General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 461: Which of the following statements regarding inhalation anesthetic agents is incorrect?

A. Sevoflurane is more potent than isoflurane. (Correct Answer)
B. Sevoflurane is less cardiodepressant than isoflurane.
C. Desflurane has a lower blood-gas partition coefficient than sevoflurane.
D. Sevoflurane has a higher MAC than isoflurane.

Explanation: To answer this question correctly, one must understand the relationship between **MAC (Minimum Alveolar Concentration)** and **Potency**. ### 1. Why Option A is the Correct (Incorrect Statement) Potency is inversely proportional to MAC ($Potency \propto 1/MAC$). A drug with a lower MAC value is more potent because it requires a lower concentration to achieve the same clinical effect (immobility in 50% of patients). * **MAC of Isoflurane:** ~1.15% * **MAC of Sevoflurane:** ~2.0% Since Isoflurane has a lower MAC, it is **more potent** than Sevoflurane. Therefore, the statement "Sevoflurane is more potent than isoflurane" is false. ### 2. Analysis of Other Options * **Option B:** Sevoflurane is indeed less cardiodepressant and less likely to cause tachycardia compared to Isoflurane, making it safer for patients with coronary artery disease. * **Option C:** Desflurane has a blood-gas partition coefficient of **0.42**, while Sevoflurane is **0.65**. A lower coefficient means Desflurane is less soluble in blood, leading to faster induction and emergence. * **Option D:** As noted above, Sevoflurane (MAC 2.0%) has a higher MAC than Isoflurane (MAC 1.15%). ### 3. High-Yield Clinical Pearls for NEET-PG * **Oil-Gas Partition Coefficient:** Directly proportional to potency (Meyer-Overton Hypothesis). * **Blood-Gas Partition Coefficient:** Inversely proportional to the speed of induction/recovery. * **Order of Potency:** Halothane > Isoflurane > Sevoflurane > Desflurane > $N_2O$. * **Order of Speed of Induction:** Desflurane > Sevoflurane > Isoflurane > Halothane. * **Agent of Choice for Induction:** Sevoflurane (non-pungent, pleasant odor). * **Pungent Agents:** Desflurane and Isoflurane (can cause breath-holding/laryngospasm).

Question 462: What does MAC stand for?

A. Minimum alveolar concentration (Correct Answer)
B. Minimal analgesic concentration
C. Minimal anaesthetic concentration
D. Maximum alveolar concentration

Explanation: **Explanation:** **Minimum Alveolar Concentration (MAC)** is a fundamental concept in inhalational anesthesia. It is defined as the concentration of an inhalational anesthetic (at 1 atmosphere) that prevents skeletal muscle movement in response to a noxious stimulus (like a surgical skin incision) in **50% of patients**. It is essentially the **ED50** of an inhalational agent, serving as a measure of its **potency**. * **Why Option A is correct:** MAC specifically refers to the concentration in the **alveoli**. Since the alveolar partial pressure of an anesthetic is in equilibrium with its partial pressure in the blood and brain at steady state, MAC is a reliable surrogate for the concentration of the drug at its site of action (the CNS). * **Why Options B, C, and D are incorrect:** While "analgesic" and "anaesthetic" describe the drug's effects, they are not the standardized terms used in this definition. "Maximum" is incorrect because MAC is a *minimum* threshold value; a lower MAC value indicates a more potent anesthetic (e.g., Halothane has a lower MAC than Sevoflurane). **High-Yield Clinical Pearls for NEET-PG:** 1. **Potency vs. MAC:** MAC is inversely proportional to potency. (High MAC = Low Potency). 2. **Oil:Gas Partition Coefficient:** MAC is inversely proportional to lipid solubility (Meyer-Overton Hypothesis). 3. **MAC-Awake:** The concentration at which 50% of patients respond to verbal commands (usually ~0.3–0.4 MAC). 4. **MAC-BAR:** The concentration required to blunt the autonomic response to stimulus (~1.5–2.0 MAC). 5. **Factors increasing MAC:** Hyperthermia, chronic alcohol abuse, hypernatremia, and increased central neurotransmitters (e.g., cocaine/MAOIs). 6. **Factors decreasing MAC:** Pregnancy, old age, acute alcohol intoxication, hypothermia, and anemia.

