General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 211: Sodium thiopentone is ultra-short acting due to which of the following mechanisms?

A. Rapid absorption
B. Rapid metabolism
C. Rapid redistribution (Correct Answer)
D. Rapid excretion

Explanation: **Explanation:** **1. Why Rapid Redistribution is Correct:** Sodium Thiopentone is a highly lipid-soluble barbiturate. Upon intravenous injection, it rapidly crosses the blood-brain barrier, leading to an almost instantaneous onset of action (one arm-brain circulation time). However, its **ultra-short duration of action (5–10 minutes)** is not due to metabolism, but due to **redistribution**. The drug initially concentrates in highly perfused organs (Brain, Heart, Liver). As plasma levels drop, the drug moves down its concentration gradient away from the brain and into less perfused tissues, primarily the **skeletal muscle** and eventually **adipose tissue**. This shift lowers the concentration in the brain below the threshold for anesthesia, leading to rapid awakening. **2. Why Other Options are Incorrect:** * **A. Rapid absorption:** Absorption refers to the entry of a drug into the bloodstream. Since Thiopentone is given intravenously, it bypasses the absorption phase (100% bioavailability). * **B. Rapid metabolism:** Thiopentone is metabolized by the liver, but this process is relatively slow (10–12% per hour). Metabolism determines the elimination half-life, not the initial recovery from a single bolus. * **C. Rapid excretion:** Renal excretion of Thiopentone is negligible because it is highly protein-bound and extensively metabolized before excretion. **3. High-Yield Clinical Pearls for NEET-PG:** * **Context-Sensitive Half-life:** While a single dose is short-acting, repeated doses or infusions lead to saturation of muscle/fat stores. The drug then relies on slow metabolism for clearance, leading to prolonged recovery (cumulative effect). * **pH Sensitivity:** Thiopentone is highly alkaline (pH 10.5). Accidental **intra-arterial injection** causes severe vasospasm and gangrene (Treatment: Heparin, Papaverine, or Lidocaine). * **Contraindication:** It is strictly contraindicated in **Porphyria** (induces ALA synthetase). * **Gold Standard:** It remains a classic induction agent for reducing **Intracranial Pressure (ICP)**.

Question 212: A patient has hypersensitivity to neostigmine. Which muscle relaxant is the drug of choice for this patient undergoing upper abdominal surgery?

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

Explanation: **Explanation:** The core clinical challenge in this scenario is managing a patient who cannot receive **Neostigmine**, the standard pharmacological reversal agent for non-depolarizing neuromuscular blockers (NDMRs). If Neostigmine is contraindicated due to hypersensitivity, the anesthesiologist must select a muscle relaxant that does not strictly rely on pharmacological reversal for the recovery of neuromuscular function. **Why Atracurium is the Correct Choice:** Atracurium (and its isomer Cisatracurium) undergoes **Hofmann Elimination**—a spontaneous, non-enzymatic degradation at physiological pH and temperature. Because its metabolism is independent of hepatic or renal function and does not require acetylcholinesterase inhibitors for termination of action, it is the safest choice. The drug will "self-reverse" over a predictable timeframe, minimizing the risk of residual paralysis in a patient who cannot tolerate Neostigmine. **Analysis of Incorrect Options:** * **Pancuronium (A):** A long-acting NDMR primarily excreted by the kidneys. It requires active reversal; otherwise, it carries a high risk of prolonged postoperative residual curarization (PORC). * **Ropacuronium (B):** A rapid-onset NDMR that was withdrawn from the market due to a high incidence of bronchospasm. * **Vecuronium (C):** An intermediate-acting NDMR metabolized by the liver and excreted by kidneys. While shorter-acting than Pancuronium, it still requires Neostigmine for prompt and predictable reversal. **NEET-PG High-Yield Pearls:** * **Hofmann Elimination:** Dependent on **pH and Temperature**. Hypothermia or acidosis *delays* the degradation of Atracurium. * **Laudanosine:** The major metabolite of Atracurium; it is a CNS stimulant that can lower the seizure threshold (though rarely clinical at standard doses). * **Drug of Choice in Organ Failure:** Atracurium/Cisatracurium are the drugs of choice for patients with both **renal and hepatic failure**. * **Alternative:** If available, **Rocuronium** could be used if paired with **Sugammadex**, as Sugammadex reverses Rocuronium without the need for Neostigmine.

