General Anesthesia Practice Questions

Q: What does the Dibucain number refer to?

Abnormal acetylcholinesterase activity. The **Dibucaine Number** is a high-yield concept in anesthesiology used to assess the quality of **pseudocholinesterase** (also known as butyrylcholinesterase or plasma cholinesterase), the enzyme responsible for metabolizing Succinylcholine and Mivacurium. ### 1. Why Option A is Correct The Dibucaine number measures the **percentage inhibition** of pseudocholinesterase activity by Dibucaine (a local anesthetic). * **Normal Enzyme:** Dibucaine inhibits normal pseudocholinesterase by about 80% (Dibucaine Number = 80). * **Abnormal Enzyme:** In patients with atypical pseudocholinesterase, the enzyme is resistant to inhibition. A Dibucaine number of 20 indicates homozygous atypical enzyme, leading to prolonged paralysis (Succinylcholine apnea) because the enzyme cannot effectively break down the drug. * *Note:* The number reflects the **quality/type** of the enzyme, not the quantity. ### 2. Why Other Options are Incorrect * **Option B:** Potency of neuromuscular blockers is measured by the **ED95** (the dose required to produce 95% suppression of a single twitch). * **Option C:** Potency of inhalational general anesthetics is measured by the **MAC (Minimum Alveolar Concentration)**. ### 3. Clinical Pearls for NEET-PG * **Normal:** Dibucaine Number 80 (Homozygous typical). * **Heterozygous:** Dibucaine Number 40–60 (Slightly prolonged block, ~20–30 mins). * **Homozygous Atypical:** Dibucaine Number 20 (Severely prolonged block, >3 hours). * **Management of Succinylcholine Apnea:** Continued mechanical ventilation and sedation until the block wears off spontaneously. Fresh frozen plasma (FFP) can be given as it contains the enzyme, but it is rarely required.

Q: Diffusion hypoxia is most commonly seen during which of the following periods?

Reversal of anesthesia. **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. Because $N_2O$ is 34 times more soluble in blood than Nitrogen, it rushes into the alveoli in large volumes, effectively "diluting" the concentration of Oxygen ($O_2$) and Carbon Dioxide ($CO_2$) present there. This leads to a transient drop in alveolar $PO_2$, resulting in hypoxia. * **Why Option B is Correct:** Diffusion hypoxia occurs during the **reversal (emergence)** phase of anesthesia. When the $N_2O$ supply is turned off and the patient breathes room air, the sudden outpouring of $N_2O$ into the lungs displaces oxygen. To prevent this, clinicians administer **100% Oxygen for 5–10 minutes** after stopping $N_2O$. * **Why Option A is Incorrect:** During induction, we see the **"Second Gas Effect."** Here, the rapid uptake of $N_2O$ from the alveoli into the blood *increases* the concentration of the co-administered volatile anesthetic, accelerating induction. * **Why Option C is Incorrect:** While respiratory complications can occur postoperatively, "Diffusion Hypoxia" specifically refers to the immediate physical displacement of gases in the alveoli at the moment $N_2O$ is discontinued. **High-Yield Clinical Pearls for NEET-PG:** 1. **Prevention:** Always supplement with 100% $O_2$ during emergence to counteract the dilution effect. 2. **The Fink Effect:** This is the formal name for Diffusion Hypoxia. 3. **Hypocapnia:** $N_2O$ also dilutes alveolar $CO_2$, which can reduce the respiratory drive, further exacerbating the hypoxia. 4. **Concentration Effect:** This is the counterpart to the Fink effect, occurring during induction where high concentrations of a gas accelerate its own uptake.

Q: Which of the following is a short-acting, non-depolarizing muscle relaxant?

