General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 111: Which of the following is an inflammable anesthetic agent?

A. Ether (Correct Answer)
B. Halothane
C. Cyclopropane
D. Trilene

Explanation: **Explanation:** The flammability of anesthetic agents is determined by their chemical structure, specifically the presence of halogen atoms (Fluorine, Chlorine, Bromine). **Correct Option: A. Ether (Diethyl Ether)** Ether is a highly volatile liquid that is extremely **inflammable and explosive**, especially when mixed with air, oxygen, or nitrous oxide. Due to this significant safety hazard (risk of theatre fires and explosions), its use has been largely abandoned in modern clinical practice, despite its advantages of being potent, analgesic, and maintaining spontaneous respiration. **Why other options are incorrect:** * **B. Halothane:** This is a halogenated hydrocarbon. The addition of three fluorine atoms and one bromine atom makes it **non-inflammable** and non-explosive under clinical conditions. * **C. Cyclopropane:** While Cyclopropane is indeed highly inflammable and explosive (similar to Ether), it is **not the single best answer** in many traditional MCQ contexts where Ether is the classic prototype. However, in modern nomenclature, both A and C are technically inflammable. In NEET-PG, Ether is the historical "gold standard" answer for this question. * **D. Trilene (Trichloroethylene):** This is a non-inflammable agent. However, it is unique because it reacts with soda lime in closed circuits to form toxic products like phosgene and heat, making it dangerous for use in rebreathing systems. **High-Yield Clinical Pearls for NEET-PG:** * **Modern Agents:** All currently used volatile agents (Sevoflurane, Desflurane, Isoflurane) are **non-inflammable** due to heavy halogenation. * **Static Electricity:** When using inflammable agents like Ether, anti-static precautions (e.g., conductive flooring, cotton gowns) are mandatory to prevent sparks. * **Trilene Warning:** Never use Trilene with a CO2 absorber (Soda Lime) as it produces **Dichloroacetylene**, which is neurotoxic (causes cranial nerve palsies, especially the Trigeminal nerve).

Question 112: What is the primary factor determining the rapid onset of inhalational general anesthesia?

A. Blood solubility of the agent
B. Cerebral blood flow
C. Partial pressure of the general anesthetic agent
D. All of the above (Correct Answer)

Explanation: The speed of induction with inhalational anesthetics depends on how quickly the **partial pressure** of the anesthetic in the brain reaches the threshold for unconsciousness. This process is governed by the transfer of the agent from the machine to the alveoli, then to the blood, and finally to the brain. **Explanation of Options:** * **Partial pressure of the agent (C):** This is the primary driving force. According to Henry’s Law, gas moves from an area of high partial pressure to low partial pressure. A higher inspired concentration (Concentration Effect) leads to a faster rise in alveolar partial pressure ($P_A$), accelerating induction. * **Blood solubility (A):** This is determined by the **Blood:Gas partition coefficient**. Agents with *low* solubility (e.g., Desflurane, Sevoflurane) do not dissolve easily in the blood; therefore, the blood saturates quickly, allowing the partial pressure to rise rapidly and reach the brain sooner. * **Cerebral blood flow (B):** Since the brain is a highly perfused organ (part of the vessel-rich group), increased blood flow delivers a larger volume of the anesthetic to the target site per unit of time, speeding up the onset of action. Because all three factors—the concentration gradient, the solubility characteristics of the drug, and the delivery mechanism via circulation—interact to determine the rate of induction, **Option D** is the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **The Second Gas Effect:** Administering a potent anesthetic with a high concentration of Nitrous Oxide ($N_2O$) speeds up the uptake of the potent agent. * **Ventilation:** Increasing minute ventilation speeds up induction (especially for soluble agents like Halothane). * **Cardiac Output:** *Increased* cardiac output actually *slows* the rate of induction because it removes the anesthetic from the alveoli too quickly, preventing the rise in alveolar partial pressure.

Question 113: Which of the following drug(s) is/are mainly metabolized extrahepatically in plasma?

