General Anesthesia — MCQs
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Diffusion hypoxia is most commonly seen during which of the following periods?
Which of the following is a short-acting, non-depolarizing muscle relaxant?
Which of the following statements is true about Halothane?
Which of the following is untrue about mivacurium?
Which of the following drugs helps in the rapid reversal of the effect of rocuronium?
Which inhalational anesthetic agent possesses analgesic properties?
Intra-arterial injection of thiopentone causes which of the following?
Process of redistribution is seen with:
Which of the following is NOT a characteristic of nondepolarizing neuromuscular blockers?
Which intravenous anesthetic agent is the drug of choice for the given procedure?
General Anesthesia Indian Medical PG Practice Questions and MCQs
Question 381: Diffusion hypoxia is most commonly seen during which of the following periods?
- A. Induction of anesthesia
- B. Reversal of anesthesia (Correct Answer)
- C. Postoperative period
- D. None of the above
Explanation: **Explanation:** **Diffusion Hypoxia (The Fink Effect)** occurs due to the rapid movement of **Nitrous Oxide ($N_2O$)** from the blood back into the alveoli once the gas is discontinued. Because $N_2O$ is 34 times more soluble in blood than Nitrogen, it rushes into the alveoli in large volumes, effectively "diluting" the concentration of Oxygen ($O_2$) and Carbon Dioxide ($CO_2$) present there. This leads to a transient drop in alveolar $PO_2$, resulting in hypoxia. * **Why Option B is Correct:** Diffusion hypoxia occurs during the **reversal (emergence)** phase of anesthesia. When the $N_2O$ supply is turned off and the patient breathes room air, the sudden outpouring of $N_2O$ into the lungs displaces oxygen. To prevent this, clinicians administer **100% Oxygen for 5–10 minutes** after stopping $N_2O$. * **Why Option A is Incorrect:** During induction, we see the **"Second Gas Effect."** Here, the rapid uptake of $N_2O$ from the alveoli into the blood *increases* the concentration of the co-administered volatile anesthetic, accelerating induction. * **Why Option C is Incorrect:** While respiratory complications can occur postoperatively, "Diffusion Hypoxia" specifically refers to the immediate physical displacement of gases in the alveoli at the moment $N_2O$ is discontinued. **High-Yield Clinical Pearls for NEET-PG:** 1. **Prevention:** Always supplement with 100% $O_2$ during emergence to counteract the dilution effect. 2. **The Fink Effect:** This is the formal name for Diffusion Hypoxia. 3. **Hypocapnia:** $N_2O$ also dilutes alveolar $CO_2$, which can reduce the respiratory drive, further exacerbating the hypoxia. 4. **Concentration Effect:** This is the counterpart to the Fink effect, occurring during induction where high concentrations of a gas accelerate its own uptake.
Question 382: Which of the following is a short-acting, non-depolarizing muscle relaxant?
- A. Mivacurium (Correct Answer)
- B. Doxacuronium
- C. Pipecurium
- D. Vecuronium
Explanation: **Explanation:** Muscle relaxants (Neuromuscular Blocking Agents) are primarily classified based on their duration of action. **Mivacurium** is the correct answer because it is the only **short-acting** non-depolarizing neuromuscular blocker (NDNMB) currently used in clinical practice. **1. Why Mivacurium is correct:** Mivacurium belongs to the benzylisoquinolone class. Its short duration of action (approximately 15–20 minutes) is due to its rapid metabolism by **plasma cholinesterase** (pseudocholinesterase), similar to succinylcholine. This makes it unique among non-depolarizing agents, which typically rely on organ-based elimination. **2. Analysis of Incorrect Options:** * **Doxacuronium & Pipecurium:** These are **long-acting** NDNMBs. They have a slow onset and a prolonged duration of action (usually >60 minutes), making them less ideal for short procedures. * **Vecuronium:** This is an **intermediate-acting** aminosteroid NDNMB. Its duration of action typically ranges from 30 to 45 minutes. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Since Mivacurium is metabolized by plasma cholinesterase, its action is significantly prolonged in patients with **atypical plasma cholinesterase deficiency**. * **Side Effect:** Mivacurium is notorious for causing **histamine release**, which can lead to cutaneous flushing, hypotension, and bronchospasm if injected rapidly. * **Classification Summary:** * *Short-acting:* Mivacurium. * *Intermediate-acting:* Vecuronium, Rocuranium, Atracurium, Cisatracurium. * *Long-acting:* Pancuronium, Doxacuronium, Pipecurium. * **Rocuronium** is the NDNMB with the fastest onset of action, often used as an alternative to succinylcholine for rapid sequence induction.
