General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 51: Which anesthetic agent is contraindicated in epilepsy?

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

Explanation: **Explanation:** The correct answer is **Enflurane**. **Why Enflurane is the correct answer:** Enflurane is unique among volatile anesthetics because it can induce **seizure-like activity** on an Electroencephalogram (EEG), characterized by high-voltage, high-frequency spikes and spike-and-wave complexes. This pro-convulsant effect is significantly potentiated by **hypocapnia** (low $PaCO_2$ due to hyperventilation) and high concentrations of the drug. In some cases, these EEG changes are accompanied by visible tonic-clonic muscle twitching. Therefore, it is strictly contraindicated in patients with a history of epilepsy or seizure disorders. **Analysis of Incorrect Options:** * **Isoflurane:** An isomer of enflurane, but it does not provoke seizure activity. In fact, it has anticonvulsant properties at higher concentrations and is often used to suppress status epilepticus. * **Halothane:** It does not induce seizures and is generally considered safe for the brain's electrical activity, though it is rarely used today due to hepatotoxicity. * **Ether:** While historically significant, ether does not have a specific association with inducing epilepsy; its primary drawbacks are flammability and slow induction/recovery. **NEET-PG High-Yield Pearls:** * **Drug of Choice for Epilepsy:** **Thiopentone** (Barbiturate) is the gold standard for brain protection and seizure suppression. Among inhalational agents, **Isoflurane** is preferred. * **Ketamine & Methohexital:** These are other intravenous agents known to lower the seizure threshold (Methohexital is often used to *induce* seizures during Electroconvulsive Therapy). * **Sevoflurane:** While generally safe, at very high concentrations in pediatric patients, it has occasionally been associated with epileptiform EEG patterns, though Enflurane remains the classic "textbook" contraindication.

Question 52: Histamine release is one of the common features with administration of which of the following drugs?

A. Atracurium (Correct Answer)
B. Adrenaline
C. Thiopentone
D. Ketamine

Explanation: **Explanation:** **Atracurium** is a benzylisoquinolinium neuromuscular blocking agent known for its potential to cause **non-immunologic histamine release** from mast cells. This occurs via direct displacement of histamine and is typically dose- and rate-dependent. Clinically, this may manifest as cutaneous flushing, tachycardia, and hypotension. To mitigate this, it is often administered slowly. Another high-yield fact about Atracurium is its metabolism via **Hofmann elimination** (spontaneous non-enzymatic degradation), making it safe in renal and hepatic failure. **Why the other options are incorrect:** * **Adrenaline:** This is a catecholamine that acts as a physiological antagonist to histamine. It is the drug of choice for anaphylaxis because it stabilizes mast cells and reverses the effects of histamine (bronchodilation and vasoconstriction). * **Thiopentone:** While Thiopentone can occasionally cause histamine release, it is significantly less common than with Atracurium. In modern exams, Atracurium remains the classic "textbook" example for histamine release among muscle relaxants. * **Ketamine:** Ketamine is a dissociative anesthetic that actually causes a sympathetic surge (bronchodilation and increased heart rate), making it a preferred agent in asthmatic patients rather than a trigger for histamine-mediated bronchospasm. **High-Yield Clinical Pearls for NEET-PG:** * **Muscle Relaxants & Histamine:** Benzylisoquinoliniums (Atracurium, Mivacurium, Tubocurarine) release histamine. Aminosteroids (Vecuronium, Rocuronium) generally do not. * **Cisatracurium:** An isomer of atracurium that is more potent and, crucially, **does not** cause histamine release. * **Laudanosine:** A metabolite of atracurium that can cross the blood-brain barrier and potentially cause seizures (pro-convulsant).

Question 53: A patient, without prior medication, breathes a gas mixture consisting of 50 percent nitrous oxide and 50 percent oxygen by volume. Which of the following effects would be expected?

