General Anesthesia Practice Questions

Q: Which anesthetic agent is contraindicated in epilepsy?

Enflurane. **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.

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

Atracurium. **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).

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

Hypertension. **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.

Q: 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?

Atracurium. **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**.

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

D-Tubocurarine. **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.

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

30%. **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.

Q: Who coined the term anesthesia?

Holmes. **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.

Q: The minimum alveolar concentration (MAC) denotes:

Potency. **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.

Question 1

Which anesthetic agent is contraindicated in epilepsy?

Accepted Answer

Enflurane

Answer

Isoflurane

Answer

Halothane

Answer

Ether

Question 2

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

Accepted Answer

Atracurium

Answer

Adrenaline

Answer

Thiopentone

Answer

Ketamine

Question 3

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?

Accepted Answer

Analgesia

Answer

Excitation

Answer

Surgical anesthesia

Answer

Respiratory arrest

Question 4

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

Accepted Answer

High lipid solubility

Answer

Rapid redistribution

Answer

Increased clearance

Answer

Metabolized in plasma

Question 5

Which of the following is a false statement regarding Mivacurium?

Accepted Answer

Hypertension

Answer

Increasing the dose produces rapid onset of action

Answer

Bronchospasm

Answer

Flushing

Question 6

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?

Accepted Answer

Atracurium

Answer

Vecuronium

Answer

Pancuronium

Answer

Rocuronium

Question 7

Maximum histamine release is associated with which neuromuscular blocking agent?

Accepted Answer

D-Tubocurarine

Answer

Succinylcholine

Answer

Pancuronium

Answer

Gallamine

Question 8

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

Accepted Answer

30%

Answer

33%

Answer

21%

Answer

66%

Question 9

Who coined the term anesthesia?

Accepted Answer

Holmes

Answer

Moon

Answer

Morgan

Answer

Priestly

Question 10

The minimum alveolar concentration (MAC) denotes:

Accepted Answer

Potency

Answer

Efficacy

Answer

Solubility

Answer

Diffusibility

General Anesthesia — MCQs

General Anesthesia — MCQs

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