Neuromuscular Blockers Flashcards
What is the difference between extrajunctional receptors and regular nicotinic receptors?
A gamma subunit replaces the epsilon subunit or it consists of 5 alpha subunits
They are far more sensitive to sux
Remain open longer
Resistant to nondepolarizers
What are some contraindications to Sux?
Burns
Spinal cord injury
Upper/lower motor neuron dx
CVA
Tetanus
Severe sepsis
Muscular dystrophy
Prolonged chemical denervation
How much does Sux increase serum potassium?
Transiently (10-15 mins) by 0.5-1.0 mEq/L
When should sux be avoid (and for how long) following a denervation injury?
24-48hrs after for at least 1 year
What is the tx for sux-induced hyperkalemia?
Calcium chloride
Insulin + glucose
Hyperventilation
Sodium bicarb
What is a phase 1 block?
When sux stimulates the presynaptic nicotinic receptor it produces mobilization Ach in the nerve terminal as usual so there is ample supple of Ach
(No fade ~ normal sux response)
What is a phase 2 block?
Nondepolarizers competitively antagonize the presynaptic nicotinic receptor. The mobilization of Ach is impaired so the nerve terminal can only release what is immediately available, which exhausts quickly.
High doses of Sux can also produce this.
What two situations increase the risk of a phase 2 block with Sux?
Dose > 7-10 mg m/kg
Infusion of greater than 30-60 minutes
Where is the best location of measure onset of blockade?
Orbicularis oculi or corrugator supercilii
(This assess the facial nerve)
Where is the best place to measure recovery?
Adductor pollicis
Flexor hallucis
(These measure the ulnar nerve or posterior tibial nerve)
What TOF ratio suggests full recovery?
> 0.9
What are some acceptable clinical endpoints for neuromuscular blockade?
Tidal volume: > 5 mL/kg
TOF: no fade
Vital capacity: > 20 mL/kg
Inspiratory force: > than a - 40 cm H2O (more negative ~ the better)
Head lift > 5 seconds
Hand grip > 5 seconds
*** tongue blade against force is the best qualitative test of neuromuscular function
How does sux cause bradycardia and asystole?
By stimulating the M2 receptor in the SA node
(Kids are more susceptible to bradycardia due to their higher baseline vagal tone.
How does sux cause tachycardia and hypertension?
Mimicking the action of Ach at the sympathetic ganglia
What are some side effects of sux?
Increased intraocular pressure
Risk of MH
Bradycardia
Tachycardia
HTN
K+ release
Increased intracranial pressure
Increased intra gastric pressure
What enzyme (or enzymes) metabolizes acetylcholine?
Acetylcholinesterase
Genuine cholinesterase
Type 1 cholinesterase
True cholinesterase
Specific cholinesterase
What metabolizes Succinylchokine, mivacurium and Ester anesthetics
Butyrlcholinesterase
Pseudocholinesterase
Type 2 cholinesterase
False cholinesterase
Plasma cholinesterase
What are some drugs that reduce pseudocholinesterase activity? Aka prolong the duration of Sux
Metoclopramide
Esmolol
Neostigmine
Echothiopate
Oral contraceptives
Cyclophosphamide
MOAs
Nitrogen mustard
What are some co-existing diseases that may reduce pseudocholinesterase activity? Aka prolong sux
Atypical PChe
Severe liver disease
Chronic renal disease
Burns
Neoplasm
Advanced age
Malnutrition
Pregnancy
What is a Normal Dibucaine test?
It inhibits normal pseudocholinesterase
Normal number is 80 or dibucaine has inhibited 80% of the pseudocholinesterase.
What is an abnormal Dibucaine test?
Dibucaine does NOT inhibit atypical pseudocholinesterase. If the patient has a number of 20, this mean the Dibucaine did not inhibit the patient’s PChE
What is typical homozygous Dibucaine number? What is the sux duration?
Typical homozygous: 70-80
Duration: 5-10 mins
What is heterozygous Dibucaine number? What is the sux duration?
50-60
Duration: 20-30 mins
What is atypical homozygous Dibucaine number? What is the sux duration?
20-30
Duration: 4-8 hours
In atypical plasma cholinesterase, is there an insufficient number of quantity of pseudocholinesterase or is the enzyme not functional?
Not functional
Why does Sux have a black box warning for kids?
Risk of cardiac arrest and/or sudden death secondary to hyperkalemia in children with undiagnosed skeletal muscle myopathy
What does mild hyperkalemia present with?