Mivacurium. **Explanation:** Muscle relaxants (Neuromuscular Blocking Agents) are primarily classified based on their duration of action. **Mivacurium** is the correct answer because it is the only **short-acting** non-depolarizing neuromuscular blocker (NDNMB) currently used in clinical practice. **1. Why Mivacurium is correct:** Mivacurium belongs to the benzylisoquinolone class. Its short duration of action (approximately 15–20 minutes) is due to its rapid metabolism by **plasma cholinesterase** (pseudocholinesterase), similar to succinylcholine. This makes it unique among non-depolarizing agents, which typically rely on organ-based elimination. **2. Analysis of Incorrect Options:** * **Doxacuronium & Pipecurium:** These are **long-acting** NDNMBs. They have a slow onset and a prolonged duration of action (usually >60 minutes), making them less ideal for short procedures. * **Vecuronium:** This is an **intermediate-acting** aminosteroid NDNMB. Its duration of action typically ranges from 30 to 45 minutes. **High-Yield Clinical Pearls for NEET-PG:** * **Metabolism:** Since Mivacurium is metabolized by plasma cholinesterase, its action is significantly prolonged in patients with **atypical plasma cholinesterase deficiency**. * **Side Effect:** Mivacurium is notorious for causing **histamine release**, which can lead to cutaneous flushing, hypotension, and bronchospasm if injected rapidly. * **Classification Summary:** * *Short-acting:* Mivacurium. * *Intermediate-acting:* Vecuronium, Rocuranium, Atracurium, Cisatracurium. * *Long-acting:* Pancuronium, Doxacuronium, Pipecurium. * **Rocuronium** is the NDNMB with the fastest onset of action, often used as an alternative to succinylcholine for rapid sequence induction.

Q: Which of the following statements is true about Halothane?

Vasodilator. **Explanation:** **Halothane** is a potent volatile anesthetic agent. The correct answer is **Vasodilator** because Halothane causes a dose-dependent reduction in arterial blood pressure. This occurs through two primary mechanisms: direct myocardial depression (reducing cardiac output) and **peripheral vasodilation** (reducing systemic vascular resistance). **Analysis of Options:** * **A. Non-irritant:** While Halothane is relatively non-pungent compared to Isoflurane or Desflurane (making it suitable for mask induction in pediatrics), it is technically considered a mild irritant to the respiratory mucosa compared to Sevoflurane, which is the gold standard for non-irritant induction. * **B. Antiarrhythmic:** This is incorrect. Halothane is famously **arrhythmogenic**. It sensitizes the myocardium to the effects of circulating catecholamines (epinephrine), which can lead to ventricular arrhythmias. * **C. It antagonizes bronchospasm:** While Halothane is a potent bronchodilator, the phrasing "antagonizes bronchospasm" is less accurate than its direct physiological effect of smooth muscle relaxation. More importantly, in the context of this specific question, its systemic **vasodilatory** effect is a more definitive pharmacological property. **High-Yield Clinical Pearls for NEET-PG:** * **Halothane Hepatitis:** A rare but serious immune-mediated hepatotoxicity (Type II) occurring after repeat exposure. * **Malignant Hyperthermia:** Like all volatile agents, Halothane is a known trigger. * **"Halothane Shakes":** Post-operative shivering is common. * **Uterine Relaxation:** It causes significant uterine atony, which can increase postpartum hemorrhage (PPH) risk if used in obstetrics. * **Blood-Gas Partition Coefficient:** 2.4 (Slow induction and recovery).

Q: Which of the following is untrue about mivacurium?

Onset of action is early. **Explanation:** Mivacurium is a short-acting, non-depolarizing neuromuscular blocking agent (NMBA) belonging to the benzylisoquinolone class. **Why Option C is the correct answer (Untrue statement):** Despite being a short-acting drug, Mivacurium has a **slow onset of action** (approximately 2–4 minutes). In contrast, Succinylcholine (a depolarizing agent) has a very rapid onset (30–60 seconds). For NEET-PG, it is vital to remember that "short duration" does not equate to "rapid onset." Mivacurium is not suitable for Rapid Sequence Induction (RSI). **Analysis of other options (True statements):** * **A. Metabolized by pseudocholinesterase:** Like succinylcholine, mivacurium is hydrolyzed by plasma cholinesterase (pseudocholinesterase). Its action is significantly prolonged in patients with atypical plasma cholinesterase deficiency. * **B. Releases histamine:** As a benzylisoquinolone, mivacurium can cause mast cell degranulation leading to histamine release, which may manifest as cutaneous flushing, hypotension, or bronchospasm, especially if injected rapidly. * **D. Short duration of action:** It has the shortest duration among all non-depolarizing NMBAs (approx. 12–20 minutes), making it ideal for short surgical procedures. **High-Yield Clinical Pearls for NEET-PG:** 1. **Metabolism:** It is the only non-depolarizing muscle relaxant metabolized by pseudocholinesterase. 2. **Reversal:** Spontaneous recovery is rapid; however, it can be reversed with neostigmine, though this is rarely required. 3. **Edrophonium:** Interestingly, edrophonium is preferred over neostigmine for reversal as it does not inhibit pseudocholinesterase as strongly as neostigmine does. 4. **Rapacuronium:** This was a non-depolarizing agent with a rapid onset, but it was withdrawn due to severe bronchospasm. Currently, **Rocuronium** is the non-depolarizing agent with the fastest onset.

