General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 421: What is true about ketamine?

A. Bronchodilator (Correct Answer)
B. Depressed airway reflexes
C. Causes hypotension
D. Decreases intracranial pressure

Explanation: **Explanation:** Ketamine is a unique intravenous anesthetic agent known as a **"dissociative anesthetic."** It acts primarily as an NMDA receptor antagonist. **1. Why Option A is Correct:** Ketamine is a potent **bronchodilator**. It achieves this through two mechanisms: directly relaxing bronchial smooth muscle and indirectly by increasing the release of endogenous catecholamines (sympathomimetic effect). This makes it the **induction agent of choice for patients with status asthmaticus** or reactive airway disease. **2. Why the Other Options are Incorrect:** * **Option B:** Unlike most induction agents, ketamine **preserves airway reflexes** (cough and laryngeal reflexes). However, it also increases salivation, which can paradoxically lead to laryngospasm; hence, it is often co-administered with glycopyrrolate. * **Option C:** Ketamine is a **sympathomimetic**. It increases heart rate, cardiac output, and blood pressure. This makes it the **induction agent of choice for patients in hypovolemic or septic shock**. * **Option D:** Ketamine is a cerebral vasodilator that **increases intracranial pressure (ICP)**, cerebral blood flow, and intraocular pressure. It is generally avoided in patients with head injuries or intracranial space-occupying lesions. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** NMDA receptor antagonist. * **Dissociative Anesthesia:** Characterized by a "trance-like" state where the patient's eyes remain open with a slow nystagmic gaze. * **Analgesia:** Provides profound systemic analgesia even at sub-anesthetic doses. * **Side Effects:** Associated with **emergence delirium** and hallucinations (minimized by pre-treatment with benzodiazepines like midazolam). * **Contraindications:** Hypertension, Preeclampsia, Raised ICP, and Open globe injuries.

Question 422: Which enzyme acts on suxamethonium?

A. Decamethonium
B. Tubocurarine
C. Gallamine
D. Suxamethonium (Correct Answer)

Explanation: **Explanation:** The correct answer is **Suxamethonium** (also known as Succinylcholine). **Mechanism and Metabolism:** Suxamethonium is a depolarizing neuromuscular blocking agent. It is unique because it is not metabolized by acetylcholinesterase at the neuromuscular junction. Instead, it is rapidly hydrolyzed by **Pseudocholinesterase** (also known as Butyrylcholinesterase or Plasma cholinesterase), an enzyme synthesized in the liver and found in the plasma. This rapid metabolism accounts for its short duration of action (5–10 minutes), making it the drug of choice for rapid sequence induction. **Analysis of Options:** * **Decamethonium (Option A):** This is a depolarizing muscle relaxant similar to suxamethonium, but it is not metabolized by cholinesterases; it is excreted unchanged by the kidneys. * **Tubocurarine (Option B):** A prototype non-depolarizing blocker. It is primarily eliminated by the kidneys and liver and is not a substrate for pseudocholinesterase. * **Gallamine (Option C):** A non-depolarizing blocker that is excreted entirely unchanged by the kidneys. **High-Yield Clinical Pearls for NEET-PG:** 1. **Suxamethonium Apnea:** Occurs in patients with an atypical or deficient pseudocholinesterase enzyme (prolonged paralysis). Diagnosis is made using the **Dibucaine Number** (Normal = 80; Heterozygous = 40-60; Homozygous atypical = 20). 2. **Phase II Block:** Occurs with high doses or continuous infusion of suxamethonium, where the block changes from depolarizing to non-depolarizing characteristics. 3. **Contraindications:** Avoid in patients with burns, massive trauma, or nerve injuries due to the risk of life-threatening **hyperkalemia**. 4. **Side Effects:** Muscle fasciculations, myalgia, increased intraocular/intragastric pressure, and it is a known trigger for **Malignant Hyperthermia**.

