Skeletal Neuromuscular Blockers Flashcards
Skeletal neuromuscular blockers
act on neuromuscular receptors
first one is curare
curare is quaternary and is not absorbed orally
Medical uses of neuromuscular blockers
surgery - abdominal and eye surgery
orthopedic procedures - overcome muscle spasm
bronchoscopy, laryngoscopy - blocks gag reflex
electroshock
artificial respiration - eliminate respiratory drive
Two types of neuromuscular blockers
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
How do you monitor neuromuscular block
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)
Curare-type drugs
vary in effect and duration
d-tubocurarine: excreted in urine (50min duration; histamine release; ganglionic block)
mivacurium: hydrolysis by plasma esterases;
Duration and action of succinylcholine
about 4 minutes
succinylcholine is two Ach molecules stuck together
hydrolyzed by pseudocholinesterase
Sequence of muscle paralysis by curare
muscles of eye and speech eyelids fingers and toes limbs become heavy intercostals diaphragm DOESNT EFFECT THE BRAIN
Sequence of paralysis by succinylcholine
arms, legs, neck first
(face not affected much initially)
respiration last
Precautions for neuromuscular blockers
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
Precaution of succinylcholine
causes malignant hyperthermia
especially with halothane and isoflurane
involved congenital myopathy (defective ryanodyne receptor –> excessive Ca++ release in muscle/mainly the jaw)
Tx: dantrolene