Question 463: Ether is still used as a general anesthetic in India, especially in peripheral hospitals because:

A. It is non-explosive
B. It is pleasant smelling and non-irritating
C. It induces anesthesia rapidly
D. It is cheap and can be administered without an anesthetic machine (Correct Answer)

Explanation: **Explanation:** Diethyl ether remains a classic example of a "safe" anesthetic for resource-limited settings. The correct answer is **Option D** because ether is highly cost-effective and possesses a unique physical property: it is potent enough to be administered via the **"Open Drop Method"** (using a Schimmelbusch mask). This eliminates the mandatory requirement for expensive vaporizers or anesthesia workstations, making it ideal for peripheral hospitals with limited infrastructure. **Analysis of Incorrect Options:** * **Option A:** Ether is highly **flammable and explosive**, especially when mixed with air or oxygen. This is its greatest disadvantage, requiring strict precautions against static electricity and cautery. * **Option B:** Ether has a **pungent, irritating odor**. It stimulates salivary and bronchial secretions (requiring atropine premedication) and can cause laryngospasm during induction. * **Option C:** Ether has a **high Blood/Gas Partition Coefficient (~12)**. According to the principles of pharmacokinetics, high solubility in blood leads to a **slow induction** and slow recovery, as it takes longer for the alveolar concentration to reach equilibrium with the brain. **High-Yield Clinical Pearls for NEET-PG:** * **Safety Profile:** Ether is respiratory-stable and maintains blood pressure due to sympathetic stimulation, making it safer for hemodynamically unstable patients in rural setups. * **Stages of Anesthesia:** Guedel’s classification of the stages of anesthesia was originally described using Ether. * **Muscle Relaxation:** It provides excellent spontaneous muscle relaxation, often negating the need for neuromuscular blockers for basic abdominal surgeries. * **Nausea:** It is associated with a high incidence of Post-Operative Nausea and Vomiting (PONV).

Question 464: An alcoholic patient with a history of diabetic nephropathy and liver failure is scheduled for open abdominal surgery. Which muscle relaxant is most appropriate for this patient?

A. Cisatracurium (Correct Answer)
B. Rocuronium
C. Vecuronium
D. Rapacuronium

Explanation: ### Explanation The correct answer is **Cisatracurium**. **Why Cisatracurium is the drug of choice:** The patient presents with a combination of **liver failure** and **diabetic nephropathy** (renal failure). Most neuromuscular blocking agents (NMBAs) rely on hepatic metabolism or renal excretion for clearance. However, Cisatracurium (an isomer of Atracurium) undergoes **Hofmann Elimination**. This is a unique organ-independent chemical degradation process that occurs at physiological pH and temperature. Because it does not rely on the liver or kidneys, its duration of action remains predictable even in multi-organ failure, making it the safest choice for this patient. **Analysis of Incorrect Options:** * **Rocuronium (B) and Vecuronium (C):** These are aminosteroid compounds. They are primarily metabolized by the **liver** and excreted via **bile and urine**. In patients with liver or renal failure, their half-life is significantly prolonged, leading to unpredictable recovery and prolonged neuromuscular blockade. * **Rapacuronium (D):** This was a rapid-onset steroid NMBA that was withdrawn from the market worldwide due to a high incidence of severe **bronchospasm**. **NEET-PG High-Yield Pearls:** * **Hofmann Elimination:** A non-enzymatic degradation. It is temperature and pH-dependent (rate increases with hyperthermia and alkalosis; decreases with hypothermia and acidosis). * **Laudanosine:** A metabolite of both Atracurium and Cisatracurium. It is a CNS stimulant that can lower the seizure threshold. However, Cisatracurium produces significantly less laudanosine than Atracurium. * **Histamine Release:** Unlike Atracurium, Cisatracurium does **not** cause significant histamine release, making it more hemodynamically stable. * **Drug of Choice in ICU:** Due to its organ-independent clearance, Cisatracurium is the preferred NMBA for long-term infusion in critically ill patients with organ dysfunction.

