Neuromuscular Blockers Flashcards
How many subunits comprise the postsynaptic nicotinic receptor at the NMJ?
5
Which subunits does acetylcholine bind to on the postsynaptic receptor?
Alpha and Alpha
How many acetylcholine molecules are required to activate postsynaptic nicotinic receptors?
Two, one for each alpha subunit
Why don’t anions pass through the pores opened during postsynaptic receptor stimulation?
The negative charge within the channel repels them
What are extrajunctional receptors?
Acetylcholine receptors that are dysfunctional and exist outside of the normal NMJ
In the event of a denervation injury, when should Succinylcholine be avoided?
Beginning 24-48 hours after the original injury, and extending 6-12 months. For burns, could be years if they still have contractures
How does the proliferation of extrajunctional receptors impact non-depolarizing NMB?
It makes patients less sensitive, because there are more receptors that require blocking
What happens when acetylcholine in the NMJ junction stimulates PREsynaptic Ach receptors?
It mobilizes stockpiled acetylcholine to the front line, so the cell is prepared to fire again
What role does calcium play in presynaptic cells?
Calcium influx destabilizes the proteins that hold acetylcholine in place, allowing exocytosis of acetylcholine
A phase one block is characterized by:
No post-tetanic potentiation
Constant diminished response to double burst stimulation
A phase two block is characterized by:
Fade with tetany
Prolonged duration
What is the best location to measure onset of blockade?
Orbicularis (Facial Nerve)
What is the best location to measure recovery from blockade?
Adductor Pollicis (Ulnar Nerve)
What are the best qualitative tests for recovery from blockade?
Tetany for > 5 seconds without fade
Head lift > 5 seconds
Holding tongue depressor in teeth against force
Central muscles are ______ resistant to paralytics than peripheral muscles
Central muscles are more resistant than peripheral muscles
Where on the body should you place the nerve stimulator to measure onset of blockade?
Where on the body should you place the nerve stimulator to measure recovery from blockade?
The genioglossus muscle doesn’t resume full function until the TOF is:
> 0.9!!! This means any amount of residual blockade will cause airway obstruction
Which response to succinylcholine is more common in adults: tachy or bradycardia?
Tachy in adults, because Succinylcholine mimics the effects of Ach at the SYMPATHETIC GANGLIA, causing an increase in SNS tone
Which response to succinylcholine is more common in pediatrics: tachy or bradycardia?
Bradycardia in peds
Succinylcholine stimulates M2 receptors in the SA node
What increases the risk of bradycardia in pediatrics?
Repeat doses. The reason is, it’s actually the metabolite of Succ that’s usually the culprit. Giving a repeat dose increases serum levels of the metabolite
If a pediatric patient requires a repeat dose of succinylcholine, what else should be given
Atropine or glyco
How much does Succinylcholine increase serum potassium levels
0.5-1 mEq/L for up to 10-15 min
Since succinylcholine increases intragastric pressure, does it increase the risk of aspiration?
No. It also increases LES tone, so the two cancel each other out
What is the role of Acetylcholinesterase?
It breaks down Ach in the NMJ
What is the role of pseudocholinesterase?
It breaks down Succ, Mivacurium, and the ester LAs
What are alternate names for pseudocholinesterase?
What are alternate names for acetylcholinesterase?
Where is pseudocholinesterase produced?
in the liver
What effect does late-stage pregnancy have on pseudocholinesterase?
It decreases Pseudocholinesterase activity, which will prolong the effects of Succ
What effect does obesity have on pseudocholinesterase?
It increases pseudocholinesterase activity, which will shorten the duration of succinylcholine
Will a patient with myasthenia gravis have an increase or decreased response to succinylcholine?
Decreased, because there are fewer receptors and therefore getting a full fasciculation is difficult
Which drugs decrease pseudocholinesterase activity?
Esmolol
Edrophonium
Metoclopramide
What are five key conditions that reduce pseudocholinesterase activity?
What is dibucaine?
It’s an amide local anesthetic that’s used to test pseudocholinesterase activity
What does a dibucaine number of 70-80 mean?
Typical homozygous
(AKA normal)
What does a dibucaine number of 50-60 mean?
Heterozygous variant
What does a dibucaine number of 20-30 mean?
Homozygous Atypical
(AKA completely abnormal)
What is the best treatment for a patient with prolonged paralysis from succinylcholine?
Sedation, ventilation, and time
How long will a patient with heterozygous pseudocholinesterase deficiency remain paralyzed after receiving succinylcholine?
20-30 min
How long will a patient with homozygous pseudocholinesterase deficiency remain paralyzed after receiving succinylcholine?
4-8 hours
Which diseases increase the risk of succinylcholine-induced hyperkalemia?
Which disease increase sensitivity to Succinylcholine?
The ED95 in NMBs is defined as:
The dose at which there is a 95% reduction in twitch height
What dose of an NMB is required for intubation?
