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Pharmacology & Anesthesiology > Local Anesthetics > Flashcards

Local Anesthetics Flashcards

1
Q

what are the two types of local anesthetics? which has a longer duration of action?

A

esters (ROR) and amides (RNR); amides have a longer duration of action

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2
Q

all new local anesthetics are

A

amides (RNR)

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3
Q

what do local anesthetics do

A

block pain without causing unconsciousness

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4
Q

what is the MOA of local anesthetics

A

block Na channels -> inhibits APs in all neurons, as well as myocytes

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5
Q

what is the order in which local anesthetics block

A

small fibres (ex. pain) are blocked before large fibres (ex. motor)

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6
Q

where is the receptor for local anesthetics and what does this imply

A

on the cytoplasmic surface; must diffuse in the cell to produce effect

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7
Q

why are local anesthetics slower to produce an effect in inflammed or infected tissues

A

because they are weak bases, so they are protonated and ionized in an acidic environment, which prevents them from diffusing into the cell to block the Na receptor and cause effect

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8
Q

what combination with local anesthetics can produce necrosis

A

when lidocaine and epinephrine are used SQ

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9
Q

why might someone use lidocaine with epinephrine in practice

A

because lidocaine works until it diffuses away; by combining with a vasoconstrictor (E) we slow its removal and therefore prolong its action

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10
Q

what are some considerations if you were to use lidocaine with epinephrine

A
  • it slows the healing
  • do not use in end-artery supplied organs (ears, teats, digits, nose, penis…)
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11
Q

what are the first signs of local anesthetic overdose

A

drowsiness and muscle twitching

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12
Q

as plasma concentration of local anesthetics rises what happens

A

convulsions, unconsciousness, coma

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13
Q

what is a potential CVS side effect of LAs

A

blocks excitability of myocardium: AV block and arrhythmia

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14
Q

what are some examples of lidocaine formulation

A
  • injectible +/- epinephrine
  • gel
  • spray (ex. for intubating cats)
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15
Q

what is a consideration before reaching for lidocaine spray in difficult to intubate cats

A

they are more susceptible to CVS effects and seizures

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16
Q

what type of LA is lidocaine

A

an amide (RNR)

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17
Q

what LA is used for equine nerve blocks

A

mepivicaine

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18
Q

why does mepivicaine diffuse better in tissues and what is a consequence of this?

A

it has a lower pKa -> favours B form (unionized); greater toxicity compared to lidocaine

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19
Q

what are 3 characteristics of bupivicaine

A
  • slower onset (higher pKa) but longer action
  • 4x as potent as lidocaine
  • greater CVS toxicity so not available as IV
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20
Q

how does levobupivicaine relate to bupivicaine

A

it is the s(-) enantiomer

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21
Q

why is levobupivicaine safer than bupivicaine

A

does not distribute as well to the CNS or heart

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22
Q

what is the least irritating LA for eyes

A

proparacaine

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23
Q

long term use of proparacaine is related to

A

corneal sloughing and delayed healing

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24
Q

what is a “use-dependent block”

A

lidocaine blocks highly active Na channels more than resting Na channels because, in order to bind to the cytoplasmic part of the Na receptor, it needs to be open (vs. closed, resting sodium channels)

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25
Q

how does lidocaine have an anti-arrhythmic effect in low concentrations

A

arrythmias are related to unusual and frequent depolarizations of Na channels in damaged cardiac muscle; lidocaine blocks these random and unusual depolarizations but preserves the
less frequent, normally functioning signals via the use-dependent block effect

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26
Q

what should you never use if giving lidocaine systemically

A

products containing epinephrine (will impact HR and BP)

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27
Q

are esters or amides more resistant to enzymatic activity

A

amides

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28
Q

T/F amide LAs are more stable under sterilization and temperature extremes

A

T

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29
Q

LA enters the nerve fiber as a _________ base and the (ionized/unionized) form blocks conduction by interacting at _______ surface of the _____ channel

A

neutral/free base; ionized; inner; Na+

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30
Q

local anesthetics with a (higher/lower) pKa have more rapid onset of action

A

lower

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31
Q

describe what determines the following chemical properties of LAs:
- potency
- duration
- onset of action

A

potency: lipid-solubility
duration: protein binding
onset of action: pKa

32
Q

lidocaine vs bupivicaine:
- which has higher potency
- which has higher duration of action
- which has higher onset of action

A

bupivicaine for all 3

33
Q

describe the channel type based on the following affinity of Na:
- low
- intermediate
- high

A
  • low: closed
  • intermediate: open
  • high: inactivated
34
Q

T/F LAs block sensory, motor and autonomic pathways

A

T

35
Q

what is the order of blockage for LAs:

A

β < C < Αδ< Aα < Aβ

36
Q

T/F all fibers can be blocked by a LA, but some fibers may NOT be blocked

A

T

37
Q

T/F cats are more sensitive to LA toxicity compared to dogs

A

T

38
Q

put sites in order of fastest to slowest rate of absorption:
- SQ
- epidural
- spinal
- intercostal
- major nerve block

