General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 271: Which anesthetic agent predisposes to the maximum number of arrhythmias?

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

Explanation: ### Explanation **Correct Answer: C. Halothane** **Why Halothane is the Correct Answer:** Halothane is notorious for its **arrhythmogenic potential** due to its unique interaction with the myocardium. The primary mechanism is the **sensitization of the myocardium to endogenous and exogenous catecholamines** (epinephrine). This sensitization lowers the threshold for arrhythmias, making the heart highly susceptible to premature ventricular contractions (PVCs), ventricular tachycardia, and even fibrillation, especially in the presence of hypercarbia or surgical stress. Among all potent inhalational agents, Halothane carries the highest risk of these cardiac disturbances. **Analysis of Incorrect Options:** * **A. Isoflurane:** While it can cause tachycardia due to peripheral vasodilation (reflex tachycardia), it does not sensitize the heart to catecholamines to the extent Halothane does. It is generally considered "heart-stable." * **B. Enflurane:** Enflurane has a lower potential for arrhythmias than Halothane. Its primary clinical concern is its potential to lower the seizure threshold (epileptogenic), particularly during hypocapnia. * **C. Ether:** Diethyl ether maintains heart rate and blood pressure well due to sympathetic stimulation, but it is not associated with the specific catecholamine-sensitization seen with Halothane. **High-Yield Clinical Pearls for NEET-PG:** * **The "Halothane Shake":** Post-operative shivering is common with Halothane. * **Halothane Hepatitis:** A rare but severe immune-mediated hepatotoxicity (Type II). * **Safe Limit:** When using epinephrine locally with Halothane, the dose should be restricted to **1 µg/kg** to avoid arrhythmias. * **Agent of Choice for Induction:** While Halothane was historically used for pediatric inhalation induction due to its non-pungent odor, **Sevoflurane** has largely replaced it in modern practice.

Question 272: The use of succinylcholine is not contraindicated in which of the following conditions?

A. Tetanus
B. Closed head injury
C. Cerebral stroke (Correct Answer)
D. Hepatic failure

Explanation: **Explanation:** The core concept tested here is the risk of **hyperkalemia** associated with Succinylcholine (SCh). Succinylcholine is a depolarizing neuromuscular blocker that causes a transient increase in serum potassium (approx. 0.5 mEq/L) in healthy individuals. However, in conditions involving **upregulation of extrajunctional acetylcholine receptors**, this potassium release can be massive and life-threatening. **Why Cerebral Stroke is the Correct Answer:** While neurological deficits are generally contraindications for SCh, the timing is critical. Hyperkalemia risk typically develops **24–72 hours after** the onset of an upper motor neuron lesion (like a stroke) and persists for several months. In the **acute phase** (immediately following a stroke), SCh is not contraindicated and is often used for rapid sequence induction. Among the given options, it is the least absolute contraindication compared to the others which represent chronic or systemic risks. **Analysis of Incorrect Options:** * **Tetanus (A):** Prolonged immobilization and neurotoxin-mediated denervation lead to massive receptor upregulation. SCh can trigger fatal hyperkalemia. * **Closed Head Injury (B):** SCh is avoided here for two reasons: it can transiently increase **intracranial pressure (ICP)** and, if associated with prolonged bed rest or neurological deficit, poses a hyperkalemia risk. * **Hepatic Failure (D):** Pseudocholinesterase (the enzyme that metabolizes SCh) is synthesized in the liver. In hepatic failure, enzyme levels are significantly low, leading to **prolonged apnea** and neuromuscular blockade. **High-Yield Clinical Pearls for NEET-PG:** * **Absolute Contraindications for SCh:** Major burns (>24 hours old), massive trauma, crush injuries, prolonged immobilization, and a personal/family history of **Malignant Hyperthermia**. * **Drug of Choice for RSI:** Succinylcholine remains the gold standard for Rapid Sequence Induction due to its rapid onset (30-60s) and short duration (5-10 mins), provided no contraindications exist. * **Pre-treatment:** A small dose of non-depolarizing NMB (defasciculating dose) can prevent SCh-induced myalgia and rise in ICP/intragastric pressure.

