General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 171: Laudanosine is a metabolite of which of the following drugs?

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

Explanation: **Explanation:** **Atracurium** is a benzylisoquinolinium neuromuscular blocking agent that undergoes unique metabolism via **Hofmann elimination** (a non-enzymatic degradation occurring at physiological pH and temperature) and ester hydrolysis. **Laudanosine** is the primary tertiary amine metabolite produced during this process. * **Why Option A is correct:** Atracurium produces significant amounts of laudanosine. Because laudanosine is metabolized by the liver and excreted in the urine, it can accumulate during prolonged infusions. * **Why Option B is incorrect:** While **Cis-atracurium** (the R-cis isomer of atracurium) also produces laudanosine via Hofmann elimination, it is **3–5 times more potent** than atracurium. Therefore, much smaller doses are required to achieve the same clinical effect, resulting in negligible levels of laudanosine that are clinically insignificant. * **Why Options C & D are incorrect:** **Pancuronium** and **Vecuronium** are aminosteroid compounds. They do not undergo Hofmann elimination and do not produce laudanosine. They are primarily cleared by hepatic metabolism and renal excretion. **Clinical Pearls for NEET-PG:** 1. **CNS Toxicity:** Laudanosine is a known **CNS stimulant**. In high concentrations (rare in routine clinical practice but possible in ICU settings), it can cross the blood-brain barrier and potentially cause **seizures**. 2. **Organ Independence:** Because atracurium relies on Hofmann elimination, it is the drug of choice (along with Cis-atracurium) for patients with **renal or hepatic failure**. 3. **Histamine Release:** Unlike Cis-atracurium, Atracurium can cause histamine release, leading to hypotension and flushing.

Question 172: Which of the following general anesthetics is administered intravenously?

A. Propofol (Correct Answer)
B. Sevoflurane
C. Naloxone
D. Flumazenil

Explanation: **Explanation:** The question asks to identify a general anesthetic administered via the intravenous (IV) route. **Correct Option: A. Propofol** Propofol is the most commonly used **intravenous induction agent** in modern anesthesia. It is a substituted isopropylphenol that works primarily by enhancing GABA-A receptor activity. It is preferred for its rapid onset (one arm-brain circulation time) and rapid recovery (due to redistribution and high clearance), making it the drug of choice for Day Care Surgery. **Why other options are incorrect:** * **B. Sevoflurane:** This is an **inhalational anesthetic** (volatile liquid). It is administered via a vaporizer and is the agent of choice for mask induction in pediatric patients due to its non-pungent odor and low airway irritability. * **C. Naloxone:** This is a **competitive opioid antagonist** used to reverse respiratory depression caused by opioid overdose. It is not an anesthetic agent. * **D. Flumazenil:** This is a **specific benzodiazepine antagonist**. It is used to reverse the sedative effects of drugs like Midazolam or Diazepam but does not possess anesthetic properties itself. **High-Yield Clinical Pearls for NEET-PG:** * **Propofol** is known as the "Milk of Amnesia" due to its white, milky emulsion (contains egg lecithin and soybean oil). * **Drug of choice** for: Induction of anesthesia, Total Intravenous Anesthesia (TIVA), and sedation in the ICU. * **Side Effects:** It causes significant hypotension (vasodilation) and pain on injection. * **Anti-emetic property:** Unlike inhalational agents, Propofol has inherent anti-emetic properties, reducing Post-Operative Nausea and Vomiting (PONV).

Question 173: A 40-year-old dental assistant presents with increased weakness and fatigue. Lab tests reveal megaloblastic anemia. Which of the following is most likely responsible for the presence of this anemia?

A. Propofol
B. Nitrous oxide (Correct Answer)
C. Lignocaine
D. Halothane

Explanation: **Explanation:** The correct answer is **Nitrous oxide (N₂O)**. The clinical presentation of megaloblastic anemia in a dental assistant—who has chronic occupational exposure to anesthetic gases—is a classic scenario for Nitrous oxide toxicity. **Mechanism of Action:** Nitrous oxide irreversibly oxidizes the cobalt atom of **Vitamin B12 (cobalamin)** from the monovalent (Co+) to the bivalent (Co++) state. This inactivation inhibits the enzyme **Methionine Synthase**, which is essential for converting homocysteine to methionine. This process is critical for DNA synthesis; its inhibition leads to impaired erythropoiesis, resulting in **megaloblastic anemia** and, in severe cases, subacute combined degeneration of the spinal cord. **Why other options are incorrect:** * **Propofol:** An intravenous sedative-hypnotic that acts via GABA-A receptors. It is associated with "Propofol Infusion Syndrome" (acidosis, rhabdomyolysis) but does not affect Vitamin B12 or DNA synthesis. * **Lignocaine:** An amide-type local anesthetic that blocks sodium channels. Toxicity typically involves CNS (seizures) and CVS (arrhythmias) effects, not hematological changes. * **Halothane:** An inhaled volatile anesthetic primarily associated with hepatotoxicity ("Halothane Hepatitis") due to the formation of trifluoroacetylated liver proteins. **High-Yield Clinical Pearls for NEET-PG:** * **Enzyme Inhibited:** Methionine Synthase. * **Occupational Hazard:** Most common in dental surgeons and operating room personnel without adequate scavenging systems. * **Bone Marrow Changes:** Acute exposure (e.g., prolonged sedation in ICU) can cause megaloblastic changes within 12–24 hours. * **Contraindication:** Avoid N₂O in patients with pre-existing Vitamin B12 deficiency or pernicious anemia.

