Local Anesthetics Flashcards

1
Q

Name the 3 basic components of all local anesthetics.

A
  1. A lipophilic group (usually a benzene ring).
  2. A hydrophilic group (tertiary amine).
  3. An intermediate bond (a hydrocarbon chain).
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2
Q

What are the 2 types of local anesthetics, and how are they classified?

A

esters = procaine, cocaine, chloroprocaine, and tetracaine

amides = lidocaine, bupivacaine, ropivacaine, mepivacaine, and prilocaine
- contain an “i” before the “-caine”

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3
Q

List the most common sites of injection in order of speed of systemic uptake (from fastest to slowest).

A

Fastest = highly vascular areas

Intravenous > tracheal > intercostal > caudal > paracervical > epidural > brachial plexus > sciatic > subcutaneous

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4
Q

What is the definition of pKa?

A

the pH = amounts ionized and un-ionized forms

low pKa = higher proportion of the un-ionized, lipid soluble form at normal tissue pH

lipid solubility –> potency
pKa –> speed of onset = lower pKa = faster onset

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5
Q

Which local anesthetics have the highest pKa, and the lowest pKa?

A

Procaine pKa 8.9

Chloroprocaine 8.7

Tetracaine 8.5

Bupivacaine 8.1

Ropivacaine 8.1

Lidocaine 7.9

Prilocaine 7.9

Mepivacaine 7.6

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6
Q

How do local anesthetics block transmission of sensory and motor signals along the neuron?

A

bind and inhibit the voltage-gated Na channels –> blocking propagation of the action potential.

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7
Q

How are ester and amide local anesthetics metabolized?

A

Esters = in the plasma by pseudocholinesterase enzymes

Amides = degraded in the liver by microsomal P-450 enzymes.

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8
Q

How does epinephrine prolong the action of local anesthetics?

A

vasoconstricting nearby blood vessels –> decreasing blood flow and slowing systemic absorption of the local anesthetic

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9
Q

Name the two organ systems most affected by local anesthetic toxicity.

A

neurological

cardiovascular

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10
Q

Name three manifestations of lidocaine toxicity in the central nervous system.

A

perioral numbness and tinnitus –> seizures and coma

initial excitatory phase = shivering, muscle tremors, and tonic-clonic seizures

progresses into a depressant phase = coma, hypoventilation and respiratory arrest.

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11
Q

Name the symptoms of cauda equina syndrome.

A

bowel and bladder dysfunction
perineal sensory loss
lower extremity motor weakness

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12
Q

What is Transient Neurological Symptoms and name three risk factors associated with its development.

A

unilateral or bilateral radicular PAIN - buttocks, lower back, and sometimes the lower extremities.

Risk factors = use of lidocaine, the lithotomy position, obesity, knee arthroscopy, and outpatient surgery.

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13
Q

How does local anesthetic toxicity affect cardiac function?

A

inhibition of sodium, potassium and calcium channels, which prolong myocardial action potentials

  1. prolongation of PR and QRS intervals
  2. depression of the SA and AV nodes
  3. QT interval is prolonged–> ventricular tachycardia, torsade de pointes and ventricular fibrillation

bupivacaine is the most arrhythmogenic, most refractory to resuscitation, resistant to traditional resuscitation may require cardiopulmonary bypass

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14
Q

What local anesthetic class is most associated with allergic reactions?

A

Esters - due to cross-reactivity to p-aminobenzoic acid (PABA).

Esters - metabolized to PABA and can cause reactions in patients sensitive to this compound

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15
Q

How do you give intralipid?

A

20% Intralipid emulsion begins with a bolus of 1.5 mL/kg intravenously over one minute, followed by a continuous infusion of 0.25 mL/kg/min

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16
Q

Name the local anesthetic and its metabolite associated with methemoglobinemia.

A

prilocaine?
Benzocaine spray

O-toluidine is the hepatic metabolite of prilocaine. It oxidizes the heme group’s ferrous (Fe2+) form to the ferric (Fe3+) form, resulting in methemoglobin, making it incapable of transporting oxygen.

17
Q

What does the addition of sodium bicarbonate do local anesthetics solution do?

A

raises pH –> more un-ionized molecules = faster onset

18
Q

What is the time of onset and duration of Transient Neurological Symptoms?

A

onset = 12 to 24 hours after spinal&raquo_space;> epidural anesthesia

duration = 6 hours to 4 days, rarely 7 or more days

19
Q

Max dose of lidocaine?

A

without epi = 300mg

WITH EPI = 500mg