Question 273: Ketamine acts on which receptors?

A. GABA
B. Muscarinic
C. 5-HT4
D. NMDA (Correct Answer)

Explanation: **Explanation:** **Ketamine** is a unique intravenous anesthetic agent that primarily acts as a non-competitive antagonist at the **NMDA (N-methyl-D-aspartate) receptors**. These receptors are a subtype of glutamate receptors located in the brain and spinal cord. By blocking these receptors, ketamine inhibits the excitatory neurotransmitter glutamate, leading to a state of **"Dissociative Anesthesia."** This state is characterized by profound analgesia, amnesia, and a cataleptic appearance where the patient’s eyes remain open with a slow nystagmic gaze, yet they are disconnected from their surroundings. **Analysis of Incorrect Options:** * **GABA (Option A):** Most intravenous anesthetics (like Propofol, Etomidate, and Thiopental) and Benzodiazepines act by enhancing GABA-A receptors. Ketamine is a notable exception as it does not primarily act on the GABA system. * **Muscarinic (Option B):** Ketamine actually possesses mild anticholinergic properties (which can lead to bronchodilation), but this is not its primary mechanism for anesthesia. * **5-HT4 (Option C):** These are serotonin receptors primarily involved in gastrointestinal motility and have no role in the anesthetic action of Ketamine. **High-Yield Clinical Pearls for NEET-PG:** 1. **Sympathomimetic Action:** Unlike other induction agents, Ketamine increases HR, BP, and CO, making it the **induction agent of choice for patients in hypovolemic shock.** 2. **Bronchodilation:** It is the drug of choice for induction in **asthmatic patients.** 3. **Emergence Delirium:** A common side effect characterized by hallucinations and vivid dreams; it can be prevented by co-administration of **Benzodiazepines (Midazolam).** 4. **Contraindications:** Avoid in patients with increased Intracranial Pressure (ICP) or Intraocular Pressure (IOP), and in those with Ischemic Heart Disease (due to increased myocardial oxygen demand).

Question 274: Which statement regarding propofol is false?

A. It causes pain on injection.
B. It is ideal in bronchial asthma.
C. It causes more hypotension than thiopentone.
D. It is contraindicated in malignant hyperthermia. (Correct Answer)

Explanation: **Explanation:** The statement "It is contraindicated in malignant hyperthermia" is **false** because Propofol is a non-triggering agent and is considered **safe** to use in patients susceptible to Malignant Hyperthermia (MH). MH is triggered by volatile inhalational anesthetics (e.g., Halothane, Isoflurane) and the depolarizing muscle relaxant Succinylcholine, but not by intravenous induction agents like Propofol. **Analysis of other options:** * **Option A (Pain on injection):** This is **true**. Propofol belongs to the alkylphenol group and frequently causes pain during injection. This is often mitigated by using larger veins or pre-treating with Lidocaine. * **Option B (Ideal in bronchial asthma):** This is **true**. Propofol has significant bronchodilatory properties, making it a preferred induction agent for asthmatic patients (second only to Ketamine). * **Option C (More hypotension than thiopentone):** This is **true**. Propofol causes a greater decrease in systemic vascular resistance and myocardial contractility compared to Thiopentone, leading to a more pronounced drop in blood pressure. **High-Yield NEET-PG Pearls:** * **Drug of Choice:** Propofol is the drug of choice for **Day Care Surgery** (due to rapid recovery) and **TIVA** (Total Intravenous Anesthesia). * **Antiemetic Property:** It possesses intrinsic antiemetic properties (useful in preventing PONV). * **Egg/Soy Allergy:** Use with caution in patients with severe allergies to egg or soy, as the emulsion contains egg lecithin and soybean oil. * **PRIS:** Propofol Infusion Syndrome is a rare, fatal complication of long-term high-dose infusion characterized by metabolic acidosis, rhabdomyolysis, and cardiac failure.