Question 383: Which of the following statements is true about Halothane?
- A. Non-irritant
- B. Antiarrhythmic
- C. It antagonizes bronchospasm
- D. Vasodilator (Correct Answer)
Explanation: **Explanation:** **Halothane** is a potent volatile anesthetic agent. The correct answer is **Vasodilator** because Halothane causes a dose-dependent reduction in arterial blood pressure. This occurs through two primary mechanisms: direct myocardial depression (reducing cardiac output) and **peripheral vasodilation** (reducing systemic vascular resistance). **Analysis of Options:** * **A. Non-irritant:** While Halothane is relatively non-pungent compared to Isoflurane or Desflurane (making it suitable for mask induction in pediatrics), it is technically considered a mild irritant to the respiratory mucosa compared to Sevoflurane, which is the gold standard for non-irritant induction. * **B. Antiarrhythmic:** This is incorrect. Halothane is famously **arrhythmogenic**. It sensitizes the myocardium to the effects of circulating catecholamines (epinephrine), which can lead to ventricular arrhythmias. * **C. It antagonizes bronchospasm:** While Halothane is a potent bronchodilator, the phrasing "antagonizes bronchospasm" is less accurate than its direct physiological effect of smooth muscle relaxation. More importantly, in the context of this specific question, its systemic **vasodilatory** effect is a more definitive pharmacological property. **High-Yield Clinical Pearls for NEET-PG:** * **Halothane Hepatitis:** A rare but serious immune-mediated hepatotoxicity (Type II) occurring after repeat exposure. * **Malignant Hyperthermia:** Like all volatile agents, Halothane is a known trigger. * **"Halothane Shakes":** Post-operative shivering is common. * **Uterine Relaxation:** It causes significant uterine atony, which can increase postpartum hemorrhage (PPH) risk if used in obstetrics. * **Blood-Gas Partition Coefficient:** 2.4 (Slow induction and recovery).
Question 384: Which of the following is untrue about mivacurium?
- A. Metabolized by pseudocholinesterase
- B. Releases histamine
- C. Onset of action is early (Correct Answer)
- D. Short duration of action
Explanation: **Explanation:** Mivacurium is a short-acting, non-depolarizing neuromuscular blocking agent (NMBA) belonging to the benzylisoquinolone class. **Why Option C is the correct answer (Untrue statement):** Despite being a short-acting drug, Mivacurium has a **slow onset of action** (approximately 2–4 minutes). In contrast, Succinylcholine (a depolarizing agent) has a very rapid onset (30–60 seconds). For NEET-PG, it is vital to remember that "short duration" does not equate to "rapid onset." Mivacurium is not suitable for Rapid Sequence Induction (RSI). **Analysis of other options (True statements):** * **A. Metabolized by pseudocholinesterase:** Like succinylcholine, mivacurium is hydrolyzed by plasma cholinesterase (pseudocholinesterase). Its action is significantly prolonged in patients with atypical plasma cholinesterase deficiency. * **B. Releases histamine:** As a benzylisoquinolone, mivacurium can cause mast cell degranulation leading to histamine release, which may manifest as cutaneous flushing, hypotension, or bronchospasm, especially if injected rapidly. * **D. Short duration of action:** It has the shortest duration among all non-depolarizing NMBAs (approx. 12–20 minutes), making it ideal for short surgical procedures. **High-Yield Clinical Pearls for NEET-PG:** 1. **Metabolism:** It is the only non-depolarizing muscle relaxant metabolized by pseudocholinesterase. 2. **Reversal:** Spontaneous recovery is rapid; however, it can be reversed with neostigmine, though this is rarely required. 3. **Edrophonium:** Interestingly, edrophonium is preferred over neostigmine for reversal as it does not inhibit pseudocholinesterase as strongly as neostigmine does. 4. **Rapacuronium:** This was a non-depolarizing agent with a rapid onset, but it was withdrawn due to severe bronchospasm. Currently, **Rocuronium** is the non-depolarizing agent with the fastest onset.
