Neuromuscular Blocking Agents — MCQs
Probable indicators of reversal of neuromuscular blockade are all EXCEPT:
Non-depolarizing neuromuscular blocker is characterized by
Mechanism of action of d-tubocurarine is:
What is the primary clinical use of Sugammadex in anesthesia?
Which among the following is most probable reason for preference of Cisatracurium over atracurium?
Patient was planned for surgery under GA, in the induction phase rocuronium was given 85mg but the anesthetist did not succeed in intubating. Which could be the best reversal agent used?
A 70 kg young athlete was planned for surgery. During anesthesia, vecuronium was not available, so repeated doses of succinylcholine were given intermittently up to 640 mg. During recovery, the patient was not able to spontaneously respire and move limbs. What is the cause?
Anaesthesia contraindicated in volvulus of gut is –
Among atracurium and cisatracurium, which of the following does not require dose modification in patients with renal or hepatic failure?
Which of the following is the most suitable anesthetic agent for use in dogs?
Neuromuscular Blocking Agents Indian Medical PG Practice Questions and MCQs
Question 1: Probable indicators of reversal of neuromuscular blockade are all EXCEPT:
- A. Sustained hand grip for 5 seconds
- B. Lift head for 5 seconds
- C. Leg lift for 10 seconds (Correct Answer)
- D. Ability to perform sustained tongue depressor test
Explanation: ***Leg lift for 10 seconds*** - A **leg lift for 10 seconds** is a test of lower limb strength, which can be affected by residual neuromuscular blockade, but it is **not a primary or standard indicator** used to assess the reversal of neuromuscular blockade for airway protection and overall recovery. - While it demonstrates muscle strength, it isn't as critical for assessing readiness for extubation as upper airway and respiratory muscle function tests. *Sustained hand grip for 5 seconds* - **Sustained hand grip for 5 seconds** demonstrates adequate neuromuscular transmission in the forearm muscles and is a generally accepted indicator of reversal of neuromuscular blockade. - It suggests sufficient recovery of peripheral muscles to perform voluntary movements effectively. *Lift head for 5 seconds* - The **ability to lift the head off the bed for 5 seconds** is a crucial clinical test indicating significant recovery of the neck and upper airway muscles, which are vital for maintaining airway patency. - This demonstrates adequate strength in the diaphragm, intercostals, and upper airway muscles, suggesting readiness for extubation. *Ability to perform sustained tongue depressor test* - The **sustained tongue depressor test** involves the patient holding an object between their teeth, indicating sufficient strength of the jaw musculature. - This test is a reliable indicator of adequate neuromuscular recovery in the muscles essential for airway protection and swallowing.
Question 2: Non-depolarizing neuromuscular blocker is characterized by
- A. Non competitive neuromuscular blocker
- B. Reversed by neostigmine (Correct Answer)
- C. Induces fasciculations
- D. Persistent stimulator of nicotinic cholinergic receptors
Explanation: ***Reversed by neostigmine*** - **Non-depolarizing neuromuscular blockers** are **competitive antagonists** at the **nicotinic acetylcholine receptors** at the neuromuscular junction. - **Neostigmine** is an **acetylcholinesterase inhibitor** that increases the concentration of acetylcholine in the synaptic cleft, thereby overcoming the competitive blockade. *Non competitive neuromuscular blocker* - Non-depolarizing neuromuscular blockers are, by definition, **competitive antagonists** at the **nicotinic acetylcholine receptors**. - A non-competitive blocker would bind to a different site on the receptor or an allosteric site to produce its effect. *Induces fasciculations* - **Fasciculations** (visible muscle twitching) are characteristic of **depolarizing neuromuscular blockers** like **succinylcholine**, as they initially activate the receptors before causing prolonged depolarization and paralysis. - Non-depolarizing blockers do not typically cause fasciculations because they prevent acetylcholine from binding and activating the receptors. *Persistent stimulator of nicotinic cholinergic receptors* - This describes the mechanism of action of **depolarizing neuromuscular blockers** like **succinylcholine**, which persistently activate the receptor, leading to initial fasciculations followed by sustained depolarization and paralysis. - **Non-depolarizing blockers** act as **antagonists**, preventing activation of the receptors.