Question 275: For morbidly obese patients, which is the inhalational agent of choice?

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

Explanation: **Explanation:** The choice of an inhalational agent in morbidly obese patients is primarily governed by the **Blood-Gas Partition Coefficient**, which determines the speed of induction and, more importantly, the speed of recovery. **Why Desflurane is the Correct Answer:** Desflurane has the lowest blood-gas partition coefficient (0.42) among the options provided. In morbid obesity, anesthetic agents tend to accumulate in the extensive adipose tissue (fat reservoirs). Agents with high lipid solubility and high blood-gas coefficients result in delayed emergence and prolonged "hangover" effects. Desflurane’s low solubility ensures **rapid washout** from the body, leading to faster recovery of airway reflexes and earlier mobilization, which is critical to prevent post-operative pulmonary complications in obese patients. **Analysis of Incorrect Options:** * **Halothane:** It has a high blood-gas coefficient (2.4) and is highly lipid-soluble, leading to prolonged recovery. It also carries a risk of "Halothane Hepatitis" and sensitizes the myocardium to catecholamines. * **Isoflurane:** While commonly used, its blood-gas coefficient (1.4) is significantly higher than Desflurane, leading to slower elimination in the obese. * **Enflurane:** It has a coefficient of 1.8 and is metabolized to inorganic fluoride, which can be nephrotoxic; it is rarely used in modern practice. **NEET-PG High-Yield Pearls:** * **Agent of Choice:** Desflurane is preferred for morbid obesity due to rapid emergence. (Note: Sevoflurane is also a good choice, but Desflurane is faster). * **Induction:** In obese patients, induction is usually performed with **Propofol** (dosed based on Lean Body Weight). * **Positioning:** Always use the **"Ramped Position"** (Head-Elevated Laryngoscopy Position - HELP) for intubation. * **Blood-Gas Coefficients (Descending Order):** Halothane (2.4) > Isoflurane (1.4) > Sevoflurane (0.65) > Nitrous Oxide (0.47) > Desflurane (0.42).

Question 276: Which of the following statements is NOT true for propofol?

A. Painful intravenous administration
B. Induction agent
C. Contraindicated in porphyria (Correct Answer)
D. Antiemetic effect

Explanation: **Explanation:** Propofol is the most commonly used intravenous induction agent in modern anesthesia. Understanding its pharmacological profile is high-yield for NEET-PG. **Why Option C is the Correct Answer (The "False" Statement):** Propofol is considered **safe** in patients with porphyria. Unlike older barbiturates (like Thiopentone), propofol does not induce the enzyme ALA synthase and is not known to trigger acute porphyric crises. Therefore, it is often the induction agent of choice for these patients. **Analysis of Other Options:** * **A. Painful intravenous administration:** This is a true statement. Propofol is a lipid emulsion that can cause significant pain on injection due to the activation of the kinin system. This is often mitigated by using larger veins or pre-administering lidocaine. * **B. Induction agent:** This is true. Due to its rapid onset (one arm-brain circulation time) and rapid recovery (short context-sensitive half-life), it is the gold standard for induction and TIVA (Total Intravenous Anesthesia). * **D. Antiemetic effect:** This is true. Propofol possesses unique sub-hypnotic antiemetic properties (likely via dopamine D2 receptor antagonism), making it ideal for patients prone to Postoperative Nausea and Vomiting (PONV). **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** For Day-care surgery, Induction, and TIVA. * **Egg/Soy Allergy:** Use with caution as the emulsion contains egg lecithin and soybean oil. * **Propofol Infusion Syndrome (PRIS):** A rare, fatal complication of prolonged high-dose infusion characterized by metabolic acidosis, rhabdomyolysis, and cardiac failure. * **Hemodynamics:** Causes significant peripheral vasodilation and myocardial depression (caution in hypovolemic/shock patients).

