General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 101: Which of the following statements regarding neuromuscular blockers are true?

A. Statements 1, 2, and 3 are true, and statements 4 and 5 are false.
B. Statements 1, 2, 3, and 5 are true, and statement 4 is false.
C. Statements 1 and 2 are true, and statements 3, 4, and 5 are false.
D. Statements 1, 2, 3, 4, and 5 are true. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**, as all five statements regarding neuromuscular blockers (NMBs) are clinically accurate. 1. **Mechanism of Action:** NMBs act at the **nicotinic acetylcholine receptors (nAChR)** at the motor endplate. Depolarizing agents (Succinylcholine) act as agonists, while Non-depolarizing agents (e.g., Vecuronium, Atracurium) act as competitive antagonists. 2. **Succinylcholine (Sch):** It is the only depolarizing NMB in clinical use. It is preferred for **Rapid Sequence Induction (RSI)** due to its rapid onset (30–60s) and short duration (5–10 mins), as it is metabolized by **pseudocholinesterase**. 3. **Hofmann Elimination:** This is a unique organ-independent chemical degradation (spontaneous) that occurs at physiological pH and temperature. It is the primary pathway for **Atracurium and Cisatracurium**, making them the drugs of choice in **renal or hepatic failure**. 4. **Reversal Agents:** Acetylcholinesterase inhibitors like **Neostigmine** increase ACh levels at the synapse to outcompete non-depolarizing blockers. **Sugammadex** is a newer agent that specifically encapsulates Aminosteroidal NMBs (Rocuronium > Vecuronium). 5. **Side Effects:** Succinylcholine is notorious for causing **hyperkalemia** (due to prolonged depolarization), muscle fasciculations, and is a potent trigger for **Malignant Hyperthermia**. **Why other options are wrong:** Options A, B, and C are incorrect because they falsely suggest that certain fundamental properties of NMBs (like Hofmann elimination or the mechanism of reversal) are untrue. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of choice in Liver/Kidney failure:** Cisatracurium (due to Hofmann elimination). * **Mivacurium:** The shortest-acting non-depolarizing NMB; metabolized by pseudocholinesterase. * **Pancuronium:** Long-acting; associated with tachycardia (vagolytic effect). * **Train-of-Four (TOF) Monitoring:** Used to assess the depth of blockade; a ratio of <0.9 indicates residual paralysis.

Question 102: The rate at which the alveolar concentration of an anesthetic approaches inspired concentration is a function of all except?

A. Alveolar ventilation
B. Water solubility of agent
C. Cardiac output
D. Saturated vapor pressure (Correct Answer)

Explanation: The rate at which the alveolar concentration ($F_A$) approaches the inspired concentration ($F_I$) is represented by the **$F_A/F_I$ curve**. This ratio determines the speed of induction; the faster $F_A$ reaches $F_I$, the faster the patient goes under anesthesia. ### **Why Saturated Vapor Pressure (SVP) is the Correct Answer** **Saturated Vapor Pressure** is a physical property of the liquid anesthetic that determines the maximum concentration achievable in the vapor phase at a given temperature. While SVP dictates how much anesthetic the vaporizer can deliver (the $F_I$), it does **not** influence the rate at which the alveoli equilibrate with that delivered concentration. Once the gas is in the breathing circuit, the kinetics are governed by uptake and distribution, not the liquid's vapor pressure. ### **Analysis of Incorrect Options** * **Alveolar Ventilation (A):** Increasing ventilation delivers more anesthetic to the alveoli per minute, causing $F_A$ to rise faster. This is the primary driver for increasing the rate of induction. * **Water (Blood) Solubility (B):** This is the most important factor slowing the rise of $F_A/F_I$. Highly soluble agents (e.g., Halothane) are "soaked up" by the blood, preventing $F_A$ from rising quickly. Insoluble agents (e.g., Desflurane, $N_2O$) stay in the alveoli, leading to rapid induction. * **Cardiac Output (C):** Increased CO removes more anesthetic from the alveoli into the systemic circulation, thereby slowing the rise of $F_A$. Conversely, in shock (low CO), induction is faster. ### **High-Yield Clinical Pearls for NEET-PG** * **The Concentration Effect:** Higher inspired concentrations ($F_I$) lead to a disproportionately faster rise in $F_A$ (relevant for $N_2O$). * **Second Gas Effect:** A high volume of a rapidly absorbed gas ($N_2O$) accelerates the uptake of a companion volatile anesthetic. * **Ventilation-Perfusion Mismatch:** Shunts (Right-to-Left) slow the induction of **insoluble** agents more than soluble ones. * **Time Constant:** Defined as the volume of the circuit divided by the flow rate.