Question 385: Which of the following drugs helps in the rapid reversal of the effect of rocuronium?
- A. Neostigmine
- B. Sugammadex (Correct Answer)
- C. Edrophonium
- D. Atropine
Explanation: **Explanation:** **Sugammadex** is the correct answer as it is a selective relaxant binding agent (SRBA) specifically designed for the rapid reversal of steroidal non-depolarizing neuromuscular blocking agents (NMBAs), primarily **Rocuronium** and Vecuronium. **Mechanism of Action:** Sugammadex is a modified $\gamma$-cyclodextrin. Its structure resembles a hollow "doughnut" that encapsulates the rocuronium molecule in the plasma, forming a stable 1:1 complex. This creates a concentration gradient that pulls rocuronium away from the nicotinic receptors at the neuromuscular junction back into the plasma, leading to a rapid and complete reversal of blockade, even if the block is deep. **Why other options are incorrect:** * **Neostigmine:** An acetylcholinesterase inhibitor. It increases the concentration of acetylcholine at the synapse to outcompete the NMBA. It is slower than Sugammadex and has a "ceiling effect," meaning it cannot reverse a deep block effectively. * **Edrophonium:** A short-acting acetylcholinesterase inhibitor primarily used for the diagnosis of Myasthenia Gravis (Tensilon test), not for the routine rapid reversal of rocuronium. * **Atropine:** An anticholinergic drug. It does not reverse muscle relaxants; it is co-administered with neostigmine to prevent bradycardia and excessive secretions caused by muscarinic stimulation. **High-Yield Clinical Pearls for NEET-PG:** * **Dosing:** 2 mg/kg for routine reversal (TOF 2); 4 mg/kg for deep block (PTC 1-2); 16 mg/kg for immediate reversal after a 1.2 mg/kg dose of rocuronium. * **Side Effects:** Anaphylaxis (rare but significant) and interference with hormonal contraceptives (patients should be advised to use backup contraception for 7 days). * **Excretion:** It is excreted unchanged by the kidneys; use with caution in severe renal impairment.
Question 386: Which inhalational anesthetic agent possesses analgesic properties?
- A. Xenon (Correct Answer)
- B. Desflurane
- C. Isoflurane
- D. Sevoflurane
Explanation: **Explanation** The correct answer is **Xenon**. **1. Why Xenon is Correct:** Most volatile inhalational anesthetics (like the "fluranes") provide unconsciousness and muscle relaxation but lack significant intrinsic analgesic properties. Xenon is unique because its primary mechanism of action involves the **non-competitive inhibition of NMDA (N-methyl-D-aspartate) receptors**. Since NMDA receptors are heavily involved in pain transmission and central sensitization, their inhibition provides potent **analgesia** along with anesthesia. Nitrous Oxide ($N_2O$) is the only other commonly discussed inhalational agent with significant analgesic properties, also via NMDA antagonism. **2. Why the Other Options are Incorrect:** * **Desflurane, Isoflurane, and Sevoflurane:** These are halogenated ethers. Their primary mechanism involves modulating **GABA-A receptors** and glycine receptors. While they produce a dose-dependent depression of the CNS (hypnosis), they do not provide effective analgesia. In fact, at sub-anesthetic concentrations, some volatile agents can be "hyperalgesic" (increasing sensitivity to pain). **3. High-Yield Clinical Pearls for NEET-PG:** * **Ideal Anesthetic:** Xenon is often called the "ideal anesthetic" because it is non-explosive, non-toxic, chemically inert, and provides rapid induction/recovery due to an extremely low **blood-gas partition coefficient (0.115)**. * **MAC Value:** The MAC of Xenon is approximately **63–71%**, making it less potent than halogenated agents but more potent than $N_2O$. * **Cardiovascular Stability:** Unlike the "fluranes," Xenon is remarkably cardio-stable and does not depress myocardial contractility. * **Environmental Impact:** It is an expensive noble gas but is environmentally friendly (no greenhouse effect), unlike $N_2O$ or Desflurane.