Question 174: All of the following are pharmacological effects of ketamine, EXCEPT?

A. Profound analgesia
B. Severe fall in blood pressure (Correct Answer)
C. Amnesia
D. Increased cerebral blood flow

Explanation: **Explanation:** Ketamine is a unique intravenous anesthetic agent that acts primarily as an **NMDA receptor antagonist**. It produces a state known as **"Dissociative Anesthesia,"** characterized by a functional dissociation between the thalamocortical and limbic systems. **Why Option B is the Correct Answer:** Unlike most induction agents (like propofol or thiopentone) which cause myocardial depression and vasodilation, Ketamine is a **sympathomimetic**. It inhibits the reuptake of catecholamines (norepinephrine), leading to an **increase in blood pressure (hypertension)**, heart rate, and cardiac output. Therefore, a "severe fall in blood pressure" is pharmacologically incorrect. **Analysis of Other Options:** * **A. Profound Analgesia:** Ketamine provides excellent somatic analgesia even at sub-anesthetic doses, making it ideal for short painful procedures and burn dressings. * **C. Amnesia:** While patients may appear awake (eyes open, slow nystagmic gaze), they experience significant anterograde amnesia and lack of awareness of the procedure. * **D. Increased Cerebral Blood Flow (CBF):** Ketamine is a potent cerebral vasodilator. It increases CBF, cerebral metabolic rate ($CMRO_2$), and consequently, **Intracranial Pressure (ICP)**. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** For induction in patients with **hypovolemic shock** or **bronchial asthma** (due to its bronchodilatory effects). * **Contraindications:** Head injuries (due to $\uparrow$ ICP), Hypertensive emergencies, and Ischemic heart disease. * **Side Effects:** **Emergence delirium** and hallucinations (minimized by co-administering benzodiazepines like Midazolam). * **Reflexes:** Pharyngeal and laryngeal reflexes are usually **preserved**, though the airway is not always fully protected.

Question 175: Which drug is not suitable for intravenous induction in patients with acute porphyria?

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

Explanation: **Explanation:** The correct answer is **Thiopentone sodium**. **1. Why Thiopentone is Contraindicated:** Acute Porphyrias (such as Acute Intermittent Porphyria) are metabolic disorders characterized by a deficiency in enzymes of the heme synthesis pathway. **Thiopentone sodium** (a barbiturate) is a potent inducer of the enzyme **ALA synthetase**. By inducing this enzyme, it increases the production of porphyrin precursors (ALA and PBG), which can precipitate a life-threatening acute porphyric crisis. This crisis manifests as severe abdominal pain, neuropsychiatric symptoms, and autonomic instability. **2. Analysis of Other Options:** * **Propofol (B):** Currently considered the induction agent of choice in porphyria. While historically debated, extensive clinical use has proven it to be safe. * **Midazolam (C):** Benzodiazepines are generally considered safe for use in patients with porphyria. * **Etomidate (D):** While some sources list etomidate as potentially porphyrinogenic in animal models, it is clinically considered a safer alternative than barbiturates when hemodynamic stability is required. **3. High-Yield Clinical Pearls for NEET-PG:** * **Safe Induction Agents:** Propofol, Ketamine (usually considered safe). * **Safe Muscle Relaxants:** Succinylcholine, Vecuronium, Atracurium. * **Safe Analgesics:** Morphine, Fentanyl. * **Absolute Contraindications:** Barbiturates (Thiopentone, Methohexital), Etomidate (relative/avoid if possible), and Pentazocine. * **Management of Crisis:** The mainstay of treatment for an acute attack is **Intravenous Hematin** (which inhibits ALA synthetase via negative feedback) and high-dose glucose infusion.

Question 176: Which of the following neurophysiological responses is least affected by anesthesia?

