General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 61: Regarding ketamine, all the following statements are true EXCEPT:

A. Ketamine acts on NMDA receptors in the brain.
B. It is an indirectly acting sympathomimetic agent.
C. It is contraindicated in shock. (Correct Answer)
D. It is an agent of choice in asthma patients.

Explanation: **Explanation:** Ketamine is a unique intravenous anesthetic agent known for producing "dissociative anesthesia." **Why Option C is the Correct Answer (The Exception):** Ketamine is **not** contraindicated in shock; in fact, it is often the **induction agent of choice for patients in hypovolemic or septic shock**. Ketamine acts as an indirect sympathomimetic, stimulating the release of endogenous catecholamines, which leads to an increase in heart rate, blood pressure, and cardiac output. This hemodynamic stability is beneficial in shocked states. *Note:* It should be used cautiously in "depleted" shock states (e.g., end-stage heart failure) where catecholamine stores are exhausted, as its direct myocardial depressant effect may then manifest. **Analysis of Incorrect Options:** * **Option A:** Ketamine primarily acts by non-competitive antagonism of **NMDA (N-methyl-D-aspartate) receptors** in the brain and spinal cord. This inhibits the excitatory neurotransmitter glutamate. * **Option B:** It is an **indirect sympathomimetic**. While it is a direct myocardial depressant in isolated tissues, in vivo, it inhibits the reuptake of norepinephrine and stimulates the sympathetic nervous system, overriding the depression. * **Option D:** Ketamine is the **agent of choice for asthmatics** because it has potent bronchodilatory properties mediated by sympathomimetic activity and direct smooth muscle relaxation. **High-Yield Clinical Pearls for NEET-PG:** * **Dissociative Anesthesia:** Characterized by eyes remaining open with a slow nystagmic gaze. * **Emergence Delirium:** A common side effect (hallucinations/vivid dreams) which can be prevented by pre-medication with **Benzodiazepines (Midazolam)**. * **Contraindications:** Raised Intracranial Pressure (ICP), Raised Intraocular Pressure (IOP), and Systemic Hypertension (due to its sympathomimetic effects). * **Secretions:** It causes significant salivation; hence, it is often co-administered with Glycopyrrolate.

Question 62: What method is used to evaluate intraoperative awareness during surgery?

A. Pulse oximetry
B. Color Doppler
C. Bispectral imaging (Correct Answer)
D. End-tidal CO2

Explanation: **Explanation:** **1. Why Bispectral Index (BIS) Imaging is Correct:** Intraoperative awareness occurs when a patient becomes conscious during general anesthesia and can recall events. The **Bispectral Index (BIS)** is a processed EEG parameter used to monitor the depth of anesthesia. It converts raw EEG signals into a single dimensionless number ranging from **0 (isoelectric/brain death) to 100 (fully awake)**. For general anesthesia, a BIS value between **40 and 60** is targeted to ensure adequate hypnosis and minimize the risk of intraoperative awareness. **2. Why the other options are incorrect:** * **Pulse Oximetry (A):** Measures oxygen saturation ($SpO_2$) and pulse rate. It monitors respiratory and cardiovascular status, not neurological depth. * **Color Doppler (B):** An ultrasound technique used to visualize blood flow through vessels and heart chambers. It has no role in monitoring consciousness. * **End-tidal $CO_2$ (Et$CO_2$) (D):** Measures the concentration of carbon dioxide at the end of expiration. It is the gold standard for confirming endotracheal tube placement and monitoring ventilation, but it does not reflect the patient's level of awareness. **3. Clinical Pearls for NEET-PG:** * **BIS Range:** 40–60 (General Anesthesia); <40 (Deep Hypnosis); >70 (Light Anesthesia/Sedation). * **Isolated Forearm Technique:** Considered the "gold standard" for detecting intraoperative awareness, though BIS is more commonly used in modern practice. * **Risk Factors for Awareness:** Cardiac surgery, obstetric general anesthesia (due to lighter planes), and trauma surgery. * **Other Depth Monitors:** Entropy and Patient State Index (PSI).

