General Anesthesia Practice Questions

Q: Which of the following best describes the significance of the partition coefficient of a gas?

It measures the solubility of the gas in a specific medium.. The **Partition Coefficient** is a fundamental concept in pharmacokinetics that describes how an inhalational anesthetic distributes itself between two phases (e.g., blood/gas, oil/gas, or tissue/blood) at equilibrium. ### 1. Why Option C is Correct The partition coefficient is a **measure of solubility**. It represents the ratio of the concentration of the anesthetic in one phase to the concentration in another phase when the partial pressures in both phases are equal. For example, the **Blood/Gas partition coefficient** indicates how soluble the gas is in blood compared to alveolar air. A higher coefficient means the gas is more soluble in blood, leading to a slower induction of anesthesia because the blood acts as a "reservoir" that must be saturated before the partial pressure in the brain can rise. ### 2. Why Other Options are Incorrect * **Option A & B:** These are incorrect because **potency** is measured by **MAC (Minimum Alveolar Concentration)**, not the partition coefficient. While the **Oil/Gas partition coefficient** correlates with potency (Meyer-Overton Hypothesis), it is not a direct measure of it. Potency is inversely proportional to MAC (Lower MAC = Higher Potency). ### 3. High-Yield Clinical Pearls for NEET-PG * **Blood/Gas Coefficient:** Determines the **speed of induction and recovery**. * *Low solubility (e.g., Desflurane 0.42):* Fast induction/emergence. * *High solubility (e.g., Halothane 2.4):* Slow induction/emergence. * **Oil/Gas Coefficient:** Determines **potency**. High lipid solubility means the drug easily crosses the blood-brain barrier. * **Meyer-Overton Hypothesis:** States that the anesthetic potency of a gas is directly proportional to its lipid solubility (Oil/Gas partition coefficient). * **Order of Blood/Gas Solubility (Low to High):** Desflurane < Sevoflurane < Nitrous Oxide < Isoflurane < Halothane.

Q: Which anesthetic drug has the highest minimum alveolar concentration?

Nitrous oxide. **Explanation:** The **Minimum Alveolar Concentration (MAC)** is the concentration of an inhaled anesthetic at 1 atmosphere that prevents skeletal muscle movement in response to a noxious stimulus (surgical incision) in 50% of patients. MAC is a measure of **anesthetic potency**; they are inversely proportional (**Potency ∝ 1/MAC**). Therefore, the drug with the highest MAC is the least potent. **1. Why Nitrous Oxide (N₂O) is correct:** Nitrous oxide has a MAC of approximately **104%**. Since it is impossible to achieve this concentration at sea level without causing hypoxia, N₂O cannot be used as a sole anesthetic agent for surgery. Its high MAC value indicates it is the least potent inhalational anesthetic among the options. **2. Why the other options are incorrect:** * **Desflurane:** Has a MAC of **6.0%**. While it has the highest MAC among the *volatile liquids*, it is significantly more potent than N₂O. * **Xenon:** An inert gas with a MAC of **63–71%**. It is more potent than N₂O but less potent than volatile liquids. * **Isoflurane:** Has a MAC of **1.15%**. It is highly potent, requiring a very low concentration to achieve anesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Order (MAC):** Halothane (0.75%) > Isoflurane (1.15%) > Sevoflurane (2%) > Desflurane (6%) > Xenon (71%) > N₂O (104%). * **Oil:Gas Partition Coefficient:** Determines potency (Meyer-Overton Hypothesis). N₂O has the lowest coefficient, correlating with its high MAC. * **Factors increasing MAC (Decreasing potency):** Hyperthermia, hypernatremia, chronic alcohol abuse, and increased central neurotransmitters (e.g., MAO inhibitors, cocaine). * **Factors decreasing MAC (Increasing potency):** Hypothermia, pregnancy, acute alcohol intoxication, old age, and anemia.

Q: Which of the following are postulated mechanisms by which propofol acts as an antiemetic?

