General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 441: Flumazenil is used for reversing the respiratory depression caused by which one of the following drugs?

A. Fentanyl
B. Midazolam (Correct Answer)
C. Propofol
D. Ketamine

Explanation: **Explanation:** **Correct Option: B (Midazolam)** Flumazenil is a specific **competitive antagonist** at the benzodiazepine (BZD) receptor site on the GABA-A receptor complex. Midazolam is a benzodiazepine commonly used for conscious sedation and induction. Flumazenil effectively reverses the sedative, psychomotor, and respiratory-depressant effects caused by BZDs by displacing them from their binding sites. **Why Incorrect Options are Wrong:** * **A. Fentanyl:** This is a potent synthetic opioid. Respiratory depression caused by opioids is reversed by **Naloxone**, a competitive opioid receptor antagonist. * **C. Propofol:** This is an intravenous anesthetic that acts primarily via GABA-A receptors but at a different binding site than BZDs. There is currently **no specific pharmacological reversal agent** for Propofol; management is supportive (ventilation). * **D. Ketamine:** This is a dissociative anesthetic that acts as an **NMDA receptor antagonist**. Like Propofol, it has no specific antagonist. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Flumazenil has a high affinity for BZD receptors but possesses no intrinsic activity (pure antagonist). * **Duration of Action:** Flumazenil has a shorter half-life (~1 hour) than many benzodiazepines (e.g., Diazepam). This can lead to **"re-sedation,"** requiring repeated doses or a continuous infusion. * **Contraindication:** Avoid Flumazenil in patients with long-term BZD use or tricyclic antidepressant (TCA) overdose, as it can precipitate **acute withdrawal seizures**. * **Dose:** The typical initial dose is 0.2 mg IV, titrated up to 1 mg.

Question 442: Transient acute adrenal insufficiency is seen with which of the following drugs?

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

Explanation: ### **Explanation** **Correct Option: A. Etomidate** Etomidate is a carboxylated imidazole derivative used for the induction of general anesthesia. Its most significant side effect is the **dose-dependent inhibition of the enzyme 11-beta-hydroxylase**. This enzyme is essential for converting 11-deoxycortisol to cortisol and 11-deoxycorticosterone to aldosterone. Even a single induction dose can suppress adrenal steroidogenesis for 24–48 hours, leading to **transient acute adrenal insufficiency**. While this makes it risky for patients in septic shock, it remains a drug of choice for hemodynamically unstable patients due to its minimal cardiovascular impact. **Incorrect Options:** * **B. Propofol:** Known for causing significant hypotension and respiratory depression. It does not affect the adrenal axis but is the agent of choice for day-care surgeries due to its anti-emetic properties and rapid recovery. * **C. Thiopentone:** A barbiturate that causes dose-dependent cardiovascular depression and venodilation. It is contraindicated in porphyria but has no inhibitory effect on adrenal enzymes. * **D. Ketamine:** A dissociative anesthetic that acts as a sympathetic stimulant (increasing HR and BP). It is preferred in patients with asthma or hypovolemic shock and does not cause adrenal suppression. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for Hemodynamic Stability:** Etomidate (minimal effect on HR and BP). * **Myoclonus:** A common side effect of Etomidate induction (can be prevented by pre-treatment with opioids or benzodiazepines). * **Drug of Choice for ECT:** Methohexital (Thiopentone is an alternative). * **Drug of Choice for Neurosurgery:** Thiopentone (decreases Cerebral Metabolic Rate and ICP).

Question 443: What is an absolute contraindication to thiopentone?