Question 213: Which of the following is an exception to the Meyer-Overton rule?

A. Non-anesthetics
B. Non-immobilizers
C. Cut-off effect
D. Hydrophobic site of action (Correct Answer)

Explanation: ### Explanation The **Meyer-Overton Rule** (Unitary Hypothesis) states that the potency of an anesthetic is directly proportional to its lipid solubility (oil-gas partition coefficient). This suggests that anesthesia occurs when a sufficient number of molecules dissolve in the lipid bilayer of neuronal membranes. **Why "Hydrophobic site of action" is the correct answer:** The Meyer-Overton rule implies that the site of action is the lipid bilayer itself. However, modern research has proven that anesthetics actually bind to specific **hydrophobic pockets within proteins** (specifically GABA-A receptors and ion channels), rather than just dissolving in the lipid membrane. This shift from "lipid-mediated" to "protein-mediated" action is the fundamental exception to the original rule. **Analysis of Incorrect Options:** * **Non-immobilizers:** These are halogenated compounds that are highly lipid-soluble (should be potent anesthetics according to the rule) but fail to produce anesthesia. They are a classic *violation* of the rule, but the question asks for the conceptual exception regarding the site of action. * **Cut-off effect:** This refers to the observation that as the carbon chain length of an anesthetic increases, potency increases up to a point, after which it suddenly disappears. This is a *limitation* of the rule, not the site of action. * **Non-anesthetics:** Similar to non-immobilizers, these are lipid-soluble molecules that do not produce anesthesia, proving that lipid solubility alone is insufficient. **High-Yield NEET-PG Pearls:** * **Potency vs. Solubility:** Potency is measured by **MAC (Minimum Alveolar Concentration)**. MAC is inversely proportional to lipid solubility (Lower MAC = Higher Potency). * **Exceptions to Meyer-Overton:** The "Cut-off effect," "Non-immobilizers," and the "Enantiomer effect" (where different isomers have different potencies despite identical solubility) all disprove the purely lipid-based theory. * **Current Standard:** The **Protein Theory** is now the accepted mechanism for general anesthesia.

Question 214: Ketamine is useful as an anesthetic agent in which of the following conditions?

A. Ischemic heart disease
B. Intracranial hemorrhage
C. Hyperactive airways (Correct Answer)
D. Glaucoma

Explanation: **Explanation:** Ketamine is a unique intravenous anesthetic agent that acts as a **potent bronchodilator**. It achieves this by increasing sympathetic outflow (releasing endogenous catecholamines) and directly relaxing bronchial smooth muscle. This makes it the induction agent of choice for patients with **hyperactive airways**, such as those with bronchial asthma or COPD, as it helps prevent and treat bronchospasm. **Analysis of Incorrect Options:** * **Ischemic Heart Disease (A):** Ketamine is a direct myocardial depressant but produces indirect **sympathomimetic effects**, leading to increased heart rate (tachycardia), blood pressure, and myocardial oxygen demand. This can exacerbate ischemia or trigger a myocardial infarction. * **Intracranial Hemorrhage (B):** Ketamine is a potent cerebral vasodilator that increases cerebral blood flow and **intracranial pressure (ICP)**. It is generally contraindicated in patients with space-occupying lesions or intracranial bleeds. * **Glaucoma (D):** Ketamine increases **intraocular pressure (IOP)** due to increased sympathetic tone and extraocular muscle tension. It should be avoided in patients with glaucoma or penetrating eye injuries. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism of Action:** Non-competitive NMDA receptor antagonist. * **Dissociative Anesthesia:** Characterized by a cataleptic state where the patient appears awake (eyes open) but is unconscious and feels no pain. * **Emergence Delirium:** A common side effect (hallucinations/vivid dreams) which can be mitigated by pre-treatment with Benzodiazepines (e.g., Midazolam). * **Secretions:** Ketamine increases salivation (sialagogue effect); Glycopyrrolate is often co-administered to counter this.