Question 465: Fasciculations are caused by which of the following agents?

A. Suxamethonium (Correct Answer)
B. Pancuronium
C. d-Tubocurarine
D. Vecuronium

Explanation: **Explanation:** The correct answer is **Suxamethonium (Succinylcholine)**. **1. Why Suxamethonium is correct:** Suxamethonium is the only **depolarizing neuromuscular blocker** used clinically. It acts as an agonist at the nicotinic acetylcholine receptors (nAChR) at the neuromuscular junction. Unlike acetylcholine, it is not metabolized by acetylcholinesterase, leading to prolonged depolarization of the post-synaptic membrane. This initial stimulation causes disorganized muscle fiber contractions known as **fasciculations** before the muscle eventually becomes flaccid (Phase I block). **2. Why the other options are incorrect:** * **Pancuronium, d-Tubocurarine, and Vecuronium** are all **non-depolarizing neuromuscular blockers**. They act as competitive antagonists at the nAChR. By simply blocking the receptor without activating it, they prevent depolarization from occurring. Consequently, they do not cause fasciculations; they result in immediate muscle relaxation. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Pre-curarization:** To prevent post-operative myalgia caused by fasciculations, a small "defasciculating dose" of a non-depolarizing agent (e.g., Vecuronium) is sometimes given before Suxamethonium. * **Metabolism:** Suxamethonium is metabolized by **Pseudocholinesterase** (Plasma cholinesterase). Deficiency of this enzyme leads to prolonged apnea. * **Side Effects:** Hyperkalemia (critical in burn/trauma patients), increased intraocular/intragastric pressure, and it is a potent trigger for **Malignant Hyperthermia**. * **Drug of Choice:** Due to its rapid onset (30–60s) and short duration (5–10 mins), it is the drug of choice for **Rapid Sequence Induction (RSI)**.

Question 466: Which of the following muscle relaxants causes maximal pain on injection?

A. Succinylcholine
B. Vecuronium
C. Rocuronium (Correct Answer)
D. Cisatracurium

Explanation: **Explanation:** **Rocuronium** is the correct answer as it is well-documented to cause the highest incidence of injection pain (up to 50–80% in awake patients) among all neuromuscular blocking agents. The underlying mechanism is attributed to its **low pH (approximately 4.0)** and the release of local mediators like **kinins**, which irritate the venous nociceptors. This often manifests as "withdrawal movement" of the limb during induction. **Analysis of Incorrect Options:** * **Succinylcholine (Option A):** While it causes post-operative muscle soreness (myalgia) due to fasciculations, it does not typically cause acute pain at the site of injection. * **Vecuronium (Option B):** It is a nearly pH-neutral, lyophilized powder. It is considered "cardiovascularly stable" and is generally painless upon administration [1]. * **Cisatracurium (Option C):** As an isomer of atracurium, it is designed to be potent and stable without significant histamine release or local irritation, making it painless on injection [1]. **Clinical Pearls for NEET-PG:** * **Mitigation:** Pain from Rocuronium can be reduced by pre-administering **Lidocaine**, using a larger vein, or priming with a small dose of an induction agent (Propofol). * **Rapidity:** Rocuronium is the non-depolarizing muscle relaxant (NDMR) with the **fastest onset of action** (60–90 seconds), making it the drug of choice for Rapid Sequence Induction (RSI) when Succinylcholine is contraindicated [1]. * **Reversal:** Its effects are specifically and rapidly reversed by **Sugammadex**.

Question 467: Which of the following gases exhibits the second gas effect?