Question 3: Mechanism of action of d-tubocurarine is:
- A. Competitive, nondepolarizing block at the Nm cholinergic receptor (Correct Answer)
- B. Noncompetitive, depolarizing block at the Nm cholinergic receptor
- C. Non-competitive, nondepolarizing block at the Nm cholinergic receptor
- D. Competitive, depolarizing block at the Nm cholinergic receptor
Explanation: ***Competitive, nondepolarizing block at the Nm cholinergic receptor*** - **d-tubocurarine** acts as a **competitive antagonist** at the **nicotinic muscle (Nm) cholinergic receptors** on the motor endplate. - It competes with **acetylcholine (ACh)** for binding sites, preventing ACh from activating the receptor and causing **muscle paralysis** without depolarization. *Noncompetitive, depolarizing block at the Nm cholinergic receptor* - This describes the mechanism of action of **depolarizing neuromuscular blockers** like **succinylcholine**, which first *depolarize* the motor endplate before causing paralysis. - d-tubocurarine does not cause initial depolarization; it directly blocks the receptor. *Non-competitive, nondepolarizing block at the Nm cholinergic receptor* - While d-tubocurarine is **nondepolarizing**, it is a **competitive antagonist**, not a non-competitive one. - A non-competitive block would involve binding to a different site on the receptor or an associated ion channel, altering receptor function indirectly. *Competitive, depolarizing block at the Nm cholinergic receptor* - This option incorrectly combines the concepts, as **depolarizing blockers** like succinylcholine act initially by **depolarizing** the endplate, whereas d-tubocurarine is purely a **nondepolarizing** agent. - The "competitive" aspect would be true for the binding of ACh to its site on a depolarizing agent, but the effect of d-tubocurarine is simply to block, not depolarize.
Question 4: What is the primary clinical use of Sugammadex in anesthesia?
- A. Organophosphate poisoning
- B. Reversal of NM blockers (Correct Answer)
- C. Treatment of local anaesthetic poisoning
- D. Treatment of central anticholinergic syndrome
Explanation: ***Reversal of NM blockers*** - **Sugammadex** is a modified gamma-cyclodextrin that specifically encapsulates steroidal **neuromuscular blocking agents (NMBAs)** like **rocuronium** and **vecuronium**. - This encapsulation rapidly inactivates the NMBAs, leading to a dose-dependent and swift **reversal of neuromuscular blockade**. *Organophosphate poisoning* - Organophosphate poisoning is treated with **atropine** to block muscarinic effects and **pralidoxime** to reactivate inhibited acetylcholinesterase. - Sugammadex has no role in antagonizing the effects of **organophosphates** or regenerating acetylcholinesterase. *Treatment of local anaesthetic poisoning* - Local anesthetic systemic toxicity (LAST) is primarily managed with supportive care, including airway management, and the administration of **lipid emulsion therapy**. - Sugammadex does not bind to local anesthetics and therefore has no efficacy in treating local anesthetic poisoning. *Treatment of central anticholinergic syndrome* - Central anticholinergic syndrome is typically treated with **physostigmine**, an acetylcholinesterase inhibitor that can cross the blood-brain barrier. - Sugammadex is not an anticholinergic antagonist and does not affect the central nervous system to reverse anticholinergic effects.
Question 5: Which among the following is most probable reason for preference of Cisatracurium over atracurium?
- A. Decreased histamine release (Correct Answer)
- B. Increased histamine release
- C. Decreased CNS toxicity
- D. Due to elimination by non-specific plasma esterases
Explanation: ***Decreased histamine release*** - **Cisatracurium** is preferred over atracurium primarily due to its significantly **lower potential for histamine release**, which can cause undesirable side effects like **hypotension**, **tachycardia**, and **bronchospasm**. - This reduced histamine release contributes to a **more stable hemodynamic profile** and **fewer allergic-type reactions**, especially in critically ill or hemodynamically unstable patients. *Increased histamine release* - This is incorrect because **atracurium** is known to cause **more histamine release** compared to cisatracurium, which is why cisatracurium is often preferred. - Increased histamine release is an **undesirable effect** that can lead to adverse cardiovascular and respiratory reactions. *Decreased CNS toxicity* - While both drugs are **quaternary ammonium compounds** and do not readily cross the blood-brain barrier, **CNS toxicity** is not a primary concern or differentiating factor between atracurium and cisatracurium in clinical practice. - The potential for CNS effects from their metabolites (like **laudanosine**) is generally low with standard dosing, and **cisatracurium produces less laudanosine**. *Due to elimination by non-specific plasma esterases* - Both cisatracurium and atracurium are eliminated primarily by **Hofmann elimination** and **non-specific plasma esterases**. This is a shared characteristic, not a reason for cisatracurium's preference over atracurium. - **Hofmann elimination** is a non-enzymatic chemical degradation process that occurs at physiological pH and temperature, making their elimination **independent of renal or hepatic function**.
