General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 91: All of the following are true regarding thiopentone, except one?

A. Thiopentone has high lipid solubility.
B. It has a rapid onset of action due to rapid redistribution of the drug. (Correct Answer)
C. It cannot be used as an analgesic agent.
D. It is contraindicated in asthma patients.

Explanation: ### Explanation The correct answer is **B**. While Thiopentone does have a rapid onset of action and its effects are terminated by redistribution, the **rapid onset** itself is due to its **high lipid solubility and high cardiac output to the brain**, not redistribution. Redistribution is the process responsible for the **short duration of action** (recovery), as the drug moves from the brain to less vascular tissues like muscle and fat. #### Analysis of Options: * **Option A (True):** Thiopentone is highly lipophilic, allowing it to cross the blood-brain barrier almost instantaneously (one arm-brain circulation time). * **Option C (True):** Thiopentone has no analgesic properties. In fact, in sub-therapeutic doses, it is considered **anti-analgesic** (lowers the pain threshold). * **Option D (True):** It is a potent **histamine releaser** and can cause bronchospasm; therefore, it is generally avoided or used with extreme caution in patients with bronchial asthma. #### High-Yield Clinical Pearls for NEET-PG: * **Mechanism of Action:** Acts on the $GABA_A$ receptor complex, increasing the **duration** of chloride channel opening. * **Metabolism:** Primarily hepatic via zero-order kinetics (at high doses). * **Absolute Contraindication:** Porphyria (it induces ALA synthetase). * **Accidental Intra-arterial Injection:** Leads to intense vasoconstriction and gangrene. Management includes injecting **Papaverine, Lidocaine, or Heparin** and performing a **Stellate Ganglion Block**. * **pH:** It is highly alkaline (pH 10.5); hence, it cannot be mixed with acidic drugs like Vecuronium or Succinylcholine in the same syringe.

Question 92: Cardioprotective effects of thiopental are effective in all of the following clinical scenarios EXCEPT:

A. Neurosurgery
B. Cardiac surgery
C. Comatose survival after cardiac arrest (Correct Answer)
D. None of the above

Explanation: ### Explanation **Concept Overview:** Thiopental, a short-acting barbiturate, provides **cerebral protection** by reducing the Cerebral Metabolic Rate of Oxygen ($CMRO_2$) and decreasing intracranial pressure (ICP). However, this protection is only effective when the brain is metabolically active (i.e., before or during an ischemic insult). **Why Option C is the Correct Answer:** In **comatose survivors after cardiac arrest**, the brain has already suffered a global hypoxic-ischemic insult. Clinical trials (such as the Brain Resuscitation Clinical Trial) have demonstrated that high-dose thiopental does not improve neurological outcomes in post-arrest patients. Once the "metabolic shutdown" or irreversible neuronal damage has occurred, the $CMRO_2$-lowering effect of thiopental offers no therapeutic benefit and may even cause harm due to systemic hypotension, which reduces cerebral perfusion pressure. **Analysis of Incorrect Options:** * **A. Neurosurgery:** Thiopental is frequently used here because it reduces cerebral blood volume and ICP while maintaining a favorable oxygen supply-demand ratio. It is protective during focal ischemia (e.g., temporary vessel clamping). * **B. Cardiac Surgery:** During procedures involving cardiopulmonary bypass or deep hypothermic circulatory arrest, thiopental is used to provide "burst suppression" on EEG, protecting the brain against potential embolic or ischemic events during the surgery. **NEET-PG High-Yield Pearls:** * **Mechanism:** Thiopental decreases $CMRO_2$ by up to 50%, but it cannot reduce it below the level required for maintaining cellular integrity (the "flat EEG" limit). * **Drug of Choice:** While thiopental was the classic choice for cerebral protection, **Propofol** is now more commonly used in practice for similar $CMRO_2$ reduction. * **Contraindication:** Absolute contraindication in **Porphyria** (induces delta-aminolevulinic acid synthetase). * **Side Effect:** Can cause **histamine release**, leading to bronchospasm; use with caution in asthmatics.

