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Anesthesia Pharm I > Neuromuscular Blockers > Flashcards

Neuromuscular Blockers Flashcards

1
Q

What is the action of NMBs?

A

Prevents muscle contraction by interfering with the transmission of an action potential from the nerve ending to the muscle

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2
Q

What are NMBs used for?

A

Facilitates endotracheal intubation, decreases muscle tone for optimal operating conditions, alleviates muscle activity with ECT, allow balanced anesthesia without patient movement, assist in controlled ventilation in ICU patients.

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3
Q

Where do NMBs work?

A

The neuromuscular junction between the nerve and muscle

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4
Q

_______ influx causes vesicles to adhere to the ________ ________ and rupture to release ________ into the cleft

A

Calcium influx causes vesicles to adhere to the presynaptic membrane and rupture to release acetylcholine into the cleft

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5
Q

ACh diffuses across _____ _____ to the _______ receptor located on the motor end plate.

A

ACh diffuses across the synaptic cleft to the nicotinic (cholinergic) receptor located on the motor end plate.

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6
Q

ACh binds with the ______ sites on the postsynaptic receptor, causing the opening of the _____ ______. Then what happens to Na and K ions?

A

ACh binds with the alpha sites on the postsynaptic receptor, causing the opening of the ion channel.

The sodium and potassium ions move through the channel causing depolarization of the motor end plate membrane (change in transmembrane potential from -90mV to -45 mV- the threshold potential.
-Sodium comes in, potassium goes out.

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7
Q

What causes a muscle contraction?

A

The action potential spreading over the surfaces of the muscle fibers.

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8
Q

Muscle contraction is initiated by _______-_______ _______

A

muscle contraction is initiated by excitation-contraction coupling.

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9
Q

What happens with ACh after muscle contraction?

A

ACh quickly diffuses away from the end plate region or is metabolized (hydrolyzed) by acetylcholinesterase (AChE), a local acetylcholine enzyme

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10
Q

Where is AChE contained?

A

In the postsynaptic membrane

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11
Q

What does it mean when a muscle repolarizes?

A

It relaxes

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12
Q

What happens if there is too much or too little of Ca when releasing acetylcholine?

A

ACh release is calcium-dependent and triggered by increases in the concentrations of free Ca ions in the nerve terminals.
-Too much Ca, too much contraction.
-Too little Ca, not enough contraction.

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13
Q

What is the process of Ca triggering ACh release?

A

A nerve action potential activates adenylate cyclase in membranes of nerve terminals leading to the formation of cyclic adenosine monophosphate (cAMP), which subsequently opens Ca ion channels, causing synaptic vesicles to fuse with the nerve membrane and release ACh.

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14
Q

What is the primary transmitter for neuromuscular junctions?

A

Acetylcholine

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15
Q

What is the principle site of neuromuscular blocking agents?

A

Neuromuscular junctions

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16
Q

What inhibits release of ACh?

A

Magnesium. This is why we treat high Ca with magnesium sulfate.

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17
Q

Acetylcholine is rapidly _______ by _________ to ______ _____ and _______

A

Acetylcholine is rapidly hydrolyzed by acetylcholinesterase to acetic acid and choline.

-Happens in less than <15 ms

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18
Q

What happens after choline is formed from the breakdown of ACh?

A

It returns to nerve ending to be used to synthesize more ACh.

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19
Q

What are the ACh receptors?

A

Presynaptic (prejunctional), extrajunctional, and postsynaptic

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20
Q

What are presynaptic receptors?

A

These are on the nerve ending and they affect neurotransmitter release. Ion channel opening allows the flow of sodium only.
-activation of these mobilizes additional ACh for subsequent release (so blocking these receptors causes a decrease in ACh release)

-This is the receptor where you see a fade on the TOF

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21
Q

Which receptor causes a decrease in ACh release when it is blocked?

A

The presynaptic receptor.

22
Q

Extrajunctional receptors are also known as

A

fetal receptors

23
Q

Describe extrajunctional receptors.

A

They are similar to the ones found in the fetus. They are throughout the muscle cell. As cells mature, fewer of these are produced, and junctional becomes dominant.

They are not involved in neuromuscular transmission.

24
Q

When does proliferation of extrajunctional receptors occur?

A

if the muscle is damaged, diseased, or denervated. Ex- burns, paralysis, stroke, muscular dystrophies

This causes more locations for ACh and neuromuscular blockers to bind. This leads to the potential for catastrophic hyperkalemia.
-Succ should be avoided in these patients.
-This happens because the receptors are as sensitive to agonist stimulation as postsynaptic, but channels remain open 4X longer, causing the risk of hyperkalemia.

25
Q

Postsynaptic receptors are in the _______ ______ of the _________ _______, aligned across from the areas where presynaptic vesicles release ACh.

A

Postsynaptic receptors are in the junction folds of the muscle membrane, aligned across from the areas where presynaptic vesicles release ACh.

26
Q

Describe the structure of postsynaptic membranes

A

They are made up of 5 linear protein subunits arranged in a rosette which reach from extracellular to intracellular and form a channel for flow of sodium, potassium, and calcium ion.

