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RUSVM Anesthesiology Summer 2019 > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

What are the two classes of local anesthetics?

A

Amides and esters

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2
Q

What is the mechanism of local anesthetics?

A

Bind to sodium channels and nerve membranes

Slows rate of depolarization

  • threshold potential is not reached
  • action potential not propagated
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3
Q

Are local anesthetics weak acids or weak bases?

A

Weak bases

Pka 7.7-9

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4
Q

During infection tissue becomes more acidic, how does this affect local anesthetics?

A

Will increase ionized portion—> more inactive (cannot pass through cell membrane)

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5
Q

If the pk of a local anesthetic is lower, how does this affect the onset of action

A

Lower pk => faster onset (closer to tissue pH)

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6
Q

High amounts of protein binding has what affect on duration of action of local anesthetics

A

Longer duration

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7
Q

Will water soluble or lipid soluble local anesthetics have higher potency?

A

Lipid soluble

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8
Q

What are the amide local anesthetics?

A 
Lidocaine 
Bupivaciane 
Mepivaciane 
Prilocaine 
—> with lidocaine in EMLA cream
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9
Q

What is the ONLY local anesthetic that may be given Iv or used for intravenous regional anesthesia?

A

Lidocaine

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10
Q

What is the onset and duration of lidocaine?

A

Fast onset

Short duration (1-2hours)

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11
Q

What are the systemic effects of lidocaine?

A 
Anti-arrhythmic 
Decrease MAC 
Analgesic 
Free radical scavenger 
Improves GI motility
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12
Q

What local anesthetic has the highest cardiovascular toxicity?

A

Bupivacaine

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13
Q

What is the onset and duration of bupivacaine?

A

Imtermediate onset

Duration: 3-8hours

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14
Q

What are the uses of mepivicaine?

A

Nerve block
Intra-articular

-common in large animal

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15
Q

What is the onset and duration of mepivaciaine?

A

Fast onset

Duration 1.5-3hours

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16
Q

What are the ester local anesthetics?

A

Procaine

Tetracaine and proparacaine (ophthalamic prep)

Benzocaine -laryngeal spray for intubation (not in cats!)

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17
Q

What site of administration will have the fastest systemic absorption of local anesthetics?

A

Intercostal blocks

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18
Q

How are esters metabolized?

A

Hydrolysis by plasma cholinesterase

One of the metabolizes, paraaminobenzoic acid (PABA) May amuse allergic reactions

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19
Q

How are amides metabolized?

A

Microsomal liver enzymes
-dependent on normal hepatic function

More likely to accumulate than esters

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20
Q

What can you do to prolong local anesthetic blockage?

A

Epinephrine

—» causes vasoconstriction and slows systemic absorption and increased duration of action at local site

21
Q

What additive can make a local anesthetic have a faster onset of action, prolonged duration, and less sting on injection

A

Bicarbonate

22
Q

T/F: toxicity of local anesthetics is addictive

A

True

-> consider this when combining drugs

23
Q

What toxicity do benzocaine and prilocaine cause?

A

Methemoglobinemia
—used to be a laryngeal spray for intubation

No used in vet med

24
Q

T/F: spinal bupivacaine causes worse neurotoxicity than lidocaine

A

False

Spinal Lidocaine causes worse neurotoxicity than bupivacaine

25
Q

The neurotoxicity effects of local anesthetics are _________ dependent

A

Concentration

26
Q

The chondrotoxicity effects of local anesthetics are ___________ dependent

A

Concentration AND time

27
Q

What local anesthetic has the most chondrotoxicity and intra-articular use should be minimized

A

Bupivacaine

28
Q

What local anesthetic is the least chondrotoxicity and is used intra-articular for equine lameness diagnosis

A

Mepivacaine

29
Q

What are signs of systemic toxicity of lidocaine?

A

Depression/sedation
Twitching
Seizures

THEN.. Cardiovascular signs

30
Q

What are signs of systemic toxicity of bupivacaine ?

A

Cardiovascular collapse

  • SVT/ VT/ AVblock
  • wide QRS complex

-hypotension, CV, collapse, death

31
Q

In formulations with epinephrine, how will systemic toxicity appear?

A

Increasing HR with IV injection

32
Q

What are risk factors for systmeic toxicity?

A

IV injection

Increased absorption sites
-intercostal> epidural> brachial plexus

Patient factors

  • hypoproteinemia
  • pregnancy
  • beta or Ca channel blockade
  • hypoxemia, acidosis
33
Q

How do you treat arrest secondary to LA?

A

Start CPR

Low dose epi

20% lipid emulsion (intralipid)

AVOID- lidocaine, Ca channel blockers, B Blockers, and vasopressin

34
Q

How do you treat allergic reactions occurring due o LA?

A

Epi
Fluids
Airway maintenance

—> most common wit procainamide in procaine penicillin G (PPG)

35
Q

What are the goals of local anesthesia?

A

Provide analgesia

MAC sparing
-decrease hypotension

Prevent central sensitization

36
Q

What is the order of nerve blockade with LA?

A 
B fibers -preganglionic sympathetic 
A-delta, and C fibers -pain 
A-y - proprioceptive 
A-B - touch and pressure 
A-a - motor

Generally smaller diameter with less myelination blocked first —> sensory

Except brachial plexus
—> motor fibers blocked first

37
Q

Route of admin is used for epidermal, eye, or laryngeal procedures ?

A

Topical

38
Q

___________ administration is used for mass removal and wounds

A

Subcutaneous

39
Q

What types of block is used for ventral midline or flanks

A

Line block

40
Q

What are the types of peripheral intravenous regional anesthesia?

A

Individual nerve
Plexus
Intercostal
Paravertebral

41
Q

What are the types of central intravenous regional anesthesia?

A

Epidural

Spinal

42
Q

What is a Bier block?

A

Limb wrapped tightly (tourniquet)

Local anesthetic into peripheral vein
-> diffuse into target tissue

When tourniquet is released—> systemic circulation (for lidocaine only)

43
Q

What is the difference between epidural and spinal anestherisia

A

Epidural space- between dura and vertebrae

Spinal -space between dura and spinal cord (containing CSF)

44
Q

What type of block is used for tail/perineum/hindlimb/abdominal/thoracic procedures

A

Epidural anesthesia

45
Q

Where does the spinal cord end in dog?

A

L6-L7

46
Q

Where does the spinal cord end in cats?

A

L7-S3

47
Q

When is an epidural contraindicated?

A 
Coagulopathies 
Hypovolemia 
Infection at injection site 
Neoplasia 
Anatomy (cannot palpate landmark)
Sepsis
48
Q

What are adverse effects of epidurals?

A

Hypotension — block of sympathetic trunk—> decrease vascular tone

Motor block/paralysis (mostly a concern in horse)

Hematoma, infection, neurotoxicity

49
Q

What tools can aid in nerve blocks?

A

Nerve locator — insulated needle -> motor response when close to the nerve

Ultrasound — visualize and LA injected peri-neurally

RUSVM Anesthesiology Summer 2019 (2 decks)

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