Q: Which of the following drugs helps in the rapid reversal of the effect of rocuronium?

Sugammadex. **Explanation:** **Sugammadex** is the correct answer as it is a selective relaxant binding agent (SRBA) specifically designed for the rapid reversal of steroidal non-depolarizing neuromuscular blocking agents (NMBAs), primarily **Rocuronium** and Vecuronium. **Mechanism of Action:** Sugammadex is a modified $\gamma$-cyclodextrin. Its structure resembles a hollow "doughnut" that encapsulates the rocuronium molecule in the plasma, forming a stable 1:1 complex. This creates a concentration gradient that pulls rocuronium away from the nicotinic receptors at the neuromuscular junction back into the plasma, leading to a rapid and complete reversal of blockade, even if the block is deep. **Why other options are incorrect:** * **Neostigmine:** An acetylcholinesterase inhibitor. It increases the concentration of acetylcholine at the synapse to outcompete the NMBA. It is slower than Sugammadex and has a "ceiling effect," meaning it cannot reverse a deep block effectively. * **Edrophonium:** A short-acting acetylcholinesterase inhibitor primarily used for the diagnosis of Myasthenia Gravis (Tensilon test), not for the routine rapid reversal of rocuronium. * **Atropine:** An anticholinergic drug. It does not reverse muscle relaxants; it is co-administered with neostigmine to prevent bradycardia and excessive secretions caused by muscarinic stimulation. **High-Yield Clinical Pearls for NEET-PG:** * **Dosing:** 2 mg/kg for routine reversal (TOF 2); 4 mg/kg for deep block (PTC 1-2); 16 mg/kg for immediate reversal after a 1.2 mg/kg dose of rocuronium. * **Side Effects:** Anaphylaxis (rare but significant) and interference with hormonal contraceptives (patients should be advised to use backup contraception for 7 days). * **Excretion:** It is excreted unchanged by the kidneys; use with caution in severe renal impairment.

Q: Which inhalational anesthetic agent possesses analgesic properties?

Xenon. **Explanation** The correct answer is **Xenon**. **1. Why Xenon is Correct:** Most volatile inhalational anesthetics (like the "fluranes") provide unconsciousness and muscle relaxation but lack significant intrinsic analgesic properties. Xenon is unique because its primary mechanism of action involves the **non-competitive inhibition of NMDA (N-methyl-D-aspartate) receptors**. Since NMDA receptors are heavily involved in pain transmission and central sensitization, their inhibition provides potent **analgesia** along with anesthesia. Nitrous Oxide ($N_2O$) is the only other commonly discussed inhalational agent with significant analgesic properties, also via NMDA antagonism. **2. Why the Other Options are Incorrect:** * **Desflurane, Isoflurane, and Sevoflurane:** These are halogenated ethers. Their primary mechanism involves modulating **GABA-A receptors** and glycine receptors. While they produce a dose-dependent depression of the CNS (hypnosis), they do not provide effective analgesia. In fact, at sub-anesthetic concentrations, some volatile agents can be "hyperalgesic" (increasing sensitivity to pain). **3. High-Yield Clinical Pearls for NEET-PG:** * **Ideal Anesthetic:** Xenon is often called the "ideal anesthetic" because it is non-explosive, non-toxic, chemically inert, and provides rapid induction/recovery due to an extremely low **blood-gas partition coefficient (0.115)**. * **MAC Value:** The MAC of Xenon is approximately **63–71%**, making it less potent than halogenated agents but more potent than $N_2O$. * **Cardiovascular Stability:** Unlike the "fluranes," Xenon is remarkably cardio-stable and does not depress myocardial contractility. * **Environmental Impact:** It is an expensive noble gas but is environmentally friendly (no greenhouse effect), unlike $N_2O$ or Desflurane.

