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RUSVM Anesthesiology > 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
The neurotoxicity effects of local anesthetics are _________ dependent
Concentration
26
The chondrotoxicity effects of local anesthetics are ___________ dependent
Concentration AND time
27
What local anesthetic has the least chondrotoxicity and intra-articular use should be minimized
Bupivacaine
28
What local anesthetic is the least chondrotoxicity and is used intra-articular for equine lameness diagnosis
Mepivacaine
29
What are signs of systemic toxicity of lidocaine?
Depression/sedation Twitching Seizures THEN.. Cardiovascular signs
30
What are signs of systemic toxicity of bupivacaine ?
Cardiovascular collapse - SVT/ VT/ AVblock - wide QRS complex -hypotension, CV, collapse, death
31
In formulations with epinephrine, how will systemic toxicity appear?
Increasing HR with IV injection
32
What are risk factors for systmeic toxicity?
IV injection Increased absorption sites -intercostal> epidural> brachial plexus Patient factors - hypoproteinemia - pregnancy - beta or Ca channel blockade - hypoxemia, acidosis
33
How do you treat arrest secondary to LA?
Start CPR Low dose epi 20% lipid emulsion (intralipid) AVOID- lidocaine, Ca channel blockers, B Blockers, and vasopressin
34
How do you treat allergic reactions occurring due o LA?
Epi Fluids Airway maintenance —> most common wit procainamide in procaine penicillin G (PPG)
35
What are the goals of local anesthesia?
Provide analgesia MAC sparing -decrease hypotension Prevent central sensitization
36
What is the order of nerve blockade with LA?
``` 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
Route of admin is used for epidermal, eye, or laryngeal procedures ?
Topical
38
___________ administration is used for mass removal and wounds
Subcutaneous
39
What types of block is used for ventral midline or flanks
Line block
40
What are the types of peripheral intravenous regional anesthesia?
Individual nerve Plexus Intercostal Paravertebral
41
What are the types of central intravenous regional anesthesia?
Epidural | Spinal
42
What is a Bier block?
Limb wrapped tightly (tourniquet) Local anesthetic into peripheral vein -> diffuse into target tissue When tourniquet is released—> systemic circulation (for lidocaine only)
43
What is the difference between epidural and spinal anestherisia
Epidural space- between dura and vertebrae Spinal -space between dura and spinal cord (containing CSF)
44
What type of block is used for tail/perineum/hindlimb/abdominal/thoracic procedures
Epidural anesthesia
45
Where does the spinal cord end in dog?
L6-L7
46
Where does the spinal cord end in cats?
L7-S3
47
When is an epidural contraindicated?
``` Coagulopathies Hypovolemia Infection at injection site Neoplasia Anatomy (cannot palpate landmark) Sepsis ```
48
What are adverse effects of epidurals?
Hypotension — block of sympathetic trunk—> decrease vascular tone Motor block/paralysis (mostly a concern in horse) Hematoma, infection, neurotoxicity
49
What tools can aid in nerve blocks?
Nerve locator — insulated needle -> motor response when close to the nerve Ultrasound — visualize and LA injected peri-neurally

RUSVM Anesthesiology (32 decks)

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