Question 387: Intra-arterial injection of thiopentone causes which of the following?
- A. Vasospasm (Correct Answer)
- B. Vasodilation
- C. Necrosis of the vessel wall
- D. Hypotension
Explanation: **Explanation:** Accidental intra-arterial injection of **Thiopentone sodium** is a known anesthetic emergency. Thiopentone is highly alkaline (pH 10.5). When injected into an artery, it reacts with the blood to form **crystals**, which trigger an intense inflammatory response and the release of **norepinephrine** from perivascular nerve endings. 1. **Why Vasospasm is Correct:** The primary and immediate pathological response to intra-arterial thiopentone is **intense vasospasm**. This is mediated by the local release of catecholamines and the mechanical irritation caused by crystal precipitation. This spasm leads to severe pain (often described as a "burning" sensation) and distal ischemia. 2. **Why other options are incorrect:** * **Vasodilation:** Thiopentone causes the opposite effect (vasoconstriction/spasm) in arteries. * **Necrosis of the vessel wall:** While prolonged ischemia can lead to gangrene of the distal limb, the immediate effect is vasospasm. Necrosis is a late complication, not the primary mechanism. * **Hypotension:** While thiopentone causes systemic hypotension when given intravenously (due to myocardial depression and peripheral venodilation), an intra-arterial injection causes localized hypertensive/ischemic effects in the affected limb. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Severe pain, blanching of the limb, and loss of distal pulses. * **Management Protocol:** 1. **Leave the needle in situ:** To administer drugs through the same port. 2. **Dilute the drug:** Inject Normal Saline. 3. **Relieve Vasospasm:** Inject **Papaverine** (drug of choice), Lidocaine, or Priscoline. 4. **Sympathetic Block:** Stellate ganglion block or Brachial plexus block to promote vasodilation. 5. **Anticoagulation:** Heparin to prevent secondary thrombosis.
Question 388: Process of redistribution is seen with:
- A. Ketamine
- B. Thiopentone (Correct Answer)
- C. Morphine
- D. Barbiturates
Explanation: **Explanation:** The correct answer is **Thiopentone (B)**. **Understanding Redistribution** Redistribution is the primary mechanism for the **termination of action** of highly lipid-soluble intravenous induction agents. When Thiopentone is injected, it rapidly reaches the brain (a highly perfused organ), causing immediate unconsciousness. However, as plasma levels fall, the drug moves down its concentration gradient from the brain back into the blood and is then redistributed to less vascular but larger volume tissues like **skeletal muscle** and eventually **adipose tissue**. This shift away from the brain causes the patient to wake up long before the drug is actually metabolized by the liver. **Analysis of Options:** * **Thiopentone (B):** This is the classic example. Its ultra-short duration of action (5–10 minutes) is entirely due to redistribution, not metabolism. * **Ketamine (A):** While Ketamine does undergo some redistribution, Thiopentone is the prototypical answer for this concept in competitive exams. Ketamine’s emergence is more complex and involves significant hepatic metabolism. * **Morphine (C):** Morphine is not highly lipid-soluble (it is relatively hydrophilic). It crosses the blood-brain barrier slowly and its termination of action is primarily due to hepatic metabolism (glucuronidation). * **Barbiturates (D):** This is a broad category. While Thiopentone is a thiobarbiturate, long-acting barbiturates (like Phenobarbitone) do not rely on redistribution for termination of action; they are cleared slowly via renal excretion and metabolism. **High-Yield NEET-PG Pearls:** * **Context-Sensitive Half-Time:** Thiopentone has a very long context-sensitive half-time. If given as a continuous infusion, the "redistribution sites" (muscles/fat) become saturated, leading to a very prolonged recovery. * **Propofol:** Like Thiopentone, Propofol also undergoes rapid redistribution, but it is cleared much faster from the body overall. * **Storage:** Thiopentone is stored in muscle first (early redistribution) and fat last (late redistribution).