All of the above. Propofol is unique among intravenous induction agents for its potent **antiemetic properties**, making it the drug of choice for Total Intravenous Anesthesia (TIVA) to prevent Postoperative Nausea and Vomiting (PONV). Its mechanism of action as an antiemetic is **multifactorial**, involving both central and peripheral pathways. ### **Mechanism of Action:** 1. **Antidopaminergic Activity:** Propofol exerts a weak antagonistic effect on **D2 receptors**. By inhibiting dopamine signaling, it reduces the stimulation of the emetic center. 2. **Depressant Effect on the CTZ:** It directly depresses the **Chemoreceptor Trigger Zone (CTZ)** in the area postrema and the subcortical centers, raising the threshold for vomiting. 3. **Neurotransmitter Modulation:** Propofol decreases the release of excitatory neurotransmitters like **Glutamate and Substance P** in the olfactory cortex. Furthermore, it reduces **serotonin (5-HT3)** levels in the area postrema, mimicking the action of specialized antiemetics like ondansetron. ### **Why "All of the Above" is Correct:** Since propofol utilizes all three pathways—dopamine antagonism, CTZ depression, and modulation of glutamate/serotonin—to suppress the vomiting reflex, option D is the most comprehensive and accurate answer. ### **High-Yield NEET-PG Pearls:** * **Sub-hypnotic Doses:** The antiemetic effect occurs at doses much lower than those required for induction (e.g., **10–20 mg IV** or a low-dose infusion of 10 µg/kg/min). * **PONV Gold Standard:** TIVA with Propofol is considered the most effective anesthetic strategy to reduce the baseline risk of PONV. * **PRIS:** Beware of **Propofol Related Infusion Syndrome** (metabolic acidosis, rhabdomyolysis, hyperkalemia) during prolonged high-dose infusions.

Q: Which of the following anesthetic agents is known to increase cardiac oxygen demand?

Ketamine. **Explanation:** **Ketamine (Correct Answer):** Ketamine is a unique anesthetic agent that acts as a **direct sympathomimetic**. It stimulates the sympathetic nervous system, leading to an increase in circulating catecholamines. This results in the "Ketamine Triad": **increased heart rate, increased blood pressure, and increased cardiac output**. These hemodynamic changes significantly elevate **myocardial oxygen demand**. Consequently, Ketamine is generally contraindicated in patients with ischemic heart disease or severe hypertension. **Incorrect Options:** * **Halothane:** This volatile anesthetic is a potent **myocardial depressant**. It decreases cardiac output and blood pressure, thereby reducing myocardial oxygen demand. However, it is high-yield for its tendency to sensitize the myocardium to catecholamines, leading to arrhythmias. * **Thiopentone:** As a barbiturate, it causes peripheral vasodilation and direct myocardial depression. While it may cause a compensatory reflex tachycardia, its overall effect is a reduction in cerebral and systemic metabolic demands. * **Nitrous oxide (N2O):** N2O has a mild direct myocardial depressant effect, which is usually offset by a slight increase in sympathetic tone. However, it does not significantly increase oxygen demand compared to the potent stimulation caused by Ketamine. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Ketamine is the induction agent of choice in **hypovolemic shock** and **cardiac tamponade** due to its pressor effects. * **Exception:** In cases of severe catecholamine depletion (e.g., end-stage heart failure), Ketamine can actually cause a decrease in BP due to its underlying direct myocardial depressant effect being unmasked. * **Key Contraindication:** Avoid Ketamine in patients with **Ischemic Heart Disease (IHD)** and **Raised Intracranial Pressure (ICP)**.

Q: An asthmatic patient is undergoing surgery for colon tumor removal. Which of the following anesthetic agents is preferred in this patient?

