Neuromuscular Blockade Monitoring

Question 0

Activation of only ___ of the ACh-receptors is sufficient to cause depolarization and contraction.

Answer 0

20%

Question 1

What do neuromuscular blockers (paralytics) do?

Answer 1

• Prevent ACh that is released by peripheral nerves at NMJs from binding to post-junctional ACh receptors on muscle membranes
• This prevents neurally-mediated muscle membrane depolarization and subsequent muscle contraction

Question 2

How do we estimate ACh-receptor occupancy with paralytic dug?

Answer 2

• Measuring muscle response to peripheral nerve stimulation

Question 3

What is the supramaximal stimulus?

Answer 3

• The stimulating current (to the peripheral nerve) that is sufficient to cause all NMJs of that nerve to release ACh
• Usually > 30-50 mA

Question 4

What is TOF stimulation?

Answer 4

• Used most commonly to estimate the occupancy of the NMJ
• 4 supramaximal neural stimuli at 2 Hz to cause 4 sequential muscular contractions - a little less ACh is released with each stimulus

Question 5

Loss of the 4th response = _____% of receptors blocked

Answer 5

75-80%

Question 6

Loss of the 3rd response = _____% of receptors blocked

Answer 6

85%

Question 7

Loss of the 2nd response = _____% of receptors blocked

Answer 7

90%

Question 8

Loss of the 1st response = _____% of receptors blocked

Answer 8

98-100%

Question 9

What is the TOF ratio?

Answer 9

Amplitude of the 4th twitch divided by amplitude of the 1st twitch

Question 10

When the TOF ratio is >70-80% that means…?

Answer 10

> 20% of the receptors are NOT blocked and normal muscle contration should occur

Question 11

As the TOF ratio goes down….?

Answer 11

• That tells you that you are getting an increased percentage of receptors that are blocked

Question 12

What is electromyography?

Answer 12

• Based on measurement of muscle compound action potential that occurs with muscle membrane depolarization (electrical not mechanical)
• We give a stimulus and the muscle depolarizes, we then measure that depolarization

Question 13

Visual or tactile evaluation of the TOF ratio…

Answer 13

• Correlates very poorly with measured TOF ratio

- Clinicians NOT able to detect TOF fade when TOF ratio >0.40

Question 14

It is easy to underestimate neuromuscular blockade blockade because most other hand muscles are …?

Answer 14

• Less sensitive to paralytics than adductor pollicis.

- If you follow hand muscles other than adductor pollicis you are likely to give too much paralytic

Question 15

What muscle is most resistant to paralytics?

Answer 15

• Diaphragm

Question 16

The ulnar nerve innervates many muscle groups in the hand. Name 2.

Answer 16

• Adductor pollicis

- Some interossei

Question 17

TOF ratios less than 0.90 are associated with _______?

Answer 17

• functional impairment of the muscles of the pharynx and upper esophagus

Question 18

What other muscle is similar to adductor pollicis for neuromuscular monitoring?

Answer 18

• Orbicularis Oculi

Question 19

Why is some spontaneous recovery necessary for reversal of NMBA to be effective?

Answer 19

• The efficacy of AChE inhibitors (neostigmine) is limited because their maximum possible effect is when enzyme inhibition is 100%
• With high levels of paralytic drug, even 100% inhibition of AChE may not be sufficient to compete off the paralytic drug from the ACh receptor

Question 20

Maximum AChE inhibition occurs at neostigmine doses of _______?

Answer 20

50-70 mcg/kg

Question 21

The maximum depth of block that can be promptly (<10min) reversed by AChE inhibitors corresponds to the reappearance of _____?

Answer 21

• the 4th response to TOF stimulation