Question 93: Which of the following statements regarding Halothane is true?

A. Hepatitis occurs in susceptible individuals after repeated doses.
B. It potentiates competitive neuromuscular blockers.
C. It causes respiratory depression.
D. All of the above. (Correct Answer)

Explanation: **Explanation:** Halothane is a classic volatile anesthetic agent, and understanding its systemic effects is crucial for NEET-PG. The correct answer is **D (All of the above)** because Halothane exhibits all the mentioned pharmacological properties: 1. **Hepatotoxicity (Option A):** Halothane is metabolized in the liver (up to 20%). In susceptible individuals, especially after repeated exposure, it can cause "Halothane Hepatitis." This is thought to be an immune-mediated reaction caused by trifluoroacetylated liver proteins. It is more common in obese, middle-aged females. 2. **Potentiation of Neuromuscular Blockers (Option B):** Like most volatile anesthetics, Halothane produces some degree of skeletal muscle relaxation and significantly potentiates the action of competitive (non-depolarizing) neuromuscular blockers like Vecuronium or Atracurium. 3. **Respiratory Depression (Option C):** Halothane causes dose-dependent respiratory depression. It decreases tidal volume and increases respiratory rate (rapid shallow breathing), leading to an overall decrease in alveolar ventilation and a rise in arterial $CO_2$. **High-Yield Clinical Pearls for NEET-PG:** * **Sweet Odor:** Halothane is non-irritating to the airways and has a pleasant smell, making it the agent of choice for **inhalational induction in children**. * **Arrhythmogenic Potential:** It sensitizes the myocardium to **catecholamines**, increasing the risk of ventricular arrhythmias if adrenaline is administered concurrently. * **Uterine Relaxation:** It causes significant uterine relaxation, which is useful for version but can lead to postpartum hemorrhage. * **Malignant Hyperthermia:** Like all volatile agents, it is a known trigger for Malignant Hyperthermia.

Question 94: Neuromuscular blockade produced by rocuronium can be reversed by?

A. Sugammadex (Correct Answer)
B. Flumazenil
C. Blood transfusion
D. Plasmapheresis

Explanation: **Explanation:** **1. Why Sugammadex is Correct:** Sugammadex is a **selective relaxant binding agent (SRBA)** specifically designed to reverse the effects of steroidal neuromuscular blocking agents (NMBAs), primarily **Rocuronium** and Vecuronium. It is a modified γ-cyclodextrin molecule with a lipophilic core that encapsulates the rocuronium molecule in a 1:1 ratio, forming a stable, inactive complex. This rapidly lowers the concentration of free rocuronium in the plasma, creating a concentration gradient that pulls the drug away from the nicotinic acetylcholine receptors at the neuromuscular junction, leading to rapid reversal of blockade. **2. Why Other Options are Incorrect:** * **Flumazenil:** This is a specific competitive antagonist for **Benzodiazepines** (e.g., Midazolam, Diazepam). It has no effect on neuromuscular blockade. * **Blood Transfusion:** Used for volume replacement or treating anemia; it does not contain enzymes or molecules capable of reversing rocuronium. * **Plasmapheresis:** While it can remove some drugs from the plasma, it is not a clinical method for reversing anesthesia. It is typically used for autoimmune conditions (e.g., Myasthenia Gravis or Guillain-Barré Syndrome). **3. High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Sugammadex works by **chelation/encapsulation**, not by inhibiting acetylcholinesterase (unlike Neostigmine). * **Advantages:** Unlike Neostigmine, Sugammadex does not require co-administration of anticholinergics (like Glycopyrrolate) because it does not cause muscarinic side effects (bradycardia, secretions). * **Speed:** It can reverse "deep" blockade (Post-Tetanic Count 1-2), which Neostigmine cannot effectively do. * **Specifics:** It is ineffective against benzylisoquinoliniums like **Atracurium or Cisatracurium**.

Question 95: Which of the following drugs potentiates neuromuscular blockade?

