General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 41: Which of the following is a depolarising muscle relaxant?

A. Scoline (Correct Answer)
B. Atracurium
C. Pancuronium
D. Cisatracurium

Explanation: **Explanation:** Neuromuscular blocking agents (NMBAs) are classified into two main categories based on their mechanism of action at the nicotinic acetylcholine receptor (nAChR) of the motor endplate: **Depolarizing** and **Non-depolarizing**. **Correct Answer: A. Scoline (Succinylcholine/Suxamethonium)** Scoline is the **only** depolarizing muscle relaxant used clinically. It acts as an acetylcholine (ACh) analog, binding to nAChRs and causing persistent depolarization of the motor endplate. This results in initial muscle twitching (fasciculations) followed by flaccid paralysis because the muscle membrane cannot repolarize to respond to subsequent stimuli. **Incorrect Options:** * **B, C, and D (Atracurium, Pancuronium, Cisatracurium):** These are all **Non-depolarizing** muscle relaxants. They act as competitive antagonists, binding to the nAChR without activating it, thereby preventing ACh from triggering depolarization. * **Pancuronium** is a long-acting steroid derivative. * **Atracurium and Cisatracurium** are benzylisoquinoliniums known for undergoing **Hofmann elimination** (organ-independent metabolism). **High-Yield Clinical Pearls for NEET-PG:** * **Onset & Duration:** Scoline has the fastest onset (30–60 seconds) and shortest duration (5–10 minutes), making it the drug of choice for **Rapid Sequence Induction (RSI)**. * **Metabolism:** It is metabolized by **Pseudocholinesterase** (Plasma cholinesterase). Deficiency of this enzyme leads to prolonged apnea (Scoline apnea). * **Contraindications:** Avoid in burns, massive trauma, and neurological injuries (due to risk of **hyperkalemia**) and in patients with a history of **Malignant Hyperthermia**. * **Side Effects:** Muscle soreness, bradycardia (especially in children), and increased intraocular/intragastric pressure.

Question 42: Which of the following has analgesic property?

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

Explanation: **Explanation:** The question asks which of the following has analgesic properties. However, there appears to be a discrepancy in the provided key: **Thiopental is actually an anti-analgesic**, while **Nitrous Oxide and Ketamine are potent analgesics.** In the context of standard medical teaching for NEET-PG, the explanation is as follows: **1. Why the Correct Answer (as per your key) is unique:** **Thiopental (Option C)** is a barbiturate used for induction. It is notorious for being **hyperalgesic** (it lowers the pain threshold). It provides no pain relief; in fact, patients may react more intensely to painful stimuli under light thiopental anesthesia. If the question intended to ask which drug *lacks* analgesic property or is *anti-analgesic*, Thiopental would be the answer. **2. Analysis of Other Options:** * **Nitrous Oxide (Option A):** A potent **analgesic** gas. Its analgesic effect is mediated via the release of endogenous opioid peptides in the periaqueductal gray matter. * **Ketamine (Option B):** A phencyclidine derivative that produces "dissociative anesthesia." It is a **profound analgesic** even at sub-anesthetic doses, acting primarily as an NMDA receptor antagonist. * **Etomidate (Option D):** An imidazole derivative used for hemodynamically unstable patients. Like Thiopental, it **lacks analgesic properties**, but unlike Thiopental, it is not typically labeled as "anti-analgesic." **3. Clinical Pearls for NEET-PG:** * **Ketamine** is the only intravenous anesthetic that possesses significant analgesic properties and stimulates the cardiovascular system. * **Propofol, Thiopental, and Etomidate** provide hypnosis but **zero analgesia**; they must be supplemented with opioids or nitrous oxide. * **Thiopental High-Yields:** Causes garlic/onion taste before unconsciousness, is the drug of choice for ECT (though Methohexital is preferred globally), and is contraindicated in Porphyria.