A. Halothane
B. Propofol
C. Lignocaine
D. Atracurium (Correct Answer)

Explanation: **Explanation:** The correct answer is **Atracurium**. **1. Why Atracurium is correct:** Atracurium is a non-depolarizing neuromuscular blocking agent unique for its metabolism. It undergoes **extrahepatic metabolism** via two primary pathways: * **Hofmann Elimination:** A spontaneous, non-enzymatic degradation that occurs at physiological pH and temperature. * **Ester Hydrolysis:** Catalyzed by non-specific plasma esterases (Note: This is distinct from pseudocholinesterase). Because it does not rely on the liver or kidneys for clearance, it is the drug of choice in patients with **hepatic or renal failure**. **2. Why the other options are incorrect:** * **Halothane:** An inhalational anesthetic primarily eliminated via the lungs, but approximately 20% undergoes **oxidative metabolism in the liver** by CYP450 enzymes. This metabolism is linked to "Halothane Hepatitis." * **Propofol:** An intravenous anesthetic primarily metabolized in the **liver** (conjugation to glucuronides). While it has some extrahepatic clearance (lungs), the liver remains the chief site. * **Lignocaine:** An amide local anesthetic that is almost entirely metabolized by **hepatic microsomal enzymes** (dealkylation). Its clearance is highly dependent on hepatic blood flow. **3. High-Yield Clinical Pearls for NEET-PG:** * **Cisatracurium:** An isomer of atracurium that undergoes *only* Hofmann elimination. It is more potent and produces less **laudanosine** (a metabolite of atracurium that can trigger seizures) and less histamine release. * **Mivacurium:** The only non-depolarizing muscle relaxant metabolized by **pseudocholinesterase** (butyrylcholinesterase), similar to Succinylcholine. * **Remifentanil:** An opioid also notable for extrahepatic metabolism via non-specific tissue and plasma esterases, giving it an ultra-short duration of action.

Question 114: Which of the following anesthetic agents has the least cardiovascular side effects?

A. Isoflurane (Correct Answer)
B. Enflurane
C. Trilene
D. Ketamine

Explanation: **Explanation:** **Isoflurane** is considered the gold standard among volatile anesthetics for cardiovascular stability. While it causes a dose-dependent decrease in systemic vascular resistance (SVR) leading to a drop in blood pressure, it uniquely **preserves cardiac output**. This is because the decrease in SVR is compensated by a mild increase in heart rate (baroreceptor reflex). Unlike other halogenated agents, it does not significantly depress myocardial contractility, making it safer for patients with compensated heart disease. **Why other options are incorrect:** * **Enflurane:** It causes significant myocardial depression and a greater reduction in cardiac output compared to Isoflurane. It is also associated with a higher risk of arrhythmias and can lower the seizure threshold. * **Trilene (Trichloroethylene):** It is highly arrhythmogenic, especially in the presence of endogenous or exogenous catecholamines (sensitizes the myocardium to adrenaline). It is no longer used in modern anesthesia due to toxicity. * **Ketamine:** While it is often used in hemodynamically unstable patients, it is **not** free of cardiovascular side effects. It is a potent sympathomimetic that causes significant increases in heart rate, blood pressure, and myocardial oxygen demand, which can be detrimental in patients with coronary artery disease. **High-Yield Clinical Pearls for NEET-PG:** * **Coronary Steal Phenomenon:** Classically associated with Isoflurane (theoretical), where it dilates small coronary arterioles, potentially diverting blood away from ischemic areas. * **Drug of Choice for Neurosurgery:** Isoflurane is preferred as it maintains cerebral blood flow autoregulation better than other older agents. * **Halothane:** Most likely to cause "Halothane Hepatitis" and myocardial sensitization to catecholamines. * **Sevoflurane:** Agent of choice for **inhalational induction** due to its non-pungent nature and low blood-gas solubility.

Question 115: Which anaesthetic agent is known to produce adrenocortical suppression in a patient with Cushing's syndrome undergoing surgery?

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

Explanation: **Explanation:** **Etomidate** is a carboxylated imidazole derivative used for induction of anesthesia. It is uniquely associated with **adrenocortical suppression** because it causes dose-dependent inhibition of the enzyme **11-beta-hydroxylase**. This enzyme is essential for converting 11-deoxycortisol to cortisol. Even a single induction dose can suppress cortisol production for 6 to 24 hours. While this side effect is generally undesirable in trauma or septic patients, it can be pharmacologically exploited in patients with **Cushing’s syndrome** to temporarily reduce excessive cortisol levels during the perioperative period. **Analysis of Incorrect Options:** * **Thiopentone (A):** An ultra-short-acting barbiturate. Its primary side effects are cardiovascular and respiratory depression; it has no specific inhibitory effect on the adrenal cortex. * **Ketamine (C):** A dissociative anesthetic that acts as a sympathetic stimulant. It actually increases plasma cortisol levels by stimulating the hypothalamic-pituitary-adrenal axis, making it the opposite of etomidate. * **Propofol (D):** The most common induction agent. While it can cause hypotension due to vasodilation, it does not interfere with steroidogenesis. **High-Yield NEET-PG Pearls:** * **Drug of Choice:** Etomidate is the induction agent of choice for patients with **compromised cardiovascular status** (e.g., valvular heart disease, CAD) because it is hemodynamically stable. * **Myoclonus:** Etomidate frequently causes involuntary muscle movements (myoclonus) on induction, which can be prevented by premedication with opioids or benzodiazepines. * **Nausea/Vomiting:** It has a high incidence of Postoperative Nausea and Vomiting (PONV). * **Contraindication:** Strictly avoided in patients with **Addison’s disease** or severe sepsis due to its adrenal suppressive effects.