A. Brainstem Auditory Evoked Response (BAER) (Correct Answer)
B. Visual Evoked Response (VER)
C. Somatosensory Evoked Potential (SSEP)
D. Electroencephalogram (EEG)

Explanation: **Explanation:** The correct answer is **Brainstem Auditory Evoked Response (BAER)**. **Why BAER is the correct answer:** Evoked potentials (EPs) measure the electrical response of the nervous system to external stimuli. The sensitivity of these potentials to anesthetic agents is generally determined by the complexity of the neural pathway and the number of synapses involved. **BAER** monitors the auditory pathway from the cochlear nerve to the brainstem. Because it involves the brainstem—a primitive, robust structure—it is **highly resistant** to almost all anesthetic agents (including volatile anesthetics and IV agents). This makes it the most reliable monitor during surgery, as it remains stable even under deep anesthesia. **Why the other options are incorrect:** * **Visual Evoked Response (VER):** These are the **most sensitive** to anesthetic agents. They involve complex cortical pathways and are easily abolished by even low concentrations of volatile anesthetics. * **Somatosensory Evoked Potential (SSEP):** These are moderately affected. While they can be used intraoperatively, they are sensitive to halogenated inhalational agents and bolus doses of IV anesthetics, which decrease amplitude and increase latency. * **Electroencephalogram (EEG):** The EEG reflects global cortical activity and is profoundly altered by anesthesia. Anesthetics typically cause a dose-dependent shift from high-frequency/low-voltage patterns to low-frequency/high-voltage patterns (and eventually burst suppression). **High-Yield Clinical Pearls for NEET-PG:** * **Hierarchy of Sensitivity:** VER (Most sensitive) > SSEP > BAER (Least sensitive/Most resistant). * **Etomidate & Ketamine Exception:** Unlike most anesthetics that depress EPs, Etomidate and Ketamine can actually **increase** the amplitude of SSEPs. * **Standard Rule:** Inhalational agents (especially Nitrous Oxide) generally decrease amplitude and increase latency of EPs. * **BAER** is primarily used to monitor the 8th cranial nerve during acoustic neuroma surgery.

Question 177: All are true regarding Xenon anesthesia except?

A. Slow induction and recovery (Correct Answer)
B. Non explosive
C. Minimal cardiovascular side-effects
D. Low blood solubility

Explanation: **Explanation:** Xenon is an inert gas that acts as an ideal anesthetic agent in many respects. The correct answer is **A (Slow induction and recovery)** because Xenon actually provides **rapid** induction and recovery, making the statement in the option false. **1. Why Option A is the correct answer (The False Statement):** The speed of induction and recovery of an inhalational anesthetic is inversely proportional to its **Blood-Gas Partition Coefficient**. Xenon has an extremely low blood-gas partition coefficient (**0.115**), which is lower than Desflurane (0.42) and Nitrous Oxide (0.47). This low solubility ensures that the alveolar concentration rises rapidly, leading to very fast induction and an equally rapid emergence once the gas is discontinued. **2. Analysis of Incorrect Options (True Statements):** * **Option B (Non-explosive):** Xenon is an inert noble gas. It is non-flammable, non-explosive, and environmentally friendly (no greenhouse effect). * **Option C (Minimal cardiovascular side-effects):** One of Xenon's greatest clinical advantages is its **hemodynamic stability**. It does not cause myocardial depression or significant changes in heart rate or blood pressure, making it ideal for high-risk cardiac patients. * **Option D (Low blood solubility):** As mentioned, its coefficient of 0.115 is the lowest among current anesthetic gases, which is the physiological basis for its rapid kinetics. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Primarily acts via **NMDA receptor antagonism** (unlike most volatile agents that act on GABA). * **Potency:** It has a **MAC of 63–71%**, making it less potent than volatile liquids but more potent than Nitrous Oxide (MAC 104%). * **Neuroprotection:** Xenon is known to have neuroprotective properties. * **Limitation:** Its main drawback is the **high cost** of extraction from the atmosphere, requiring closed-circuit delivery systems with recycling.

Question 178: Which of the following volatile anesthetics interacts with non-depolarizing neuromuscular-blocking drugs?