Question 43: The complete fluorination in Desflurane produces all the following effects except:

A. Decreases blood and tissue solubility
B. High vapor pressure
C. High potency (Correct Answer)
D. Requirement of special vaporizer

Explanation: **Explanation:** Desflurane is a fluorinated methyl ethyl ether. The "complete fluorination" refers to the substitution of all chlorine atoms with fluorine atoms (specifically, replacing the chlorine atom found in Isoflurane). **Why "High Potency" is the Correct Answer (The Exception):** Potency of an anesthetic agent is inversely proportional to its **Minimum Alveolar Concentration (MAC)** and directly related to its lipid solubility (Meyer-Overton hypothesis). Fluorination significantly **decreases lipid solubility**, which in turn **decreases potency**. Desflurane has a MAC of approximately 6%, making it the least potent among commonly used volatile anesthetics (compared to Isoflurane at 1.15% or Sevoflurane at 2%). **Analysis of Incorrect Options:** * **A. Decreases blood and tissue solubility:** Fluorination reduces the blood-gas partition coefficient (0.42 for Desflurane). This ensures rapid induction and, more importantly, the fastest emergence/recovery among volatile agents. * **B. High vapor pressure:** The fluorine atoms increase the vapor pressure significantly (669 mmHg at 20°C). This is near atmospheric pressure, meaning it would boil at room temperature in high altitudes. * **C. Requirement of special vaporizer:** Due to its high vapor pressure and low boiling point (22.8°C), Desflurane requires a specialized, heated, and pressurized vaporizer (e.g., **Tec 6** or Apex) to deliver a constant concentration. **Clinical Pearls for NEET-PG:** * **Pungency:** Desflurane is highly pungent and an irritant to the airway; it can cause coughing, breath-holding, and laryngospasm. Therefore, it is **not** used for inhalation induction (Sevoflurane is preferred). * **Sympathetic Stimulation:** Rapid increases in Desflurane concentration can lead to transient tachycardia and hypertension. * **Carbon Monoxide:** Desflurane produces the highest amount of Carbon Monoxide (CO) when passed through dry soda lime.

Question 44: Which drug is responsible for Phase II block?

A. Succinylcholine (Correct Answer)
B. Pancuronium
C. Atracurium
D. Dexacurium

Explanation: **Explanation:** **Succinylcholine** is a depolarizing neuromuscular blocker (DNMR) that typically produces a **Phase I block** (characterized by fasciculations followed by flaccid paralysis). However, when administered in high doses, repeated boluses, or via continuous infusion, it can lead to a **Phase II block** (also known as a dual block or desensitization block). In a Phase II block, the post-junctional membrane becomes repolarized but is desensitized to acetylcholine. Clinically, the block begins to resemble a non-depolarizing block, showing **fade** on Train-of-Four (TOF) stimulation and **post-tetanic facilitation**. **Analysis of Incorrect Options:** * **Pancuronium:** A long-acting non-depolarizing neuromuscular blocker (NDNMR). It produces a competitive block, not a Phase II block. * **Atracurium:** An intermediate-acting NDNMR. It is unique for its metabolism via **Hofmann elimination** and ester hydrolysis, but it does not cause a Phase II block. * **Dexacurium (Doxacurium):** A long-acting NDNMR of the benzylisoquinolone class. Like other NDNMRs, it produces a competitive blockade from the onset. **High-Yield Clinical Pearls for NEET-PG:** * **Phase I Block:** No fade on TOF (ratio > 0.7), no post-tetanic facilitation, preceded by fasciculations. * **Phase II Block:** Shows fade on TOF, presence of post-tetanic facilitation. It can be reversed by anticholinesterases (like Neostigmine), whereas Phase I block is **augmented** by them. * **Pseudocholinesterase Deficiency:** Patients with atypical plasma cholinesterase may develop a Phase II block even with standard doses of Succinylcholine due to prolonged exposure at the NMJ.

Question 45: Which non-depolarizing muscle relaxant is contraindicated in the patient shown?

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

Explanation: ***Gallamine*** - **100% renal excretion** unchanged makes it absolutely contraindicated in **end-stage renal disease** patients with AV fistulas for hemodialysis. - Prolonged **neuromuscular blockade** can occur due to impaired kidney function and inability to clear the drug. *Pancuronium* - Only **80% renal excretion** with **20% hepatic metabolism**, making it relatively safer in renal impairment. - **Dose reduction** may be needed, but not absolutely contraindicated like gallamine. *Vecuronium* - Primarily **hepatic metabolism** with only **30% renal excretion**, making it safer in kidney disease. - **Shorter duration** and predictable recovery even in renal failure patients. *Rocuronium* - Predominantly **hepatic elimination** with minimal renal excretion (**10-20%**), making it suitable for renal patients. - **Rapid onset** and **intermediate duration** with reliable recovery regardless of kidney function.

Question 46: Atracurium is metabolized by which of the following mechanisms?