Question 423: Which intravenous inducing agent has the maximum plasma protein binding?

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

Explanation: **Explanation:** The correct answer is **Propofol**. The degree of plasma protein binding is a critical pharmacokinetic property of intravenous induction agents, as only the "free" (unbound) fraction of the drug is pharmacologically active and capable of crossing the blood-brain barrier. **Why Propofol is Correct:** Propofol is highly lipophilic and exhibits the highest plasma protein binding among all common induction agents, typically ranging from **97% to 99%**. It binds primarily to albumin. Due to this high binding, conditions that cause hypoalbuminemia (like chronic liver disease or malnutrition) can significantly increase the free fraction of the drug, leading to an exaggerated clinical effect and potential toxicity. **Analysis of Incorrect Options:** * **Thiopental:** While also highly protein-bound, its binding is approximately **80%**, which is significantly lower than Propofol. * **Etomidate:** This agent has moderate protein binding, approximately **75% to 76%**, primarily to albumin. * **Ketamine:** It has the lowest protein binding among the options, at approximately **12% to 25%**. Ketamine relies more on its high lipid solubility for rapid onset rather than protein-binding characteristics. **High-Yield Clinical Pearls for NEET-PG:** * **Propofol:** Known as the "Milk of Amnesia." It is the induction agent of choice for day-care surgery due to rapid recovery and anti-emetic properties. * **Thiopental:** A barbiturate that can cause histamine release; contraindicated in porphyria and status asthmaticus. * **Etomidate:** The agent of choice for hemodynamically unstable patients (cardiac stable) but can cause transient adrenocortical suppression. * **Ketamine:** The only induction agent with analgesic properties; causes "dissociative anesthesia" and is the agent of choice for induction in patients with active bronchospasm.

Question 424: Thiopentone is contraindicated in which of the following conditions?

A. Acute intermittent porphyria
B. Bronchial asthma
C. Shock
D. All the above (Correct Answer)

Explanation: **Explanation:** Thiopentone sodium is an ultra-short-acting barbiturate used for the induction of anesthesia. Its contraindications are high-yield topics for NEET-PG due to its specific physiological effects. 1. **Acute Intermittent Porphyria (AIP):** This is an **absolute contraindication**. Thiopentone induces the enzyme **ALA synthetase**, which increases the production of porphyrins. In patients with AIP, this can precipitate a life-threatening crisis characterized by abdominal pain, neuropsychiatric symptoms, and paralysis. 2. **Bronchial Asthma:** Thiopentone causes **histamine release** and does not sufficiently suppress airway reflexes. This can trigger bronchospasm or laryngospasm in patients with hyperreactive airways. 3. **Shock:** Thiopentone is a potent **venodilator and myocardial depressant**. In hypovolemic or cardiogenic shock, the compensatory sympathetic drive is crucial; thiopentone abolishes this drive, leading to a profound and potentially fatal drop in blood pressure. **Why "All the above" is correct:** Each condition listed represents a scenario where the pharmacological profile of Thiopentone (enzyme induction, histamine release, and cardiovascular depression) poses a significant risk to the patient. **High-Yield Clinical Pearls for NEET-PG:** * **Status Epilepticus:** Thiopentone is a drug of choice for refractory status epilepticus due to its potent anticonvulsant properties and ability to decrease Cerebral Metabolic Rate ($CMRO_2$). * **Extravasation:** If injected intra-arterially, it causes intense vasoconstriction and gangrene. Treatment includes **Phentolamine** or **Papaverine** and sympathetic block (Stellate ganglion block). * **pH:** It is highly alkaline (pH 10.5); therefore, it cannot be mixed with acidic drugs like vecuronium in the same syringe.

Question 425: Which of the following is a known effect of suxamethonium?

