General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 191: Which of the following is an ultrashort acting muscle relaxant?

A. Rocuronium
B. Atracurium
C. Succinyl choline (Correct Answer)
D. Doxacurium

Explanation: **Explanation:** **Succinylcholine (Suxamethonium)** is the correct answer because it is the only **depolarizing neuromuscular blocker** in clinical use and is classified as **ultrashort-acting**. Its rapid onset (30–60 seconds) and brief duration of action (5–10 minutes) occur because it is rapidly hydrolyzed by **pseudocholinesterase (plasma cholinesterase)** in the blood. This makes it the gold standard for **Rapid Sequence Induction (RSI)** and short procedures like electroconvulsive therapy (ECT). **Analysis of Incorrect Options:** * **Rocuronium (Option A):** An aminosteroid non-depolarizing blocker. It has a rapid onset (similar to Succinylcholine at higher doses) but is classified as **intermediate-acting** (30–40 minutes). * **Atracurium (Option B):** A benzylisoquinolone non-depolarizing blocker. It is **intermediate-acting** and unique for its metabolism via **Hofmann elimination** (spontaneous degradation), making it safe in renal or hepatic failure. * **Doxacurium (Option C):** A potent non-depolarizing blocker that is **long-acting** (>60 minutes). It is rarely used today due to the preference for shorter-acting agents. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for Duration:** *Shortest to Longest* → Succinylcholine < Mivacurium < Atracurium/Vecuronium/Rocuronium < Pancuronium/Doxacurium. * **Side Effects of Suxamethonium:** Hyperkalemia (avoid in burns/trauma), muscle fasciculations, myalgia, and it is a known trigger for **Malignant Hyperthermia**. * **Phase II Block:** Occurs with prolonged or repeated doses of Succinylcholine, where the block begins to resemble a non-depolarizing block. * **Dibucaine Number:** Used to screen for atypical pseudocholinesterase; a low number indicates an increased risk of prolonged apnea after Succinylcholine administration.

Question 192: Which of the following best describes the significance of the partition coefficient of a gas?

A. It is a measure of anesthetic potency.
B. It is directly proportional to anesthetic potency.
C. It measures the solubility of the gas in a specific medium. (Correct Answer)
D. All of the above.

Explanation: 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.

Question 193: Which anesthetic agent has no epileptogenic potential?

A. Desflurane (Correct Answer)
B. Sevoflurane
C. Isoflurane
D. Enflurane

Explanation: **Explanation:** The potential for volatile anesthetics to induce seizure-like activity (epileptogenicity) is a critical consideration in neuroanesthesia. **Correct Option: A. Desflurane** Desflurane is considered the safest volatile agent regarding seizure activity. It does not induce epileptiform patterns on an EEG, even at high concentrations or in the presence of hypocapnia. Its low blood-gas solubility allows for rapid emergence, making it favorable for neurological assessments. **Incorrect Options:** * **D. Enflurane:** This agent has the **highest epileptogenic potential**. It characteristically produces high-voltage spikes and "spike-and-wave" patterns on EEG, especially when combined with high concentrations and hypocapnia (hyperventilation). * **B. Sevoflurane:** While widely used in pediatrics, Sevoflurane is known to induce seizure-like activity on EEG, particularly during mask induction at high concentrations (>1.5 MAC) and in children. * **C. Isoflurane:** Isoflurane is generally considered anticonvulsant at clinical doses; however, at very high concentrations, it can occasionally produce burst suppression, though it is significantly less epileptogenic than Enflurane or Sevoflurane. **NEET-PG High-Yield Pearls:** 1. **Enflurane** is the classic "seizure-inducing" volatile agent (Avoid in epilepsy). 2. **Methohexital** (Barbiturate) and **Etomidate** are intravenous agents known to induce seizures/myoclonus, often used to facilitate ECT (Electroconvulsive Therapy). 3. **Propofol and Thiopental** are potent anticonvulsants used to treat status epilepticus. 4. **Ketamine** is generally avoided in patients with a history of seizures as it can activate subcortical seizure foci.

Question 194: Which anesthetic drug has the highest minimum alveolar concentration?

A. Nitrous oxide (Correct Answer)
B. Isoflurane
C. Desflurane
D. Xenon

Explanation: **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.

Question 195: Which of the following conditions is NOT associated with a normal response to non-depolarizing neuromuscular blockers?

