Neuromuscular Blockers Flashcards
(62 cards)
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
