General Anesthesia Practice Questions

Q: Which of the following anesthetic agents has the least diffusion coefficient?

Nitrous Oxide (N2O). ### Explanation The correct answer is **Nitrous Oxide (N₂O)**. **1. Why Nitrous Oxide is Correct:** The **diffusion coefficient** of a gas refers to its ability to move across biological membranes (like the alveolar-capillary membrane). Nitrous oxide has a significantly higher solubility in blood compared to nitrogen, but more importantly, it possesses a very high diffusion coefficient. It is approximately **34 times more soluble** than nitrogen in blood. Because of its high diffusion coefficient and low blood-gas partition coefficient (0.47), N₂O moves rapidly from the alveoli into the blood. This rapid diffusion is the basis for the **"Concentration Effect"** and the **"Second Gas Effect,"** where N₂O accelerates the uptake of a co-administered volatile anesthetic. **2. Why Other Options are Incorrect:** * **Isoflurane, Enflurane, and Halothane:** These are potent volatile halogenated liquids. While they are lipid-soluble, their molecular weights are much higher than N₂O, and their diffusion coefficients are significantly lower. They do not diffuse across membranes with the same velocity as N₂O. Among these, Halothane has the highest blood-gas partition coefficient (2.4), making it the slowest to equilibrate. **3. Clinical Pearls for NEET-PG:** * **Diffusion Hypoxia (Fink Effect):** At the end of surgery, N₂O diffuses rapidly from the blood back into the alveoli, diluting oxygen. To prevent this, 100% O₂ must be administered for 5–10 minutes after stopping N₂O. * **Expansion of Closed Spaces:** Due to its high diffusion coefficient, N₂O enters air-filled cavities (e.g., pneumothorax, obstructed bowel, middle ear, or intraocular gas bubbles) faster than nitrogen can leave, causing dangerous increases in volume or pressure. * **Blood-Gas Partition Coefficient (Solubility):** Desflurane (0.42) < **Nitrous Oxide (0.47)** < Sevoflurane (0.65) < Isoflurane (1.4) < Halothane (2.4).

Q: Which crystalloid solution has an osmolality closest to serum osmolality?

Ringer's lactate. **Explanation:** The concept of **osmolality** refers to the concentration of particles in a solution. In clinical practice, the goal of fluid resuscitation is often to use a solution that mimics the physiological properties of human plasma (Normal serum osmolality: **275–295 mOsm/kg**). **Why Ringer’s Lactate (RL) is correct:** RL is considered a "balanced salt solution." Its calculated osmolarity is approximately **273 mOsm/L**. Because this value falls almost exactly at the lower limit of normal serum osmolality, it is the most "physiologic" crystalloid among the options. It contains electrolytes (Sodium, Potassium, Calcium, Chloride) and Lactate (which acts as a buffer) in concentrations that closely resemble plasma. **Analysis of Incorrect Options:** * **Normal Saline (0.9% NaCl):** Despite its name, it is hyper-physiologic. It has an osmolarity of **308 mOsm/L**. Its high chloride content (154 mEq/L vs. plasma's 100 mEq/L) can lead to hyperchloremic metabolic acidosis. * **5% Dextrose in Water (D5W):** It has an osmolarity of **252 mOsm/L**. However, once infused, the dextrose is rapidly metabolized, leaving behind "free water," making it functionally hypotonic. * **Dextrose Normal Saline (DNS):** This is a hypertonic solution with an osmolarity of approximately **560 mOsm/L** (308 from Saline + 252 from Dextrose). **High-Yield Clinical Pearls for NEET-PG:** 1. **Fluid of Choice:** RL is the preferred fluid for trauma, burns, and most intraoperative replacements. 2. **Avoid RL in:** Head injuries (due to relative hypotonicity which may worsen cerebral edema) and alongside blood transfusions (Calcium in RL can cause clotting in the IV line if mixed with citrated blood). 3. **NS is preferred in:** Hypochloremic metabolic alkalosis (e.g., persistent vomiting/pyloric stenosis) and neurosurgery.

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: Laudanosine is a metabolite of which of the following neuromuscular blocking agents?

