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Apex Review > Neuromuscular blockers > Flashcards

Neuromuscular blockers Flashcards

1
Q

Which subunits MUST be occupied to open the nicotinic receptor at the motor endplate?
a. alpha and alpha
b. alpha and gamma
c. alpha and delta
d. alpha and epsilon

A

a. alpha and alpha

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2
Q

The neuromuscular junction is the synaptic connection between a

A

motor nerve and skeletal muscle

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3
Q

When the presynaptic nerve terminal depolarizes, it releases ___________ into the synaptic cleft

A

acetylcholine

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4
Q

__________________ is a pentameric ligand-gated ion channel located in the motor endplate at the neuromuscular junction

A

The postsynaptic nicotinic receptor

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5
Q

_______________ is an enzyme that terminates the effect of Ach

A

acetylcholinesterase

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6
Q

When acetylcholine binds to the _____________ on the postsynaptic nicotinic receptor, it allows _______ to enter the skeletal muscle.

A

two alpha-subunits; Na+

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7
Q

What are the type types of nicotinic acetylcholine receptors at the neuromuscular junction?

A

prejunctional Nn receptor is present on the presynaptic nerve (n= nerve)
postsynaptic Nm receptor is present at the motor endplate on the muscle cell (m= muscle)

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8
Q

What are the subunits of the postsynaptic nicotinic receptor?

A

2 alpha
1 beta
1 delta
1 epsilon

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9
Q

At rest, the inside of the muscle cell is ____ relative to the outside of the cell.

A

negative

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10
Q

Why don’t anions (like Cl-) pass through the postsynaptic nicotinic receptor channel?

A

they’re repelled by the negative charge in the channel

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11
Q

How is the action of Ach terminated at the post-junctional nicotinic receptor?

A
  1. Ach is metabolized by acetylcholinesterase to choline and acetate
  2. it diffuses away from the receptor
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12
Q

All of the following statements regarding extrajunctional nicotinic receptors are true EXCEPT:
a. it’s opened by choline
b. an epsilon subunit replaces a gamma subunit
c. it opens for a longer period of time
d. denervation allows for its proliferation

A

b. an epsilon subunit replaces a gamma subunit

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13
Q

______________ or ______________ can lead to the proliferation of extrajunctional receptors

A

Denervation injury or prolonged immobility

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14
Q

In the absence of extrajunctional receptors, succinylcholine can transiently increase serum potassium by ________________ for up to ____________.

A

0.5-1.0 mEq/L for up to 10-15 minutes

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15
Q

The presence of extrajunctional receptors predisposes the patient to _________ following succinylcholine administration.

A

hyperkalemia

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16
Q

As a general rule, in the event of a denervation injury, succinylcholine is best avoided ______________ following the injury and at least ______________

A

24-48 hours and at least one year after

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17
Q

Treatment of succinylcholine-induced hyperkalemia includes

A

IV calcium chloride
hyperventilation
glucose+ insulin
sodium bicarbonate

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18
Q

Patients with upregulation of extrajunctional receptors are ______________ to nondepolarizers.

A

resistant
this reduces the potency of these drugs

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19
Q

How many pathologic variants of the nicotinic receptor are there?

A

two

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20
Q

What are the two pathologic variants of the nicotinic receptor?

A

The a7 subtype consists of five alpha subunits
The a2B1… subtype has a gamma subunit instead of an epsilon subunit

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21
Q

What conditions represent contraindications to the use of succinylcholine?

A

upper or lower motor neuron injury
spinal cord injury
burns
skeletal muscle trauma
cerebrovascular accident
tetanus
severe sepsis
muscular dystrophy
prolonged chemical denervation (magnesium, long term NMB infusion, clostridial toxin)

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22
Q

________ may be an exception to this rule, as risk of hyperkalemia can persist for several years after

A

Burns

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23
Q

Fade during train-of-four stimulation is caused by:
a. agonism of presynaptic nicotinic receptors
b. antagonism of presynaptic nicotinic receptors
c. impaired presynaptic acetylcholine reuptake
d. decreased acetylcholine synthesis

A

b. antagonism of presynaptic nicotinic receptors

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24
Q

Fade during train-of-four stimulation is most likely caused by

A

antagonism of presynaptic Nn receptors

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25
Q

Fade is observed with

A

nondepolarizers because they competitively antagonize the presynaptic Nn receptors

26
Q

Fade is not observed with

A

succinylcholine (assuming a phase 1 block) because it stimulates presynaptic Nn receptors

27
Q

With succinylcholine, acetylcholine mobilization in the presynaptic nerve terminal is

A

preserved

28
Q

With nondepolarizers, acetylcholine mobilization in the presynaptic nerve terminal is

A

impaired

29
Q

Acetylcholine is synthesized from

A

choline & acetyl CoA in the presence of the enzyme choline acetyltransferase

30
Q

What are the two supplies of Ach vesicles?