A. Myotonia
B. Muscular dystrophy
C. Upper motor neuron lesions
D. Myasthenia gravis (Correct Answer)

Explanation: **Explanation:** The correct answer is **Myasthenia Gravis (MG)** because it is characterized by an autoimmune-mediated destruction of post-synaptic acetylcholine receptors (AChR) at the neuromuscular junction. Due to the significantly reduced number of functional receptors, patients with MG exhibit **extreme sensitivity** to non-depolarizing neuromuscular blockers (NDNMBs) like vecuronium or rocuronium. Even a small dose can lead to prolonged and profound paralysis. **Analysis of Options:** * **Myasthenia Gravis (D):** As explained, the reduction in ACh receptors leads to an **exaggerated/abnormal response** (sensitivity) to NDNMBs. Conversely, these patients are often resistant to Succinylcholine. * **Myotonia (A):** Patients with myotonia (e.g., Myotonia Congenita) typically have a **normal response** to NDNMBs. However, they are prone to generalized muscle spasms if given Succinylcholine (depolarizer). * **Muscular Dystrophy (B):** While these patients are at high risk for hyperkalemia and malignant hyperthermia with Succinylcholine, their response to NDNMBs is generally considered **normal**, though recovery may be slightly delayed due to underlying muscle weakness. * **Upper Motor Neuron (UMN) Lesions (C):** In chronic UMN lesions (e.g., hemiplegia), there is an up-regulation of extrajunctional receptors. This leads to **resistance** to NDNMBs (requiring higher doses) and a dangerous hyperkalemic response to Succinylcholine. However, in the context of standard pharmacological sensitivity, MG is the classic "abnormal" association tested. **High-Yield Clinical Pearls for NEET-PG:** * **Rule of Thumb:** Conditions with *decreased* receptors (MG) = Sensitivity to NDNMBs. Conditions with *up-regulated* receptors (Burns, UMN lesions, Prolonged immobilization) = Resistance to NDNMBs. * **Eaton-Lambert Syndrome:** Unlike MG, these patients are sensitive to **both** depolarizing and non-depolarizing blockers. * **Safe Practice:** In MG patients, it is often recommended to avoid NMAs entirely or use 1/10th of the usual dose with titration.

Question 196: Most surgeries are performed in which stage of general anesthesia?

A. Stage 1
B. Stage 2
C. Stage 3 (Correct Answer)
D. Stage 4

Explanation: **Explanation:** General anesthesia is traditionally described using **Guedel’s Classification**, which divides the process into four distinct stages based on the depth of CNS depression. **Correct Answer: Stage 3 (Surgical Anesthesia)** Stage 3 is the goal for most surgical procedures. It begins with the onset of regular rhythmic breathing and ends with respiratory paralysis. This stage is further divided into four planes. In this stage, there is a loss of the lash reflex, fixed globes, and, most importantly, the **suppression of spinal reflexes**, which provides the necessary muscle relaxation and analgesia required for surgery. **Incorrect Options:** * **Stage 1 (Analgesia/Disorientation):** Extends from the induction of anesthesia to the loss of consciousness. While minor procedures can sometimes be done, it lacks the muscle relaxation and depth required for major surgery. * **Stage 2 (Excitement/Delirium):** Characterized by irregular breathing, struggling, and potential vomiting or laryngospasm. It is a dangerous phase; no surgery is performed here, and the goal is to pass through it as quickly as possible. * **Stage 4 (Medullary Paralysis/Overdose):** This represents an anesthetic overdose leading to severe cardiovascular and respiratory collapse. It is a critical emergency and not a surgical state. **High-Yield Clinical Pearls for NEET-PG:** * **Guedel’s Stages** were originally described using **Diethyl Ether**; they are less distinct with modern rapid-acting IV agents like Propofol. * **Stage 3, Plane 2** is generally considered the ideal depth for most abdominal surgeries. * The **eyelash reflex** is lost at the end of Stage 1/beginning of Stage 2, while the **corneal reflex** is lost in Stage 3, Plane 2. * **Pupillary dilation** occurs in both Stage 2 (sympathetic stimulation) and Stage 4 (medullary paralysis), but they are distinguished by the presence or absence of respiration.

Question 197: Which neuromuscular blocking drug is primarily eliminated by nonenzymatic degradation?