Question 63: In which of the following stages is general anesthesia surgery performed?

A. Stage I
B. Stage II
C. Stage III plane 2
D. Stage III plane 3 (Correct Answer)

Explanation: This question refers to **Guedel’s Classification**, which describes the signs of anesthesia depth primarily observed with ether. While modern intravenous agents bypass these stages rapidly, the classification remains a fundamental concept for NEET-PG. ### **Why Stage III Plane 3 is Correct** **Stage III (Surgical Anesthesia)** is divided into four planes. **Plane 3 (Deep Plane)** is the ideal stage for most major surgeries. * **Key Features:** It is characterized by the onset of intercostal muscle paralysis, a fixed/centralized eyeball, and the **loss of the light reflex**. * **Clinical Rationale:** This plane provides the necessary triad of general anesthesia: unconsciousness, profound analgesia, and significant muscle relaxation required for abdominal and major systemic procedures. ### **Analysis of Incorrect Options** * **Stage I (Analgesia):** Extends from the induction of anesthesia to the loss of consciousness. Surgery cannot be performed here as the patient is conscious and feels pain. * **Stage II (Delirium/Excitement):** Characterized by struggling, breath-holding, and potential vomiting. It is a "danger zone" where sympathetic stimulation is high; performing surgery here risks laryngospasm or arrhythmias. * **Stage III Plane 2:** While some minor procedures can occur here (as the blink and laryngeal reflexes are lost), it does not provide sufficient muscle relaxation for major surgery. ### **High-Yield Clinical Pearls for NEET-PG** * **Stage III Plane 1:** Loss of conjunctival reflex, but the pupillary light reflex is preserved. * **Stage III Plane 4:** Complete intercostal paralysis (pure diaphragmatic breathing) and dilated pupils. This is a sign of anesthetic overdose. * **Stage IV (Medullary Paralysis):** Respiratory and vasomotor failure; this is a terminal stage leading to death if not reversed. * **Modern Context:** In current practice, "Balanced Anesthesia" (using NMBAs) makes these physical signs less visible, but the sequence of CNS depression remains the same.

Question 64: What is the skeletal muscle relaxant of choice in patients with liver and renal disease?

A. Mivacurium
B. Atracurium (Correct Answer)
C. Gallamine
D. Vecuronium

Explanation: **Explanation:** The muscle relaxant of choice in patients with liver and renal failure is **Atracurium** (or its isomer, Cisatracurium). **Why Atracurium is the Correct Answer:** Atracurium is unique because its metabolism is independent of organ function. It undergoes **Hofmann Elimination** (a spontaneous non-enzymatic degradation at physiological pH and temperature) and **Ester Hydrolysis** (by non-specific plasma esterases). Since it does not rely on the liver for metabolism or the kidneys for excretion, its duration of action remains predictable even in end-organ failure. **Analysis of Incorrect Options:** * **Mivacurium:** While it is metabolized by plasma cholinesterase, its duration can be significantly prolonged in patients with liver disease due to reduced synthesis of the cholinesterase enzyme. * **Gallamine:** This is a long-acting relaxant that is excreted almost entirely (95-100%) unchanged by the **kidneys**. It is strictly contraindicated in renal failure as it leads to profound cumulative toxicity. * **Vecuronium:** It is primarily metabolized by the liver and excreted via bile (40-50%) and urine. Its action is prolonged in patients with hepatic dysfunction and, to a lesser extent, renal failure. **High-Yield NEET-PG Pearls:** * **Cisatracurium:** It is more potent than atracurium and is preferred because it produces less **laudanosine** (a metabolite that can cause seizures) and does not cause histamine release. * **Drug of Choice for RSI in Renal Failure:** Rocuronium (if Succinylcholine is contraindicated due to hyperkalemia). * **Hofmann Elimination** is faster in states of **hyperthermia and alkalosis**, and slower in hypothermia and acidosis.

Question 65: Which of the following inhalational agents is contraindicated in renal disease?