Question 277: Abnormal plasma choline esterase produces apnea due to which of the following?

A. Halothane
B. Lignocaine
C. Suxamethonium (Correct Answer)
D. Isoflurane

Explanation: **Explanation:** The correct answer is **Suxamethonium (Succinylcholine)**. **Mechanism and Pathophysiology:** Suxamethonium is a depolarizing neuromuscular blocking agent widely used for rapid sequence induction. It is metabolized by the enzyme **Pseudocholinesterase** (also known as Plasma Cholinesterase or Butyrylcholinesterase). In patients with a genetic variation resulting in **Abnormal Plasma Cholinesterase** (atypical enzyme), the metabolism of Suxamethonium is significantly delayed. This leads to a prolonged neuromuscular block, resulting in extended muscle paralysis and **prolonged apnea**, necessitating continued mechanical ventilation until the drug eventually wears off. **Analysis of Incorrect Options:** * **Halothane & Isoflurane (Options A & D):** These are volatile inhalational anesthetics. Their action is terminated by redistribution and exhalation through the lungs, not by plasma esterases. While Halothane is associated with hepatotoxicity, it does not cause apnea via cholinesterase deficiency. * **Lignocaine (Option B):** This is an amide-type local anesthetic. Amide local anesthetics are metabolized by hepatic microsomal enzymes (Cytochrome P450), whereas ester-type local anesthetics (like Procaine) are metabolized by plasma cholinesterase. **High-Yield Clinical Pearls for NEET-PG:** * **Dibucaine Number:** This is the screening test for atypical cholinesterase. Dibucaine inhibits normal enzyme by 80% and atypical enzyme by only 20%. A **low Dibucaine number** indicates an atypical enzyme. * **Management:** The primary treatment for Suxamethonium apnea is **continued sedation and mechanical ventilation** until muscle power returns. * **Mivacurium:** This is the only non-depolarizing muscle relaxant also metabolized by plasma cholinesterase; its action is also prolonged in these patients.

Question 278: Which of the following metabolites of Atracurium is responsible for seizures?

A. Cis-atracurium
B. FK-506
C. Laudanosine (Correct Answer)
D. Gallamine

Explanation: **Explanation:** **Atracurium** is a benzylisoquinolone neuromuscular blocking agent unique for its metabolism via **Hofmann elimination** (a non-enzymatic degradation occurring at physiological pH and temperature) and ester hydrolysis. **Why Laudanosine is the correct answer:** The primary metabolite of Atracurium is **Laudanosine**. Unlike the parent drug, Laudanosine has no neuromuscular blocking activity. However, it is a tertiary amine that readily crosses the blood-brain barrier. At high plasma concentrations, it acts as a **central nervous system stimulant**, which can lower the seizure threshold and potentially induce **seizures**. While this is rarely seen in routine clinical anesthesia, it is a significant concern during prolonged infusions in ICU settings or in patients with hepatic failure (as Laudanosine is metabolized by the liver). **Analysis of Incorrect Options:** * **A. Cis-atracurium:** This is an isomer of atracurium, not a metabolite. It is more potent, produces significantly less laudanosine, and does not cause histamine release. * **B. FK-506 (Tacrolimus):** This is an immunosuppressant used in organ transplants; it has no metabolic relationship with atracurium. * **D. Gallamine:** This is an older long-acting muscle relaxant known for causing tachycardia (due to vagolytic effects), not a metabolite of atracurium. **High-Yield Clinical Pearls for NEET-PG:** * **Hofmann Elimination:** Atracurium and Cis-atracurium are the drugs of choice in **renal and hepatic failure** because their metabolism is independent of organ function. * **Histamine Release:** Atracurium can cause skin flushing, hypotension, and bronchospasm due to histamine release (Cis-atracurium does not). * **Temperature/pH Sensitivity:** Since Hofmann elimination is temperature and pH-dependent, the duration of action of atracurium is prolonged in patients with **hypothermia or acidosis**.

