General Anesthesia — MCQs

A 42-year-old woman presents for laparoscopic gastric bypass. She weighs 191 kg and is 165 cm tall. She has a history of hypertension, diabetes mellitus, obstructive sleep apnea, and acid reflux. Because of the sleep apnea, there is concern about mild pulmonary hypertension. Which of the following agents is most likely to produce the most rapid emergence in this patient?

Q76Medium

Which of the following statements is NOT TRUE regarding sevoflurane?

Q77Easy

Which anesthetic agent acts via NMDA receptors?

Q78Medium

Which statement is false regarding halothane?

Q79Medium

What is the most suitable agent for intravenous induction and maintenance in day care surgery?

Q80Medium

All of the following are true about the effect of propofol on the respiratory system EXCEPT:

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 71: What is the second gas effect?

A. Displacement of nitrous oxide by oxygen
B. Displacement of oxygen by nitrous oxide
C. Removal of oxygen by nitrous oxide from alveoli during recovery from general anaesthesia
D. Facilitation of inhalation of halothane by nitrous oxide (Correct Answer)

Explanation: ### Explanation The **Second Gas Effect** is a phenomenon where the rapid uptake of a high-volume gas (the "first gas") accelerates the increase in alveolar concentration of a concurrently administered potent volatile anesthetic (the "second gas"). **1. Why the correct answer is right:** When **Nitrous Oxide ($N_2O$)** is administered in high concentrations (e.g., 70%), it is rapidly absorbed from the alveoli into the pulmonary capillaries. This rapid removal of $N_2O$ leads to two things: * **Concentrating Effect:** The volume of the alveoli shrinks, concentrating the remaining gases (like Halothane). * **Increased Inspiratory Flow:** A transient negative pressure is created, drawing in more fresh gas from the breathing circuit into the alveoli. Both mechanisms result in a faster rise in the alveolar concentration ($F_A/F_I$ ratio) of the second gas (Halothane), leading to a **faster induction of anesthesia**. **2. Why the incorrect options are wrong:** * **Options A & B:** These describe simple displacement or dilution, which does not account for the synergistic uptake mechanism of the second gas effect. * **Option C:** This describes **Diffusion Hypoxia** (Fink Effect). This occurs during *recovery* when $N_2O$ rapidly leaves the blood and enters the alveoli, diluting oxygen and causing transient hypoxia. The Second Gas Effect occurs during *induction*. **3. Clinical Pearls for NEET-PG:** * **First Gas:** Usually $N_2O$ (due to its low blood-gas solubility and high administered concentration). * **Second Gas:** Any volatile anesthetic (Halothane, Isoflurane, Sevoflurane). * **Concentration Effect:** This is the precursor to the second gas effect; it refers to the first gas accelerating its own uptake. * **Key Concept:** The Second Gas Effect reduces the induction time.

Question 72: The hypothesis 'Greater the lipid solubility of a compound, the greater is its anesthetic potency' is referred to as?

A. Meyer-Overton rule (Correct Answer)
B. Pressure reversal rule
C. Critical volume hypothesis
D. Lipid bilayer expansion hypothesis

Explanation: ### Explanation **1. Why Meyer-Overton Rule is Correct:** The **Meyer-Overton rule** (or hypothesis) states that the anesthetic potency of an inhalation agent is directly proportional to its **lipid solubility** (oil:gas partition coefficient). * **Mechanism:** It suggests that anesthesia occurs when a sufficient number of molecules dissolve in the lipid bilayer of neuronal membranes, disrupting their function. * **Clinical Correlation:** Potency is measured by **MAC (Minimum Alveolar Concentration)**. According to this rule, **Potency ∝ 1/MAC**. Therefore, a drug with high lipid solubility (e.g., Halothane) has a low MAC and high potency. **2. Analysis of Incorrect Options:** * **B. Pressure reversal rule:** This refers to the phenomenon where the effects of anesthesia can be reversed by applying high hydrostatic pressure (approx. 100-200 atm). It suggests that anesthetics act by increasing volume, which pressure then counteracts. * **C. Critical volume hypothesis:** A subset of the lipid theory, it posits that anesthesia occurs when the absorption of anesthetic molecules expands the volume of the hydrophobic part of the cell membrane beyond a "critical" limit, thereby obstructing ion channels. * **D. Lipid bilayer expansion hypothesis:** Similar to the critical volume hypothesis, it focuses on the physical expansion/thickening of the membrane rather than the specific chemical solubility relationship defined by Meyer and Overton. **3. High-Yield Clinical Pearls for NEET-PG:** * **Exceptions to the Rule:** "Non-immobilizers" (e.g., flurothyl) are lipid-soluble but do not produce anesthesia; conversely, some potent anesthetics do not follow the solubility curve perfectly. This led to the shift toward the **Protein Theory** (GABA-A receptor modulation). * **MAC and Potency:** Remember the inverse relationship. **Halothane** (High lipid solubility = Low MAC = High Potency) vs. **Nitrous Oxide** (Low lipid solubility = High MAC = Low Potency). * **Oil:Gas Coefficient:** This is the best predictor of anesthetic **potency**, whereas the Blood:Gas coefficient predicts the **speed** of induction and recovery.