Atracurium. **Explanation:** **Atracurium** is a benzylisoquinolinium neuromuscular blocking agent (NMBA) that undergoes a unique form of spontaneous degradation known as **Hofmann elimination** (a non-enzymatic, pH and temperature-dependent process) and ester hydrolysis. **Laudanosine** is the primary tertiary amine metabolite produced during this breakdown. * **Why Atracurium is correct:** Laudanosine is the major metabolite of both Atracurium and its isomer, Cisatracurium. However, Atracurium produces significantly higher levels of laudanosine (approximately 3–5 times more) compared to Cisatracurium. * **Why other options are incorrect:** * **Cisatracurium:** While it also produces laudanosine, Atracurium is the classic textbook answer associated with high levels of this metabolite. In many MCQ formats, if both are present, Atracurium is the primary choice unless the question specifies "lesser amounts." * **Pancuronium:** An aminosteroid NMBA that is primarily excreted unchanged by the kidneys; it does not produce laudanosine. * **Gallamine:** An older long-acting NMBA that is excreted 100% unchanged in urine. **High-Yield Clinical Pearls for NEET-PG:** 1. **CNS Toxicity:** Laudanosine is a **CNS stimulant**. In very high concentrations, it can cross the blood-brain barrier and potentially cause **seizures** (proconvulsant). 2. **Organ Independence:** Because of Hofmann elimination, Atracurium is the drug of choice in patients with **renal or hepatic failure**. 3. **Histamine Release:** Unlike Cisatracurium, Atracurium is associated with significant histamine release, which can cause hypotension and flushing. 4. **Temperature/pH Sensitivity:** Hofmann elimination is slowed by acidosis and hypothermia, prolonging the drug's duration of action.

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.

Q: Non-depolarizing muscle relaxants are potentiated by all except?

Phenytoin. **Explanation:** The potentiation or antagonism of non-depolarizing muscle relaxants (NDMRs) depends on their interaction with the neuromuscular junction (NMJ) and hepatic enzyme induction. **Why Phenytoin is the correct answer:** Phenytoin is a potent **hepatic enzyme inducer**. Chronic administration of phenytoin (and carbamazepine) leads to an increased rate of metabolism of NDMRs (especially vecuronium and rocuronium). Furthermore, it causes an up-regulation of acetylcholine receptors at the NMJ. Both mechanisms lead to **resistance** to NDMRs, meaning higher doses are required and the duration of action is shortened. Therefore, it does not potentiate but rather **antagonizes** the effect. **Why the other options are incorrect:** * **Aminoglycosides (e.g., Neomycin, Gentamicin):** These potentiate NDMRs by inhibiting the pre-junctional release of Acetylcholine (ACh) and reducing post-junctional sensitivity to ACh. * **Polymyxins:** These exert a potent neuromuscular blocking effect by acting like "membrane stabilizers," significantly prolonging the block. * **Quinidine:** This Class IA antiarrhythmic potentiates NDMRs by depressing muscle fiber excitability and decreasing ACh release. **High-Yield Clinical Pearls for NEET-PG:** * **Antibiotics that potentiate NDMRs:** Aminoglycosides, Tetracyclines, Polymyxin, and Lincomycin. (Note: Penicillins and Cephalosporins do **not** have this effect). * **Electrolytes that potentiate NDMRs:** Hypokalemia, Hypermagnesemia, and Hypocalcemia. * **Other potentiators:** Inhalational anesthetics (Desflurane > Sevoflurane > Isoflurane), Local anesthetics, and Hypothermia. * **Acute vs. Chronic Phenytoin:** While chronic use causes resistance, an *acute* IV dose of phenytoin can occasionally potentiate the block. However, for exam purposes, Phenytoin is the classic example of resistance/antagonism.

Question 1

Which of the following anesthetic agents has the least diffusion coefficient?

Accepted Answer

Nitrous Oxide (N2O)

Answer

Isoflurane

Answer

Enflurane

Answer

Halothane

Question 2

Which crystalloid solution has an osmolality closest to serum osmolality?

Accepted Answer

Ringer's lactate

Answer

Normal saline (0.9% NaCl)

Answer

5% dextrose in water

Answer

Dextrose Normal Saline (DNS)

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 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 7

Laudanosine is a metabolite of which of the following neuromuscular blocking agents?

Accepted Answer

Atracurium

Answer

Cisatracurium

Answer

Pancuronium

Answer

Gallamine

Question 8

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

Question 9

Which of the following fluorinated anesthetic agents does not produce toxic fluoride ions?

Accepted Answer

Desflurane

Answer

Sevoflurane

Answer

Methoxyflurane

Answer

Enflurane

Question 10

Non-depolarizing muscle relaxants are potentiated by all except?

Accepted Answer

Phenytoin

Answer

Aminoglycoside antibiotics

Answer

Polymyxin

Answer

Quinidine

General Anesthesia — MCQs

General Anesthesia — MCQs

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