A. Analgesia (Correct Answer)
B. Excitation
C. Surgical anesthesia
D. Respiratory arrest

Explanation: **Explanation:** The correct answer is **Analgesia (Option A)**. This is based on the pharmacological properties and potency of Nitrous Oxide ($N_2O$). **1. Why Analgesia is correct:** Nitrous oxide is a potent analgesic but a very weak general anesthetic. Its potency is measured by its **Minimum Alveolar Concentration (MAC)**, which is approximately **104%**. This means that even at 100% concentration (which is clinically impossible as it would cause hypoxia), it cannot consistently produce surgical anesthesia in all patients. However, at a concentration of **50%**, $N_2O$ provides significant pain relief (analgesia) equivalent to approximately 10–15 mg of morphine. This 50:50 mixture is commercially known as **Entonox**. **2. Why other options are incorrect:** * **Excitation (Option B):** While some patients may experience mild euphoria (hence "laughing gas"), 50% $N_2O$ is generally used for sedation and pain relief rather than inducing the formal "Excitement Stage" (Guedel’s Stage II) of anesthesia. * **Surgical Anesthesia (Option C):** As mentioned, the MAC of $N_2O$ is 104%. To achieve surgical anesthesia (Stage III), the concentration must exceed the MAC. 50% is insufficient to reach this depth. * **Respiratory Arrest (Option D):** $N_2O$ is relatively safe regarding respiratory drive. It does not cause respiratory arrest at therapeutic concentrations; in fact, it is often used to maintain spontaneous ventilation. **High-Yield Clinical Pearls for NEET-PG:** * **Second Gas Effect:** $N_2O$ is used to speed up the induction of other volatile anesthetics (like Halothane or Isoflurane). * **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 5–10 minutes post-procedure. * **Contraindications:** $N_2O$ expands closed gas spaces. Avoid in pneumothorax, intestinal obstruction, air embolism, and middle ear surgeries (tympanoplasty). * **Vitamin B12:** Chronic exposure can lead to megaloblastic anemia by inactivating methionine synthase.

Question 54: Thiopentone is a fast-acting induction agent because of which of the following?

A. Rapid redistribution
B. Increased clearance
C. Metabolized in plasma
D. High lipid solubility (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. High Lipid Solubility** The rapid onset of action of Thiopentone (an ultra-short-acting barbiturate) is primarily due to its **high lipid solubility**. When injected intravenously, Thiopentone exists largely in a non-ionized, lipid-soluble form. This allows it to cross the blood-brain barrier (BBB) almost instantaneously. Since the brain receives a high percentage of cardiac output (vessel-rich group), the drug reaches peak concentrations in the brain within 30–60 seconds, leading to immediate induction of anesthesia. **Analysis of Incorrect Options:** * **A. Rapid redistribution:** This is a common point of confusion. Rapid redistribution is the reason for the **short duration of action** (recovery), not the fast onset. After the initial peak in the brain, the drug redistributes to leaner tissues (muscles and fat), causing the patient to wake up. * **B. Increased clearance:** Thiopentone has a low hepatic extraction ratio and a long elimination half-life (approx. 11.6 hours). It is cleared slowly from the body, which is why repeated doses can lead to "hangover" effects or saturation. * **C. Metabolized in plasma:** Thiopentone is metabolized primarily in the **liver** via oxidative metabolism. Drugs like Succinylcholine or Remifentanil are examples of agents metabolized by plasma esterases. **High-Yield Clinical Pearls for NEET-PG:** * **pH and Ionization:** Thiopentone is stored in an alkaline solution (pH 10.5). In the physiological pH of the body (7.4), it becomes more non-ionized. In **acidosis**, the non-ionized fraction increases, potentially leading to toxicity. * **Garlic Breath:** Patients often report a transient garlic or onion-like taste/smell during induction. * **Contraindication:** It is strictly contraindicated in **Porphyria** (induces ALA synthetase). * **Complication:** Accidental intra-arterial injection causes severe vasospasm and gangrene. Treatment includes Heparin, Papaverine, and Lidocaine (to vasodilate) or a Brachial plexus block.

Question 55: Which of the following is a false statement regarding Mivacurium?

A. Hypertension (Correct Answer)
B. Increasing the dose produces rapid onset of action
C. Bronchospasm
D. Flushing

Explanation: **Explanation:** **Mivacurium** is a short-acting, non-depolarizing neuromuscular blocking agent (NMBA) belonging to the benzylisoquinolinium class. **Why Option A is the Correct Answer (False Statement):** Mivacurium is notorious for causing **histamine release**, especially when administered rapidly or in high doses. Histamine release leads to peripheral vasodilation, which results in **hypotension** (a decrease in blood pressure), not hypertension. Therefore, the statement that it causes hypertension is false. **Analysis of Other Options:** * **Option B (Rapid Onset):** Like most non-depolarizing relaxants, increasing the dose (e.g., to 2x or 3x ED95) shortens the onset time, allowing for faster tracheal intubation, though this increases the risk of side effects. * **Options C & D (Bronchospasm and Flushing):** These are classic manifestations of systemic **histamine release**. Other associated symptoms include tachycardia and an erythematous rash (flushing). **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Mivacurium is unique among non-depolarizing NMBAs because it is metabolized by **plasma cholinesterase (pseudocholinesterase)**, similar to Succinylcholine. * **Prolonged Block:** Patients with atypical plasma cholinesterase levels or deficiency will experience a significantly prolonged duration of action with Mivacurium. * **Reversal:** While it can be reversed with neostigmine, its short half-life often makes spontaneous recovery sufficient. * **Avoidance:** It should be used with caution in asthmatic patients due to the risk of histamine-induced bronchospasm.