Question 116: What is the recommended dose of thiopental sodium?

A. 3-5 mg/kg (Correct Answer)
B. 5-10 mg/kg
C. 1-2 mg/kg
D. 10-15 mg/kg

Explanation: **Explanation:** **Thiopental Sodium** is a short-acting thiobarbiturate used primarily for the induction of general anesthesia. The correct induction dose is **3–5 mg/kg** intravenously in healthy adults. 1. **Why 3–5 mg/kg is correct:** This dosage range is calculated to achieve a rapid loss of consciousness (within 30–45 seconds) by crossing the blood-brain barrier quickly due to its high lipid solubility. It acts by facilitating GABA-A receptors, increasing the duration of chloride channel opening, which leads to CNS depression. 2. **Why other options are incorrect:** * **1–2 mg/kg:** This is an under-dose for induction in healthy adults but may be used in elderly patients or those in hypovolemic shock, as thiopental can cause significant myocardial depression and peripheral vasodilation. * **5–10 mg/kg & 10–15 mg/kg:** These doses are excessively high and would lead to prolonged apnea, severe hypotension, and delayed emergence due to the drug's cumulative effects and saturation of redistribution sites. **High-Yield Clinical Pearls for NEET-PG:** * **Redistribution:** The rapid recovery from a single bolus of thiopental is due to **redistribution** from the brain to lean tissues (muscle), not metabolism. * **pH & Solubility:** It is highly alkaline (pH 10.5). Accidental **intra-arterial injection** causes severe vasospasm and gangrene; treatment includes papaverine, lidocaine, or a sympathetic block. * **Contraindication:** It is strictly contraindicated in **Porphyria** (induces ALA synthetase). * **Context-Sensitive Half-life:** It has a long context-sensitive half-life, making it unsuitable for maintenance via infusion.

Question 117: Which of the following is used to measure the depth of anesthesia?

A. Bispectral index (Correct Answer)
B. Immobility of patient
C. MAC of anesthetic drug
D. None of the above

Explanation: **Explanation:** **1. Why Bispectral Index (BIS) is the correct answer:** The Bispectral Index (BIS) is a processed EEG parameter used to monitor the **hypnotic component** (depth) of anesthesia. It converts complex raw EEG data into a single dimensionless number ranging from **0 to 100**. * **100:** Awake/Alert * **40–60:** Recommended range for general anesthesia (low probability of consciousness/recall). * **0:** Isoelectric EEG (brain inactivity). By analyzing phase coupling and frequency, BIS provides a real-time assessment of the patient's level of consciousness, helping to prevent intraoperative awareness. **2. Why the other options are incorrect:** * **B. Immobility of patient:** While immobility is a goal of anesthesia, it is not a reliable measure of depth. A patient can be paralyzed by neuromuscular blockers (muscle relaxants) but still be fully conscious and aware. * **C. MAC (Minimum Alveolar Concentration):** MAC is a measure of the **potency** of an inhalational anesthetic, not the depth of anesthesia in an individual patient. It represents the concentration required to prevent movement in 50% of patients in response to a surgical stimulus. It does not account for individual variability or the use of intravenous adjuncts. **3. Clinical Pearls for NEET-PG:** * **Other Depth Monitors:** Entropy (State and Response), Narcotrend, and Patient State Index (PSI). * **Isolated Forearm Technique:** The "gold standard" for detecting intraoperative awareness (though rarely used clinically). * **Factors affecting BIS:** Ketamine and Nitrous Oxide can increase BIS values despite a deep plane of anesthesia, while Hypothermia can decrease it. * **High-Yield Range:** Aim for **40–60** to prevent awareness while avoiding excessive anesthetic depth (which is linked to increased post-operative mortality).

Question 118: Which anesthetic agent is known to cause hallucinations?