A

intercostal > spinal > epidural > major nerve block > SQ

39
Q

what should you keep a dose below for the following LAs:
- lidocaine
- bupivicaine

A

lidocaine: below 8 mg/kg
bupivicaine: below 2 mg/kg

40
Q

T/F most blocks are like IM/SQ injection

A

T

41
Q

With LA toxicity, we see ______ signs before ______ signs, but anesthesia masks _____ signs. Thus, you should watch ____ signs when a patient is anesthetized and ____ signs when a patient is awake

A

CNS; CVS; CNS; CVS; CNS

42
Q

in terms of LAs, you can only give ____________ intravenously

A

lidocaine

43
Q

LAs: __ blood loss, __ thromboembolism risk, __ perfusion

A

decrease; decrease; increase

44
Q

what is the general rule for the dose of LA (mL/kg)

A

0.2 mL/kg

45
Q

what are the 8 ways to clinically apply local anesthetics

A

1) topical
2) regional
3) catheter
4) splash
5) IVRA
6) neuraxial
7) infiltration
8) IV

46
Q

what is topical administration of local anesthetic

A

direct application to eyes, skin, mucous membranes, wounds

47
Q

what are three examples of topical LAs

A

1) lidocaine spray: facilitates intubation
2) skin: EMLA cream
3) proparacaine for direct application to cornea and conjunctiva

48
Q

what is a splash block

A

direct application to surgical site/cavity before closure

49
Q

what is infiltration

A

injected into tissue without anatomical concern regarding innervation

50
Q

what are examples of infiltration

A

incisional block for laparotomy, ring block

51
Q

what amount (mL) do you give for infiltration in the following species:
- horse/cow
- dog/sheep/goat
- cat

A
  • horse/cow: 100-200 mL
  • dog/sheep/goat: 5-15 mL
  • cat: 1-2 mL
52
Q

testicular block is an example of

A

infiltration

53
Q

inverted L block is an example of

A

infiltration

54
Q

where is the LA for a testicular block deposited

A

spermatic cord and testicular tissue

55
Q

what is a regional block

A

when LA is injected adjacent to sensory neurons

56
Q

what are some examples of regional blocks

A
  • brachial plexus block
  • sciatic block
  • RUMM block
  • retrobulbar block
  • head block
  • paravertebral block
57
Q

what nerves does the retrobulbar block stop

A

CN II, III, IV, V, VI and the ciliary ganglion

58
Q

what is the risk with retrobulbar blocks and what do we take from it

A

can cause proptosis, blindness, globe perforation, retrobulbar hemorrhage; should only use if you are enucleating

59
Q

what 4 head blocks are performed in small animals every day

A

1) mental
2) infraorbital
3) maxillary
4) mandibular (inferior alveolar)

60
Q

what nerves does the brachial plexus block stop

A

C6-8, T1

61
Q

what is blocked by the paravertebral thoracolumbar block

A

T13, L1, L2, L3 dorsal and ventral branches

62
Q

what 3 nerves do we block in a cornual nerve block and what is the additional nerve if an adult

A

All:
- cornual
- infratrochlear
- supraorbital

Adult:
- branches from C2

63
Q

what is another name for the cornual nerve

A

zygomaticotemporal

64
Q

dehorning in goats is different because they receive dual supply from

A

zygomaticotemporal and infratrochlear

65
Q

what is IVRA

A

intra-venous regional anesthesia: IV in a distal limb that has had its blood supply isolated using a tourniquet

66
Q

what are the two most common neuraxial LAs and what is used more often in vetmed

A

epidural and subarachnoid: epidural more common in vetmed

67
Q

what are the 2 epidurals we use

A

caudal and lumbosacral

68
Q

what does a lumbosacral epidural block

A

hindlimb and caudal abdomen as well as motor fibres

69
Q

how do we commonly administer a lumbosacral block (what drugs)

A

opioid and lidocaine or bupivacaine

70
Q

what does a sacrococygeal epidural block

A

anus, vulva, vagina, perineum, rectum, tail

71
Q

what is a useful block for feline urethral obstruction

A

sacrococygeal

72
Q

what do we commonly use for sacrococygeal block and why

A

lidocaine: faster onset

73
Q

what are some applications of IV lidocaine

A
  • analgesia/ MAC reduction
  • antiarrhythmic
  • antiinflammatory
  • anti-endotoxic
  • good for GI motility
  • neuropathic pain
74
Q

because local anesthetics can be cardiotoxic, it is important to monitor (2)

A

ECG and blood pressure

75
Q

what are some contraindications for local anesthetics

A
  • infection
  • allergic reacton
  • tumors
  • coagulopathies
  • cardiac disease

Pharmacology & Anesthesiology (22 decks)

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