Question 389: Which of the following is NOT a characteristic of nondepolarizing neuromuscular blockers?
- A. Fade on train-of-four stimulation
- B. Tetanic stimulation is followed by post-tetanic facilitation
- C. Shows fasciculations (Correct Answer)
- D. Reversed by neostigmine
Explanation: **Explanation:** Neuromuscular blockers (NMBs) are classified into two categories: **Depolarizing** (e.g., Succinylcholine) and **Nondepolarizing** (e.g., Vecuronium, Atracurium). **Why Option C is the Correct Answer:** **Fasciculations** are a hallmark of **Depolarizing NMBs** (Succinylcholine). These drugs act as acetylcholine (ACh) agonists, causing initial stimulation and persistent depolarization of the motor endplate, which manifests clinically as muscle twitching (fasciculations) before paralysis sets in. Nondepolarizing NMBs, conversely, act as **competitive antagonists**; they simply sit on the nicotinic receptors and block ACh from binding, resulting in immediate flaccid paralysis without any initial stimulation or fasciculations. **Analysis of Incorrect Options:** * **Option A (Fade on TOF):** Nondepolarizing blocks exhibit "fade" because they block pre-junctional receptors, reducing the mobilization of ACh during repetitive stimulation. * **Option B (Post-tetanic facilitation):** In a nondepolarizing block, a tetanic stimulus causes a transient increase in ACh release. Immediately following this, a single twitch stimulus will show an exaggerated response (facilitation) compared to pre-tetanic levels. * **Option D (Reversed by Neostigmine):** Since nondepolarizing agents are competitive inhibitors, increasing the concentration of ACh at the synapse using an acetylcholinesterase inhibitor (like Neostigmine) will displace the blocker and restore muscle function. **High-Yield Clinical Pearls for NEET-PG:** * **Phase II Block:** If Succinylcholine is given in high or repeated doses, it can begin to show characteristics of a nondepolarizing block (fade and post-tetanic facilitation). * **Drug of Choice for RSI:** Succinylcholine remains the gold standard for Rapid Sequence Induction due to its fast onset and short duration, despite the side effect of fasciculations (which can cause post-op myalgia). * **Sugammadex:** A novel reversal agent specifically for aminosteroidal nondepolarizing agents (Rocuronium > Vecuronium) that works by encapsulation.
Question 390: Which intravenous anesthetic agent is the drug of choice for the given procedure?
- A. Thiopentone
- B. Propofol
- C. Etomidate
- D. Methohexitone (Correct Answer)
Explanation: ***Methohexitone*** - **Lowers seizure threshold** and produces **longer, higher quality seizures**, making it ideal for **electroconvulsive therapy (ECT)**. - Has **rapid onset and offset** with minimal interference with seizure activity, allowing for optimal therapeutic outcomes. *Thiopentone* - **Raises seizure threshold** and **shortens seizure duration**, reducing the effectiveness of ECT. - Its **anticonvulsant properties** make it unsuitable for procedures requiring seizure induction. *Propofol* - Has **anticonvulsant properties** that **raise seizure threshold**, making seizure induction difficult during ECT. - May result in **inadequate seizure duration** and reduced therapeutic efficacy of the procedure. *Etomidate* - Although it **lowers seizure threshold**, it commonly causes **myoclonus** which can interfere with the procedure. - Associated with **adrenal suppression** even after single doses, making it less favorable for ECT.
Practice by Chapter
History of Anesthesia
Practice Questions
Preoperative Evaluation
Practice Questions
Pharmacology of Inhalational Anesthetics
Practice Questions
Pharmacology of Intravenous Anesthetics
Practice Questions
Neuromuscular Blocking Agents
Practice Questions
Airway Management
Practice Questions
Endotracheal Intubation
Practice Questions
Difficult Airway Algorithms
Practice Questions
Intraoperative Monitoring
Practice Questions
Depth of Anesthesia Monitoring
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Emergence from Anesthesia
Practice Questions
Postoperative Care
Practice Questions
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