Question 103: Which of the following inhalational agents has characteristic features that make it ideal?

A. Xenon (Correct Answer)
B. Desflurane
C. Sevoflurane
D. N2O

Explanation: **Explanation:** **Xenon** is considered the closest to an **"Ideal Inhalational Anesthetic"** due to its unique pharmacological profile. It is an inert noble gas that is non-explosive, non-flammable, and environmentally friendly (no greenhouse effect). **Why Xenon is the Correct Answer:** * **Pharmacokinetics:** It has an extremely low blood-gas partition coefficient (0.115), leading to the fastest induction and emergence among all agents. * **Hemodynamic Stability:** Unlike other agents, it does not depress the myocardium or alter systemic vascular resistance, making it ideal for cardiac patients. * **Neuroprotection:** It acts as an NMDA receptor antagonist, providing significant neuroprotective benefits. * **Safety:** It is non-toxic, non-metabolized, and does not trigger Malignant Hyperthermia. **Why Other Options are Incorrect:** * **Desflurane:** While it has a low blood-gas coefficient (0.42), it is pungent, causes airway irritation (tachycardia/breath-holding), and is a potent greenhouse gas. * **Sevoflurane:** Though excellent for mask induction, it can be metabolized to Compound A (nephrotoxicity risk in low-flow states) and has a higher blood-gas coefficient (0.65) than Xenon. * **N2O (Nitrous Oxide):** It is a weak anesthetic (MAC 104%), supports combustion, causes megaloblastic anemia (B12 inhibition), and expands closed gas spaces. **High-Yield Clinical Pearls for NEET-PG:** * **MAC of Xenon:** 63–71%. * **Blood-Gas Partition Coefficient:** Xenon (0.115) < Desflurane (0.42) < N2O (0.47) < Sevoflurane (0.65). * **Limitation:** The primary reason Xenon is not used routinely is its **prohibitive cost** and the need for specialized closed-circuit delivery systems.

Question 104: Plasma expanders are used in which of the following conditions?

A. Severe anemia
B. Severe trauma (Correct Answer)
C. Pulmonary edema
D. Cardiac failure

Explanation: **Explanation:** **Plasma expanders** are intravenous fluids (colloids or crystalloids) used to restore circulating blood volume and maintain hemodynamic stability. **Why Severe Trauma is correct:** In severe trauma, the primary concern is **hypovolemic shock** due to acute blood loss or fluid shifts. Plasma expanders (like Hydroxyethyl starch, Dextran, or Gelatins) increase the oncotic pressure of the blood, drawing fluid into the vascular compartment and expanding the volume more effectively than crystalloids alone. This maintains cardiac output and organ perfusion until definitive blood transfusion or surgery can occur. **Why other options are incorrect:** * **Severe Anemia:** The primary deficit is oxygen-carrying capacity (Hemoglobin), not necessarily volume. Treatment requires Packed Red Blood Cells (PRBCs). Giving plasma expanders would further dilute the existing hemoglobin (hemodilution), worsening tissue hypoxia. * **Pulmonary Edema:** This condition is characterized by fluid overload in the lungs. Adding plasma expanders would increase hydrostatic pressure and worsen the edema. Treatment involves diuretics and fluid restriction. * **Cardiac Failure:** The heart is unable to pump the existing volume effectively. Increasing the preload with plasma expanders can lead to acute decompensation and congestive heart failure. **Clinical Pearls for NEET-PG:** * **Ideal Plasma Expander:** Should be iso-oncotic with plasma, pharmacologically inert, non-pyrogenic, and have a long shelf life. * **Dextran Warning:** Dextran-40 can cause "Dextran-induced Anaphylactoid Reaction" (DIAR) and may interfere with blood grouping/cross-matching. * **Gelatins:** These are the plasma expanders of choice in renal failure as they are excreted by the kidneys without causing significant damage. * **Albumin:** The only natural colloid; used in cirrhosis with ascites and severe burns.