A. Conjugation
B. Hoffman degradation (Correct Answer)
C. Pseudocholinesterase
D. Methylation

Explanation: **Explanation:** **Atracurium** is a benzylisoquinolinium non-depolarizing neuromuscular blocking agent. Its unique metabolism makes it a favorite topic for NEET-PG. **Why Hoffman Degradation is Correct:** Atracurium undergoes **Hoffman elimination (degradation)**, a non-enzymatic, spontaneous chemical breakdown that occurs at physiological pH and temperature. It is also metabolized by **non-specific ester hydrolysis** (by carboxylic ester hydrolases). Because it does not rely on renal or hepatic clearance for its termination of action, it is the **drug of choice for patients with liver or kidney failure.** **Analysis of Incorrect Options:** * **A. Conjugation:** This is a Phase II metabolic reaction (e.g., glucuronidation) common for drugs like morphine but not involved in atracurium metabolism. * **C. Pseudocholinesterase:** This enzyme metabolizes **Succinylcholine** and **Mivacurium**. While atracurium is an ester, it is *not* metabolized by pseudocholinesterase. * **D. Methylation:** This is a minor metabolic pathway for certain catecholamines and drugs, not applicable to neuromuscular blockers. **High-Yield Clinical Pearls for NEET-PG:** 1. **Laudanosine Toxicity:** The major metabolite of Hoffman degradation is **laudanosine**. It can cross the blood-brain barrier and act as a CNS stimulant, potentially causing **seizures** (especially during prolonged infusions in ICU). 2. **Temperature/pH Sensitivity:** Since Hoffman degradation is temperature and pH-dependent, the drug's duration of action is **prolonged in hypothermia and acidosis**. 3. **Histamine Release:** Atracurium can cause significant histamine release, leading to flushing, hypotension, and bronchospasm. 4. **Cisatracurium:** An isomer of atracurium that also undergoes Hoffman degradation but is more potent, produces less laudanosine, and does **not** cause histamine release.

Question 47: Which of the following muscles is affected first by a neuromuscular blocker?

A. Face
B. Proximal limb
C. Diaphragm and vocal cords (Correct Answer)
D. Distal limb

Explanation: The sequence of muscle paralysis during the administration of neuromuscular blocking agents (NMBAs) follows a predictable pattern based on muscle size, blood flow, and fiber type. **Explanation of the Correct Answer:** The **diaphragm and vocal cords** are among the **first** muscles to be paralyzed (along with the extraocular muscles). This occurs because these muscles have a very high density of nicotinic acetylcholine receptors and, more importantly, receive a **higher blood flow** per gram of tissue compared to peripheral muscles. This allows the NMBA to reach the neuromuscular junctions of the central muscles faster and in higher concentrations initially. **Analysis of Incorrect Options:** * **A. Face:** Facial muscles are affected after the diaphragm but before the limbs. * **B & D. Proximal and Distal Limbs:** Peripheral muscles (limbs) are more resistant and are affected **later** in the sequence. The general rule is that paralysis moves from the center (eyes/diaphragm) to the periphery (fingers/toes). **High-Yield Clinical Pearls for NEET-PG:** 1. **Sequence of Paralysis:** Small, rapidly moving muscles (Eyes) → Central muscles (Diaphragm/Larynx) → Large peripheral muscles (Trunk/Limbs) → Small distal muscles. 2. **Sequence of Recovery:** This is the **exact reverse** of paralysis. The diaphragm is the first to be paralyzed but also the **first to recover**. The last muscle to recover is typically the adductor pollicis (thumb). 3. **Monitoring Tip:** To monitor **onset** (intubation readiness), the orbicularis oculi (facial nerve) is preferred as it reflects the diaphragm. To monitor **recovery** (extubation readiness), the adductor pollicis (ulnar nerve) is used as it is the last to recover.

Question 48: Which anesthetic agent is explosive in the presence of cautery?