A. Cardiotoxicity
B. Acute intermittent porphyria (Correct Answer)
C. Malignant hyperthermia
D. Methemoglobinemia

Explanation: **Explanation:** **Thiopentone Sodium** is an ultra-short-acting barbiturate used for the induction of anesthesia. **1. Why Acute Intermittent Porphyria (AIP) is the Correct Answer:** Thiopentone is an **absolute contraindication** in patients with porphyria (specifically AIP, Variegate Porphyria, and Hereditary Coproporphyria). Barbiturates strongly induce the enzyme **delta-aminolevulinic acid (δ-ALA) synthase**. This induction accelerates the heme biosynthetic pathway, leading to the toxic accumulation of porphyrins and their precursors. This can precipitate a life-threatening crisis characterized by severe abdominal pain, neurological deficits, psychiatric symptoms, and cardiovascular instability. **2. Analysis of Incorrect Options:** * **Cardiotoxicity:** While thiopentone causes dose-dependent myocardial depression and peripheral vasodilation (leading to hypotension), it is a **relative contraindication** in patients with hypovolemia or shock, not an absolute one. * **Malignant Hyperthermia (MH):** Thiopentone is actually considered **safe** in MH-susceptible patients. The primary triggers for MH are volatile inhalational agents (e.g., Halothane) and Succinylcholine. * **Methemoglobinemia:** This is a concern primarily with local anesthetics like **Prilocaine** and **Benzocaine**, which can oxidize hemoglobin. Thiopentone does not affect hemoglobin oxidation states. **High-Yield Clinical Pearls for NEET-PG:** * **pH:** Thiopentone is highly alkaline (pH 10.5). Accidental **intra-arterial injection** causes severe vasospasm and gangrene (Treatment: Heparin, Papaverine, or Brachial plexus block). * **Context-Sensitive Half-Life:** It has a long context-sensitive half-life, making it unsuitable for prolonged infusions. * **Gold Standard:** Despite newer agents, it remains the gold standard for rapid sequence induction in patients with increased intracranial pressure (due to its ability to reduce cerebral metabolic rate and blood flow).

Question 444: All of the following statements regarding minimum alveolar concentration (MAC) are true, except one?

A. A lower MAC indicates higher potency.
B. The rate of induction is dependent on MAC. (Correct Answer)
C. Nitrous oxide has a MAC value of 104 and is therefore the least potent.
D. Methoxyflurane has the lowest MAC value.

Explanation: ### Explanation **1. Why Option B is the Correct Answer (The Exception)** The **rate of induction** is primarily determined by the **Blood-Gas Partition Coefficient (Solubility)**, not the Minimum Alveolar Concentration (MAC). * **Solubility:** Agents with low blood-gas solubility (e.g., Desflurane, Sevoflurane) reach equilibrium between the alveoli and blood faster, leading to a rapid rise in alveolar concentration ($F_A/F_I$ ratio) and faster induction. * **MAC:** This is a measure of **potency** (pharmacodynamics), representing the concentration required to prevent movement in 50% of patients in response to a surgical stimulus. It does not dictate how quickly a patient goes to sleep. **2. Analysis of Other Options** * **Option A:** MAC is inversely proportional to potency ($Potency \propto 1/MAC$). Therefore, the lower the MAC, the more potent the anesthetic. * **Option C:** Nitrous Oxide ($N_2O$) has a MAC of 104%. Since it is impossible to achieve this concentration at sea level without sacrificing oxygenation, it is considered the least potent inhalational agent. * **Option D:** Methoxyflurane has a MAC of approximately 0.16%, making it the most potent inhalational anesthetic ever used clinically (though it is now obsolete due to nephrotoxicity). **3. High-Yield Clinical Pearls for NEET-PG** * **Meyer-Overton Hypothesis:** Potency of an anesthetic is directly proportional to its lipid solubility. * **Factors Increasing MAC (Need more drug):** Hyperthermia, chronic alcoholism, hypernatremia, and increased central neurotransmitters (e.g., MAO inhibitors, cocaine, ephedrine). * **Factors Decreasing MAC (Need less drug):** Hypothermia, pregnancy, acute alcohol intoxication, old age, and concurrent use of opioids or benzodiazepines. * **MAC-Awake:** The concentration at which 50% of patients respond to verbal commands (usually ~0.3–0.5 MAC). * **MAC-BAR:** The concentration required to block autonomic responses (usually ~1.5–2.0 MAC).

