General Anesthesia Practice Questions

Q: What is the second gas effect?

Facilitation of inhalation of halothane by nitrous oxide. ### 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.

Q: Which anesthetic agent acts via NMDA receptors?

Xenon. **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.

Q: Which statement is false regarding halothane?

It decreases vagal tone.. **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.

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

Propofol. **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.

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

Inhibits hypoxic pulmonary vasoconstriction. **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.

Question 1

What is the second gas effect?

Accepted Answer

Facilitation of inhalation of halothane by nitrous oxide

Answer

Displacement of nitrous oxide by oxygen

Answer

Displacement of oxygen by nitrous oxide

Answer

Removal of oxygen by nitrous oxide from alveoli during recovery from general anaesthesia

Question 2

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

Accepted Answer

Meyer-Overton rule

Answer

Pressure reversal rule

Answer

Critical volume hypothesis

Answer

Lipid bilayer expansion hypothesis

Question 3

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?

Accepted Answer

Second gas effect

Answer

Fink effect

Answer

Concentration effect

Answer

Third gas effect

Question 4

Thiopental sodium is administered intravenously as which concentration?

Accepted Answer

2.5% solution

Answer

25% solution

Answer

0.25% solution

Answer

0.025% solution

Question 5

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?

Accepted Answer

Desflurane

Answer

Isoflurane

Answer

Sevoflurane

Answer

Nitrous oxide

Question 6

Which of the following statements is NOT TRUE regarding sevoflurane?

Accepted Answer

Sevoflurane is less cardio depressant than isoflurane.

Answer

Minimum alveolar concentration (MAC) is higher than isoflurane.

Answer

Blood gas partition coefficient is higher than desflurane.

Answer

Potency is more cardio depressant than isoflurane.

Question 7

Which anesthetic agent acts via NMDA receptors?

Accepted Answer

Xenon

Answer

Nitrous oxide

Answer

Succinylcholine

Answer

Etomidate

Question 8

Which statement is false regarding halothane?

Accepted Answer

It decreases vagal tone.

Answer

It has a pleasant smell.

Answer

It sensitizes the myocardium to catecholamines.

Answer

It can cause postoperative hepatitis.

Question 9

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

Accepted Answer

Propofol

Answer

Etomidate

Answer

Ketamine

Answer

Thiopentone

Question 10

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

Accepted Answer

Inhibits hypoxic pulmonary vasoconstriction

Answer

Depresses the respiratory center

Answer

Depresses the respiratory drive

Answer

Bronchodilator

General Anesthesia — MCQs

General Anesthesia — MCQs

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