgesia? Max effect?
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
What is unique about EMLA cream?
-Lower melting point which facilitates absorption -Can use nitro to hasten absorption -Cover with Tegaderm -Has to be on intact skin
94
Contraindications with EMLA cream?
It's metabolized to o-toluidine which oxidizes Hgb into methemoglobin. Infants and small children are at increased odds for toxicity
95
EMLA dosage chart
96
What drugs prolong duration of action of locals?
Epi - vasoconstriction (does better with intermediate locals) Dexamethasone - Glucocorticoid activity on the steroid receptor Dextran - Due to low molecular weight Cocaine
97
What block does dexamethasone increase the best? What percentage?
Brachial Plexus 50%
98
What drugs provide supplemental analgesia ?
Clonidine (100mcg to the solution) Epi through alpha 2 Opioids except chloroprocaine
99
Which local reduces the effectiveness of opioids?
Chloroprocaine
100
What drugs shorten onset time?
Sodium bicarb - 1mL of 8.4%
101
What drug improves diffusion through tissues?
Hyaluronidase Great in Opthalmic blocks Potential for allergies

Local + Opioids (3 decks)

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