Neuromuscular blockers

Question 1

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

Answer 1

a. alpha and alpha

Question 2

The neuromuscular junction is the synaptic connection between a

Answer 2

motor nerve and skeletal muscle

Question 3

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

Answer 3

acetylcholine

Question 4

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

Answer 4

The postsynaptic nicotinic receptor

Question 5

_______________ is an enzyme that terminates the effect of Ach

Answer 5

acetylcholinesterase

Question 6

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

Answer 6

two alpha-subunits; Na+

Question 7

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

Answer 7

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)

Question 8

What are the subunits of the postsynaptic nicotinic receptor?

Answer 8

2 alpha
1 beta
1 delta
1 epsilon

Question 9

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

Answer 9

negative

Question 10

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

Answer 10

they’re repelled by the negative charge in the channel

Question 11

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

Answer 11

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

Question 12

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

Answer 12

b. an epsilon subunit replaces a gamma subunit

Question 13

______________ or ______________ can lead to the proliferation of extrajunctional receptors

Answer 13

Denervation injury or prolonged immobility

Question 14

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

Answer 14

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

Question 15

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

Answer 15

hyperkalemia

Question 16

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

Answer 16

24-48 hours and at least one year after

Question 17

Treatment of succinylcholine-induced hyperkalemia includes

Answer 17

IV calcium chloride
hyperventilation
glucose+ insulin
sodium bicarbonate

Question 18

Patients with upregulation of extrajunctional receptors are ______________ to nondepolarizers.

Answer 18

resistant
this reduces the potency of these drugs

Question 19

How many pathologic variants of the nicotinic receptor are there?

Answer 19

two

Question 20

What are the two pathologic variants of the nicotinic receptor?

Answer 20

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

Question 21

What conditions represent contraindications to the use of succinylcholine?

Answer 21

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)

Question 22

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

Answer 22

Burns

Question 23

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

Answer 23

b. antagonism of presynaptic nicotinic receptors

Question 24

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

Answer 24

antagonism of presynaptic Nn receptors

Question 25

Fade is observed with

Answer 25

nondepolarizers because they competitively antagonize the presynaptic Nn receptors

Question 26

Fade is not observed with

Answer 26

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

Question 27

With succinylcholine, acetylcholine mobilization in the presynaptic nerve terminal is

Answer 27

preserved

Question 28

With nondepolarizers, acetylcholine mobilization in the presynaptic nerve terminal is

Answer 28

impaired

Question 29

Acetylcholine is synthesized from

Answer 29

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

Question 30

What are the two supplies of Ach vesicles?

Answer 30

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

Question 31

A fraction of the Ach molecules binds to

Answer 31

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

Question 32

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

Answer 32

1. fade with tetany 4. prolonged duration

Question 33

A phase 2 block occurs with

Answer 33

an excessive dose of succinylcholine

Question 34

__________________ distinguishes between a phase 1 and phase 2 block.

Answer 34

The presence or absence of fade

Question 35

_____________ does not exhibit fade

Answer 35

Phase 1

Question 36

___________ exhibits fade

Answer 36

Phase 2

Question 37

_______________ produce a phase 2 block

Answer 37

Nondepolarizers

Question 38

Under normal circumstances, succinylcholine produces a

Answer 38

phase 1 block

Question 39

What is a phase 1 block?

Answer 39

membrane depolarizes, causing initial muscular contraction followed by flaccid paralysis

Question 40

What is a phase 2 block?

Answer 40

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

Question 41

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

Answer 41

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

Question 42

A phase 1 response to stimulation is

Answer 42

diminished but equal- there's no fade

Question 43

A phase 2 response to stimulation is characterized by a

Answer 43

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

Question 44

There's no post-tetanic potentiation with

Answer 44

a phase 1 block

Question 45

There is post-tetanic potentiation with

Answer 45

a phase 2 block

Question 46

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

Answer 46

d. inspiratory force better than ~40 cmH2O

Question 47

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

Answer 47

80%

Question 48

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

Answer 48

70%

Question 49

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

Answer 49

70-75%

Question 50

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

Answer 50

50%

Question 51

Recovery from neuromuscular blockade is defined as a TOF ratio of

Answer 51

>0.9

Question 52

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

Answer 52

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

Question 53

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

Answer 53

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

Question 54

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

Answer 54

onset, duration, and sensitivity

Question 55

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

Answer 55

20-40%

Question 56

The best qualitative bedside tests of recovery include

Answer 56

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

Question 57

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

Answer 57

Electromyography & acceleromyography

Question 58

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

Answer 58

The return ofa normal tidal volume

Question 59

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

Answer 59

>0.9

Question 60

__________________________ is exquisitely sensitive to the effects of muscle relaxants

Answer 60

The upper airway musculature (e.g. genioglossus)

Question 61

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

Answer 61

subjective; visual or tactile fade

Question 62

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

Answer 62

central muscles; peripheral muscles