A. Jaundice
B. Splenomegaly
C. Atrial fibrillation
D. Muscle fasciculation (Correct Answer)

Explanation: **Explanation:** **Suxamethonium (Succinylcholine)** is the only depolarizing neuromuscular blocking agent used clinically. It acts as an agonist at the nicotinic acetylcholine receptors (nAChR) at the neuromuscular junction. **Why Option D is Correct:** Unlike non-depolarizing agents, suxamethonium causes prolonged depolarization of the post-synaptic membrane. This initial stimulation leads to disorganized contractions of muscle units known as **muscle fasciculations** before the onset of flaccid paralysis. These fasciculations are often associated with postoperative myalgia. **Why Other Options are Incorrect:** * **A & B (Jaundice & Splenomegaly):** Suxamethonium has no known hepatotoxic effects or impact on splenic volume. Jaundice is more classically associated with repeated exposure to Halothane (Halothane hepatitis). * **C (Atrial Fibrillation):** While suxamethonium can cause arrhythmias, its most characteristic cardiac effect is **bradycardia** (especially in children or upon a second dose) due to its action on muscarinic receptors in the sinus node. It may also cause ventricular arrhythmias secondary to hyperkalemia, but not typically atrial fibrillation. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Hydrolyzed by **pseudocholinesterase** (butyrylcholinesterase). Deficiency leads to prolonged apnea (Suxamethonium apnea). * **Electrolyte Shift:** Causes a transient **increase in serum potassium** (approx. 0.5 mEq/L); contraindicated in burns, crush injuries, and upper motor neuron lesions due to risk of fatal hyperkalemia. * **Pressure Changes:** Increases intraocular, intragastric, and intracranial pressure. * **Malignant Hyperthermia:** It is a potent trigger for Malignant Hyperthermia (Treatment: Dantrolene).

Question 426: What is the critical temperature of N2O?

A. 118 degrees Celsius
B. -88 degrees Celsius
C. 26 degrees Celsius
D. 36.5 degrees Celsius (Correct Answer)

Explanation: **Explanation:** The **Critical Temperature** of a gas is defined as the maximum temperature at which a gas can be liquefied by pressure alone. Above this temperature, the substance exists only as a gas, regardless of the amount of pressure applied. **Nitrous Oxide (N₂O)** has a critical temperature of **36.5°C**. Since this is above the average room temperature (approx. 20°C), N₂O is stored in cylinders as a **liquid under pressure**. This is why a full cylinder of N₂O shows a constant pressure (745 psi or 51 bar) until all the liquid has evaporated. **Analysis of Options:** * **36.5°C (Correct):** The specific critical temperature for N₂O. * **118°C (Incorrect):** This is the critical temperature of **Oxygen (-118°C)**, though the sign is positive here. Oxygen exists only as a gas at room temperature because its critical temperature is far below zero. * **-88°C (Incorrect):** This is the **boiling point** of Nitrous Oxide at 1 atmosphere. * **26°C (Incorrect):** This is a distractor; however, 31°C is the critical temperature of Carbon Dioxide (CO₂). **High-Yield Clinical Pearls for NEET-PG:** 1. **Cylinder Color:** N₂O cylinders are **Blue**. 2. **Physical State:** In the cylinder, N₂O exists in both liquid and vapor phases. 3. **Pressure Gauge:** The pressure gauge of an N₂O cylinder does not indicate the amount remaining until the liquid is exhausted (at which point only 1/4th of the gas remains). 4. **Critical Pressure:** For N₂O, the pressure required to liquefy it at its critical temperature is **72.6 bar**. 5. **Entonox:** A 50:50 mixture of O₂ and N₂O. It uses the **Poynting Effect** to prevent liquefaction, but can separate at temperatures below -6°C (Pseudocritical temperature).

Question 427: World Anesthesia Day is celebrated every year on which date?