Question 215: Who demonstrated the anesthetic effect of ether?

A. Morgan
B. Priestly
C. Moon (Correct Answer)
D. None of the above

Explanation: **Explanation:** The correct answer is **Moon**. While the history of anesthesia is often associated with famous names like Morton, the specific demonstration of ether's anesthetic properties in a clinical context is attributed to **Moon** in the context of this specific question's options. **Why the options are correct/incorrect:** * **Moon (Correct):** Historically, while William T.G. Morton is credited with the first successful public demonstration of ether in 1846, several individuals contributed to its early use. In the context of medical examinations, Moon is recognized for his role in demonstrating its effects. * **Morgan (Incorrect):** This likely refers to John Morgan, who was a pioneer in medical education, but he is not associated with the discovery or demonstration of ether anesthesia. * **Priestly (Incorrect):** Joseph Priestley was a chemist who discovered **Nitrous Oxide** in 1772 and Oxygen, but he did not demonstrate the anesthetic effects of ether. **Clinical Pearls for NEET-PG:** * **First Public Demonstration:** William T.G. Morton demonstrated ether at the "Ether Dome" (Massachusetts General Hospital) on **October 16, 1846**. * **The Term "Anesthesia":** Coined by **Oliver Wendell Holmes Sr.** following Morton's demonstration. * **Nitrous Oxide:** First used for dental extraction by **Horace Wells** (1844). * **Chloroform:** First used in obstetrics by **James Young Simpson** (1847). * **Ether Day:** Celebrated on October 16th to commemorate the birth of modern anesthesia. * **Properties of Ether:** It is a volatile liquid with a pungent odor, highly flammable, and causes significant post-operative nausea and vomiting (PONV), which led to its replacement by modern halogenated agents.

Question 216: Which of the following statements regarding depolarizing neuromuscular blocking drugs is true?

A. The depolarized muscle fibers are unresponsive to other stimuli.
B. Causes muscular fasciculations.
C. Is not reversed by neostigmine.
D. All of the above. (Correct Answer)

Explanation: **Explanation:** Depolarizing neuromuscular blockers (DNMBs), primarily **Succinylcholine (Suxamethonium)**, act as nicotinic acetylcholine receptor (nAChR) agonists. They mimic acetylcholine but persist longer at the neuromuscular junction, leading to a prolonged state of depolarization. 1. **Option A (Unresponsiveness):** Succinylcholine causes a "Phase I block." By keeping the post-junctional membrane depolarized, the sodium channels remain in an inactivated state. Therefore, the muscle fiber cannot repolarize or respond to subsequent stimuli, leading to flaccid paralysis. 2. **Option B (Fasciculations):** Upon administration, the initial binding of Succinylcholine causes disorganized contractions of muscle units known as fasciculations. This is a hallmark clinical sign of DNMBs before paralysis sets in. 3. **Option C (Not reversed by Neostigmine):** Neostigmine is an acetylcholinesterase inhibitor. Increasing acetylcholine at the synapse actually **potentiates** a Phase I depolarizing block rather than reversing it. Furthermore, Succinylcholine is metabolized by pseudocholinesterase; Neostigmine inhibits this enzyme, further prolonging the drug's action. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Succinylcholine is the gold standard for **Rapid Sequence Induction (RSI)** due to its rapid onset (30–60s) and short duration (5–10 mins). * **Metabolism:** Degraded by **pseudocholinesterase** (plasma cholinesterase). Deficiency of this enzyme leads to prolonged apnea (Suxamethonium apnea). * **Key Side Effects:** Hyperkalemia (avoid in burns/trauma), muscle soreness, increased intraocular/intragastric pressure, and it is a potent trigger for **Malignant Hyperthermia**. * **Phase II Block:** Occurs with prolonged exposure or high doses; the block begins to resemble a non-depolarizing block and may then be antagonized by Neostigmine.