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

Explanation: **Explanation:** The correct answer is **Methoxyflurane**. **1. Why Methoxyflurane is correct:** Methoxyflurane is highly lipid-soluble and undergoes extensive hepatic metabolism (up to 50–70%). This metabolism releases high concentrations of **inorganic fluoride ions (F⁻)**. Fluoride ions are nephrotoxic; they interfere with the concentrating mechanism of the distal convoluted tubules and collecting ducts, leading to **Vasopressin-resistant high-output renal failure** (polyuric renal failure). Due to this high risk of nephrotoxicity, it is no longer used for general anesthesia. **2. Why the other options are incorrect:** * **Sevoflurane:** While Sevoflurane also releases fluoride ions and can produce **Compound A** (a vinyl ether) when reacting with soda lime, clinical studies have shown it does not cause significant renal injury in humans under standard conditions. It is frequently used in clinical practice. * **Desflurane & Isoflurane:** These agents undergo minimal metabolism (0.02% and 0.2% respectively). They release negligible amounts of fluoride ions and are considered safe for patients with renal impairment. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism Gradient:** Methoxyflurane (50%) > Halothane (20%) > Sevoflurane (2%) > Enflurane (2%) > Isoflurane (0.2%) > Desflurane (0.02%). * **Compound A:** Associated with Sevoflurane; produced in CO₂ absorbers (especially with low-flow anesthesia and Baralyme). * **Agent of Choice in Renal Failure:** **Isoflurane** or **Desflurane** are generally preferred due to minimal metabolism. * **Current Use:** Methoxyflurane is now only used in low doses as a self-administered analgesic for trauma/emergency procedures (the "green whistle").

Question 66: Which of the following statements about thiopentone is incorrect?

A. Sodium carbonate is used as a preservative.
B. It is contraindicated in porphyria.
C. It is the agent of choice in shock. (Correct Answer)
D. It possesses cerebroprotective action.

Explanation: **Explanation:** **Why Option C is the correct (incorrect statement):** Thiopentone is **contraindicated in shock**. It is a potent venodilator and a direct myocardial depressant. In patients with hypovolemia or shock, these effects can lead to a profound, life-threatening drop in blood pressure and cardiovascular collapse. The induction agent of choice in shock is **Etomidate** (due to cardiovascular stability) or **Ketamine** (due to sympathetic stimulation). **Analysis of other options:** * **Option A (Sodium Carbonate):** Thiopentone is stored as a hygroscopic yellow powder. 6% Sodium Carbonate is added to the preparation to prevent the formation of free acid by atmospheric CO₂ and to ensure high alkalinity (pH 10.5), which makes the solution bacteriostatic. * **Option B (Porphyria):** Thiopentone is strictly contraindicated in Acute Intermittent Porphyria. It induces the enzyme **ALA synthetase**, which increases the production of porphyrins, potentially precipitating a fatal neurovisceral crisis. * **Option D (Cerebroprotective):** Thiopentone is highly cerebroprotective. It reduces the Cerebral Metabolic Rate of Oxygen (CMRO₂) and causes cerebral vasoconstriction, which decreases Cerebral Blood Flow (CBF) and **Intracranial Pressure (ICP)**. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Acts on GABA-A receptors (prolongs the opening of Chloride channels). * **Redistribution:** The short duration of action of a single bolus is due to redistribution from the brain to muscle and fat, not metabolism. * **Garlic Taste:** Patients often report a garlic or onion-like taste during induction. * **Accidental Intra-arterial Injection:** Causes severe vasospasm and gangrene. Treatment includes Heparin, Papaverine/Lidocaine (vasodilation), and Brachial plexus block.

Question 67: Which of the following does not have analgesic properties?