Q: Intra-arterial injection of thiopentone causes which of the following?

Vasospasm. **Explanation:** Accidental intra-arterial injection of **Thiopentone sodium** is a known anesthetic emergency. Thiopentone is highly alkaline (pH 10.5). When injected into an artery, it reacts with the blood to form **crystals**, which trigger an intense inflammatory response and the release of **norepinephrine** from perivascular nerve endings. 1. **Why Vasospasm is Correct:** The primary and immediate pathological response to intra-arterial thiopentone is **intense vasospasm**. This is mediated by the local release of catecholamines and the mechanical irritation caused by crystal precipitation. This spasm leads to severe pain (often described as a "burning" sensation) and distal ischemia. 2. **Why other options are incorrect:** * **Vasodilation:** Thiopentone causes the opposite effect (vasoconstriction/spasm) in arteries. * **Necrosis of the vessel wall:** While prolonged ischemia can lead to gangrene of the distal limb, the immediate effect is vasospasm. Necrosis is a late complication, not the primary mechanism. * **Hypotension:** While thiopentone causes systemic hypotension when given intravenously (due to myocardial depression and peripheral venodilation), an intra-arterial injection causes localized hypertensive/ischemic effects in the affected limb. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Presentation:** Severe pain, blanching of the limb, and loss of distal pulses. * **Management Protocol:** 1. **Leave the needle in situ:** To administer drugs through the same port. 2. **Dilute the drug:** Inject Normal Saline. 3. **Relieve Vasospasm:** Inject **Papaverine** (drug of choice), Lidocaine, or Priscoline. 4. **Sympathetic Block:** Stellate ganglion block or Brachial plexus block to promote vasodilation. 5. **Anticoagulation:** Heparin to prevent secondary thrombosis.

Question 1

What does the Dibucain number refer to?

Accepted Answer

Abnormal acetylcholinesterase activity

Answer

Potency of neuromuscular blocking agents

Answer

Potency of general anesthetics

Answer

None of the above

Question 2

Diffusion hypoxia is most commonly seen during which of the following periods?

Accepted Answer

Reversal of anesthesia

Answer

Induction of anesthesia

Answer

Postoperative period

Answer

None of the above

Question 3

Which of the following is a short-acting, non-depolarizing muscle relaxant?

Accepted Answer

Mivacurium

Answer

Doxacuronium

Answer

Pipecurium

Answer

Vecuronium

Question 4

Which of the following statements is true about Halothane?

Accepted Answer

Vasodilator

Answer

Non-irritant

Answer

Antiarrhythmic

Answer

It antagonizes bronchospasm

Question 5

Which of the following is untrue about mivacurium?

Accepted Answer

Onset of action is early

Answer

Metabolized by pseudocholinesterase

Answer

Releases histamine

Answer

Short duration of action

Question 6

Which of the following drugs helps in the rapid reversal of the effect of rocuronium?

Accepted Answer

Sugammadex

Answer

Neostigmine

Answer

Edrophonium

Answer

Atropine

Question 7

Which inhalational anesthetic agent possesses analgesic properties?

Accepted Answer

Xenon

Answer

Desflurane

Answer

Isoflurane

Answer

Sevoflurane

Question 8

Intra-arterial injection of thiopentone causes which of the following?

Accepted Answer

Vasospasm

Answer

Vasodilation

Answer

Necrosis of the vessel wall

Answer

Hypotension

Question 9

Nitrous oxide is contraindicated in patients with pneumothorax, pneumopericardium, or intestinal obstruction because it:

Accepted Answer

Causes the expansion of air-filled body cavities

Answer

Depresses an already compromised myocardium

Answer

Permits the use of a limited FIO2 only

Answer

Is less soluble than nitrogen

Question 10

Which of the following is NOT a characteristic of nondepolarizing neuromuscular blockers?

Accepted Answer

Shows fasciculations

Answer

Fade on train-of-four stimulation

Answer

Tetanic stimulation is followed by post-tetanic facilitation

Answer

Reversed by neostigmine

General Anesthesia — MCQs

General Anesthesia — MCQs

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