A. Ketamine (Correct Answer)
B. Trilene
C. Halothane
D. Trichloroethylene

Explanation: **Explanation:** **Ketamine** is the correct answer because it is a phencyclidine derivative that acts as a non-competitive NMDA receptor antagonist. It produces a unique state known as **"Dissociative Anesthesia,"** where the patient appears awake but is unconscious and unresponsive to pain. During the recovery phase, ketamine is notorious for causing **emergence delirium**, which includes vivid dreams, illusions, and **hallucinations**. These psychotomimetic effects occur because ketamine dissociates the thalamocortical system from the limbic system. **Analysis of Incorrect Options:** * **Trilene & Trichloroethylene:** These are the same agent. Trichloroethylene (Trilene) is an older volatile anesthetic no longer used in modern practice. Its primary concern was the formation of toxic **phosgene gas** and neurotoxicity (cranial nerve palsies, especially the trigeminal nerve) when used with soda lime. It does not typically cause hallucinations. * **Halothane:** A potent inhalational agent primarily known for causing **"Halothane Hepatitis"** and sensitizing the myocardium to catecholamines (leading to arrhythmias). It is not associated with emergence hallucinations. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Ketamine is the induction agent of choice for **hypovolemic shock** (due to sympathetic stimulation) and **bronchial asthma** (due to bronchodilation). * **Contraindications:** It is contraindicated in patients with **head injuries** (increases ICP) and **glaucoma** (increases IOP). * **Prevention:** Emergence delirium/hallucinations caused by Ketamine can be minimized by pre-medicating the patient with **Benzodiazepines** (e.g., Midazolam). * **Reflexes:** Unlike other anesthetics, Ketamine preserves airway reflexes and increases lacrimation and salivation.

Question 119: What is commonly known as laughing gas?

A. Nitrous oxide (Correct Answer)
B. Halothane
C. Chloroform
D. Diethylether

Explanation: **Explanation:** **Nitrous Oxide ($N_2O$)** is famously known as **"Laughing Gas"** because it often induces a state of euphoria, exhilaration, and involuntary laughter upon inhalation. Discovered by Joseph Priestley and first used clinically by Horace Wells, it is a colorless, odorless, and non-flammable inorganic gas used extensively in modern anesthesia. **Analysis of Options:** * **Nitrous Oxide (Correct):** It is the least potent inhalational agent (MAC of 104%) but has a very low blood-gas partition coefficient (0.47), leading to rapid induction and recovery. * **Halothane:** A potent volatile anesthetic known for causing "Halothane Hepatitis" and sensitizing the myocardium to catecholamines. It does not induce euphoria. * **Chloroform:** Historically used as an anesthetic but abandoned due to severe hepatotoxicity and cardiotoxicity. * **Diethylether:** Known for its "ether dome" history; it is highly flammable and explosive, causing significant post-operative nausea and vomiting (PONV). **High-Yield Clinical Pearls for NEET-PG:** 1. **Second Gas Effect:** $N_2O$ is used to speed up the induction of a second, more potent volatile anesthetic. 2. **Diffusion Hypoxia (Fink Effect):** Occurs during recovery when $N_2O$ rushes out of the blood into the alveoli, diluting oxygen. Prevention: Administer 100% $O_2$ for 3–5 minutes post-procedure. 3. **Closed Space Expansion:** $N_2O$ is 34 times more soluble than Nitrogen. It rapidly enters air-filled cavities, making it **contraindicated** in pneumothorax, intestinal obstruction, middle ear surgeries, and air embolism. 4. **Vitamin $B_{12}$ Interaction:** Prolonged exposure inhibits methionine synthase, leading to megaloblastic anemia and peripheral neuropathy.

Question 120: What is true about thiopental?

A. Long acting
B. Good analgesic action
C. Cerebroprotective (Correct Answer)
D. Good muscle relaxation

Explanation: **Explanation:** Thiopental sodium is an ultra-short-acting barbiturate used for the induction of general anesthesia. **Why "Cerebroprotective" is correct:** Thiopental is a potent **cerebral vasoconstrictor**, which leads to a significant reduction in **Cerebral Blood Flow (CBF)** and **Cerebral Metabolic Rate of Oxygen (CMRO2)**. By decreasing the metabolic demand of the brain and lowering **Intracranial Pressure (ICP)**, it provides a "brain-shielding" effect during neurosurgical procedures or periods of cerebral ischemia. This makes it a gold standard for neuro-anesthesia induction. **Why other options are incorrect:** * **A. Long acting:** Thiopental is **ultra-short-acting**. Its rapid onset (30–45 seconds) and short duration of action (5–10 minutes) are due to its high lipid solubility and rapid **redistribution** from the brain to less vascular tissues (muscle and fat), not due to rapid metabolism. * **B. Good analgesic action:** Thiopental has **no analgesic properties**. In fact, in sub-anesthetic doses, it is considered **anti-analgesic** (lowers the pain threshold). * **D. Good muscle relaxation:** It provides poor muscle relaxation. While it may slightly potentiate neuromuscular blockers, it is not used for this purpose and does not suppress laryngeal reflexes effectively. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Acts on the $GABA_A$ receptor complex, increasing the **duration** of chloride channel opening. * **Contraindication:** Strictly contraindicated in **Porphyria** (induces ALA synthetase). * **Complication:** Accidental intra-arterial injection causes severe spasm and gangrene. Treatment includes **Papaverine**, Heparin, and Brachial plexus block (for vasodilation). * **Storage:** Prepared in 2.5% solution; it is highly alkaline (pH 10.5) and bacteriostatic.

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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