Ketamine. ### Explanation **Correct Option: B. Ketamine** Ketamine is the induction agent of choice for patients with bronchial asthma or reactive airway disease. Its primary mechanism for this indication is its **direct bronchodilatory effect**. Ketamine acts by: 1. **Sympathomimetic action:** It increases the release of endogenous catecholamines, which stimulate $\beta_2$ receptors in the lungs. 2. **Direct smooth muscle relaxation:** It inhibits vagal tone and directly relaxes bronchial smooth muscle. This makes it ideal for preventing or treating intraoperative bronchospasm. **Incorrect Options:** * **A. Ether:** While Ether is a potent bronchodilator, it is highly **irritant** to the respiratory mucosa. This irritation can trigger coughing, laryngospasm, and excessive tracheobronchial secretions during induction, making it unfavorable for asthmatics. * **C. Tetrachloroethylene:** This is primarily an anthelmintic agent (used for hookworms) and is not used as a clinical anesthetic agent in modern practice due to its high toxicity. * **D. Nitrous Oxide ($N_2O$):** $N_2O$ is a gas with neutral effects on bronchial tone. It does not provide bronchodilation and is generally avoided in surgeries where there is a risk of air-filled space expansion (though not specifically contraindicated in asthma, it is not "preferred" over Ketamine). **High-Yield Clinical Pearls for NEET-PG:** * **Inhalational Agent of Choice:** **Sevoflurane** is the preferred volatile anesthetic for asthmatics because it is non-pungent and a potent bronchodilator. * **Agent to Avoid:** **Thiopentone** is generally avoided in asthma as it may cause histamine release and can precipitate bronchospasm if the plane of anesthesia is light. * **Desflurane** should be avoided for induction in asthmatics due to its irritant nature, which can trigger airway hyperactivity.

Q: What is a known adverse effect of succinylcholine?

Severe hyperkalemia. **Explanation:** **Succinylcholine** is a depolarizing neuromuscular blocker that acts as an agonist at the nicotinic acetylcholine receptors (nAChR) of the motor endplate. **Why Severe Hyperkalemia is the Correct Answer:** When succinylcholine binds to the receptors, it causes prolonged depolarization of the muscle cell membrane. This process opens ion channels, leading to an efflux of intracellular **potassium (K+)** into the extracellular space. In a healthy individual, this typically raises serum potassium by only **0.5 mEq/L**. However, in patients with "upregulation" of extrajunctional receptors (e.g., major burns, crush injuries, massive trauma, or prolonged immobilization), the massive release of potassium can lead to **severe hyperkalemia**, potentially resulting in cardiac arrest. **Why Other Options are Incorrect:** * **B. Paraplegia:** Succinylcholine does not cause paraplegia. In fact, patients with pre-existing paraplegia are at a high risk of hyperkalemia if given succinylcholine due to denervation supersensitivity. * **C & D. Liver and Renal Failure:** Succinylcholine is metabolized by **pseudocholinesterase** (plasma cholinesterase) in the blood, not primarily by the liver or kidneys. While liver disease can lower pseudocholinesterase levels (prolonging the drug's action), the drug itself does not cause organ failure. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Still preferred for **Rapid Sequence Induction (RSI)** due to its rapid onset (30–60s) and short duration (5–10 mins). * **Malignant Hyperthermia:** Succinylcholine is a known trigger (along with volatile anesthetics). * **Phase II Block:** Occurs with repeated doses or infusion, where the block starts behaving like a non-depolarizing block. * **Contraindications:** Burns (>24 hours old), massive trauma, upper motor neuron lesions, and a personal/family history of malignant hyperthermia.

Q: Which of the following anesthetic agents is known to be nephrotoxic?