Question 6: Patient was planned for surgery under GA, in the induction phase rocuronium was given 85mg but the anesthetist did not succeed in intubating. Which could be the best reversal agent used?
- A. Neostigmine (non-specific acetylcholinesterase inhibitor)
- B. Glycopyrrolate (anticholinergic agent)
- C. Edrophonium (non-specific acetylcholinesterase inhibitor)
- D. Sugammadex (specific reversal agent for rocuronium) (Correct Answer)
Explanation: ***Sugammadex (specific reversal agent for rocuronium)*** - **Sugammadex** is a modified gamma-cyclodextrin that forms a tight, water-soluble complex with **rocuronium**, effectively encapsulating and inactivating it. - It is highly effective for rapid reversal of **rocuronium**-induced neuromuscular blockade, especially in situations where immediate reversal is critical, such as a "cannot intubate, cannot ventilate" scenario. *Neostigmine (non-specific acetylcholinesterase inhibitor)* - **Neostigmine** acts by inhibiting **acetylcholinesterase**, increasing the amount of acetylcholine at the neuromuscular junction to overcome the competitive block. - Its reversal effect is slower and less reliable than sugammadex, especially after a large dose of rocuronium or deep blockade. *Glycopyrrolate (anticholinergic agent)* - **Glycopyrrolate** is an **anticholinergic** agent used to counteract the muscarinic side effects (e.g., bradycardia, salivation) of **acetylcholinesterase inhibitors** like neostigmine, but it has no direct reversal effect on neuromuscular blockade. - It is typically co-administered with neostigmine, not used as a standalone reversal agent for **rocuronium**. *Edrophonium (non-specific acetylcholinesterase inhibitor)* - **Edrophonium** is a short-acting **acetylcholinesterase inhibitor**, similar to neostigmine but with a more rapid onset and shorter duration of action. - It is less potent and effective than neostigmine for reversing moderate to deep neuromuscular blockade and would not be the best choice after a significant dose of **rocuronium**.
Question 7: A 70 kg young athlete was planned for surgery. During anesthesia, vecuronium was not available, so repeated doses of succinylcholine were given intermittently up to 640 mg. During recovery, the patient was not able to spontaneously respire and move limbs. What is the cause?
- A. Phase II blockade (Correct Answer)
- B. Muscle weakness due to repeated fasciculations
- C. Undiagnosed muscular dystrophy
- D. Pseudocholinesterase deficiency
Explanation: **Phase II blockade** - Prolonged administration of **succinylcholine** (> 30-60 minutes or high cumulative doses) can lead to a shift from Phase I to **Phase II block**. - In Phase II block, the neuromuscular junction exhibits characteristics similar to a **nondepolarizing block**, including fade on train-of-four stimulation and post-tetanic potentiation, leading to prolonged paralysis. *Muscle weakness due to repeated fasciculations* - While succinylcholine initially causes **fasciculations** due to depolarization, prolonged paralysis is not directly explained by muscle weakness from repeated fasciculations alone. - Fasciculations are a transient early effect and do not account for the sustained paralysis seen with high-dose, repeated administration. *Undiagnosed muscular dystrophy* - While certain **neuromuscular disorders** can alter response to muscle relaxants, there is no information in the scenario to suggest pre-existing muscular dystrophy. - Administering a large amount of succinylcholine accounts for the prolonged paralysis without needing to invoke an undiagnosed condition. *Pseudocholinesterase deficiency* - A deficiency in **pseudocholinesterase** would lead to a prolonged initial Phase I block with a typical dose of succinylcholine due to impaired metabolism. - However, the scenario describes **repeated doses** adding up to a very high cumulative amount (640 mg), pushing the patient into a Phase II block even if pseudocholinesterase levels were normal.