Question 56: The dose of which of the following muscle relaxants needs to be calculated on the basis of total body weight of an obese person rather than their ideal weight?

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

Explanation: **Explanation:** In obese patients, drug dosing is a critical clinical decision. Most muscle relaxants are polar (water-soluble) and do not distribute extensively into adipose tissue. Therefore, dosing them based on **Total Body Weight (TBW)** can lead to overdose and prolonged paralysis. **1. Why Atracurium is the Correct Answer:** Atracurium (and its isomer Cisatracurium) are unique because they undergo **Hofmann elimination** (spontaneous non-enzymatic degradation at physiological pH and temperature). Because of this rapid, organ-independent clearance, the risk of accumulation is lower. Clinical studies have shown that dosing Atracurium based on **Total Body Weight (TBW)** provides more predictable intubating conditions and a more consistent duration of action in obese patients compared to Ideal Body Weight (IBW). **2. Why the Other Options are Incorrect:** * **Vecuronium, Rocuronium, and Pancuronium:** These are steroidal neuromuscular blockers. They are highly water-soluble and have a limited volume of distribution. If dosed on TBW, the plasma concentration becomes excessively high, leading to a significantly prolonged duration of neuromuscular blockade. Therefore, these drugs must be calculated based on **Ideal Body Weight (IBW)** or **Lean Body Weight (LBW)** to avoid delayed recovery. **High-Yield Clinical Pearls for NEET-PG:** * **Succinylcholine:** Unlike non-depolarizers, the dose of Succinylcholine should be calculated based on **Total Body Weight (TBW)** in obese patients because pseudocholinesterase activity increases with body weight. * **Propofol:** Induction dose is based on **LBW**, but the maintenance dose (infusion) is based on **TBW**. * **Opioids (Fentanyl/Sufentanil):** Generally dosed based on **LBW** to prevent respiratory depression. * **Rule of Thumb:** When in doubt for obese patients, most anesthetic drugs are dosed on **LBW/IBW**, except for **Succinylcholine** and **Atracurium**.

Question 57: Maximum histamine release is associated with which neuromuscular blocking agent?

A. D-Tubocurarine (Correct Answer)
B. Succinylcholine
C. Pancuronium
D. Gallamine

Explanation: **Explanation:** **D-Tubocurarine (DTC)** is the correct answer because it is a benzylisoquinolinium compound known for causing the most significant non-immunological (direct) release of histamine from mast cells. This histamine release often leads to clinical manifestations such as hypotension, flushing, tachycardia, and bronchospasm. Due to this side effect profile and the availability of safer alternatives, its clinical use has largely been phased out. **Analysis of Incorrect Options:** * **Succinylcholine:** While it is a depolarizing blocker that can cause various side effects (hyperkalemia, fasciculations, malignant hyperthermia), it is not associated with significant histamine release. * **Pancuronium:** An aminosteroid muscle relaxant. It does not cause histamine release; instead, it has **vagolytic effects**, leading to tachycardia and hypertension. * **Gallamine:** An older non-depolarizing agent that primarily causes tachycardia due to its strong antimuscarinic (vagolytic) action, but it does not trigger significant histamine release compared to DTC. **High-Yield Clinical Pearls for NEET-PG:** * **Histamine Release Ranking:** D-Tubocurarine > Mivacurium > Atracurium. (Modern aminosteroids like Vecuronium and Rocuronium are virtually free of histamine release). * **Drug of Choice for Asthmatics:** Avoid DTC and Atracurium (due to histamine-induced bronchospasm). **Vecuronium** or **Rocuronium** are preferred. * **Hoffman Elimination:** Remember that **Atracurium** and **Cisatracurium** undergo spontaneous degradation (Hoffman elimination), making them safe in renal and hepatic failure. * **Laudanosine Toxicity:** A metabolite of Atracurium that can cross the BBB and cause seizures.

Question 58: What is the minimum mandatory percentage of oxygen used in general anaesthesia?