Question 105: Which of the following is the fastest acting anesthetic agent?

A. Sevoflurane (Correct Answer)
B. Desflurane
C. Isoflurane
D. None of the above

Explanation: **Explanation:** The speed of induction and recovery of an inhalational anesthetic agent is primarily determined by its **Blood-Gas Partition Coefficient (λ)**. A lower coefficient indicates lower solubility in blood, allowing the partial pressure of the gas in the alveoli to rise rapidly, leading to faster equilibration with the brain. **Why Sevoflurane is the Correct Answer:** While **Desflurane** actually has a lower blood-gas partition coefficient (0.42) than **Sevoflurane** (0.65), Sevoflurane is clinically considered the fastest agent for **inhalation induction**. This is because Desflurane is highly pungent and irritates the airway, causing coughing, breath-holding, and laryngospasm, making it unsuitable for rapid mask induction. Sevoflurane is non-pungent, pleasant-smelling, and a potent bronchodilator, allowing for a smooth and rapid "single-breath" induction, especially in pediatric practice. **Analysis of Incorrect Options:** * **B. Desflurane:** Although it has the fastest *emergence* (recovery) due to its lowest solubility, its pungency prevents it from being the fastest agent for *induction*. * **C. Isoflurane:** It has a higher blood-gas partition coefficient (1.4), making it significantly slower in both induction and recovery compared to Sevoflurane and Desflurane. **High-Yield Clinical Pearls for NEET-PG:** * **Lowest Blood-Gas Coefficient:** Desflurane (0.42) > Sevoflurane (0.65) > Nitrous Oxide (0.47) > Isoflurane (1.4) > Halothane (2.4). * **Agent of Choice for Induction:** Sevoflurane (due to non-pungency). * **Agent of Choice for Maintenance in Day-care Surgery:** Desflurane (due to fastest recovery). * **Compound A:** A nephrotoxic byproduct formed when Sevoflurane reacts with dry soda lime. * **Carbon Monoxide:** Highest production is seen with Desflurane when used with dry CO2 absorbers.

Question 106: Which intravenous anesthetic agent produces a cocaine-like effect on the cardiovascular system?

A. Thiopentone
B. Propofol
C. Ketamine (Correct Answer)
D. Etomidate

Explanation: ### Explanation **Correct Answer: C. Ketamine** Ketamine is a unique intravenous anesthetic that acts as a **sympathomimetic** agent. Its "cocaine-like" effect on the cardiovascular system is due to two primary mechanisms: 1. **Direct Stimulation:** It stimulates the central sympathetic nervous system. 2. **Inhibition of Reuptake:** Like cocaine, it inhibits the neuronal reuptake of catecholamines (norepinephrine) into postganglionic sympathetic nerve endings. This results in an **increase in heart rate, arterial blood pressure, and cardiac output**, making it the induction agent of choice for patients in hypovolemic shock. --- ### Why the other options are incorrect: * **A. Thiopentone:** A barbiturate that causes dose-dependent myocardial depression and peripheral vasodilation (venodilation), leading to a **decrease in blood pressure**. * **B. Propofol:** Known for causing the most significant **hypotension** among induction agents due to profound vasodilation and decreased myocardial contractility. It also blunts the baroreceptor reflex. * **D. Etomidate:** Renowned for its **cardiovascular stability**. It causes minimal changes in heart rate and blood pressure, making it ideal for patients with cardiac disease, but it does not produce a sympathomimetic "cocaine-like" surge. --- ### High-Yield Clinical Pearls for NEET-PG: * **Dissociative Anesthesia:** Ketamine produces a state where the patient appears awake (eyes open) but is unconscious and feels no pain. * **Bronchodilation:** Ketamine is the induction agent of choice for **Asthmatic patients**. * **Contraindications:** Avoid Ketamine in patients with **Ischemic Heart Disease (IHD)** or Hypertension (due to increased myocardial oxygen demand) and in cases of **increased Intracranial Pressure (ICP)**. * **Emergence Delirium:** A common side effect of Ketamine, which can be pre-treated with Benzodiazepines (e.g., Midazolam).