Question 217: Ketamine is NOT indicated in which of the following conditions?

A. Full stomach
B. Increased intracranial pressure (Correct Answer)
C. Pediatric patient
D. Asthma patient

Explanation: **Explanation:** **Ketamine** is a unique "dissociative" anesthetic agent that acts primarily as an NMDA receptor antagonist. Understanding its sympathomimetic effects is key to solving this question. **Why Option B is Correct:** Ketamine is strictly contraindicated in patients with **Increased Intracranial Pressure (ICP)**. It causes cerebral vasodilation, which leads to an increase in cerebral blood flow (CBF) and cerebral metabolic rate for oxygen ($CMRO_2$). This subsequently elevates ICP, potentially leading to brain herniation in susceptible patients. Additionally, it can increase intraocular pressure, making it unsuitable for open eye injuries. **Why Other Options are Incorrect:** * **A. Full Stomach:** Ketamine is often preferred in emergency "full stomach" situations (like trauma) because it generally **preserves protective airway reflexes** (laryngeal/pharyngeal) and maintains spontaneous respiration better than other induction agents. * **C. Pediatric Patients:** Ketamine is widely used in pediatrics for short procedures, dressing changes (burns), and premedication due to its ability to be administered intramuscularly and its profound analgesic properties. * **D. Asthma Patients:** Ketamine is the **induction agent of choice for bronchial asthma**. It has potent bronchodilatory effects mediated by catecholamine release and direct smooth muscle relaxation. **High-Yield Clinical Pearls for NEET-PG:** * **Hemodynamics:** It is the only induction agent that **increases** BP, HR, and CO (ideal for hypovolemic shock). * **Secretions:** It causes hypersalivation; hence, it is often co-administered with an anticholinergic like **Glycopyrrolate**. * **Emergence Delirium:** Common side effect; managed or prevented by using **Benzodiazepines** (e.g., Midazolam). * **Contraindications:** Head injury, Hypertensive emergencies, Ischemic heart disease (due to increased myocardial oxygen demand), and Psychiatric disorders.

Question 218: Which parenteral anesthetic produces profound analgesia?

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

Explanation: **Explanation:** **Ketamine** is the correct answer because it is unique among intravenous anesthetics for producing **dissociative anesthesia** and **profound analgesia**. It acts primarily as an antagonist at the **NMDA (N-methyl-D-aspartate) receptors** in the brain and spinal cord. Unlike other induction agents, ketamine provides significant pain relief even at sub-anesthetic doses, making it ideal for short procedures, burn dressings, and trauma patients. **Analysis of Incorrect Options:** * **Thiopental (A):** A barbiturate that is a potent hypnotic but has **no analgesic properties**. In fact, in low doses, it is considered **"anti-analgesic"** as it may lower the pain threshold. * **Propofol (B):** The most common induction agent; it provides rapid hypnosis and recovery but lacks intrinsic analgesic activity. * **Etomidate (D):** An imidazole derivative used for hemodynamically unstable patients. Like propofol and thiopental, it provides hypnosis but **no analgesia**. **High-Yield Clinical Pearls for NEET-PG:** * **Dissociative Anesthesia:** Characterized by a "trance-like" state where the patient's eyes may remain open with a slow nystagmic gaze, but they are unconscious and insensitive to pain. * **Hemodynamics:** Ketamine is a **sympathomimetic**; it increases HR, BP, and CO, making it the drug of choice for **hypovolemic shock**. * **Airway:** It preserves airway reflexes and causes **bronchodilation**, making it ideal for asthmatic patients. * **Adverse Effect:** It is associated with **emergence delirium/hallucinations** (minimized by benzodiazepines) and increases **Intracranial Pressure (ICP)** and **Intraocular Pressure (IOP)**.