2-3x the ED95
What is the intubating dose of Cisatracurium?
0.1 mg/kg
What is the intubating dose of Vecuronium?
0.1 mg/kg
What is the intubating dose of Atracurium?
0.5 mg/kg
What is the intubating dose of Rocuronium?
0.6 mg/kg
What is the longest-acting NMB?
Pancuronium at 85 minutes!
What is the shortest acting NMB?
Mivacurium at 18 minutes
What are the two classes of non-depolarizers?
Benzylisoquinoliniums
AND
Aminosteroid
Name the benzylisoquinolinium NMBs
The -curiums
Name the aminosteroid NMBs
The -oniums
Metabolism of which drugs is less likely to be effected with renal insufficiency?
The Benzyls, because they undergo spontaneous degradation in the plasma
Which NMB is eliminated by Hoffman Elimination?
Cisatracurium (77%)
Atracurium (30%)
Which NMB is metabolized by pseudocholinesterase?
Mivacurium
How is hoffman elimination impacted by temperature?
Alkalosis and hyperthermia: FASTER
Acidosis and Hypothermia: SLOWER
Which NMBs produce laudanosine?
Atracurium and Cisatracurium
Laudanosine can cause seizures with prolonged use
What is Rocuronium’s primary method of elimination?
It undergoes almost no metabolism in the liver. It’s eliminated as a whole molecule through biliary excretion
Only 10-25% of it is renally excreted
Which aminosteroid is primarily eliminated renally?
Pancuronium (85%)
Name two NMBs that don’t produce any active metabolites
Rocuronium and Mivacurium
How does serum calcium impact NMB potentiation?
Hypocalcemia increases potentiation (no calcium, no contraction)
How does serum lithium impact NMB potentiation?
Elevated serum lithium increases NMB potency
How does magnesium impact NMB potentiation?
An increase in Mg competes with Ca, resulting in less Ach mobilization in the presynaptic nerve terminals
How does serum potassium impact NMB potentiation?
Just like Ca. Decreased K means increased paralysis
Which inhaled anesthetic potentiates paralysis the most?
Desflurane
Which NMBs cause histamine release?
Succinylcholine
Atracurium
Mivacurium
What are the cardiovascular effects of Pancuronium?
It has a vagolytic effect.
It inhibits M2 receptors in the heart, causing tachycardia and catecholamine release
Which patients absolutely should not receive Pancuronium?
Patients with HOCM
What is the most common cause of allergic reactions in the OR?
NMBs
Which NMBs have the highest rates of anaphylaxis?
Succ and Roc
What serum lab value is used to assess an allergic reaction?
Tryptase levels
Exposure to _______ can increase the risk of sensitivity to NMBs
Soaps or cosmetics. Someone who has a lot of allergies to topical things may be more at risk
There are three AchE inhibitors that are used to reverse NMBs:
Edrophonium
Neostigmine
Pyridostigmine
AchE inhibitors reverse the effects of NMBs in two ways:
Enzyme Inhibition
Presynaptic Effects
AchE breaks Ach into:
Acetate and Choline
How do AchE inhibitors impact pseudocholinesterase?
Neostigmine and Pyridostigmine inhibit pseudocholinesterase
Edrophonium does not
What would happen if you gave succinylcholine after reversing Roc with Neostigmine?
The effect of the succ would be prolonged, because it inhibits Pseudocholinesterase
Edrophonium is best paired with _______
Atropine
Glycopyrrolate is best paired with ________
neostigmine or pyridostigmine
What is the dose of edrophonium?
0.5 - 1 mg/kg
What is the dose of neostigmine?
0.05 mg/kg
What is the dose of pyridostigmine?
0.1 - 0.3 mg/kg
What is the onset time of edrophonium?
1-2 minutes
What is the onset time of neostigmine?
5-15 min
What is the onset time of pyridostigmine?
10 - 20 min
Should the dose of AchE inhibitors be increased in patients with renal failure?
No. Renal failures prolongs the MOA for both NMBs and AchE inhibitors, so you can dose them the same
What is the dose of intrathecal neostigmine?
50-100 mcg
What are the side effects of intrathecal neostigmine?
Nausea, vomiting, prolonged sensory and motor block
Which AchE decreases postoperative shivering?
Physostigmine
It actually works better than demerol or clonidine
What are the general side effects of AchE inhibitors?
Bradycardia
Bronchoconstriction
Nausea
Vomiting
Miosis
If you reversed a patient with sugammadex, when can you re-paralyze with Rocuronium?
If they received less than 4 mg/kg:
5 min - 4 hrs: 1.5 mg/kg Roc
> 4hrs: 0.6 mg/kg Roc
If they received 16 mg/kg, you have to wait 24 hours
There is only one AchE inhibitor that crosses the BBB:
Physostigmine
You can give this for symptomatic confusion from scopolamine