Question 8: Anaesthesia contraindicated in volvulus of gut is –
- A. Ketamine
- B. Halothane
- C. Pancuronium
- D. Nitrous oxide (Correct Answer)
Explanation: ***Nitrous oxide*** - **Nitrous oxide** rapidly diffuses into air-filled cavities, such as bowel loops distended by volvulus. - This diffusion can cause rapid expansion of the bowel, increasing pressure and potentially leading to **bowel perforation** or worsening the vascular compromise. *Ketamine* - Ketamine can be used in patients with gut volvulus, particularly if there is concern for hypovolemia or hemodynamic instability, as it generally **maintains cardiovascular stability**. - It does not directly exacerbate bowel distension. *Halothane* - Halothane is an inhalational anesthetic that can cause **myocardial depression** and vasodilation, which might be a concern in hemodynamically unstable patients but does not directly worsen bowel distension due to gas expansion. - While other volatile agents might be preferred due to its side effect profile, it's not specifically contraindicated due to gas expansion. *Pancuronium* - Pancuronium is a **non-depolarizing neuromuscular blocker** used for muscle relaxation during surgery. - It does not have a direct effect on bowel gas volume or distension and is not contraindicated in volvulus.
Question 9: Among atracurium and cisatracurium, which of the following does not require dose modification in patients with renal or hepatic failure?
- A. Both atracurium and cisatracurium (Correct Answer)
- B. Cisatracurium
- C. Atracurium
- D. Neither atracurium nor cisatracurium
Explanation: ***Both atracurium and cisatracurium*** - Both **atracurium** and **cisatracurium** are metabolized primarily via **Hofmann elimination**, a non-enzymatic chemical degradation. - This mechanism is independent of renal or hepatic function, making them safe choices for patients with organ failure without requiring dose adjustment. *Cisatracurium* - While **cisatracurium** is known for its metabolism via **Hofmann elimination**, excluding atracurium from this category is incorrect. - Atracurium also undergoes significant Hofmann elimination, sharing this characteristic for organ-independent metabolism. *Atracurium* - While **atracurium** is metabolized via **Hofmann elimination**, excluding cisatracurium is incorrect, as cisatracurium also primarily utilizes this pathway. - Both agents are advantageous in patients with renal or hepatic impairment. *Neither atracurium nor cisatracurium* - This statement is incorrect because both drugs demonstrate metabolism independent of renal or hepatic function, which is a key advantage. - Their primary degradation pathway, **Hofmann elimination**, ensures that their elimination is not significantly affected by organ dysfunction.
Question 10: Which of the following is the most suitable anesthetic agent for use in dogs?
- A. Propofol (Correct Answer)
- B. Medetomidine hydrochloride
- C. Ketamine
- D. Midazolam
Explanation: ***Propofol*** - **Propofol** is a widely used and highly effective intravenous anesthetic in dogs due to its **rapid induction** and **rapid recovery**. - It produces minimal cumulative effects when administered as a constant rate infusion, making it suitable for both short procedures and maintenance of anesthesia. *Medetomidine hydrochloride* - **Medetomidine** is an **alpha-2 agonist** primarily used as a sedative and analgesic in dogs, not typically as the sole anesthetic agent for general anesthesia. - While it provides profound sedation, it is usually combined with other drugs (e.g., ketamine) to achieve surgical planes of anesthesia, and its effects on reducing heart rate and blood pressure can be significant. *Ketamine* - **Ketamine** is a **dissociative anesthetic** that provides good analgesia and somatic anesthesia but often causes muscle rigidity and can increase sympathetic tone. - It is typically used in combination with other sedatives or tranquilizers (e.g., diazepam, midazolam) to ensure smooth induction and recovery and prevent adverse effects like seizures. *Midazolam* - **Midazolam** is a **benzodiazepine** primarily used as a sedative, anxiolytic, and muscle relaxant, often as a premedicant or co-induction agent, not as a primary anesthetic for general anesthesia in dogs. - It offers minimal cardiovascular and respiratory depression when used alone, but it does not produce sufficient anesthetic depth for surgical procedures.
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