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Local Anesthetics Flashcards

1
Q

What was the first local anesthetic and when was it introduced?

A

Cocaine- 1884

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2
Q

What is unique to cocaine as a LA?

A

It causes profound vasoconstriction

others will cause vasodilation

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3
Q

Is cocaine still in use today? If yes, what is it typically used for?

A

Yes! It is a schedule II drug typically used for nasal surgery in humans (or other highly vascular surgeries)

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4
Q

What are the two classifications of LAs?

A

Ester-CO-

Amide -NHC-

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5
Q

What is the general structure of LAs?

A

Aromatic ring and hydrophilic portion joined by a hydrocarbon chain

They are classified by the hydrocarbon chain

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6
Q

What are the esters?

A

Cocaine, procaine, chloroprocaine, tetracaine

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7
Q

What are the amides?

A

Lidocaine, mepivicaine, bupivicaine, etodicaine, prilocaine, ropivacaine

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8
Q

What is the general MOA of LAs?

A

Bind to sodium channels in nerve membranes slowing rate of depolarization

Threshold potential cannot be reached and action potentials are not propagated

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9
Q

T/F: LAs are weak acids.

A

False- all LAs are weak bases

pK ~7.7-9

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10
Q

What kind of tissues will increase ionization of LAs?

A

Acidic tissues (ie infection esp) which makes them inactive

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11
Q

What three things affect potency, onset, and duration?

A
  • pK
  • protein binding
  • lipid solubility
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12
Q

Will a higher or lower pK increase onset time?

A

Lower- closer to tissue pH

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13
Q

Will a greater or lesser affinity to protein binding increase duration of action?

A

High protein binding affinity

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14
Q

Will a higher or lower lipid solubility increase potency?

A

Higher the lipid solubility, higher the potency

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15
Q

What is the only LA that can be given IV or for IVRA?

A

Lidocaine

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16
Q

What is lidocaine onset/duration?

A

Fast onset, short duration

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17
Q

Is lidocaine absorbed transcutaneously?

A

Yes

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18
Q

What are the systemic/IV effects of lidocaine?

A
  1. Antiarrhythmic
  2. Decrease MAC
  3. Analgesic
  4. Free radical scavenger
  5. Improves GI motility
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19
Q

What is the onset/duration of bupivicaine?

A

Immediate onset, moderate duration (3-8hr)

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20
Q

T/F: Bupivicaine has the lowest cardiovascular toxicity.

A

FALSE- highest toxicity, do not give IV

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21
Q

What is mepivacaine used for?

A

Nerve blocks, intra-articular analgesia (large animals)

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22
Q

What is the onset/duration of mepivacaine?

A

Fast onset, short duration (1.5-3)

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23
Q

What is the onset/duration of ropicacaine?

A

Intermediate onset, moderate duration (3-8hr)

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24
Q

T/F: Ropivacaine is less cardiotoxic than bupivacaine.

A

True

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25
What is procaine commonly used for?
Procaine penicillin G suspensions (PPG)
26
What are tetracaine and proparacaine commonly used for?
Ophthalmic preparations
27
What is benzocaine commonly used for?
Historically used as a laryngeal spray for intubation
28
What does systemic absorption depend on?
1. Site of injection 2. Dosage 3. Drug Characteristics 4. If epinephrine is used
29
What site of injection has the fastest absorption?
Intercostal blocks
30
How are esters metabolized?
Hydrolysis of plasma cholinesterases
31
How are amides metabolized?
Microsomal liver enzymes
32
Are amides or esters more likely to accumulate?
Amides
33
Do amides or esters have a metabolite that may cause allergic reactions?
Esters PABA may cause subsequent allergic reactions
34
Why is epinephrine used with LAs?
To prolong duration of block via vasoconstriction
35
Why is bicarbonate used with LAs?
Shorten onset and prolong duration, decrease sting on injection
36
Why would LAs be combined?
Shorter onset and longer duration combining lidocaine and bupivicaine? Not really useful overall and may increase toxicity
37
What drugs cause methemoglobinemia?
Benzocaine and prilocaine Benzocaine + tetracaine (cetacaine) laryngeal spray especially in cats (discontinued used in vet med)
38
T/F: Neurotoxicity is concentration dependent and can cause permanent damage.
True, although permanent damage is rare with normal clinical use
39
What drugs are the most neurotoxic?
Spinal lidocaine most, bupivacaine
40
What kinds of LAs should be used for spinal anesthesia/epidurals to avoid neurotoxiticy?
Preservative free
41
T/F: Chondrotoxicity is concentration and time dependent.
True
42
What is the most chondrotoxic LA?
Bupivicaine, no longer administered IA
43
What is the least chondrotoxic LA?
Mepivacaine (carbocaine)- most often used for equine lameness dx
44
What is systemic toxicity caused by?
Excessive plasma concentrations due to inadvertent IV infection or excessive doses/intolerant patient
45
What are the signs of systemic toxicity with lidocaine?
Depression/sedation, twitching, CV signs
46
What are the signs of systemic toxicity with bupicavaine?
Cardiovascular collapse and death
47
If epinephrine is used, what is the first sign of accidental IV injection?
Increased HR
48
What are the goals of local anesthesia?
1. Provide analgesia before, during, and after a procedure 2. May allow decreased dosage of systemic drugs 3. Prevents central sensitization 4. Important for multimodal anesthesia
49
What is the order of the nerve blockade?
Smaller, less myelinated fibers first 1. B fibers- pre-gang. sympathetic 2. A-delta and C fibers- pain 3. A-gamma fibers- prorioception 4. A-beta fibers- touch/pressure 5. A-alpha fibers- motor
50
What is the exception to the order of nerve blockade?
Brachial plexus- motor neurons blocked fist | motor nearer to periphery
51
What are the three types of local anesthesia?
1. Topical 2. Subcutaneous 3. Line block
52
What are the three types of regional anesthesia?
1. IVRA 2. Peripheral- individual nerves or areas 3. Central (neuraxial)- epidural or spinal
53
What type of anesthesia is a bier block?
Intravenous regional anesthesia
54
What is the procedure for a bier block?
Tourniquet is placed and anesthetic is injected to a peripheral vein and allowed to diffuse into target tissues
55
What LA is used for bier blocks and why?
Lidocaine only- it will be released into systemic circulation after procedure is finished
56
What is the difference between epidural and spinal anesthesia?
Epidural- injection into the space between the dura and vertebrae Spinal- injection into the space between the dura and spinal cord, into CSF
57
Where are epidurals used?
Tail/perineum, hindlimb, and abdominal/thoracic pain/procedures
58
Where does the spinal cord end?
Dogs- L6-L7 Cats- L7-S3 Horses, ruminants, pigs- mid sacrum
59
How should the doses be adjusted if CSF is encountered?
Decreased by 50%
60
What are contraindications to epidurals?
CHINAS - Coagulopathy - Hypovolemia - Infection at site - Neoplasia at site - Anatomy- Inability to palpate landmarks - Sepsis
61
What are adverse effects of epidurals?
- Hypotension - Motor block/paralysis (concerning for LA) - Hematoma - Infection - Neurotoxicity
62
What is a nerve locator?
Electrostim unit with an insulated needle that produces a motor response when needle is close to a nerve
63
Can ultrasound be used to locate nerves?
Yes

Anesthesiology (27 decks)

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