Methoxyflurane. **Explanation:** **Methoxyflurane** is the correct answer because it is the most potent inhalational anesthetic but is notorious for its dose-dependent **nephrotoxicity**. The underlying mechanism involves the extensive hepatic metabolism of methoxyflurane (up to 50-70%), which releases high levels of **inorganic fluoride ions (F⁻)**. These ions interfere with the concentrating mechanism of the renal tubules, leading to "high-output renal failure" (polyuric renal failure). Due to this severe side effect, its use as a general anesthetic has been largely abandoned. **Analysis of Incorrect Options:** * **Halothane:** Primarily known for **hepatotoxicity** ("Halothane Hepatitis") and sensitization of the myocardium to catecholamines, leading to arrhythmias. It does not cause significant renal damage. * **Ether:** Known for its irritating effect on the airways and high flammability. While it causes sympathetic stimulation, it is not directly nephrotoxic. * **Cyclopropane:** An explosive gas that causes significant cardiac sensitization to adrenaline. Like ether, it lacks specific nephrotoxic properties. **High-Yield Clinical Pearls for NEET-PG:** * **Fluoride Threshold:** Serum fluoride levels >50 µmol/L are typically associated with renal toxicity. * **Sevoflurane:** Another modern agent that releases fluoride ions; however, it is generally safe. Its main concern is the formation of **Compound A** (a nephrotoxic vinyl ether) when reacting with soda lime, though this is rarely clinically significant in humans. * **Metabolism Rule:** Methoxyflurane (70%) > Halothane (20%) > Sevoflurane (2-5%) > Enflurane (2%) > Isoflurane (0.2%) > Desflurane (0.02%). * **Current Use:** Methoxyflurane is now only used in low doses (via the "Penthrox" inhaler) for emergency analgesia, where fluoride levels remain below the toxic threshold.

Question 1

Which of the following best describes the significance of the partition coefficient of a gas?

Accepted Answer

It measures the solubility of the gas in a specific medium.

Answer

It is a measure of anesthetic potency.

Answer

It is directly proportional to anesthetic potency.

Answer

All of the above.

Question 2

Which anesthetic drug has the highest minimum alveolar concentration?

Accepted Answer

Nitrous oxide

Answer

Isoflurane

Answer

Desflurane

Answer

Xenon

Question 3

Which of the following are postulated mechanisms by which propofol acts as an antiemetic?

Accepted Answer

All of the above

Answer

Antidopaminergic activity

Answer

Depressant effect on the chemoreceptor trigger zone

Answer

Decreased release of glutamate and substance P in the olfactory cortex and decreased serotonin

Question 4

Which of the following conditions is NOT associated with a normal response to non-depolarizing neuromuscular blockers?

Accepted Answer

Myasthenia gravis

Answer

Myotonia

Answer

Muscular dystrophy

Answer

Upper motor neuron lesions

Question 5

Which of the following anesthetic agents is known to increase cardiac oxygen demand?

Accepted Answer

Ketamine

Answer

Halothane

Answer

Thiopentone

Answer

Nitrous oxide (N2O)

Question 6

An asthmatic patient is undergoing surgery for colon tumor removal. Which of the following anesthetic agents is preferred in this patient?

Accepted Answer

Ketamine

Answer

Ether

Answer

Tetrachloroethylene

Answer

Nitrous Oxide

Question 7

What is a known adverse effect of succinylcholine?

Accepted Answer

Severe hyperkalemia

Answer

Paraplegia

Answer

Liver failure

Answer

Renal failure

Question 8

Which of the following anesthetic agents is known to be nephrotoxic?

Accepted Answer

Methoxyflurane

Answer

Halothane

Answer

Ether

Answer

Cyclopropane

Question 9

A seventy-year-old patient is posted for a surgery likely to last 4-6 hours. What is the best inhalational agent of choice for maintenance of anesthesia in this case?

Accepted Answer

Desflurane

Answer

Methoxyflurane

Answer

Sevoflurane

Answer

Trichlorethylene

Question 10

Which inhaled anesthetic has the least diffusion coefficient?

Accepted Answer

Nitrous Oxide (N2O)

Answer

Isoflurane

Answer

Enflurane

Answer

Halothane

General Anesthesia — MCQs

General Anesthesia — MCQs

On this page

Practice by Chapter

Want unlimited practice?