Question 445: Which of the following statements is not true regarding Xenon anesthesia?

A. It is non-explosive.
B. It has minimal cardiovascular side effects.
C. It causes slow induction and slow recovery. (Correct Answer)
D. It has low blood gas solubility.

Explanation: **Explanation:** Xenon is an inert noble gas that acts as an ideal anesthetic agent in many respects. The correct answer is **C** because Xenon actually provides **rapid induction and rapid recovery**, not slow. **1. Why Option C is the correct (false) statement:** The speed of induction and recovery of an inhalational anesthetic is inversely proportional to its **blood-gas partition coefficient**. Xenon has an extremely low blood-gas solubility coefficient (**0.115**), which is significantly lower than Desflurane (0.42) or Nitrous Oxide (0.47). This low solubility ensures that the partial pressure in the blood rises and falls very quickly, leading to the fastest induction and emergence among all known inhalational agents. **2. Analysis of incorrect (true) options:** * **Option A:** Xenon is an inert gas; it is non-flammable, non-explosive, and environmentally friendly (no greenhouse effect). * **Option B:** Xenon is remarkably **cardioprotective**. It does not suppress myocardial contractility and maintains stable hemodynamics, making it ideal for high-risk cardiac patients. * **Option D:** As mentioned, its blood-gas solubility is 0.115, which is the lowest of all anesthetic gases. **High-Yield Clinical Pearls for NEET-PG:** * **MAC of Xenon:** Approximately **63–71%** (less potent than volatile liquids but more potent than $N_2O$). * **Mechanism:** Primarily acts via **NMDA receptor antagonism** (unlike most volatiles that act on $GABA_A$). * **Neuroprotection:** It is known for its potent neuroprotective properties. * **Main Limitation:** High cost and the requirement for specialized closed-circuit delivery systems to prevent wastage.

Question 446: What is the MAC of halothane?

A. 0.75% (Correct Answer)
B. 1-2%
C. 6%
D. 2%

Explanation: **Explanation:** The **Minimum Alveolar Concentration (MAC)** is the concentration of an inhalation anesthetic at 1 atmosphere that prevents skeletal muscle movement in response to a noxious stimulus (surgical incision) in 50% of patients. It is the standard measure of **anesthetic potency**; the lower the MAC, the more potent the agent. **Why 0.75% is correct:** Halothane is a highly lipid-soluble volatile anesthetic with a high oil-gas partition coefficient. Because of its high potency, it requires a very low alveolar concentration to achieve anesthesia. Its standard MAC value is **0.75%**, making it one of the most potent inhalation agents historically used in clinical practice. **Analysis of incorrect options:** * **B (1-2%):** This range corresponds to the MAC of **Isoflurane (1.15%)** and **Enflurane (1.68%)**. * **C (6%):** This is the MAC of **Desflurane (approx. 6.0%)**. Desflurane has low lipid solubility, meaning a much higher concentration is required to achieve the same anesthetic effect as Halothane. * **D (2%):** This is the MAC of **Sevoflurane (approx. 2.0%)**, the most commonly used induction agent in modern pediatric anesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **Potency vs. Speed:** Halothane is the most potent (lowest MAC), but **Desflurane** is the fastest acting (lowest Blood-Gas partition coefficient). * **Halothane Hepatitis:** A rare but serious immune-mediated hepatotoxicity associated with repeated exposure. * **Catecholamine Sensitivity:** Halothane sensitizes the myocardium to epinephrine, increasing the risk of ventricular arrhythmias. * **MAC-Awake:** The concentration at which 50% of patients will open their eyes to command (usually ~0.33 MAC). * **MAC-BAR:** The concentration required to block autonomic responses to incision (usually ~1.5 to 2.0 MAC).

Question 447: Which of the following side effects are seen with etomidate?