A

ach that is available for immediate release
ach that must be mobilized before it can be made available for immediate release

31
Q

A fraction of the Ach molecules binds to

A

prejunctional receptors on the nerve terminal allowing for mobilization of Ach vesicles to the frontline

32
Q

Identify the statement that BEST characterizes a phase 2 block following succinylcholine (select 2.):
1. fade with tetany
2. post-tetanic potentiation is absent
3. constant but diminished response to double burst stimulation
4. prolonged duration

A
  1. fade with tetany
  2. prolonged duration
33
Q

A phase 2 block occurs with

A

an excessive dose of succinylcholine

34
Q

__________________ distinguishes between a phase 1 and phase 2 block.

A

The presence or absence of fade

35
Q

_____________ does not exhibit fade

A

Phase 1

36
Q

___________ exhibits fade

A

Phase 2

37
Q

_______________ produce a phase 2 block

A

Nondepolarizers

38
Q

Under normal circumstances, succinylcholine produces a

A

phase 1 block

39
Q

What is a phase 1 block?

A

membrane depolarizes, causing initial muscular contraction followed by flaccid paralysis

40
Q

What is a phase 2 block?

A

membrane repolarizes but the nicotinic receptor remains unable to respond to Ach

41
Q

What two situations favor the development of a phase 2 block with succinylcholine?

A

dose > 7-10 mg/kg
greater than 30-60 minutes of continuous exposure (IV infusion)

42
Q

A phase 1 response to stimulation is

A

diminished but equal- there’s no fade

43
Q

A phase 2 response to stimulation is characterized by a

A

progressive decrease in the intensity of the response- there’s fade

44
Q

There’s no post-tetanic potentiation with

A

a phase 1 block

45
Q

There is post-tetanic potentiation with

A

a phase 2 block

46
Q

Identify the MOST sensitive indicator of recovery rom neuromuscular blockade.
a. nerve stimulator shows 4/4 twitches with no fade
b. tidal volumes 6 mL/kg
c. vital capacity >20 mL/kg
d. inspiratory force better than ~40 cmH2O

A

d. inspiratory force better than ~40 cmH2O

47
Q

A tidal volume of 6 mL/kg is possible when no more than ______________ of the receptors are blocked

A

80%

48
Q

A vital capacity that exceeds 20 mL/kg is possible when no more than _________ of the receptors are blocked

A

70%

49
Q

4/4 twitches without fade is possible when no more than __________ of the receptors are blocked

A

70-75%

50
Q

An inspiratory force better than ~40 cmH2O is possible when no more than ____________ of the receptors are blocked

A

50%

51
Q

Recovery from neuromuscular blockade is defined as a TOF ratio of

A

> 0.9

52
Q

The best place to measure the onset of blockade (intubation conditions):

A

muscle: orbicularis oculi (closes eyelid) or corrugator supercilii (eyebrow twitch)
nerve: facial nerve

53
Q

The best place to measure recovery of blockade (return of upper airway muscle function):

A

muscle= adductor pollicis (thumb adduction) or flexor hallucis (big toe flexion)
nerve= ulnar nerve or posterior tibial nerve

54
Q

Muscle groups respond differently in terms of _____, ______, & ________ to neuromuscular blockade

A

onset, duration, and sensitivity

55
Q

Despite our best efforts, the risk of residual neuromuscular blockade is

A

20-40%

56
Q

The best qualitative bedside tests of recovery include

A

sustained tetany >5 seconds, sustained head lift >5 seconds, and the patient’s ability to hold a tongue blade in his mouth against force

57
Q

______________ & _______________ are quantitative assessments that provide a more accurate assessment of the patient’s true degree of recovery from neuromuscular blockade

A

Electromyography & acceleromyography

58
Q

____________________ is a poor endpoint for assessing the return of neuromuscular function

A

The return ofa normal tidal volume

59
Q

The ability to protect the airway may not fully return until the TOF ratio is

A

> 0.9

60
Q

__________________________ is exquisitely sensitive to the effects of muscle relaxants

A

The upper airway musculature (e.g. genioglossus)

61
Q

The data we obtain from the PNS is highly ________________, and it’s difficult to detect ________ or _________ when the TOF ratio is >0.4.

A

subjective; visual or tactile fade

62
Q

As a general rule, more ________ are more resistant to the effects of NMBs and recover sooner than ______________

A

central muscles; peripheral muscles

Apex Review (224 decks)

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