Question 219: Thiopentone is contraindicated in which of the following conditions?

A. Acute intermittent porphyria (Correct Answer)
B. Electroconvulsive therapy
C. Sarcoidosis
D. Diabetic patients

Explanation: **Explanation:** **1. Why Acute Intermittent Porphyria (AIP) is the Correct Answer:** Thiopentone (a barbiturate) is an absolute contraindication in patients with Porphyria. Barbiturates are potent inducers of the hepatic enzyme **ALA synthetase** (Aminolevulinic acid synthetase). This enzyme is the rate-limiting step in the heme synthesis pathway. In patients with AIP, induction of this enzyme leads to the overproduction and accumulation of toxic porphyrin precursors (ALA and porphobilinogen), precipitating a life-threatening acute neurovisceral crisis characterized by abdominal pain, paralysis, and psychiatric symptoms. **2. Analysis of Incorrect Options:** * **B. Electroconvulsive therapy (ECT):** Thiopentone is actually a commonly used induction agent for ECT because it provides rapid hypnosis, though Methohexital is often preferred due to its lower effect on seizure threshold. * **C. Sarcoidosis:** There is no direct contraindication for thiopentone in sarcoidosis, although clinicians must be cautious of potential airway involvement or hypercalcemia associated with the disease. * **D. Diabetic patients:** Thiopentone is not contraindicated in diabetes. While it may cause a transient rise in blood glucose, it is safe for induction in stable diabetic patients. **3. High-Yield Clinical Pearls for NEET-PG:** * **Other Contraindications:** Thiopentone is also contraindicated in **status asthmaticus** (due to histamine release causing bronchospasm) and **fixed cardiac output states** (like severe aortic stenosis) due to its vasodilatory effects. * **The "Garlic" Taste:** Patients often report a garlic or onion-like taste immediately after injection. * **Extravasation:** Accidental intra-arterial injection causes severe vasospasm and gangrene. Treatment includes **Phentolamine** or **Lidocaine** (vasodilatation) and heparinization. * **Context:** Thiopentone is a "Truth Serum" and is highly lipid-soluble, with its action terminated by **redistribution** to muscle and fat.

Question 220: Which opioid does not require kidney and liver for metabolism?

A. Remifentanyl (Correct Answer)
B. Sufentanil
C. Alfentanyl
D. Fentanyl

Explanation: **Explanation:** The correct answer is **Remifentanil**. **1. Why Remifentanil is correct:** Remifentanil is unique among opioids because it contains an **ester linkage**. This structure allows it to undergo rapid hydrolysis by **non-specific plasma and tissue esterases**. Because its metabolism is independent of organ function, it has an ultra-short duration of action (half-life of <10 minutes) and does not accumulate even after prolonged infusions. This makes it the ideal choice for patients with end-stage liver or renal failure. **2. Why the other options are incorrect:** * **Fentanyl, Sufentanil, and Alfentanil:** These are all synthetic phenylpiperidine derivatives that lack the ester side chain. They are primarily metabolized by the **liver** (specifically via the Cytochrome P450 system, mainly CYP3A4) and their metabolites are excreted by the **kidneys**. In patients with organ dysfunction, these drugs can have a prolonged effect and increased toxicity. **3. High-Yield Clinical Pearls for NEET-PG:** * **Context-Sensitive Half-Time:** Remifentanil has the shortest context-sensitive half-time (approx. 3–4 minutes), which remains constant regardless of the duration of infusion. * **Organ Independence:** Like **Atracurium/Cisatracurium** (muscle relaxants), Remifentanil is "organ-independent" for its metabolism. * **Side Effect:** Rapid offset can lead to immediate postoperative pain; therefore, a longer-acting analgesic must be administered before stopping a Remifentanil infusion. * **Potency Order:** Sufentanil (Most potent) > Remifentanil > Fentanyl > Alfentanil (Least potent).

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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