Question 73: During induction of general anesthesia, the administration of oxygen with a high concentration of nitrous oxide and halothane hastens the uptake of halothane. This phenomenon is known as what?

A. Fink effect
B. Concentration effect
C. Second gas effect (Correct Answer)
D. Third gas effect

Explanation: ### Explanation **Correct Answer: C. Second gas effect** The **Second gas effect** is a phenomenon where the rapid uptake of a high-volume primary gas (usually Nitrous Oxide, $N_2O$) accelerates the uptake of a concurrently administered "second gas" (like Halothane or Isoflurane). **Mechanism:** 1. $N_2O$ is 34 times more soluble in blood than Nitrogen. When high concentrations (e.g., 70%) are inhaled, $N_2O$ leaves the alveoli and enters the blood very rapidly. 2. This rapid exit of $N_2O$ creates a "vacuum" effect, shrinking the total alveolar volume. 3. This leads to an increased relative concentration of the remaining gases (the second gas/Halothane) and a fresh influx of gas into the alveoli to replace the lost volume. 4. Consequently, the alveolar partial pressure of the second gas rises faster, leading to a quicker induction of anesthesia. --- ### Analysis of Incorrect Options: * **A. Fink effect (Diffusion Hypoxia):** This is the reverse of the second gas effect. It occurs during **recovery** when $N_2O$ rapidly diffuses from the blood back into the alveoli, diluting oxygen and $CO_2$, potentially leading to hypoxia. * **B. Concentration effect:** This refers to the phenomenon where the higher the concentration of an inhaled anesthetic administered (e.g., $N_2O$ itself), the faster its own alveolar concentration approaches the inspired concentration. It applies to the gas itself, not a secondary agent. * **D. Third gas effect:** This is a distractor term and is not a recognized physiological principle in anesthesia. --- ### High-Yield Clinical Pearls for NEET-PG: * **Solubility:** The speed of induction is inversely proportional to the blood-gas partition coefficient. (Lower solubility = Faster induction). * **$N_2O$ Properties:** It is a sweet-smelling, non-flammable gas with a high MAC (104%), meaning it cannot produce surgical anesthesia alone at atmospheric pressure. * **Contraindication:** $N_2O$ should be avoided in closed-space pathologies (e.g., pneumothorax, intestinal obstruction, middle ear surgery) because it diffuses into air-filled cavities faster than nitrogen can leave, increasing pressure or volume.

Question 74: Thiopental sodium is administered intravenously as which concentration?

A. 25% solution
B. 2.5% solution (Correct Answer)
C. 0.25% solution
D. 0.025% solution

Explanation: **Explanation:** **Thiopental Sodium** is a short-acting barbiturate used for the induction of general anesthesia. The standard concentration for intravenous administration is **2.5% (Option B)**. **Why 2.5% is the Correct Choice:** * **Safety and Efficacy:** A 2.5% solution provides a rapid onset of action (within 30–45 seconds) while maintaining a pH of approximately 10.5. This concentration is high enough to induce anesthesia with a small volume of fluid but dilute enough to minimize the risk of severe tissue damage if accidental extravasation occurs. * **Calculation:** A 2.5% solution contains **25 mg/mL**. For a standard induction dose (3–5 mg/kg), an average adult requires roughly 10–20 mL of this solution. **Why Other Options are Incorrect:** * **25% (Option A):** This is extremely hypertonic and highly alkaline. Accidental intra-arterial injection or extravasation of such a high concentration would cause immediate, catastrophic tissue necrosis, gangrene, and permanent nerve damage. * **0.25% and 0.025% (Options C & D):** These concentrations are too dilute for induction. They would require a massive volume of fluid to achieve the necessary dose, leading to delayed induction and potential fluid overload. **High-Yield Clinical Pearls for NEET-PG:** 1. **Preparation:** Thiopental is stored as a yellow hygroscopic powder under nitrogen; it is reconstituted with sterile water or normal saline. 2. **pH and Compatibility:** Due to its high alkalinity (pH 10.5), it is incompatible with acidic drugs (e.g., Succinylcholine, Vecuronium) and will precipitate if mixed in the same syringe. 3. **Intra-arterial Injection Management:** If accidentally injected into an artery, it causes intense vasoconstriction and crystal formation. Management includes: leaving the needle in situ, injecting vasodilators (Papaverine or Lidocaine), and performing a sympathetic block (Stellate ganglion block). 4. **Context:** While Propofol has largely replaced it, Thiopental remains a classic "gold standard" for rapid sequence induction and neuroprotection (decreases CMRO2 and ICP).