A. Propranolol
B. Amlodipine (Correct Answer)
C. Metformin
D. Penicillin

Explanation: **Explanation:** The correct answer is **Amlodipine**. **Mechanism of Potentiation:** Calcium channel blockers (CCBs) like Amlodipine, Verapamil, and Nifedipine potentiate both depolarizing and non-depolarizing neuromuscular blocking agents (NMBAs). The underlying mechanism is twofold: 1. **Pre-junctional:** CCBs inhibit the entry of calcium into the motor nerve terminal, which is essential for the release of Acetylcholine (ACh) into the synaptic cleft. 2. **Post-junctional:** They interfere with the excitation-contraction coupling in the muscle fiber and may stabilize the post-junctional membrane. **Analysis of Incorrect Options:** * **Propranolol:** While some older studies suggest high-dose beta-blockers might slightly prolong blockade, they are not classically recognized as potentiation agents in standard clinical practice compared to CCBs. * **Metformin:** This biguanide used for diabetes has no known interaction with the nicotinic receptors at the neuromuscular junction. * **Penicillin:** Most penicillins do not affect NMBAs. However, other antibiotic classes—specifically **Aminoglycosides** (e.g., Neomycin, Gentamicin), **Polymyxins**, and **Tetracyclines**—are high-yield causes of potentiation. **High-Yield Clinical Pearls for NEET-PG:** * **Antibiotics that potentiate NMBAs:** Aminoglycosides (most potent), Clindamycin, and Lincomycin. * **Electrolyte abnormalities:** Hypokalemia, Hypermagnesemia, and Hypocalcemia all potentiate neuromuscular blockade. * **Other Drugs:** Lithium, Quinidine, Local Anesthetics, and Volatile Anesthetics (Isoflurane > Sevoflurane) also prolong the block. * **Note:** CCBs can also increase the risk of hypotension when combined with volatile anesthetics.

Question 96: Potency of an inhalational anesthetic agent is measured by:

A. Minimum alveolar concentration (Correct Answer)
B. Diffusion coefficient
C. Dead space concentration
D. Alveolar blood concentration

Explanation: ### Explanation **1. Why Minimum Alveolar Concentration (MAC) is Correct:** MAC is defined as the concentration of an inhalational anesthetic at 1 atmosphere (at steady state) that prevents skeletal muscle movement in response to a noxious stimulus (like a skin incision) in 50% of patients. It is the standard measure of **potency** for volatile anesthetics. * **Concept:** Potency is inversely proportional to MAC ($Potency \propto 1/MAC$). For example, Halothane (MAC 0.75%) is more potent than Sevoflurane (MAC 2.0%) because a lower concentration is required to achieve the same clinical effect. **2. Why Other Options are Incorrect:** * **B. Diffusion Coefficient:** This refers to the rate at which gas molecules move across a membrane (e.g., the alveolar-capillary membrane). While it affects the speed of induction, it does not measure anesthetic potency. * **C. Dead Space Concentration:** Dead space refers to the volume of ventilated air that does not participate in gas exchange. It is a physiological parameter of the respiratory system, not a measure of drug potency. * **D. Alveolar Blood Concentration:** While the concentration in the blood (determined by the Blood:Gas partition coefficient) dictates the **speed of induction and recovery**, it does not define the potency of the agent itself. **3. High-Yield Clinical Pearls for NEET-PG:** * **Meyer-Overton Hypothesis:** States that potency is directly proportional to **lipid solubility**. * **MAC Values to Remember:** * **Highest MAC (Least Potent):** Nitrous Oxide (~104%). * **Lowest MAC (Most Potent):** Halothane (0.75%). * **Factors Increasing MAC (Requirement increases):** Hyperthermia, young age (highest at 6 months), chronic alcohol abuse, hypernatremia, and increased central neurotransmitters (e.g., Cocaine/MAOIs). * **Factors Decreasing MAC (Requirement decreases):** Hypothermia, elderly age, pregnancy, acute alcohol intoxication, and opioids/sedatives.