Question 107: Which of the following drugs has caused hyperkalemia leading to cardiac arrest in patients with neurological disorders?

A. Baclofen
B. Dantrolene
C. Succinylcholine (Correct Answer)
D. Tubocurarine

Explanation: **Explanation:** **Succinylcholine (Suxamethonium)** is a depolarizing neuromuscular blocker that acts as an agonist at the nicotinic acetylcholine receptors (nAChR) at the neuromuscular junction. **Why Succinylcholine is the correct answer:** In normal individuals, succinylcholine causes a transient rise in serum potassium (~0.5 mEq/L). However, in patients with **neurological disorders** (e.g., stroke, spinal cord injury, burns, or muscular dystrophy), there is an **upregulation of extrajunctional acetylcholine receptors**. When succinylcholine binds to these widespread receptors, it causes massive, prolonged depolarization, leading to an efflux of potassium from the cells into the extracellular fluid. This **exaggerated hyperkalemia** can lead to fatal cardiac arrhythmias and cardiac arrest. **Why the other options are incorrect:** * **Baclofen:** A GABA-B receptor agonist used as a muscle relaxant for spasticity; it does not act on nAChR and does not cause hyperkalemia. * **Dantrolene:** Acts intracellularly by inhibiting the ryanodine receptor (RyR1) to prevent calcium release from the sarcoplasmic reticulum. It is the treatment of choice for Malignant Hyperthermia and does not cause hyperkalemia. * **Tubocurarine:** A non-depolarizing neuromuscular blocker. These drugs are competitive antagonists and do not cause depolarization; therefore, they do not trigger potassium release and are generally safe in patients at risk for hyperkalemia. **NEET-PG High-Yield Pearls:** * **Avoid Succinylcholine in:** Burns (>24 hours), massive trauma, prolonged immobilization, and upper/lower motor neuron lesions. * **Drug of choice for RSI:** Succinylcholine (due to rapid onset and short duration), but **Rocuronium** is the preferred alternative if hyperkalemia is a concern. * **Malignant Hyperthermia:** Succinylcholine is a known trigger.

Question 108: A patient develops the arrhythmia shown in the ECG below, intra-operatively. What is the drug of choice (DOC)?

A. Propranolol (Correct Answer)
B. Adrenaline
C. Hyoscine
D. Neostigmine

Explanation: ***Propranolol*** - **Beta-blocker** that effectively controls **intraoperative sinus tachycardia** by blocking sympathetic stimulation and reducing heart rate. - Drug of choice for **perioperative tachycardia** due to its predictable onset and ability to counteract **catecholamine-induced** arrhythmias. *Adrenaline* - **Sympathomimetic agent** that would **worsen tachycardia** by increasing heart rate and cardiac contractility through beta-1 receptor stimulation. - Contraindicated in **sinus tachycardia** as it would exacerbate the underlying sympathetic overactivity. *Hyoscine* - **Anticholinergic drug** that can cause **tachycardia** as a side effect by blocking parasympathetic tone. - Would be inappropriate for treating tachycardia and may actually **worsen the arrhythmia** in this clinical scenario. *Neostigmine* - **Cholinesterase inhibitor** primarily used for **reversal of neuromuscular blockade** rather than arrhythmia management. - While it may have some **bradycardic effects**, it's not the appropriate first-line treatment for intraoperative tachycardia.