-This is 2 alpha, 1 beta, 1 delta, and 1epsilon.

27
Q

What is the width of postsynaptic receptors?

A

20 to 30 nm wide and is filled with extracellular fluid.

28
Q

What receptor do we really want to block?

A

Postsynaptic.

29
Q

What must happen to open the channels with a postsynaptic receptor?

A

ACH must bind to extracellular sites on 2 alpha subunits to cause the receptor to open the channel to open and cations to flow through.
-Ca and Na flow into and K leaves the cell, causing the change in transmembrane potential and the muscle contraction.

30
Q

Both ______ ______ must be bound with ACh for what?

A

Both alpha subunits must be bound with ACh to cause the channels within the postsynaptic receptor to open.

31
Q

How do depolarizing and nondepolarizing blockers act on the alpha subunits in postsynaptic receptors?

A

These binding sites on alpha subunits are the points of action of both depolarizing blockers (attached to both sites, mimics ACh and causes depolarization) and nondepolarizing blockers (attached to one site to prevent ACh from binding, and thus prevents depolariztion.

32
Q

What is channel blockade?

A

This is when drugs physically block an open channel or a closed channel around the extracellular entrance.

-This can occur with antibiotics, quinidine, tricyclic antidepressants, and naloxone. Local anesthetics have this MoA (Na channel blockade.

33
Q

What is onset time?

A

The time from administration to maximum effect

34
Q

What is clinical duration?

A

The time from administration to 25% recovery of twitch response

35
Q

What is total duration?

A

The time from administration to 90% recovery of twitch response

36
Q

What is recovery index?

A

Time from 25% to 75% recovery of twitch response. The time from 1 twitch to 4 twitches.

37
Q

What is ED 95?

A

The dose needed to produce 95% suppression of single twitch response.

38
Q

Is NMB rapid, intermediate, or slow onset?

A

Prefer rapid.

39
Q

What are the objectives of clinical monitoring of NM function?

A

The titration of dosage of NMB to desired effect
Monitor for unusual resistance or sensitivity or prolonged action of a NMB
Evaluation of reversibility
Determine recovery from block in conjunction with clinical evaluation

40
Q

How do we monitor NMB?

A

Electrical stimulation of the peripheral motor nerve to observe the muscular contractions in response.

41
Q

Adult muscles have _______ NM junction per ______ with the exception of?

A

Adult muscles have one NM junction per muscle cell with the exception of the extraocular and facial muscles which have multiple innervations.

-this is why superficial nerves can give false twitches on the face.

42
Q

The ulnar nerve is located _______ to the _____ _____ _____ _____ and medial to the _____ _____.

When stimulated it will cause _________ of the thumb via the _____ _____ _____ muscle.

A

The ulnar nerve is located lateral to the flexor carpi ulnaris tendon and medial to the ulnar artery.

When stimulated it will cause adduction of the thumb via the adductor pollicis brevis muscle.

43
Q

The posterior tibial nerve is located behind _____ _____ of the _____ and posteromedial to the _____ _______ artery.

When stimulated it causes ______ _____ of the great toe.

A

The posterior tibial nerve is located behind the medial maleolus of the tibia and posteromedial to the posterior tibial artery.

When stimulated it causes plantar flexion of the great toe.

44
Q

The lateral popliteal or ______ ______ is located behind the head of the ________ and around the ______ of the ______.

When stimulated, the foot will ________

A

The lateral popliteal or peroneal nerve is located behind the head of the fibula and around the neck of the fibula.

When stimulated, the foot will dorsiflex.

-This is a bigger movement and easier to notice than the p.t. nerve.

45
Q

The facial nerve lies within the ______ ______ after it emerges from the ________ _________.

Place black electrode near the _____ of the ______

A

The facial nerve lies within the parotid gland after it emerges from the stylomastoid foramen.

Place black electrode near the tragus of the ear.

46
Q

What should you be aware of when stimulating facial nerves?

A

That the nerve has 5 different branches and that direct stimulation of superficial muscles (orbicularis oculi or the frontalis).

47
Q

What must we be mindful of when monitoring the OO for NMB?

A

It is possible to overdose the relaxant and overestimate the recovery from the block.

48
Q

What is the frequency for single twitch stimulus?

A

Between 0.1 Hz (1 stimulus every 10 seconds) and 4.0 Hz (4 stimuli every 1 second.)

49
Q

What is the frequency for TOF?

A

The delivery of 4 stimuli at a frequency of 2 Hz (four stimuli un 2 seconds)

50
Q

What is important to remember for TOF?

A

It relies on the reduction of ACh release with rapid rates of stimulation; so it is important to not repeat TOF too often. (wait 10 to 12 seconds)

-Within the initiation of blockade, all twitches decrease and disappear together.

51
Q

Does it mean that blockade is gone if all 4 twitches are present?

A

No, there can still be 70 to 75% of nerve receptors blocked.

-Think Spare receptor complex.

Anesthesia Pharm I (1 decks)

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