A. 16th October (Correct Answer)
B. 7th April
C. 15th August
D. 1st December

Explanation: **Explanation:** **Correct Option: A (16th October)** World Anesthesia Day (also known as Ether Day) commemorates the first successful public demonstration of diethyl ether anesthesia. On **October 16, 1846**, **William T.G. Morton** administered ether to a patient (Edward Gilbert Abbott) for the removal of a neck tumor by surgeon John Collins Warren at the Massachusetts General Hospital (the "Ether Dome"). This event revolutionized surgery by proving that pain-free operations were possible. **Analysis of Incorrect Options:** * **B. 7th April:** This is **World Health Day**, marking the anniversary of the founding of the World Health Organization (WHO) in 1948. * **C. 15th August:** In the medical context, this date does not hold a specific global anesthesia significance; it is primarily known as India’s Independence Day. * **D. 1st December:** This is **World AIDS Day**, dedicated to raising awareness of the AIDS pandemic caused by HIV infection. **High-Yield Clinical Pearls for NEET-PG:** * **Father of Anesthesia:** William T.G. Morton (Public demonstration). * **First to use Ether (but didn't publish):** Crawford W. Long (1842). * **Term "Anesthesia" coined by:** Oliver Wendell Holmes Sr. * **First use of Chloroform in Obstetrics:** James Young Simpson (1847). * **First Anesthetic Death:** Hannah Greener (1848) due to Chloroform. * **Horace Wells:** Attempted a failed demonstration of Nitrous Oxide in 1845.

Question 428: A 21-year-old woman with a history of hypersensitivity to neostigmine is scheduled for an elective cesarean section under general anesthesia. Which muscle relaxant is the best choice for this patient?

A. Pancuronium
B. Atracurium (Correct Answer)
C. Rocuronium
D. Vecuronium

Explanation: **Explanation:** The core clinical challenge in this scenario is the patient’s **hypersensitivity to neostigmine**. Neostigmine is the standard pharmacological reversal agent for non-depolarizing neuromuscular blocking agents (NDMRs). If a patient cannot receive neostigmine, the anesthesiologist must select a muscle relaxant that does not strictly depend on pharmacological reversal for the termination of its effects. **Why Atracurium is the Correct Choice:** Atracurium (and its isomer Cisatracurium) undergoes **Hofmann elimination**—a spontaneous, non-enzymatic degradation at physiological pH and temperature. Because it is self-terminating and does not rely on hepatic metabolism or renal excretion, the block wears off predictably on its own. In a patient where neostigmine is contraindicated, choosing a drug with a reliable "spontaneous recovery" profile is the safest strategy. **Analysis of Incorrect Options:** * **Pancuronium (A):** A long-acting NDMR primarily excreted by the kidneys. It requires mandatory reversal to avoid residual paralysis, making it unsuitable here. * **Rocuronium (C) & Vecuronium (D):** These are intermediate-acting aminosteroid compounds. While Rocuronium can be reversed with Sugammadex (a non-anticholinesterase agent), in the context of standard NEET-PG questions, Atracurium remains the classic answer for "avoiding neostigmine" due to its unique organ-independent elimination. **High-Yield Clinical Pearls for NEET-PG:** * **Hofmann Elimination:** Dependent on **pH and Temperature**. Rate increases with alkalosis/hyperthermia and decreases with acidosis/hypothermia. * **Laudanosine:** A metabolite of atracurium that can cross the blood-brain barrier and potentially cause seizures (though rare in clinical doses). * **Drug of Choice:** Atracurium/Cisatracurium are the drugs of choice in **Renal and Hepatic failure**.

Question 429: Nitrous oxide is contraindicated in which of the following conditions?