A. Ether
B. Nitrous oxide (Correct Answer)
C. Desflurane
D. Sevoflurane

Explanation: **Explanation:** The **Second Gas Effect** is a phenomenon where the rapid uptake of a high-volume primary gas (usually Nitrous Oxide) accelerates the rate of increase in the alveolar concentration of a concurrently administered "second gas" (a potent volatile anesthetic). **Why Nitrous Oxide is Correct:** Nitrous oxide ($N_2O$) is highly insoluble in blood but is administered in high concentrations (up to 70%). When $N_2O$ is inhaled, it is rapidly absorbed from the alveoli into the pulmonary capillaries. This rapid removal of $N_2O$ causes the remaining gases in the alveoli to be "concentrated" into a smaller volume. This increases the fractional concentration ($F_A$) of the second gas (e.g., Halothane or Sevoflurane), leading to a faster induction of anesthesia. **Why Other Options are Incorrect:** * **Ether:** It is highly soluble in blood, leading to a slow induction. It does not achieve the rapid alveolar uptake required to produce a concentration effect for other gases. * **Desflurane & Sevoflurane:** These are potent volatile anesthetics typically used as the "second gas." They are administered in low concentrations (usually <8%) and therefore do not occupy enough volume in the alveoli to trigger the second gas effect for other agents. **High-Yield NEET-PG Pearls:** * **Concentration Effect:** This is the precursor to the second gas effect; the higher the concentration of gas administered, the faster the arterial tension rises. * **Diffusion Hypoxia (Fink Effect):** The reverse of the second gas effect. When $N_2O$ is discontinued, it rushes out of the blood into the alveoli, diluting oxygen and $CO_2$. This is prevented by giving **100% $O_2$ for 5–10 minutes** after stopping $N_2O$. * **Blood-Gas Partition Coefficient:** $N_2O$ has a low coefficient (0.47), explaining its rapid onset and offset.

Question 468: All of the following are disadvantages of anesthetic ether, except?

A. Induction is slow
B. Irritant nature of ether increases salivary and bronchial secretions
C. Cautery cannot be used
D. Affects blood pressure and is liable to produce arrhythmias (Correct Answer)

Explanation: **Explanation:** Diethyl ether is a classic volatile anesthetic that, despite being largely obsolete in modern practice, remains a high-yield topic for NEET-PG due to its unique pharmacological profile. **Why Option D is the Correct Answer:** Unlike many modern halogenated agents (like Halothane), ether is remarkably **cardio-stable**. It stimulates the sympathetic nervous system, leading to a release of catecholamines. This compensatory mechanism maintains blood pressure and heart rate even at deeper planes of anesthesia. Furthermore, ether does not sensitize the myocardium to catecholamines, making it **non-arrhythmogenic**. Therefore, saying it "affects blood pressure and produces arrhythmias" is incorrect, making it the "except" choice. **Analysis of Disadvantages (Incorrect Options):** * **Option A (Slow Induction):** Ether has a high **Blood:Gas partition coefficient (~12)**. High solubility in blood means it takes longer to reach equilibrium in the brain, resulting in a slow, prolonged induction and recovery. * **Option B (Irritant Nature):** Ether is highly pungent and irritates the respiratory mucosa. This leads to excessive salivation and bronchial secretions, necessitating the use of atropine as a premedication. It can also trigger coughing and laryngospasm during induction. * **Option C (Flammability):** Ether is highly **inflammable and explosive**. This precludes the use of cautery or diathermy in the operating room, which is a major safety disadvantage. **High-Yield Clinical Pearls for NEET-PG:** * **Guedel’s Stages:** Ether is the agent used to describe the four stages of General Anesthesia. * **Muscle Relaxation:** It has excellent intrinsic neuromuscular blocking properties. * **Safety Margin:** It is considered very safe for spontaneous respiration as it does not depress the respiratory center until very deep planes are reached. * **Vomiting:** Post-operative nausea and vomiting (PONV) is very high with ether.

Question 469: Which anaesthetic agent is not metabolized by the body?