A. Myoclonus, adrenal suppression, hemodynamic imbalance
B. Myoclonus, adrenal suppression, pain on IV injection (Correct Answer)
C. Pain on IV injection, adrenal suppression, hemodynamic imbalance
D. Pain on IV injection, hemodynamic imbalance, myoclonus

Explanation: **Explanation:** Etomidate is a carboxylated imidazole derivative used for the induction of general anesthesia. It is highly favored for its **hemodynamic stability**, making it the induction agent of choice for patients with cardiovascular disease, shock, or hypovolemia. **Why Option B is Correct:** The three hallmark side effects of Etomidate are: 1. **Adrenal Suppression:** It causes dose-dependent inhibition of the enzyme **11-beta-hydroxylase**, which is essential for cortisol and aldosterone synthesis. This effect can last for 24–48 hours after a single dose. 2. **Myoclonus:** Involuntary muscle movements occur in up to 70% of patients (without premedication) due to disinhibition of subcortical structures. 3. **Pain on Injection:** Because etomidate is poorly water-soluble, it is formulated in **propylene glycol**, which causes significant venous irritation and pain during administration. **Why Other Options are Incorrect:** * **Options A, C, and D** are incorrect because they include **"Hemodynamic Imbalance."** Etomidate is unique because it has minimal to no effect on heart rate, systemic vascular resistance, or myocardial contractility. It maintains a stable blood pressure, unlike propofol or thiopentone. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** For induction in patients with **Ruptured Ectopic Pregnancy, Cardiac Tamponade, or Severe Valvular Heart Disease.** * **Cerebral Effects:** It decreases Cerebral Metabolic Rate (CMRO2) and Intracranial Pressure (ICP) while maintaining Cerebral Perfusion Pressure. * **Nausea/Vomiting:** Etomidate has a high incidence of Postoperative Nausea and Vomiting (PONV). * **Contraindication:** Avoid in patients with **Addison’s disease** or severe sepsis due to its adrenocortical suppressive effects.

Question 448: Which of the following is NOT true about Rocuronium bromide?

A. It is one of the most commonly used non-depolarizing agents.
B. It is a non-depolarizing agent of choice for rapid sequence induction.
C. Sugammadex is its specific reversal agent.
D. It is most preferred in hepatic and renal failure. (Correct Answer)

Explanation: **Explanation:** **Rocuronium bromide** is an amino-steroid, non-depolarizing neuromuscular blocking agent (NMBA) with an intermediate duration of action. **Why Option D is the Correct Answer (The False Statement):** Rocuronium is primarily eliminated via **hepatic metabolism and biliary excretion** (approx. 70%), with the remainder excreted by the kidneys. In patients with hepatic or renal failure, its clearance is significantly reduced, leading to a prolonged duration of action and unpredictable recovery. For these patients, **Cisatracurium** is the drug of choice because it undergoes **Hofmann elimination** (organ-independent degradation), making it safer in organ failure. **Analysis of Other Options:** * **Option A:** It is indeed one of the most commonly used NMBAs due to its rapid onset and stable cardiovascular profile. * **Option B:** At a dose of 0.9–1.2 mg/kg, Rocuronium provides excellent intubating conditions in <60 seconds, making it the best non-depolarizing alternative to Succinylcholine for **Rapid Sequence Induction (RSI)**. * **Option C:** **Sugammadex** is a selective relaxant binding agent designed specifically to encapsulate and rapidly reverse Rocuronium (and Vecuronium), even during deep blockade. **High-Yield Clinical Pearls for NEET-PG:** * **Onset of Action:** Fastest among non-depolarizing NMBAs (60–90 seconds). * **Storage:** Should be stored in a refrigerator (2–8°C) to maintain potency. * **RSI Dose:** 1.2 mg/kg (double the standard intubating dose of 0.6 mg/kg). * **Side Effects:** It is relatively cardiovascular stable but can rarely cause mild tachycardia. Unlike older agents, it has minimal histamine release.

Question 449: Ketamine is safe in which of the following conditions?