Question 97: Indications for hypotensive anesthesia include:

A. Mastoid surgery
B. Spinal surgery
C. Arteriovenous malformations
D. All of the above (Correct Answer)

Explanation: **Explanation:** **Hypotensive anesthesia** (controlled hypotension) is a technique used to deliberately reduce the mean arterial pressure (MAP) to 50–65 mmHg or by 30% of the patient’s baseline. The primary goal is to **minimize blood loss** and **improve the surgical field visibility** by reducing capillary oozing. **Why "All of the Above" is Correct:** * **Mastoid Surgery (A):** In microsurgeries of the ear, even a tiny amount of blood can obscure the microscopic view, potentially leading to complications like facial nerve injury. Controlled hypotension ensures a "dry" surgical field. * **Spinal Surgery (B):** Extensive procedures like scoliosis correction or multi-level laminectomies involve significant blood loss from bone and epidural veins. Reducing MAP decreases the need for blood transfusions. * **Arteriovenous Malformations (C):** AVMs are high-flow vascular lesions. Lowering the pressure reduces the risk of intraoperative rupture and facilitates easier dissection and clipping of the vessels. **Clinical Pearls for NEET-PG:** * **Commonly used agents:** Sodium Nitroprusside (fastest), Nitroglycerin, Magnesium sulfate, and potent inhalational agents (Isoflurane/Sevoflurane). * **Contraindications:** These are high-yield! Avoid in patients with **uncontrolled hypertension**, **cerebrovascular disease** (risk of stroke), **severe renal/hepatic dysfunction**, and **closed-angle glaucoma**. * **Monitoring:** Invasive arterial blood pressure monitoring is mandatory to ensure real-time accuracy. * **Safe Limit:** In healthy individuals, the lower limit of MAP is generally kept at **50-60 mmHg** to maintain cerebral autoregulation.

Question 98: Which inhalational anesthetic agent has the lowest blood-gas coefficient?

A. Isoflurane
B. Nitrous oxide
C. Xenon (Correct Answer)
D. Enflurane

Explanation: **Explanation:** The **Blood-Gas Partition Coefficient** is the primary determinant of the speed of induction and recovery of an inhalational anesthetic. A lower coefficient indicates low solubility in the blood, meaning the partial pressure in the alveoli rises rapidly, leading to faster equilibration with the brain and quicker induction/emergence. **Why Xenon is Correct:** Xenon is an inert gas that possesses the **lowest blood-gas partition coefficient (0.115–0.14)** among all known anesthetic agents. This makes it the fastest-acting anesthetic in terms of induction and recovery. It is also considered an "ideal" anesthetic because it is non-explosive, provides NMDA antagonism, and has minimal hemodynamic side effects. **Why Other Options are Incorrect:** * **Nitrous Oxide (B):** While very insoluble, its coefficient is **0.47**, which is significantly higher than Xenon. * **Isoflurane (A):** A commonly used volatile liquid with a coefficient of **1.4**, making it much more soluble and slower to act than Xenon. * **Enflurane (D):** Has a high coefficient of **1.8**, leading to slower induction and recovery compared to modern agents. **High-Yield NEET-PG Pearls:** 1. **Order of Solubility (Lowest to Highest):** Xenon (0.14) < Desflurane (0.42) < Nitrous Oxide (0.47) < Sevoflurane (0.65) < Isoflurane (1.4) < Halothane (2.4). 2. **Desflurane** has the lowest coefficient among *volatile liquids* (0.42), but **Xenon** is the lowest among all *gaseous* agents. 3. **MAC Value:** Xenon has a high MAC (approx. 63–71%), meaning it is less potent than volatile liquids like Halothane (MAC 0.75%). 4. **Second Gas Effect:** Nitrous oxide is typically used to speed up the induction of a second volatile agent.

Question 99: Arrhythmias are most common when adrenaline is used with which of the following inhaled anesthetics?