A. Nitrous oxide (Correct Answer)
B. Gallamine
C. Sevoflurane
D. Halothane

Explanation: **Explanation:** The correct answer is **Nitrous oxide (N₂O)**. **1. Why Nitrous Oxide is correct:** Nitrous oxide is a unique inhalational anesthetic because it is **not metabolized** by human enzymes. It is extremely insoluble in blood and tissues, allowing it to be excreted almost entirely (99.9%) unchanged through the lungs. A negligible amount may be reduced to nitrogen by anaerobic bacteria in the gastrointestinal tract, but for clinical and pharmacological purposes, its metabolism in the human body is considered zero. **2. Analysis of Incorrect Options:** * **Gallamine:** This is a long-acting non-depolarizing muscle relaxant. While it is not significantly metabolized by the liver, it is excreted unchanged **by the kidneys**. It is not an anesthetic agent but a neuromuscular blocker. * **Sevoflurane:** This is a modern inhalational agent that undergoes approximately **2–5% hepatic metabolism** via the Cytochrome P450 (CYP2E1) system, releasing inorganic fluoride. * **Halothane:** This agent undergoes significant hepatic metabolism (up to **15–20%**). Its metabolites (trifluoroacetic acid) are implicated in "Halothane Hepatitis," a rare but severe immune-mediated liver injury. **3. High-Yield Clinical Pearls for NEET-PG:** * **Second Gas Effect:** N₂O is used to speed up the induction of other volatile agents. * **Diffusion Hypoxia:** Occurs during recovery if 100% oxygen is not administered, as N₂O rushes out of the blood into the alveoli, diluting oxygen. * **Contraindication:** N₂O must be avoided in closed-space pathologies (e.g., pneumothorax, intestinal obstruction, middle ear surgery) because it expands air-filled cavities. * **Enzyme Inhibition:** Chronic exposure inhibits **Methionine Synthase** (Vitamin B12 metabolism), potentially leading to megaloblastic anemia or myeloneuropathy.

Question 470: Fasciculations are caused by which of the following agents?

A. Scoline (Correct Answer)
B. Ketamine
C. Halothane
D. Atracurium

Explanation: **Explanation:** The correct answer is **Scoline (Succinylcholine)**. **1. Why Scoline is correct:** Scoline is a **depolarizing neuromuscular blocker**. It acts as an agonist at the nicotinic acetylcholine receptors (nAChR) at the motor endplate. Unlike acetylcholine, it is not metabolized by acetylcholinesterase, leading to prolonged depolarization. This initial stimulation of the muscle fibers causes disorganized, involuntary contractions known as **fasciculations** before the onset of flaccid paralysis (Phase I block). **2. Why the other options are incorrect:** * **Ketamine:** An intravenous induction agent that acts primarily as an NMDA receptor antagonist. It causes "dissociative anesthesia" and does not act on the neuromuscular junction to cause fasciculations. * **Halothane:** An inhalational anesthetic agent. While it can trigger malignant hyperthermia in susceptible individuals, it does not cause initial muscle fasciculations; rather, it provides some degree of muscle relaxation. * **Atracurium:** A **non-depolarizing** neuromuscular blocker. It acts as a competitive antagonist at the nAChR, preventing depolarization. Therefore, it causes immediate paralysis without any preceding fasciculations. **3. High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Scoline is metabolized by **Pseudocholinesterase** (Plasma cholinesterase). * **Side Effects:** Fasciculations can lead to postoperative myalgia, increased intraocular pressure, increased intragastric pressure, and increased intracranial pressure. * **Pre-curarization:** A small dose of a non-depolarizing agent (like vecuronium) can be given beforehand to prevent Scoline-induced fasciculations. * **Contraindication:** Avoid in patients with burns, massive trauma, or nerve injuries due to the risk of **hyperkalemia**.

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

Practice Questions

Emergence from Anesthesia

Practice Questions

Postoperative Care

Practice Questions

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