A. Nitrous Oxide
B. Ether (Correct Answer)
C. Trilene
D. Halothane

Explanation: **Explanation:** The correct answer is **Ether (Diethyl Ether)**. **1. Why Ether is the Correct Answer:** Ether is a highly volatile liquid that produces vapors heavier than air. Its chemical structure makes it extremely **flammable and explosive** when mixed with air, oxygen, or nitrous oxide. In the presence of an ignition source, such as **electrocautery** or static electricity in the operating theater, it can lead to devastating fires or explosions. Due to this significant safety hazard, its use has been entirely phased out in modern anesthetic practice in favor of non-flammable fluorinated hydrocarbons. **2. Analysis of Incorrect Options:** * **Nitrous Oxide (A):** While it is a **supporter of combustion** (it can make an existing fire burn more intensely), it is not flammable or explosive by itself. * **Trilene (C):** Trichloroethylene is non-flammable at clinical concentrations. However, it is contraindicated in closed circuits because it reacts with soda lime to form toxic products like phosgene and cranial nerve toxins (e.g., heat-induced decomposition). * **Halothane (D):** Halothane is a halogenated hydrocarbon designed specifically to be **non-flammable and non-explosive**, which was its primary advantage over ether when it was introduced. **3. High-Yield Clinical Pearls for NEET-PG:** * **Modern Volatile Agents:** All current agents (Isoflurane, Sevoflurane, Desflurane) are non-flammable. * **Cyclopropane:** Another historical agent (not listed here) that is even more explosive than ether. * **Fire Triad:** Surgical fires require an oxidizer (O2/N2O), an ignition source (Cautery/Laser), and fuel (Drapes/Alcohol-based preps). * **Ether Day:** October 16, 1846 (First public demonstration by W.T.G. Morton).

Question 49: Which muscle relaxant is the drug of choice in a patient with renal failure?

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

Explanation: **Explanation:** The drug of choice for muscle relaxation in patients with renal failure is **Atracurium** (or its isomer, Cisatracurium). **Why Atracurium is correct:** Most neuromuscular blocking agents rely on hepatic metabolism or renal excretion for elimination. In renal failure, these drugs can accumulate, leading to prolonged paralysis. Atracurium is unique because it undergoes **Hofmann Elimination**—a spontaneous, non-enzymatic degradation at physiological pH and temperature—and ester hydrolysis by non-specific plasma esterases. Since its clearance is independent of kidney or liver function, its duration of action remains predictable even in end-stage renal disease. **Analysis of Incorrect Options:** * **Rocuronium:** Primarily eliminated by the liver (70%) but significantly excreted by the kidneys (30%). Its duration of action is prolonged in renal failure. * **Vecuronium:** Highly dependent on both biliary and renal excretion. It has an active metabolite (3-desacetyl vecuronium) that can accumulate in renal failure, causing prolonged blockade. * **Rapacuronium:** A rapid-onset agent that was withdrawn from the market due to severe side effects (bronchospasm) and is not a preferred choice. **High-Yield Clinical Pearls for NEET-PG:** * **Cisatracurium** is more potent than Atracurium and is often preferred because it produces less **Laudanosine** (a metabolite of Atracurium that can cause seizures at high levels) and does not cause histamine release. * **Drug of choice for RSI in Renal Failure:** Succinylcholine (provided potassium levels are <5.5 mEq/L). If hyperkalemic, Rocuronium is used. * **Hofmann Elimination** is dependent on **pH and Temperature**. Acidosis and hypothermia slow down the degradation, prolonging the drug's effect.

Question 50: Which of the following intravenous anesthetic agents is considered the most immunogenically safe?

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

Explanation: **Explanation:** The correct answer is **Etomidate**. Immunogenic safety in intravenous anesthetics refers to the drug’s potential to trigger histamine release or anaphylactoid reactions. **Why Etomidate is the Correct Answer:** Etomidate is a carboxylated imidazole derivative. It is uniquely characterized by its **lack of histamine release**, making it the most immunogenically safe agent among the options. Clinically, this makes it a preferred choice for patients with reactive airway disease (asthma) or those with a high risk of allergic sensitivity. Additionally, its hemodynamic stability (minimal effect on heart rate and blood pressure) makes it the gold standard for induction in patients with cardiovascular compromise. **Analysis of Incorrect Options:** * **Thiopentone:** This is the most common IV anesthetic associated with true anaphylaxis and significant dose-dependent histamine release. It is strictly contraindicated in patients with porphyria and should be used with caution in asthmatics. * **Propofol:** While generally safe, propofol is formulated in an emulsion containing soybean oil and egg lecithin. It can trigger allergic reactions in susceptible individuals and has been known to cause rare but documented anaphylaxis. * **Ketamine:** Although ketamine is a bronchodilator, it can occasionally cause mild histamine release and increased secretions, making it less "immunogenically inert" than etomidate. **NEET-PG High-Yield Pearls:** * **Etomidate Side Effect:** Its most significant drawback is **adrenocortical suppression** (inhibits 11-beta-hydroxylase), which can last for 24 hours after a single dose. * **Drug of Choice:** Etomidate is the drug of choice for **cardiac induction** and **ECT** (due to its minimal effect on seizure threshold). * **Thiopentone:** Known for its "garlic/onion" taste during induction and its role as a potent cerebral protectant.

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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