Skeletal Neuromuscular Blockers

Question 1

Skeletal neuromuscular blockers produced a profound…

Answer 1

skeletal muscle relaxation

—act on Nm receptors

Question 2

What was the first neuromuscular blocker introduced into medical practice?

Answer 2

Curare

Question 3

When are neuromuscular blockers useful?

Answer 3

Surgery
Orthopedic procedures
Bronchoscopy
Artificial respiration

Also used with electroshock for depression

Question 4

Neuromuscular blockers and surgery

Answer 4

Especially abdominal and eye surgery

Minimize amount of anesthetic needed b/c can produce relaxation with theses neuromuscular blockers
—Make it easy to manipulate mm tissue

Question 5

Neuromuscular blockers and orthopedic procedures

Answer 5

Used to overcome muscle spasms with occur sometimes with compound fractures
—relaxation makes it easier to realign and split bone

Question 6

Neuromuscular blockers and bronchoscopy, laryngoscopy

Answer 6

Used to overcome the gag reflex so that the bronchoscope can be inserted
—done under general anesthesia

Question 7

Neuromuscular blockers in electroshock to treat depression

Answer 7

To eliminate possible injury during convulsive episode

Question 8

Neuromuscular blockers and artificial respiration

Answer 8

Used to eliminate any respiratory drive which would interfere with artificial rhythm

Usually involves infants or elderly

Question 9

What are the types of neuromuscular blockers?

Answer 9

Competitive - curare type

Non-competitive - succinylcholine

Question 10

Competitive - curare type - neuromuscular blockers

Answer 10

Newborns and myasthenics sensitive

Reversed by neostigmine

Question 11

Non-competitive - succinylcholine - neuromuscular blockers

Answer 11

Newborns and myasthenics resistant

Not reversed by neostigmine (at least initially)

Cause a “depolarizing block” at first but then block becomes “curare-like”

Associated with transient mm twitch and postoperative mm soreness

Question 12

Monitoring Neuromuscular Block

• -how is this done?
• -what is measured/determined?

Answer 12

Done with transdermal electrical stimulation of hands or face

Train of Four (“TOF”) impulses

Response of 4th twitch is relative to 1st –> TOF ratio

• –“fade” occurs with non-depolarizng block”
  - –curare
• –recovery to 0.7 needed for spontaneous ventilation
• –0.9 for full clinical recover

No fade with depolarizing block - succinylcholine
—however, fade can occur with phase II block with succinylcholine

Question 13

What are the curare type nm blockers?

Answer 13

D-tubocurarine

Mivacurium

Question 14

D-tubocurarine

• -eliminated how?
• -duration?
• -histamine release?
• -ganglionic block?

Answer 14

Excreted in urine (40%)
Lasts 50 min
Yes histamine release
Yes ganglionic block

Question 15

Mivacurium

• -eliminated how?
• -duration?
• -histamine release?
• -ganglionic block?

Answer 15

Hydrolyzed by plasma esterase’s
Lasts 15 min
Little histamine release
No ganglionic block

Question 16

Succinylcholine

• -duration
• -structure
• -elminiated?

Answer 16

Lasts about 4 minutes
Two molecules of Ach stuck together

Hydrolysized by pseudocholinesterase

Question 17

What is sequence of mm paralysis seen with curare?

Answer 17

Mm of eyes and speech first
Then eyelids
Then fingers, toes
Then limbs become heavy
Then intercoastals effected
Then diaphragm

Note - mm necessary for life are the last effected

Question 18

What is the sequence of mm paralysis seen with succinylcholine?

Answer 18

Arms, leg, neck first
Face not affected much initially
Respiration last

Question 19

Precautions for neuromuscular blocker use

Answer 19

• -always given IV or IM
• -individual variation
• -need to have artificial respiratory device available
• -some drugs increased the effect
• -succnylcholine hydrolysed to choline - bp
• -succinylcholine muscarinic effect - bradycardia
• -malignant hyperthermia

Question 20

What drugs increased the effects of nm blockers?

Answer 20

Some antibiotics
Streptomycin
General anesthetics, enfluarne

Question 21

What does choline do?

Answer 21

It stimulates ganglion and causes increased blood pressure

Question 22

Malignant hyperthermia and Succinylcholine

Answer 22

Especially seen with halothane and isoflurane

Involves congential myopathy
—defective ryanodyne receptor -> excess Ca++ release in muscle

Question 23

Why is dantrolene used in combination with succinylcholine?

Answer 23

To block the ryanodyne receptor and prevent excess release of calcium