A. Halothane (Correct Answer)
B. Isoflurane
C. Enflurane
D. Sevoflurane

Explanation: **Explanation:** The correct answer is **Halothane**. **1. Why Halothane is correct:** Halothane is notorious for **sensitizing the myocardium to the arrhythmogenic effects of catecholamines** (like adrenaline). It inhibits the reuptake of norepinephrine and interferes with the conduction system, significantly lowering the threshold for ventricular arrhythmias. When exogenous adrenaline is administered (e.g., for local hemostasis) during halothane anesthesia, it can trigger premature ventricular contractions (PVCs), ventricular tachycardia, or even fibrillation. Clinical guidelines suggest limiting adrenaline to no more than **1 µg/kg** when using halothane. **2. Why other options are incorrect:** * **Isoflurane, Enflurane, and Sevoflurane:** These are modern halogenated ethers. While all volatile anesthetics sensitize the heart to catecholamines to some degree, they do so significantly less than halothane (an alkane). * **Sevoflurane and Isoflurane** are considered much safer; the dose of adrenaline required to produce arrhythmias is several times higher (approx. 3–5 times) than that required with halothane. **3. High-Yield Clinical Pearls for NEET-PG:** * **Arrhythmogenic Potency:** Halothane > Enflurane > Isoflurane > Sevoflurane/Desflurane. * **Halothane Hepatitis:** A rare but serious immune-mediated hepatotoxicity associated with repeat exposure. * **Catecholamine Limit:** In the presence of halothane, the maximum dose of adrenaline is **1 µg/kg**; with isoflurane, it is approximately **3 µg/kg**. * **Drug of Choice:** For induction in pediatric cases (due to sweet smell and non-irritancy), **Sevoflurane** has largely replaced halothane.

Question 100: Which of the following statements regarding Non-Depolarizing Muscle Relaxants is FALSE?

A. Vecuronium can be used safely in patients with renal failure.
B. Aminoglycosides can worsen neuromuscular blockade in patients with renal failure.
C. Pancuronium possesses vagolytic effects.
D. Non-depolarizing agents trigger malignant hyperthermia. (Correct Answer)

Explanation: ### Explanation **1. Why Option D is the Correct (False) Statement:** Malignant Hyperthermia (MH) is a pharmacogenetic hypermetabolic state triggered exclusively by **volatile inhalational anesthetics** (e.g., Halothane, Isoflurane) and the **depolarizing** muscle relaxant **Succinylcholine**. Non-depolarizing muscle relaxants (NDMRs) like Vecuronium, Atracurium, and Pancuronium do **not** trigger MH. In fact, NDMRs are considered safe alternatives for patients susceptible to MH. **2. Analysis of Other Options:** * **Option A (True):** Vecuronium is primarily metabolized by the liver and excreted via bile (40-70%). While a small portion is excreted renally, it is considered relatively safe in renal failure compared to long-acting agents like Pancuronium. (Note: Cisatracurium is the gold standard for renal failure due to Hofmann elimination). * **Option B (True):** Aminoglycosides (e.g., Gentamicin, Neomycin) inhibit the pre-junctional release of Acetylcholine and decrease post-junctional sensitivity. This synergistically **potentiates** the blockade of NDMRs, especially in renal failure where drug clearance is reduced. * **Option C (True):** Pancuronium is a long-acting NDMR that possesses **vagolytic** properties (blocks muscarinic receptors in the SA node), leading to tachycardia and hypertension. **3. High-Yield Clinical Pearls for NEET-PG:** * **Hofmann Elimination:** A non-enzymatic, pH and temperature-dependent degradation unique to **Atracurium** and **Cisatracurium**, making them the drugs of choice in liver and kidney failure. * **Mivacurium:** The only NDMR metabolized by **pseudocholinesterase**. * **Rocunorium:** Has the fastest onset among NDMRs, making it suitable for Rapid Sequence Induction (RSI) when Succinylcholine is contraindicated. * **Reversal:** Sugammadex specifically reverses aminosteroid NDMRs (Rocunorium > Vecuronium).

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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