L4 Flashcards
What are the uses of neuromuscular blockers?
Muscle relaxants - intubation, surgery
Muscle paralysis - botox
Ortho
Describe the structure of the NMJ
Pre-synapse w/ active zones
Basal lamina w/ AChE
Post-synapse w/ dense nAChR
Peri-jxnal Na+ channels deep in synaptic folds
What are the 2 forms of botulinum toxin?
Both work to disrupt the SNARE proteins for vesicle fusion to release ACh at NMJ
BoNT A = botox, cleaves SNAP 25
BoNT B = myobloc, cleaves synaptobrevin
4 clinical uses of botulinum toxins
- Strabismus = misaligned eyes
- Excessive sweating
- Cervical dystonia (head twisting)
- Cosmetic
What is the structure of AChR?
Ion channel - Na/K
5 subunits: 2 alpha, beta, delta, gamma or epsilon (development)
ACh binds alpha subunit - need 2 AChs
Therefore blockers that bind 1 alpha inactivate the entire receptor
5 non-depol NM blockers
- d-Tubocurarine
- Pancuronium
- Vecuronium
- Cisatracurium
- Rocuronium
1 depolarizing NM blocker & metabolism
Succinyl choline
Hydrolyzed (aka metabolized) by BChE
Mechanism of non-depol NM blockers
Works by competitively blocking nAChR
See:
- ↓mepp & epp - proportionally
Why are non-depol NM blockers competitive blockers?
With repeated stimulation, see temporal summation
- ↑ACh in synapse yields larger and large depol - adds with each release to eventually reach threshold
Mechanism of depol NM blockers
Na channel inactivation
Binds nAChR - causing depol - then inactivates it
- Add drug slowly to suppress initial depol from happening all at once
If stim nerve, still get epps but don’t reach threshold b/c not opening any channels
What is the train of 4 stimulation
Tests depth of NM block
Fade = muscle twitch starts high then fades in correlation to the degree to which the non-depol is blocking
What does recovery from an NM block look like?
Looks like a train of 4
Starts high - goes low
See net amplitude grow with recovery until all twitches return to same baseline amplitude
NM blocker toxicity - what are 3 things you’re worried about
- Breathing - toxic level will arrest diaphragm muscle too
- Stimulating histamine release
- Inducing malignant hyperthermia
Can NM blockers cross BBB?
No - all charged
Also why can’t give PO - poor tissue penetration
Give IV
Babies response to NM blockers
More sen to ND blockers (use less)
Less sen D
B/c of how NMJ matures
Hypothermic response to NM blockers
Less sen to ND blocker
More sen to D
Lower temp = less efficient ATPase = membrane potential is more positive than normal (closer to threshold)
Genetic variant that would dictate NM blocker response
BChE variants for succinylcholine metabolism
Which electrolytes should you be aware of affecting the NMJ/NM blockers?
Ca2+
K
Hypokalemia response to NM blockers
Hyperpolarized
More sen to ND
Less sen to D
Hyperkalemia response to NM blocker
Closer to threshold
Less sen to ND
More sen to D
Which pts might be hypovolemic? How does this effect NM blockers?
Burn & trauma
Artificial hyperkalemia
DON’T use succinylcholine
How do MG pts respond to NM blockers?
Fewer nAChR there b/c autoimmune attack
BUT whatever is there is hypersensitized
VERY sen to ND blockers (acts directly on receptor)
How do pts with small cell (bronchiogenic) carcinoma respond to NM blockers?
No Ca2+ channels on pre-synaptic side
Less vesicle fusion –> less ACh release
Sen to BOTH ND and D
How do pts with liver disease respond to NM blockers? Which 3 NM blocker are specifically effected?
Liver makes less BChE
Decrease SuCh, vecuronium, rocuronium metab