Peaked T waves and PR prolongation
What are the 3 goals if hyperkalemia results following administration of Sux to a child?
Stabilize the myocardium (give calcium 20 mg/kg or 60 mg/kg)
Shift K+ into cells (hyperventilation, glucose and insulin)
Enhance K+ excretion (lasix, volume, hemodialysis)
Who has the highest incidence of myalgia?
Young adults (girls > boys) undergoing ambulatory surgeries
What can be administered to lessen myalgia following Sux administration?
2 mg Roc, 0.3 mg Vec
What is Duchenne’s muscular dystrophy response to sux and/or a nondepolarizer?
Sux: hyperkalemia/rhabdo
Roc: sensitive
What is guillain-barre response to sux and/or a nondepolarizer?
Sux: hyperkalemia
Roc: sensitive
What is multiple sclerosis response to sux and/or a nondepolarizer?
Sux: hyperkalemia
Roc: sensitive
What is amyotrophic lateral sclerosis response to sux and/or a nondepolarizer?
Sux: hyperkalemia
Roc: sensitive
What is up regulation of AChRs response to sux and/or a nondepolarizer?
Sux: hyperkalemia
Roc: resistant/normal
What is Charcot-Marie Tooth response to sux and/or a nondepolarizer?
Sux: hyperkalemia
Roc: normal
What is hyperkalemic periodic paralysis response to sux and/or a nondepolarizer?
Sux: hyperkalemia
Roc: normal
What is hypokalemic periodic paralysis response to sux and/or a nondepolarizer?
Sux: MH?
Roc: normal
What is MH response to sux and/or a nondepolarizer?
Sux: MH
Roc: normal
What is myotonic dystrophy response to sux and/or a nondepolarizer?
Sux: contractures (not hyperkalemia)
Roc: normal or sensitive
What is Huntington Chorea response to sux and/or a nondepolarizer?
Sux: sensitive
Roc: sensitive
What is myasthenia Gravis response to sux and/or a nondepolarizer?
Sux: resistant
Roc: sensitive
What is a short acting nondepolarizing neuromuscular blocker?
Mivacurium
Dose (0.15 mg/kg)
Duration: 16.8 mins
What are the intermediate-acting neuromuscular blockers?
Cisatracurium (0.1 mg/kg)
Duration: 45 mins
Vecuronium (0.1 mg/kg)
Duration: 45 mins
Atracurium ( 0.5 mg/kg)
Duration: 45 mins
Rocuronium (0.6 mg/kg)
Duration 35 mins
What is a long-acting nondepolarizing neuromuscular blocker?
Pancuronium (0.08 mg/kg)
Duration: 85 mins
How is Atracurium metabolized?
Hofmann elimination and non-specific esterases
How is cisatracurium metabolized?
Hoffman elimination
How is Mivacurium metabolized?
Pseudocholinesterase
How does temperature and pH affect Hofmann elimination?
Reaction is faster with alkalosis and HYPERthermia
Reaction is slower with acidosis and HYPOThermia
What is Laundanosine?
Metabolite of both Atracurium and cisatracurium
This metabolite can produce seizures
How is rocuronium metabolized?
Biliary excretion
Renal: 10-25%
How is vecuronium metabolized?
Hepatic clearance
Renal elimination: 50-60%
How is pancuronium metabolized?
Hepatic clearance
Renal Elimination: 85%
In what order do the volatile agents potentiate neuromuscular blockers?
Des > Sevo > Iso > N2O > propofol
What other medications may potentiate neuromuscular blockade?
Dantrolene
Lasix
Local anesthetics
Verapamil, amlodipine
Aminoglycosides, Clindamycin, tetracycline
What electrolyte imblanaces potentiate the neuromuscular blockade?
^ Lithium
^ Magnesium
Decrease in calcium
Decrease in Potassium
How does temperature affect neuromuscular blockade?
Hypothermia ^ duration
What neuromuscular blockers have a histamine release?
Sux, Mivacurium, Atracurium
Which neuromuscular blocker has a vasolytic effect?
Pancurium
What type of patient should kit receive pancuronium?
A patient with hypertrophic cardiomyopathy
What are the most common cause of perioperative allergic reactions?
Neuromuscular blockers
Which NMB has the highest rate of anaphylaxis?
Sux (but roc is also shown a bunch in the literature)