A. Ether
B. Ketamine
C. Halothane (Correct Answer)
D. Morphine

Explanation: **Explanation:** The core concept in general anesthesia is the "triad of anesthesia," which includes **amnesia (unconsciousness), analgesia (pain relief), and muscle relaxation.** Not all anesthetic agents provide all three components. **Why Halothane is the correct answer:** Halothane is a potent inhalational anesthetic known for its smooth induction and bronchodilatory properties. However, it is a **poor analgesic**. At sub-anesthetic concentrations, it may even cause "hyperalgesia" (increased sensitivity to pain). Therefore, it must be supplemented with analgesic agents (like opioids or nitrous oxide) to ensure patient comfort during and after surgery. **Analysis of Incorrect Options:** * **Ether:** Historically significant, ether is a "complete anesthetic." It provides excellent analgesia, amnesia, and muscle relaxation. * **Ketamine:** A phencyclidine derivative that produces "dissociative anesthesia." It is a **potent analgesic** even at sub-anesthetic doses, acting primarily via NMDA receptor antagonism. * **Morphine:** The gold standard opioid agonist. Its primary clinical use is for profound systemic analgesia. **High-Yield Clinical Pearls for NEET-PG:** * **Inhalational Agents & Analgesia:** Most volatile liquids (Halothane, Sevoflurane, Isoflurane) are poor analgesics. **Nitrous Oxide ($N_2O$)** is the notable exception, providing significant analgesia. * **Halothane Side Effects:** Watch for "Halothane Hepatitis" and its ability to sensitize the myocardium to catecholamines (leading to arrhythmias). * **Ketamine:** The drug of choice for induction in patients with asthma or hypovolemic shock, but contraindicated in head injuries due to increased intracranial pressure (ICP).

Question 68: Which of the following statements is NOT true regarding non-depolarizing muscle relaxants?

A. Magnesium predisposes to the neuromuscular block.
B. Calcium antagonizes the neuromuscular block.
C. Metabolized by pseudocholinesterase. (Correct Answer)
D. Acts as a competitive inhibitor of acetylcholine.

Explanation: ### Explanation **Correct Answer: C. Metabolized by pseudocholinesterase.** **Why Option C is NOT true:** Non-depolarizing muscle relaxants (NDMRs) like Atracurium, Vecuronium, and Rocuronium are metabolized through various pathways such as **Hofmann elimination** (Atracurium/Cisatracurium) or **hepatic/renal excretion**. **Pseudocholinesterase** (butyrylcholinesterase) is specifically responsible for the metabolism of **Succinylcholine** (the only depolarizing muscle relaxant) and ester-type local anesthetics. NDMRs are not metabolized by this enzyme. **Analysis of Other Options:** * **Option A (Magnesium):** Magnesium inhibits the pre-synaptic release of Acetylcholine (ACh) and decreases post-junctional sensitivity. Therefore, it **potentiates** (predisposes to) the block of both depolarizing and non-depolarizing agents. * **Option B (Calcium):** Calcium is essential for the release of ACh from the motor nerve terminal. High levels of calcium can increase ACh release, thereby **antagonizing** the competitive block produced by NDMRs. * **Option D (Mechanism):** NDMRs act as **competitive antagonists** at the nicotinic ACh receptors (Nm) of the motor endplate. They bind to the receptor but do not trigger an action potential, preventing ACh from binding. **High-Yield Clinical Pearls for NEET-PG:** 1. **Mivacurium** is the only NDMR that is actually metabolized by pseudocholinesterase (making it the shortest-acting NDMR). 2. **Hofmann Elimination:** A non-enzymatic, spontaneous degradation dependent on pH and temperature (seen with Atracurium and Cisatracurium). It is the method of choice in patients with **liver or kidney failure**. 3. **Sugammadex:** A specific reversal agent for Rocuronium and Vecuronium (aminosteroid NDMRs). 4. **Electrolyte Interactions:** Hypokalemia, hypocalcemia, and hypermagnesemia all **potentiate** the action of NDMRs.

Question 69: What is the proposed mechanism of the dissociative anesthesia effect of ketamine?