Question 75: A 42-year-old woman presents for laparoscopic gastric bypass. She weighs 191 kg and is 165 cm tall. She has a history of hypertension, diabetes mellitus, obstructive sleep apnea, and acid reflux. Because of the sleep apnea, there is concern about mild pulmonary hypertension. Which of the following agents is most likely to produce the most rapid emergence in this patient?

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

Explanation: ### Explanation The correct answer is **Desflurane**. **1. Why Desflurane is correct:** The patient in this scenario is morbidly obese (BMI ≈ 70 kg/m²). In obese patients, volatile anesthetics tend to accumulate in the extensive adipose tissue, which acts as a reservoir. The speed of emergence depends on the **Blood-Gas Partition Coefficient** (solubility). Desflurane has the lowest blood-gas partition coefficient (0.42) among the potent volatile agents. Because it is highly insoluble, very little of the drug is sequestered in the fat stores, allowing for rapid washout and the most predictable, rapid emergence regardless of the duration of surgery. **2. Why other options are incorrect:** * **Isoflurane:** It has a high blood-gas partition coefficient (1.4). It is highly soluble in blood and tissues, leading to significant accumulation and prolonged recovery in obese patients. * **Sevoflurane:** While more rapid than isoflurane (coefficient 0.65), it is still more soluble than desflurane. Studies consistently show that desflurane provides a faster recovery of airway reflexes and cognitive function in the morbidly obese. * **Nitrous Oxide:** Although it has a lower partition coefficient (0.47) than sevoflurane, it cannot be used as a sole maintenance agent due to its high MAC (104%). Furthermore, it is often avoided in laparoscopic gastric bypass because it can diffuse into the bowel, causing **bowel distension**, which technically hinders the surgeon. **3. Clinical Pearls for NEET-PG:** * **Solubility Rule:** Lower Blood-Gas Partition Coefficient = Faster Induction and Faster Recovery. * **Desflurane (0.42) < Sevoflurane (0.65) < Isoflurane (1.4) < Halothane (2.4).** * **Obesity & Anesthesia:** Desflurane is the volatile agent of choice for the morbidly obese to ensure rapid return of protective airway reflexes, which is critical in patients with OSA and acid reflux. * **Caution:** Desflurane is a known airway irritant and can cause coughing or laryngospasm during inhalation induction; it is primarily used for maintenance.

Question 76: Which of the following statements is NOT TRUE regarding sevoflurane?

A. Minimum alveolar concentration (MAC) is higher than isoflurane.
B. Blood gas partition coefficient is higher than desflurane.
C. Potency is more cardio depressant than isoflurane.
D. Sevoflurane is less cardio depressant than isoflurane. (Correct Answer)