A. Raised intracranial pressure (ICT)
B. Open eye injury
C. Ischemic heart disease
D. Severe shock (Correct Answer)

Explanation: **Explanation:** **Ketamine** is a unique dissociative anesthetic that acts primarily as an **NMDA receptor antagonist**. **Why "Severe Shock" is the Correct Answer:** Ketamine is the induction agent of choice in hemodynamically unstable patients (severe shock, trauma, or hypovolemia). Unlike most induction agents (like Propofol or Thiopental) which cause myocardial depression and vasodilation, Ketamine stimulates the **sympathetic nervous system**. It causes an indirect release of catecholamines, leading to an **increase in heart rate, blood pressure, and cardiac output**, which helps maintain perfusion in shock states. **Why Other Options are Incorrect:** * **Raised Intracranial Pressure (ICT):** Ketamine is traditionally contraindicated in head injuries because it increases cerebral blood flow (CBF), cerebral metabolic rate ($CMRO_2$), and ICP, potentially worsening brain herniation. * **Open Eye Injury:** Ketamine increases **Intraocular Pressure (IOP)** due to its effect on extraocular muscle tone and sympathetic stimulation. This can lead to the extrusion of intraocular contents in an open-globe injury. * **Ischemic Heart Disease (IHD):** Because Ketamine increases myocardial oxygen demand (due to tachycardia and hypertension), it can precipitate myocardial ischemia or infarction in patients with pre-existing coronary artery disease. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Dissociative anesthesia (eyes remain open with a slow nystagmic gaze). * **Airway:** It preserves airway reflexes and is a potent **bronchodilator** (drug of choice for induction in status asthmaticus). * **Secretions:** It causes **hypersalivation**; hence, premedication with Glycopyrrolate is often required. * **Emergence:** Associated with **emergence delirium/hallucinations**, which can be prevented by co-administering Benzodiazepines (e.g., Midazolam).

Question 450: What is the use of Thiopentone?

A. Seizure
B. Truth spell
C. Reduction of Intracranial Pressure (ICP)
D. All of the above (Correct Answer)

Explanation: **Explanation:** Thiopentone sodium is a short-acting barbiturate that acts by enhancing GABA-mediated inhibition in the CNS. It is a versatile drug with several clinical applications beyond induction of anesthesia. * **Reduction of Intracranial Pressure (ICP):** Thiopentone causes potent cerebral vasoconstriction, which leads to a decrease in cerebral blood flow (CBF) and cerebral blood volume, thereby lowering ICP. It also reduces the Cerebral Metabolic Rate of Oxygen (CMRO2), providing a "cerebral protective" effect during neurosurgery or head injuries. * **Seizure Management:** Due to its potent anticonvulsant properties, Thiopentone is used to terminate status epilepticus that is refractory to first-line agents like benzodiazepines or phenytoin. * **Truth Spell (Narcoanalysis):** In forensic psychiatry, Thiopentone is historically known as a "truth serum." At sub-anesthetic doses, it induces a state of disinhibition and relaxation, making a person more likely to divulge information, though its legal and scientific validity is debated. **High-Yield Clinical Pearls for NEET-PG:** * **Drug of Choice:** Thiopentone remains a classic choice for rapid sequence induction in patients with increased ICP (provided they are hemodynamically stable). * **Contraindication:** It is strictly contraindicated in **Porphyria** (induces ALA synthetase). * **Complication:** Accidental intra-arterial injection causes severe spasm and gangrene. Treatment includes heparin, papaverine, and sympathetic block (Stellate ganglion block). * **Storage:** It is stored in an atmosphere of **Nitrogen** and contains 6% anhydrous sodium carbonate to prevent precipitation by atmospheric CO2.

Practice by Chapter

History of Anesthesia

Practice Questions

Preoperative Evaluation

Practice Questions

Pharmacology of Inhalational Anesthetics

Practice Questions

Pharmacology of Intravenous Anesthetics

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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

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