A. Isoflurane
B. Desflurane
C. Sevoflurane
D. All of the above (Correct Answer)

Explanation: **Explanation:** The correct answer is **D. All of the above.** **Underlying Medical Concept:** All potent volatile anesthetic agents (Inhalational Anesthetics) produce a dose-dependent **potentiation** of the effects of non-depolarizing neuromuscular-blocking drugs (NMBDs) like Vecuronium, Rocuronium, and Atracurium. This interaction occurs through several mechanisms: 1. **Post-junctional effect:** They decrease the sensitivity of the post-junctional nicotinic acetylcholine receptors to depolarization. 2. **Central effect:** They inhibit alpha-motor neurons in the spinal cord, leading to generalized muscle relaxation. 3. **Increased Muscle Blood Flow:** They cause peripheral vasodilation, which increases the delivery of NMBDs to the neuromuscular junction. **Analysis of Options:** * **A, B, and C:** Isoflurane, Desflurane, and Sevoflurane all significantly potentiate NMBDs. While the degree of potentiation varies slightly (Desflurane > Sevoflurane > Isoflurane > Halothane), all three are clinically significant. Therefore, selecting any single agent would be incomplete. **High-Yield Clinical Pearls for NEET-PG:** * **Potency Order:** The degree of NMBD potentiation follows the order: **Desflurane > Sevoflurane > Isoflurane > Halothane > Nitrous Oxide (N₂O).** Note that N₂O has minimal to no effect on NMBDs. * **Clinical Implication:** When using volatile agents, the dose of the NMBD should be reduced (by approximately 25–50%) to achieve the same level of blockade and to avoid prolonged recovery. * **Monitoring:** Quantitative neuromuscular monitoring (Train-of-Four) is essential when combining these agents to ensure safe reversal.

Question 179: Diffusion hypoxia is seen during which phase of anesthesia?

A. Induction of anesthesia
B. Recovery from anesthesia (Correct Answer)
C. Preoperative period
D. Postoperative period

Explanation: **Explanation:** **Diffusion Hypoxia (The Fink Effect)** occurs due to the rapid movement of **Nitrous Oxide ($N_2O$)** from the blood back into the alveoli once the gas is discontinued. 1. **Why "Recovery from anesthesia" is correct:** $N_2O$ is highly insoluble in blood but is administered in high concentrations (up to 70%). At the end of surgery (recovery phase), when the patient starts breathing room air, the large volume of $N_2O$ dissolved in the blood rushes into the alveoli. This "flooding" of the alveoli dilutes the concentration of Oxygen ($O_2$) and Carbon Dioxide ($CO_2$). The drop in $PAO_2$ leads to hypoxia, while the drop in $PACO_2$ reduces the respiratory drive, worsening the condition. 2. **Why other options are incorrect:** * **Induction:** During induction, the "Second Gas Effect" occurs, where the rapid uptake of $N_2O$ *increases* the concentration of the co-administered volatile anesthetic. * **Preoperative/Postoperative:** These periods refer to times before the administration or long after the elimination of anesthetic gases, where $N_2O$ kinetics are not applicable. **High-Yield NEET-PG Pearls:** * **Prevention:** To prevent diffusion hypoxia, the patient should be administered **100% Oxygen for 5–10 minutes** after $N_2O$ is discontinued. * **Concentration Effect:** This is the counterpart to diffusion hypoxia, occurring during induction where high concentrations of a gas accelerate its own uptake. * **Second Gas Effect:** $N_2O$ (the first gas) speeds up the onset of a more potent anesthetic (the second gas, e.g., Halothane) during induction.

Question 180: Which of the following anesthetic agents is known to cause respiratory irritation?

A. Ether
B. Halothane
C. Trichloroethylene (Correct Answer)
D. Cyclopropane

Explanation: **Explanation:** The correct answer is **Trichloroethylene (Trilene)**. **1. Why Trichloroethylene is correct:** Trichloroethylene is a potent analgesic but a poor anesthetic agent. It is highly irritating to the respiratory tract, which can lead to tachypnea (rapid shallow breathing) and potential cardiac arrhythmias. Most importantly, for NEET-PG purposes, it is known to react with **soda lime** (used in closed-circuit CO2 absorbers) to form toxic products like **dichloroacetylene** and **phosgene**, which are neurotoxic and can cause cranial nerve palsies (especially the trigeminal nerve). **2. Why the other options are incorrect:** * **Ether:** While Diethyl ether is an irritant to the airways and causes significant secretions, it was historically used for induction. However, in the context of specific "respiratory irritation" leading to rapid, irregular breathing patterns and its chemical instability compared to Trilene, Trilene is the classic textbook answer for this specific side effect profile. * **Halothane:** Halothane is actually a **bronchodilator** and is non-irritant to the respiratory tract. It was traditionally the agent of choice for smooth inhalational induction in pediatric patients. * **Cyclopropane:** This is a sweet-smelling, non-irritant gas. Its primary concerns are its extreme flammability and its tendency to sensitize the myocardium to catecholamines. **High-Yield Clinical Pearls for NEET-PG:** * **Agent of choice for smooth induction:** Sevoflurane (least irritant). * **Most irritant volatile anesthetic:** Desflurane (causes coughing/laryngospasm during induction). * **Trichloroethylene + Soda Lime:** Produces Dichloroacetylene (Neurotoxic). * **Halothane:** Can cause "Halothane Hepatitis" and sensitizes the heart to adrenaline.

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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