A. Inhibition of the thalamocortical pathway
B. Stimulation of the limbic system
C. Both (Correct Answer)
D. None

Explanation: **Explanation:** Ketamine is a unique anesthetic agent that produces a state known as **"Dissociative Anesthesia."** This state is characterized by a functional and electrophysiological dissociation between the thalamocortical system and the limbic system. 1. **Why "Both" is correct:** * **Inhibition of the Thalamocortical Pathway:** Ketamine acts as a non-competitive antagonist at the **NMDA receptors**. By inhibiting this pathway, it prevents the transmission of sensory impulses (pain, touch, sound) from the periphery to the cerebral cortex. This results in profound analgesia and amnesia. * **Stimulation of the Limbic System:** While the cortex is depressed, the limbic system (involved in emotions and memory) remains active or even stimulated. This "dissociation" explains why patients may appear awake (eyes open, slow nystagmic gaze) but are unable to process or respond to sensory input. 2. **Analysis of Options:** * **Option A & B:** These are individual components of the mechanism. Selecting only one would be incomplete, as the "dissociative" effect specifically requires the simultaneous depression of the sensory relay (thalamocortical) and the relative excitation of the emotional center (limbic). **High-Yield Clinical Pearls for NEET-PG:** * **Emergence Delirium:** The stimulation of the limbic system is responsible for "emergence reactions" (hallucinations/vivid dreams). This can be prevented by pre-treating with **Benzodiazepines** (Midazolam). * **Sympathomimetic Effect:** Unlike most induction agents, Ketamine increases HR, BP, and CO, making it the **drug of choice for hypovolemic shock**. * **Respiratory Effects:** It is a potent **bronchodilator** (ideal for asthmatics) and uniquely preserves protective airway reflexes and respiratory drive. * **Contraindication:** It increases Intraocular Pressure (IOP) and Intracranial Pressure (ICP), so it should be avoided in head injuries and glaucoma.

Question 70: Which of the following anesthetic agents has the least diffusion coefficient?

A. Isoflurane
B. Enflurane
C. Halothane
D. Nitrous Oxide (N2O) (Correct Answer)

Explanation: ### Explanation The correct answer is **Nitrous Oxide (N₂O)**. **1. Why Nitrous Oxide is Correct:** The **diffusion coefficient** of a gas refers to its ability to move across biological membranes (like the alveolar-capillary membrane). Nitrous oxide has a significantly higher solubility in blood compared to nitrogen, but more importantly, it possesses a very high diffusion coefficient. It is approximately **34 times more soluble** than nitrogen in blood. Because of its high diffusion coefficient and low blood-gas partition coefficient (0.47), N₂O moves rapidly from the alveoli into the blood. This rapid diffusion is the basis for the **"Concentration Effect"** and the **"Second Gas Effect,"** where N₂O accelerates the uptake of a co-administered volatile anesthetic. **2. Why Other Options are Incorrect:** * **Isoflurane, Enflurane, and Halothane:** These are potent volatile halogenated liquids. While they are lipid-soluble, their molecular weights are much higher than N₂O, and their diffusion coefficients are significantly lower. They do not diffuse across membranes with the same velocity as N₂O. Among these, Halothane has the highest blood-gas partition coefficient (2.4), making it the slowest to equilibrate. **3. Clinical Pearls for NEET-PG:** * **Diffusion Hypoxia (Fink Effect):** At the end of surgery, N₂O diffuses rapidly from the blood back into the alveoli, diluting oxygen. To prevent this, 100% O₂ must be administered for 5–10 minutes after stopping N₂O. * **Expansion of Closed Spaces:** Due to its high diffusion coefficient, N₂O enters air-filled cavities (e.g., pneumothorax, obstructed bowel, middle ear, or intraocular gas bubbles) faster than nitrogen can leave, causing dangerous increases in volume or pressure. * **Blood-Gas Partition Coefficient (Solubility):** Desflurane (0.42) < **Nitrous Oxide (0.47)** < Sevoflurane (0.65) < Isoflurane (1.4) < Halothane (2.4).

Practice by Chapter

History of Anesthesia

Practice Questions

Preoperative Evaluation

Practice Questions

Pharmacology of Inhalational Anesthetics

Practice Questions

Pharmacology of Intravenous Anesthetics

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Neuromuscular Blocking Agents

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Airway Management

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Endotracheal Intubation

Practice Questions

Difficult Airway Algorithms

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Intraoperative Monitoring

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Depth of Anesthesia Monitoring

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Emergence from Anesthesia

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Postoperative Care

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