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Anesthesiology > Local Anesthetics > Flashcards

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
Q

What is procaine commonly used for?

A

Procaine penicillin G suspensions (PPG)

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26
Q

What are tetracaine and proparacaine commonly used for?

A

Ophthalmic preparations

27
Q

What is benzocaine commonly used for?

A

Historically used as a laryngeal spray for intubation

28
Q

What does systemic absorption depend on?

A
  1. Site of injection
  2. Dosage
  3. Drug Characteristics
  4. If epinephrine is used
29
Q

What site of injection has the fastest absorption?

A

Intercostal blocks

30
Q

How are esters metabolized?

A

Hydrolysis of plasma cholinesterases

31
Q

How are amides metabolized?

A

Microsomal liver enzymes

32
Q

Are amides or esters more likely to accumulate?

A

Amides

33
Q

Do amides or esters have a metabolite that may cause allergic reactions?

A

Esters

PABA may cause subsequent allergic reactions

34
Q

Why is epinephrine used with LAs?

A

To prolong duration of block via vasoconstriction

35
Q

Why is bicarbonate used with LAs?

A

Shorten onset and prolong duration, decrease sting on injection

36
Q

Why would LAs be combined?

A

Shorter onset and longer duration combining lidocaine and bupivicaine?

Not really useful overall and may increase toxicity

37
Q

What drugs cause methemoglobinemia?

A

Benzocaine and prilocaine

Benzocaine + tetracaine (cetacaine) laryngeal spray especially in cats (discontinued used in vet med)

38
Q

T/F: Neurotoxicity is concentration dependent and can cause permanent damage.

A

True, although permanent damage is rare with normal clinical use

39
Q

What drugs are the most neurotoxic?

A

Spinal lidocaine most, bupivacaine

40
Q

What kinds of LAs should be used for spinal anesthesia/epidurals to avoid neurotoxiticy?

A

Preservative free

41
Q

T/F: Chondrotoxicity is concentration and time dependent.

A

True

42
Q

What is the most chondrotoxic LA?

A

Bupivicaine, no longer administered IA

43
Q

What is the least chondrotoxic LA?

A

Mepivacaine (carbocaine)- most often used for equine lameness dx

44
Q

What is systemic toxicity caused by?

A

Excessive plasma concentrations due to inadvertent IV infection or excessive doses/intolerant patient

45
Q

What are the signs of systemic toxicity with lidocaine?

A

Depression/sedation, twitching, CV signs

46
Q

What are the signs of systemic toxicity with bupicavaine?

A

Cardiovascular collapse and death

47
Q

If epinephrine is used, what is the first sign of accidental IV injection?

A

Increased HR

48
Q

What are the goals of local anesthesia?

A
  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
Q

What is the order of the nerve blockade?

A

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
Q

What is the exception to the order of nerve blockade?

A

Brachial plexus- motor neurons blocked fist

motor nearer to periphery

51
Q

What are the three types of local anesthesia?

A
  1. Topical
  2. Subcutaneous
  3. Line block
52
Q

What are the three types of regional anesthesia?

A
  1. IVRA
  2. Peripheral- individual nerves or areas
  3. Central (neuraxial)- epidural or spinal
53
Q

What type of anesthesia is a bier block?

A

Intravenous regional anesthesia

54
Q

What is the procedure for a bier block?

A

Tourniquet is placed and anesthetic is injected to a peripheral vein and allowed to diffuse into target tissues

55
Q

What LA is used for bier blocks and why?

A

Lidocaine only- it will be released into systemic circulation after procedure is finished

56
Q

What is the difference between epidural and spinal anesthesia?

A

Epidural- injection into the space between the dura and vertebrae

Spinal- injection into the space between the dura and spinal cord, into CSF

57
Q

Where are epidurals used?

A

Tail/perineum, hindlimb, and abdominal/thoracic pain/procedures

58
Q

Where does the spinal cord end?

A

Dogs- L6-L7
Cats- L7-S3
Horses, ruminants, pigs- mid sacrum

59
Q

How should the doses be adjusted if CSF is encountered?

A

Decreased by 50%

60
Q

What are contraindications to epidurals?

A

CHINAS

  • Coagulopathy
  • Hypovolemia
  • Infection at site
  • Neoplasia at site
  • Anatomy- Inability to palpate landmarks
  • Sepsis
61
Q

What are adverse effects of epidurals?

A
  • Hypotension
  • Motor block/paralysis (concerning for LA)
  • Hematoma
  • Infection
  • Neurotoxicity
62
Q

What is a nerve locator?

A

Electrostim unit with an insulated needle that produces a motor response when needle is close to a nerve

63
Q

Can ultrasound be used to locate nerves?

A

Yes

Anesthesiology (27 decks)

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