Question 109: Which of the following drugs is known to cause severe pain on injection?

A. Thiopentone (Correct Answer)
B. Pethidine
C. Phenobarbitone
D. Ketamine

Explanation: **Explanation** The correct answer is **Thiopentone (Option A)**. **Why Thiopentone is correct:** Thiopentone sodium is an ultra-short-acting barbiturate used for the induction of anesthesia. It is highly alkaline, with a **pH of approximately 10.5**. Due to this high alkalinity, it is extremely irritating to the vascular endothelium. If injected into a small vein or accidentally administered **intra-arterially**, it causes intense pain, severe vasoconstriction (vasospasm), and can lead to tissue necrosis or gangrene. To minimize pain and the risk of thrombophlebitis, it is typically administered in a dilute concentration (2.5%). **Why the other options are incorrect:** * **Pethidine (Option B):** While pethidine can cause local histamine release leading to redness or itching along the vein, it is not primarily known for "severe pain on injection" in the same clinical context as alkaline barbiturates. * **Phenobarbitone (Option C):** Although also a barbiturate, it is a long-acting sedative/anticonvulsant. While alkaline, it is not the classic "high-yield" answer associated with induction-related injection pain in anesthesiology exams compared to Thiopentone or Propofol. * **Ketamine (Option D):** Ketamine is generally non-irritating to the veins and is often used in pediatric or emergency settings because it can be given intramuscularly without causing significant tissue damage or severe pain. **Clinical Pearls for NEET-PG:** * **Propofol** is the other common induction agent notorious for pain on injection (mitigated by using larger veins or pre-treating with Lidocaine). * **Management of Intra-arterial Thiopentone:** If accidental intra-arterial injection occurs, the needle should be left in place to administer vasodilators (e.g., **Papaverine** or **Phentolamine**) and a sympathetic block (e.g., Stellate ganglion block) to prevent gangrene. * **Etomidate** also causes significant pain on injection and a high incidence of myoclonus.

Question 110: Which inhalational agent acts on the NMDA receptor?

A. Xenon (Correct Answer)
B. Desflurane
C. Sevoflurane
D. Isoflurane

Explanation: **Explanation:** The mechanism of action for most volatile inhalational anesthetics primarily involves the enhancement of inhibitory neurotransmission via **GABA-A receptors**. However, a specific group of anesthetic gases works by inhibiting excitatory neurotransmission, specifically by acting as **non-competitive antagonists at the N-methyl-D-aspartate (NMDA) receptor**. **Why Xenon is correct:** Xenon is an inert gas that produces anesthesia by binding to the glycine site of the NMDA receptor, thereby inhibiting it. This unique mechanism contributes to its remarkable profile: it provides rapid induction and emergence (due to an extremely low blood-gas partition coefficient of 0.115), offers significant neuroprotection, and maintains hemodynamic stability. Other agents that share this NMDA-antagonist mechanism include **Ketamine** and **Nitrous Oxide (N₂O)**. **Why other options are incorrect:** * **Options B, C, and D (Desflurane, Sevoflurane, Isoflurane):** These are halogenated ethers (volatile liquids). Their primary molecular target is the **GABA-A receptor**, where they increase chloride conductance, leading to hyperpolarization of the postsynaptic neuron and CNS depression. While they may have minor effects on other channels, they are not classified as primary NMDA antagonists. **High-Yield Clinical Pearls for NEET-PG:** * **Ideal Anesthetic:** Xenon is often called the "ideal anesthetic" because it is non-explosive, non-toxic, and has minimal cardiovascular side effects. * **Blood-Gas Partition Coefficients:** Xenon (0.115) < Desflurane (0.42) < Nitrous Oxide (0.47) < Sevoflurane (0.65) < Isoflurane (1.4). * **MAC of Xenon:** Approximately 63–71%, making it less potent than volatile liquids but more potent than Nitrous Oxide. * **Key NMDA Antagonists in Anesthesia:** Xenon, Nitrous Oxide, Ketamine, and Magnesium.

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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