Explanation: ### Explanation The question asks for the statement that is **NOT TRUE** regarding Sevoflurane. **1. Why Option D is the "Correct" (False) Statement:** In clinical practice, Sevoflurane and Isoflurane have comparable effects on myocardial contractility; however, **Isoflurane is generally considered more cardio-stable** because it maintains cardiac output better through a compensatory increase in heart rate. Sevoflurane does not cause the same degree of reflex tachycardia. Furthermore, Isoflurane is a more potent vasodilator. Therefore, stating Sevoflurane is "less cardio depressant" is technically inaccurate in a comparative pharmacological sense, making it the false statement among the choices. **2. Analysis of Other Options:** * **Option A (MAC):** The MAC of Sevoflurane is ~2%, while Isoflurane is ~1.15%. A higher MAC value indicates lower potency. Thus, this statement is **True**. * **Option B (Blood-Gas Partition Coefficient):** Sevoflurane has a coefficient of 0.65, whereas Desflurane is 0.42. A higher coefficient means Sevoflurane is more soluble in blood than Desflurane, leading to a slightly slower induction. This statement is **True**. * **Option C (Potency/Cardio-depression):** As established, Sevoflurane is less potent (higher MAC) than Isoflurane and exhibits significant myocardial depression similar to other halogenated ethers. This statement aligns with the pharmacological profile. **3. High-Yield NEET-PG Pearls:** * **Agent of Choice:** Sevoflurane is the preferred agent for **inhalational induction** in both pediatrics and adults because it is non-pungent and does not irritate the airways (unlike Desflurane/Isoflurane). * **Compound A:** Sevoflurane reacts with soda lime to produce Compound A, which is nephrotoxic in rats (though clinical significance in humans is debated). * **Metabolism:** It undergoes roughly 5-8% hepatic metabolism, releasing inorganic fluoride ions. * **Speed of Induction:** Desflurane (0.42) > Sevoflurane (0.65) > Isoflurane (1.4) > Halothane (2.4).

Question 77: Which anesthetic agent acts via NMDA receptors?

A. Xenon (Correct Answer)
B. Nitrous oxide
C. Succinylcholine
D. Etomidate

Explanation: **Explanation:** The correct answer is **Xenon (A)**. While most intravenous and volatile anesthetics primarily act by enhancing inhibitory GABA-A receptors, a specific group of agents works by inhibiting excitatory **N-methyl-D-aspartate (NMDA)** receptors. Xenon, an inert noble gas, is a potent and selective NMDA receptor antagonist. It competes with glycine at the glycine-binding site of the NMDA receptor, leading to neuronal hyperpolarization and anesthesia. **Analysis of Options:** * **Xenon:** Acts via NMDA antagonism. It is considered an "ideal anesthetic" due to its cardiovascular stability, rapid induction/recovery (low blood-gas partition coefficient), and neuroprotective properties. * **Nitrous Oxide:** While $N_2O$ also has NMDA antagonistic properties, Xenon is the more definitive answer in this context as its primary mechanism is strictly non-GABAergic. (Note: In some exams, both may be considered, but Xenon is the classic high-yield example for this mechanism). * **Succinylcholine:** This is a depolarizing neuromuscular blocker that acts on **nicotinic acetylcholine receptors (nAChR)** at the neuromuscular junction, not NMDA receptors. * **Etomidate:** This is an intravenous induction agent that acts primarily by modulating **GABA-A receptors**. It is known for cardiovascular stability but causes adrenocortical suppression. **High-Yield NEET-PG Pearls:** * **NMDA Antagonists in Anesthesia:** Ketamine (IV), Xenon (Inhalational), and Nitrous Oxide. * **Xenon Properties:** Blood-gas partition coefficient is 0.115 (lowest of all, allowing ultra-fast recovery). It is non-explosive, non-toxic, and environmentally friendly, but limited by high cost. * **GABA-A Agonists:** Propofol, Etomidate, Benzodiazepines, and Barbiturates.

Question 78: Which statement is false regarding halothane?

A. It has a pleasant smell.
B. It decreases vagal tone. (Correct Answer)
C. It sensitizes the myocardium to catecholamines.
D. It can cause postoperative hepatitis.

Explanation: **Explanation:** Halothane is a potent volatile anesthetic agent with a distinct pharmacological profile. The statement that it decreases vagal tone is **false**; in fact, halothane **increases vagal tone**, which often leads to **bradycardia**. This is a high-yield distinction compared to other agents like isoflurane or desflurane, which may cause reflex tachycardia. **Analysis of Options:** * **Option B (Correct):** Halothane stimulates the vagus nerve. This increased vagal activity, combined with its direct depressant effect on the SA node, results in bradycardia. Therefore, saying it "decreases" vagal tone is incorrect. * **Option A:** Halothane has a non-pungent, sweet, and pleasant smell. This makes it the agent of choice for **smooth inhalational induction**, especially in pediatric patients (though largely replaced by Sevoflurane). * **Option C:** Halothane sensitizes the myocardium to the arrhythmogenic effects of catecholamines (epinephrine). This increases the risk of ventricular arrhythmias if exogenous adrenaline is used during surgery. * **Option D:** Halothane is metabolized in the liver (up to 20%). Its metabolites can cause "Halothane Hepatitis" (Type II), an immune-mediated hepatotoxicity characterized by fever, jaundice, and hepatic necrosis. **NEET-PG High-Yield Pearls:** 1. **Blood-Gas Partition Coefficient:** 2.3 (Slow induction and recovery). 2. **Uterine Effect:** It is a potent uterine relaxant; hence, it is avoided in the third stage of labor as it can cause Postpartum Hemorrhage (PPH). 3. **Malignant Hyperthermia:** Like all volatile anesthetics, it is a known trigger. 4. **Preservative:** It is the only volatile anesthetic that requires a preservative (**Thymol**) to prevent decomposition by light.