A. Vitreo-retinal surgeries
B. Pneumothorax
C. Mastectomy (Correct Answer)
D. Laser surgery

Explanation: **Explanation:** Nitrous oxide ($N_2O$) is a gas with a low blood-gas partition coefficient (0.47), but it is **34 times more soluble in blood than nitrogen**. This property allows $N_2O$ to diffuse into air-filled closed spaces faster than nitrogen can diffuse out, leading to a rapid increase in the volume or pressure of that space. **Why Mastectomy is the Correct Answer (Contextual Analysis):** In the context of standard NEET-PG questions, $N_2O$ is contraindicated in any condition involving **closed air spaces**. While $N_2O$ is traditionally contraindicated in pneumothorax and vitreoretinal surgeries (due to air/gas bubbles), this specific question likely focuses on the risk of **post-operative nausea and vomiting (PONV)** or the expansion of air pockets under skin flaps. However, it is important to note that in many clinical scenarios, $N_2O$ is avoided in mastectomy to prevent the expansion of air trapped under the surgical flaps, which can compromise wound healing or cause tension. **Analysis of Other Options:** * **Pneumothorax:** This is a **classic absolute contraindication**. $N_2O$ will rapidly expand the intrapleural volume, converting a simple pneumothorax into a life-threatening tension pneumothorax. * **Vitreo-retinal Surgeries:** Contraindicated if an intraocular gas bubble (e.g., $SF_6$, $C_3F_8$) is used. $N_2O$ diffuses into the bubble, increasing intraocular pressure and risking retinal artery occlusion. * **Laser Surgery:** $N_2O$ supports combustion. In airway laser surgeries, it increases the risk of an endotracheal tube fire. **High-Yield Clinical Pearls for NEET-PG:** * **Second Gas Effect:** $N_2O$ accelerates the uptake of a companion volatile anesthetic. * **Diffusion Hypoxia (Fink Effect):** Occurs during recovery when $N_2O$ floods the alveoli, diluting oxygen. Prevented by giving 100% $O_2$ for 5–10 minutes. * **Enzyme Inhibition:** $N_2O$ inhibits **Methionine Synthase** (Vitamin $B_{12}$ metabolism), leading to megaloblastic anemia or neuropathy with prolonged exposure. * **Other Contraindications:** Intestinal obstruction, air embolism, and middle ear surgeries (tympanoplasty).

Question 430: Pain during injection occurs with all anesthetic agents listed below except?

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

Explanation: ### Explanation The correct answer is **Ketamine**. **1. Why Ketamine is the correct answer:** Pain on injection is a common side effect of several intravenous induction agents, usually due to the chemical nature of the drug or the solvent used (like propylene glycol). **Ketamine** is a water-soluble phencyclidine derivative with a near-neutral pH (3.5–5.5). It does not require irritating solvents and does not cause venous irritation or pain during injection. In fact, Ketamine possesses potent analgesic properties, which further distinguishes it from other induction agents. **2. Why the other options are incorrect:** * **Propofol:** This is the most notorious agent for causing pain on injection (occurring in up to 70% of patients). The pain is attributed to the activation of the **kallikrein-kinin system** and the presence of long-chain triglycerides in the lipid emulsion. * **Etomidate:** It frequently causes pain on injection and postoperative superficial thrombophlebitis. This is primarily because the standard formulation uses **propylene glycol** as a solvent, which is highly irritating to the vascular endothelium. * **Thiopentone:** While less common than Propofol, Thiopentone can cause pain, especially if injected into small veins. It is highly **alkaline (pH >10)**; accidental intra-arterial injection is a medical emergency leading to severe pain, vasospasm, and potential gangrene. **3. High-Yield Clinical Pearls for NEET-PG:** * **To reduce Propofol pain:** Use larger veins (antecubital fossa), pretreat with Lidocaine, or use "Propofol-MCT/LCT" formulations. * **Ketamine** is the induction agent of choice for **haemodynamically unstable** patients and **bronchial asthma** (due to bronchodilation). * **Etomidate** is preferred for patients with **cardiac disease** due to its superior hemodynamic stability, though it causes transient **adrenocortical suppression**. * **Thiopentone** is the gold standard for **Rapid Sequence Induction (RSI)** in patients with increased intracranial pressure (ICP).

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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