A. 33%
B. 30% (Correct Answer)
C. 21%
D. 66%

Explanation: **Explanation:** In modern general anesthesia, the minimum mandatory concentration of oxygen delivered to a patient is **30%**. This is a safety standard designed to provide a "margin of safety" above the atmospheric oxygen concentration (21%) to prevent accidental hypoxia during surgery. **Why 30% is correct:** Modern anesthesia machines are equipped with a **Hypoxic Guard System** (e.g., Link-25 or Oxygen-Nitrous Oxide Proportioning System). This mechanical or electronic linkage ensures that the flow of nitrous oxide cannot be increased without a proportional increase in oxygen flow, maintaining a minimum FiO2 (Fraction of Inspired Oxygen) of approximately 25–30%. This prevents the delivery of a hypoxic gas mixture. **Analysis of Incorrect Options:** * **21% (Option C):** While this is the concentration of oxygen in room air, it is considered the absolute minimum for life but insufficient as a safety buffer in a clinical setting where factors like hypoventilation, V/Q mismatch, or increased metabolic demand may occur. * **33% (Option A):** Historically, some older texts mentioned a 1:2 ratio of O2 to N2O (33% O2), but the standardized safety limit for hypoxic guards is calibrated to 25–30%. * **66% (Option D):** This is often the concentration of Nitrous Oxide used (in a 2:1 ratio), not the minimum oxygen requirement. **High-Yield Clinical Pearls for NEET-PG:** * **Hypoxic Guard:** Also known as the "Fail-safe" mechanism, though technically the fail-safe valve (Pressure Sensor Shut-off Valve) specifically shuts off other gases if the oxygen supply pressure drops below 30 psi. * **Color Coding:** Oxygen cylinders are **Black with a White shoulder** (International) or Green (USA). * **Pin Index System:** The pin index for Oxygen is **2, 5**. * **Critical Flow:** If the oxygen supply fails, the anesthesia machine is designed to ensure that the patient never receives 100% Nitrous Oxide.

Question 59: Who coined the term anesthesia?

A. Moon
B. Holmes (Correct Answer)
C. Morgan
D. Priestly

Explanation: **Explanation:** The term **"Anesthesia"** (derived from the Greek words *an-* meaning "without" and *aisthesis* meaning "sensation") was coined by **Oliver Wendell Holmes Sr.** in 1846. 1. **Why Holmes is correct:** Following William T.G. Morton’s successful public demonstration of ether at the "Ether Dome" in Boston, he sought a suitable name for the state of insensibility produced. Oliver Wendell Holmes, a prominent physician and poet, suggested the term in a letter to Morton, defining it as a state of "insensibility" to describe the effects of ether inhalation. 2. **Why the other options are incorrect:** * **Moon:** Likely refers to Henry Moon, who was involved in early dental anesthesia, but he did not name the specialty. * **Morgan:** John Morgan was a pioneer in American medical education, but not associated with the nomenclature of anesthesia. * **Priestly:** Joseph Priestley was the chemist who discovered **Nitrous Oxide** in 1772 and Oxygen in 1774, but he did not coin the term anesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **Father of Anesthesia:** William T.G. Morton (first successful public demonstration). * **First use of Ether:** Crawford Long (1842), though he did not publish his results immediately. * **First use of Chloroform:** James Young Simpson (1847) for obstetric analgesia. * **Father of Modern Anesthesia:** John Snow (first to calculate dosages for ether and chloroform). * **Ether Day:** October 16, 1846.

Question 60: The minimum alveolar concentration (MAC) denotes:

A. Efficacy
B. Potency (Correct Answer)
C. Solubility
D. Diffusibility

Explanation: **Explanation:** **1. Why Potency is Correct:** The Minimum Alveolar Concentration (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 surgical incision) in 50% of patients. In pharmacology, **potency** refers to the amount of drug required to produce a specific effect. MAC is **inversely proportional** to potency ($Potency \propto 1/MAC$). Therefore, an anesthetic with a low MAC (e.g., Halothane, MAC 0.75%) is more potent than one with a high MAC (e.g., Desflurane, MAC 6.0%). This relationship is governed by the **Meyer-Overton Hypothesis**, which states that the potency of an anesthetic is directly proportional to its lipid solubility. **2. Why Other Options are Incorrect:** * **Efficacy:** This refers to the maximum effect a drug can produce regardless of dose. All volatile anesthetics can achieve surgical anesthesia; MAC only measures the dose required to get there. * **Solubility:** This is measured by the **Blood-Gas Partition Coefficient**. Solubility determines the speed of induction and recovery (lower solubility = faster onset), not the potency. * **Diffusibility:** This refers to the rate at which gas moves across the alveolar-capillary membrane, which is governed by Fick’s Law, not the MAC value. **3. High-Yield Clinical Pearls for NEET-PG:** * **MAC-Awake:** Concentration at which 50% of patients respond to verbal commands (usually ~0.3–0.4 MAC). * **MAC-BAR:** Concentration required to block autonomic responses to incision (~1.5 MAC). * **Factors increasing MAC (Decreasing Potency):** Hyperthermia, hypernatremia, chronic alcohol abuse, and young age (highest at 6 months). * **Factors decreasing MAC (Increasing Potency):** Hypothermia, hyponatremia, pregnancy, acute alcohol intoxication, elderly patients, and concurrent use of opioids or benzodiazepines.

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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