Skeletal Neuromuscular Blockers

Question 1

Skeletal neuromuscular blockers

Answer 1

act on neuromuscular receptors
first one is curare
curare is quaternary and is not absorbed orally

Question 2

Medical uses of neuromuscular blockers

Answer 2

surgery - abdominal and eye surgery
orthopedic procedures - overcome muscle spasm
bronchoscopy, laryngoscopy - blocks gag reflex
electroshock
artificial respiration - eliminate respiratory drive

Question 3

Two types of neuromuscular blockers

Answer 3

competitive - curare type
newborn and myasthenics sensitive; reversed by neostigmine

non-competitive (succinylcholine)
newborn and myasthenics resistant
not reversed by neostigmine; causes a depolarizing block that can become a curare-like block; associated with transient muscle twitch and post-op muscle soreness

Question 4

How do you monitor neuromuscular block

Answer 4

TOF: train of four impulses
response of 4th twitch relative to 1st twitch
Fade occurs with non-depolarizing block
recovery to 0.7 for spontaneous ventilation
0.9 for full clinical recovery

No fade with depolarizing block (fade can occur with phase II block with succinylcholine)

Question 5

Curare-type drugs

Answer 5

vary in effect and duration
d-tubocurarine: excreted in urine (50min duration; histamine release; ganglionic block)

mivacurium: hydrolysis by plasma esterases;

Question 6

Duration and action of succinylcholine

Answer 6

about 4 minutes
succinylcholine is two Ach molecules stuck together
hydrolyzed by pseudocholinesterase

Question 7

Sequence of muscle paralysis by curare

Answer 7

muscles of eye and speech
eyelids
fingers and toes
limbs become heavy 
intercostals 
diaphragm 
DOESNT EFFECT THE BRAIN

Question 8

Sequence of paralysis by succinylcholine

Answer 8

arms, legs, neck first
(face not affected much initially)
respiration last

Question 9

Precautions for neuromuscular blockers

Answer 9

always given IV or IM
lots of individual variation
apparatus for artificial respiration must be available
some drugs increase the effect (antibiotics, streptomycin, general anesthetics, enflurane)
succinylcholine hydrolyzed to choline which stimulates ganglia to increase BP
succinylcholine muscarinic effect –> bradycardia

Question 10

Precaution of succinylcholine

Answer 10

causes malignant hyperthermia
especially with halothane and isoflurane
involved congenital myopathy (defective ryanodyne receptor –> excessive Ca++ release in muscle/mainly the jaw)

Tx: dantrolene