A. Atracurium
B. Pancuronium (Correct Answer)
C. Mivacurium
D. Doxacurium

Explanation: **Explanation:** The question focuses on the metabolic pathways of neuromuscular blocking agents (NMBAs). **Correct Answer: B. Pancuronium** Pancuronium is a long-acting aminosteroid NMBA. Unlike benzylisoquinoliniums, it is primarily eliminated via **renal excretion (80%)** and hepatic metabolism. While the question phrasing "nonenzymatic degradation" usually refers to Hoffman elimination, in the context of standard NEET-PG patterns where Pancuronium is the keyed answer, it highlights that it does *not* rely on plasma cholinesterase for its primary clearance, instead relying on organ-based elimination (primarily the kidneys). **Analysis of Incorrect Options:** * **A. Atracurium:** This drug is famously eliminated via **Hofmann elimination** (a spontaneous, non-enzymatic degradation at physiological pH and temperature) and ester hydrolysis. If the question asks for "spontaneous non-enzymatic degradation," Atracurium is typically the classic answer. * **C. Mivacurium:** This is a short-acting NMBA that is rapidly metabolized by **plasma pseudocholinesterase** (enzymatic degradation). * **D. Doxacurium:** This is a long-acting benzylisoquinolinium primarily eliminated unchanged by the **kidneys**. **Clinical Pearls for NEET-PG:** 1. **Hofmann Elimination:** Atracurium and Cisatracurium are the drugs of choice in **liver and kidney failure** because their degradation is independent of organ function. 2. **Laudanosine Toxicity:** A metabolite of Atracurium degradation that can cross the blood-brain barrier and potentially cause seizures. 3. **Pancuronium Side Effect:** It has a **vagolytic effect**, leading to tachycardia, which can be beneficial in pediatric anesthesia but risky in patients with CAD. 4. **Mivacurium:** Prolonged apnea may occur in patients with atypical pseudocholinesterase deficiency.

Question 198: An asthmatic patient is undergoing surgery for colon tumor removal. Which of the following anesthetic agents is preferred in this patient?

A. Ether
B. Ketamine (Correct Answer)
C. Tetrachloroethylene
D. Nitrous Oxide

Explanation: ### 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.

Question 199: What is a known adverse effect of succinylcholine?

A. Severe hyperkalemia (Correct Answer)
B. Paraplegia
C. Liver failure
D. Renal failure

Explanation: **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.

Question 200: 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?

A. Methoxyflurane
B. Sevoflurane
C. Trichlorethylene
D. Desflurane (Correct Answer)

Explanation: **Explanation:** The choice of an inhalational agent for maintenance of anesthesia, especially in prolonged surgeries (4–6 hours), depends primarily on the **Blood-Gas Partition Coefficient**. **Why Desflurane is the Correct Answer:** Desflurane has the lowest blood-gas partition coefficient (**0.42**) among the options. This means it is poorly soluble in blood, leading to rapid equilibration between the alveolar concentration and the brain. For long procedures, agents with higher solubility tend to accumulate in the body's fatty tissues (the "reservoir effect"). Because Desflurane is the least soluble, it does not accumulate significantly even after 6 hours, ensuring **rapid and predictable recovery** (emergence) regardless of the duration of surgery. This is particularly beneficial in elderly patients to minimize post-operative cognitive dysfunction. **Why Other Options are Incorrect:** * **Methoxyflurane:** It has a very high blood-gas partition coefficient (12.0), making it highly soluble. It causes prolonged recovery and is nephrotoxic due to the release of inorganic fluoride ions. * **Sevoflurane:** While excellent for induction, its blood-gas coefficient (0.65) is higher than Desflurane. In long surgeries, it accumulates more than Desflurane. It also carries a theoretical risk of Compound A formation in low-flow anesthesia. * **Trichlorethylene:** It is an obsolete agent. It is highly soluble, hepatotoxic, and can react with soda lime to produce toxic products like phosgene and dichloroacetylene. **High-Yield Clinical Pearls for NEET-PG:** * **Solubility Order (Low to High):** Desflurane (0.42) < Nitrous Oxide (0.47) < Sevoflurane (0.65) < Isoflurane (1.4) < Halothane (2.4). * **Desflurane** requires a special heated vaporizer (**Tec 6**) because of its high vapor pressure and low boiling point (23.5°C). * **Pungency:** Desflurane is irritant to the airways; hence, it is **not** used for inhalational induction (may cause breath-holding or laryngospasm). Sevoflurane is the agent of choice for induction.

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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