Neuro-Muscle Junction & Action Potential
What must happen with for the neuromuscular junction to initiate skeletal muscle contraction?
A) Acetylcholine (Ach) must be degraded in the synaptic cleft
B) Acetylcholine must bind to both alpha subunits of the N1 receptor
C) Potassium must influx into the cell
D) Calcium must be removed from the cytoplasm
What is B) Acetylcholine must bind to both alpha subunits of the N1 receptor
What classification does succinylcholine (sux) belong to?
A) Non-depolarizing benzylisoquinoline
B) Non-depolarizing aminosteroid
C) Depolarizing agent
D) Reversal agent
What is C) Depolarizing agent
What is the primary clinical use of sugammadex?
A) Reversal of benzylisoquinoline NDMRs
B) Reversal of steroidal NDMRs
C) Reversal of depolarizing neuromuscular blockers
D) Enhancing the action of succinylcholine
B) Reversal of steroidal NDMRs
A patient receives succinylcholine and experiences severe hyperkalemia. What is the most likely predisposing condition?
A) Myasthenia gravis
B) Chronic kidney disease
C) A history of major burn injury
D) Hypocalcemia
C) A history of major burn injury (upregulation of nicotinic receptors increases potassium release)
A patient undergoing surgery is monitored for neuromuscular blockade. Which nerve is preferred for assessing complete recovery before extubation?
A) Facial nerve
B) Ulnar nerve
C) Peroneal nerve
D) Vagus nerve
B) Ulnar Nerve
What occurs immediately after sodium and calcium enter the skeletal muscle cell at the neuromuscular junction?
A) The muscle relaxes due to hyperpolarization
B) The sarcoplasmic reticulum releases calcium into the cytoplasm
C) The N1 receptor closes, terminating the action potential
D) The acetylcholinesterase enzyme becomes inactive
What is B) The sarcoplasmic reticulum releases calcium into the cytoplasm
What differentiates non-depolarizing neuromuscular blockers (NDMRs) from depolarizing agents?
A) Non-depolarizing agents cause prolonged depolarization, leading to paralysis
B) Non-depolarizing agents competitively bind to alpha subunits, preventing depolarization
C) Depolarizing agents inhibit acetylcholine release at the presynaptic terminal
D) Depolarizing agents are more potent than all non-depolarizing agents
What is B) Non-depolarizing agents competitively bind to alpha subunits, preventing depolarization
Which reversal agent works by forming a tight water-soluble complex with rocuronium?
A) Neostigmine
B) Edrophonium
C) Sugammadex
D) Pyridostigmine
C) Sugammadex
After receiving succinylcholine, a pediatric patient develops bradycardia following a repeat dose. What is the recommended management?
A) Stop all neuromuscular blockers
B) Administer atropine
C) Give an additional dose of succinylcholine
D) Reverse with sugammadex
B) Administer atropine (bradycardia is common after a second dose, especially in pediatrics)
Why is quantitative monitoring preferred over qualitative neuromuscular blockade assessment?
A) It provides a subjective measurement of twitches
B) It relies on visual interpretation, which is more reliable
C) It directly measures train-of-four (TOF) ratios and reduces residual paralysis
D) It is not necessary for extubation decisions
C) It directly measures train-of-four (TOF) ratios and reduces residual paralysis
If a patient has atypical pseudocholinesterase, how will the action of succinylcholine (sux) be affected?
A) The patient will experience an exaggerated initial muscle contraction
B) The patient will recover from paralysis faster than normal
C) The duration of paralysis will be prolonged
D) The drug will have no effect on the neuromuscular junction
What is C) The duration of paralysis will be prolonged
Which of the following neuromuscular blockers is best suited for a patient with severe liver disease?
A) Rocuronium
B) Pancuronium
C) Cisatracurium
D) Vecuronium
What is C) Cisatracurium (eliminated via Hoffman degradation, independent of liver function)
Why is neostigmine not recommended for deep neuromuscular blockade reversal?
A) It only reduces the effect of depolarizing agents
B) It does not reduce the amount of neuromuscular blocker at the junction
C) It has a rapid onset and short duration
D) It causes irreversible enzyme inhibition
B) It does not reduce the amount of neuromuscular blocker at the junction
Which of the following is a hallmark feature that distinguishes malignant hyperthermia (MH) from other intraoperative complications?
A) Profound muscle rigidity despite neuromuscular blockade
B) Bradycardia unresponsive to atropine
C) Hypothermia with metabolic acidosis
D) Immediate hypotension after succinylcholine administration
A) Profound muscle rigidity despite neuromuscular blockade (caused by sustained sarcoplasmic reticulum calcium release)
A patient receiving neuromuscular blockade exhibits a TOF ratio of 0.7 but can lift their head for five seconds. What does this indicate?
A) The patient is fully recovered and ready for extubation
B) The patient has residual neuromuscular blockade and is not safe for extubation
C) The TOF measurement is inaccurate
D) The patient requires immediate neostigmine administration
B) The patient has residual neuromuscular blockade and is not safe for extubation
Why do patients with myasthenia gravis who are NOT on an acetylcholinesterase inhibitor show resistance to succinylcholine?
A) They lack enough nicotinic receptors for succinylcholine to bind effectively
B) Their acetylcholinesterase enzyme is overactive
C) They have an overabundance of functioning nicotinic receptors
D) They experience upregulation of potassium channels
What is A) They lack enough nicotinic receptors for succinylcholine to bind effectively
What effect does hyperkalemia have on the sensitivity of a patient to non-depolarizing neuromuscular blockers?
A) It increases sensitivity to NDMRs
B) It decreases sensitivity to NDMRs
C) It has no effect
D) It enhances acetylcholine release
B) It decreases sensitivity to NDMRs (due to a lowered membrane potential)
What is a potential contraindication for sugammadex administration?
A) Patients with renal failure
B) Patients on anticoagulants
C) Patients taking oral contraceptives
D) Patients undergoing rapid sequence intubation
C) Patients taking oral contraceptives
What immediate drug should be administered for bradycardia after a second dose of succinylcholine?
What is the minimum TOF ratio required for safe extubation?
TOF >0.9
How does lithium affect the response to depolarizing neuromuscular blockers?
A) It enhances the breakdown of acetylcholine, reducing depolarization
B) It increases the sensitivity to succinylcholine by activating potassium channels
C) It blocks calcium release from the sarcoplasmic reticulum
D) It competes with nicotinic receptors, decreasing succinylcholine binding
What is B) It increases the sensitivity to succinylcholine by activating potassium channels
In which clinical scenario would a non-depolarizing agent be preferred over succinylcholine?
A) A patient with an open globe eye injury
B) A patient undergoing rapid sequence intubation (RSI)
C) A patient with myasthenia gravis who is resistant to succinylcholine
D) A patient with an acute denervation injury less than 24 hours ago
A) A patient with an open globe eye injury (to prevent increased intraocular pressure)
What is the critical Train-of-Four (TOF) ratio required for safe extubation?
A) 0.7
B) 0.8
C) 0.9
D) 1.0
C) 0.9
Which feature distinguishes malignant hyperthermia from other intraoperative events?
Masseter Spasm
What is the gold standard monitoring method for neuromuscular blockade depth?
Quantitative TOF ratio, Twitch View