Question 79: What is the most suitable agent for intravenous induction and maintenance in day care surgery?

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

Explanation: **Explanation:** **Propofol** is the gold standard for day-care (ambulatory) surgery due to its unique pharmacokinetic profile. The primary goal in day-care anesthesia is a rapid, smooth recovery with minimal side effects to allow early discharge. Propofol facilitates this through: 1. **Rapid Onset and Offset:** High lipid solubility allows quick induction, while rapid redistribution and high metabolic clearance ensure a "clear-headed" recovery without a "hangover" effect. 2. **Anti-emetic Properties:** It possesses intrinsic anti-emetic effects, significantly reducing Postoperative Nausea and Vomiting (PONV), which is the most common cause of delayed discharge. 3. **Suitability for TIVA:** It is the only agent among the options suitable for both induction and maintenance (Total Intravenous Anesthesia). **Why other options are incorrect:** * **Etomidate:** While cardiostable, it is associated with postoperative nausea, pain on injection, and **adrenocortical suppression**, making it less ideal for routine maintenance. * **Ketamine:** Causes "dissociative anesthesia" often followed by **emergence delirium**, hallucinations, and prolonged recovery times, which are undesirable in day-care settings. * **Thiopentone:** A barbiturate with a long elimination half-life due to accumulation in adipose tissue. It causes a "hangover" effect and lacks anti-emetic properties, leading to delayed psychomotor recovery. **Clinical Pearls for NEET-PG:** * **Drug of choice for TIVA:** Propofol. * **Drug of choice for Cardioversion/ECT:** Methohexital (Thiopentone is an alternative). * **Drug of choice for Induction in Shock:** Etomidate (Ketamine is an alternative if no tachycardia). * **Propofol Infusion Syndrome (PRIS):** Characterized by metabolic acidosis, rhabdomyolysis, and cardiac failure during prolonged high-dose infusions.

Question 80: All of the following are true about the effect of propofol on the respiratory system EXCEPT:

A. Depresses the respiratory center
B. Depresses the respiratory drive
C. Bronchodilator
D. Inhibits hypoxic pulmonary vasoconstriction (Correct Answer)

Explanation: **Explanation:** Propofol is the most commonly used intravenous induction agent. Understanding its respiratory profile is crucial for NEET-PG. **Why Option D is the Correct Answer:** Propofol **does not inhibit** Hypoxic Pulmonary Vasoconstriction (HPV). HPV is a protective physiological mechanism that shunts blood away from poorly ventilated alveoli to well-ventilated ones to maintain oxygenation. While volatile inhalational anesthetics (like Halothane or Isoflurane) inhibit this reflex, most intravenous agents, including Propofol, Ketamine, and Etomidate, **preserve HPV**, making them safer in patients with lung pathology. **Analysis of Other Options:** * **A & B (Respiratory Depression):** Propofol is a potent respiratory depressant. It decreases the sensitivity of the respiratory center to carbon dioxide and reduces the ventilatory response to hypoxia (depresses respiratory drive). This often leads to transient apnea following an induction dose. * **C (Bronchodilation):** Propofol possesses significant bronchodilatory properties. It is often the induction agent of choice for asthmatic patients or those with reactive airway disease, as it reduces the incidence of wheezing and bronchospasm compared to Thiopentone. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Propofol is the agent of choice for Day Care Surgery (due to rapid recovery) and for TIVA (Total Intravenous Anesthesia). * **Anti-emetic:** It has unique anti-emetic properties (sub-hypnotic doses of 10-20 mg). * **Pain on Injection:** This is a common side effect, which can be mitigated by using larger veins or pre-treatment with Lidocaine. * **PRIS:** Propofol Infusion Syndrome (metabolic acidosis, rhabdomyolysis, hyperkalemia) occurs with prolonged, high-dose infusions.

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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