Question 279: All of the following decrease the mean alveolar concentration (MAC) of inhalational anesthetics except?

A. Hypoxia
B. Hypercapnia
C. Hypothyroidism (Correct Answer)
D. Hypovolemia

Explanation: **Explanation:** The **Minimum Alveolar Concentration (MAC)** is the concentration of an inhalational anesthetic at 1 atmosphere that prevents skeletal muscle movement in response to a noxious stimulus in 50% of patients. It is a measure of anesthetic potency (Lower MAC = Higher Potency). **Why Hypothyroidism is the Correct Answer:** Contrary to common clinical intuition, **hypothyroidism does not decrease MAC**. While hypothyroid patients may have a decreased cardiac output or slower metabolism, the anesthetic requirement of the brain remains unchanged. Therefore, MAC is independent of thyroid status (both hyper- and hypothyroidism). **Analysis of Incorrect Options (Factors that DO decrease MAC):** * **Hypoxia (Option A):** Severe hypoxia ($PaO_2 < 38\ mmHg$) causes global CNS depression, reducing the amount of anesthetic required to achieve immobility. * **Hypercapnia (Option B):** Significant respiratory acidosis ($PaCO_2 > 95\ mmHg$) exerts a direct narcotic effect on the brain, thereby lowering MAC. * **Hypovolemia (Option D):** Acute hypotension and decreased cerebral perfusion reduce the delivery and requirement of anesthetics, effectively lowering the MAC. **High-Yield Clinical Pearls for NEET-PG:** * **Factors that Decrease MAC:** Old age, pregnancy, acute ethanol ingestion, hyponatremia, hypothermia, and drugs like opioids, benzodiazepines, and $\alpha_2$ agonists (Clonidine/Dexmedetomidine). * **Factors that Increase MAC:** Young age (highest at 6 months), hypernatremia, hyperthermia, chronic ethanol abuse, and drugs that increase CNS catecholamines (Cocaine, Ephedrine, MAO inhibitors). * **Factors with NO effect on MAC:** Gender, duration of anesthesia, thyroid status, and hyper/hypokalemia.

Question 280: Which of the following is a dissociative anesthetic agent?

A. Propofol
B. Ketamine (Correct Answer)
C. Thiopental
D. Halothane

Explanation: **Explanation:** **Ketamine** is the classic example of a **dissociative anesthetic**. It works primarily as a non-competitive antagonist at the **NMDA (N-methyl-D-aspartate) receptor**. The term "dissociative" refers to the functional and electrophysiological dissociation between the thalamocortical and limbic systems. Clinically, the patient appears to be in a trance-like state (eyes may remain open with a slow nystagmic gaze) while being profoundly analgesic and amnesic. **Analysis of Incorrect Options:** * **Propofol (A):** An intravenous sedative-hypnotic that acts via **GABA-A receptors**. It is known for rapid onset/recovery but does not produce dissociation or significant analgesia. * **Thiopental (C):** An ultra-short-acting **barbiturate** that also acts on GABA-A receptors. It is a potent hypnotic but lacks analgesic properties (it may even be anti-analgesic at low doses). * **Halothane (D):** A volatile **inhalational anesthetic**. While it produces unconsciousness, it does not cause the specific "dissociative" state characteristic of ketamine. **High-Yield Clinical Pearls for NEET-PG:** * **Sympathetic Stimulation:** Unlike most anesthetics, ketamine increases HR, BP, and CO, making it the **drug of choice for induction in hypovolemic shock**. * **Respiratory Effects:** It is a potent **bronchodilator** (ideal for asthmatics) and uniquely **preserves airway reflexes** and respiratory drive. * **Emergence Delirium:** A common side effect characterized by hallucinations/vivid dreams; this can be mitigated by co-administering **Benzodiazepines** (e.g., Midazolam). * **Contraindications:** Avoid in patients with raised Intracranial Pressure (ICP) or Intraocular Pressure (IOP), and severe Ischemic Heart Disease.

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

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

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