General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 391: Which induction agent is the drug of choice in a patient with bronchial asthma?

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

Explanation: **Explanation:** **Ketamine** is the induction agent of choice for patients with bronchial asthma due to its potent **bronchodilatory properties**. It acts by increasing sympathetic outflow (releasing endogenous catecholamines) and directly relaxing bronchial smooth muscle. This makes it ideal for preventing or managing bronchospasm during induction and intubation. **Analysis of Options:** * **A. Thiopentone:** It is contraindicated in asthma. It can cause histamine release and may lead to life-threatening bronchospasm. It also does not sufficiently suppress airway reflexes. * **B. Methohexitone:** Similar to other barbiturates, it can trigger histamine release and lacks bronchodilatory effects. * **D. Propofol:** While Propofol is a good bronchodilator and is often used in stable asthmatics because it effectively suppresses airway reflexes, **Ketamine remains the "drug of choice"** in emergency or severe cases due to its active sympathomimetic action. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Ketamine’s bronchodilation is mediated via $\beta_2$ adrenoceptor stimulation (indirect) and inhibition of vagal tone. * **Alternative:** If Ketamine cannot be used, **Propofol** is the second-best choice due to its ability to reduce airway resistance. * **Avoid:** Barbiturates (Thiopentone) and certain Muscle Relaxants (Atracurium, Mivacurium) in asthmatics as they trigger histamine release. * **Volatile Agents:** **Sevoflurane** is the preferred inhalational agent for induction in asthmatics because it is non-pungent and a potent bronchodilator. Desflurane should be avoided as it can irritate the airway.

Question 392: Which muscles are the first to recover after administration of muscle relaxants?

A. Laryngeal muscles
B. Abdominal muscles
C. Diaphragm (Correct Answer)
D. Thenar muscles

Explanation: **Explanation:** The sensitivity of muscles to neuromuscular blocking agents (NMBAs) follows a predictable pattern based on muscle fiber type, blood flow, and the density of acetylcholine receptors. **1. Why the Diaphragm is Correct:** The **diaphragm** is the most resistant muscle to NMBAs and is the **first to recover** from a neuromuscular block. This is due to its high density of acetylcholine receptors and its central location, which ensures high regional blood flow, allowing for rapid delivery and subsequent washout of the relaxant. Conversely, because it is resistant, the diaphragm is also the **last to be paralyzed** during induction. **2. Analysis of Incorrect Options:** * **Laryngeal muscles (A):** These recover after the diaphragm but before the peripheral muscles. They are relatively resistant but not as much as the diaphragm. * **Abdominal muscles (B):** These are intermediate in sensitivity. They are paralyzed after the diaphragm but before the small muscles of the hand. * **Thenar muscles (D):** These are peripheral muscles (like the adductor pollicis). Peripheral muscles are the **first to be paralyzed** and the **last to recover**. This is why monitoring the adductor pollicis with a nerve stimulator is a "safe" indicator; if the thumb has recovered, the diaphragm has certainly recovered. **3. High-Yield Clinical Pearls for NEET-PG:** * **Sequence of Paralysis:** Small muscles (eyes/fingers) → Limbs → Trunk (Abdomen) → Intercostals → Diaphragm. * **Sequence of Recovery:** Exactly the reverse (Diaphragm recovers first; Eye muscles recover last). * **Monitoring Tip:** To monitor **onset** (intubation readiness), the orbicularis oculi is preferred (reflects the diaphragm). To monitor **recovery** (extubation readiness), the adductor pollicis is preferred (reflects the return of airway protection).

Question 393: The rate of induction of anesthesia is increased by all of the following except?

A. Agents with low blood-gas solubility
B. High cardiac output (Correct Answer)
C. Second gas effect
D. High alveolar ventilation

Explanation: The rate of induction of inhalational anesthesia depends on how quickly the **alveolar partial pressure (PA)** of the anesthetic gas reaches the **inspired partial pressure (PI)**. The faster the alveolar concentration rises, the faster the brain concentration rises, leading to induction. ### Why High Cardiac Output is the Correct Answer Contrary to intuition, a **high cardiac output (CO) slows down induction**. When CO is high, a larger volume of blood passes through the pulmonary capillaries per minute. This "washes away" the anesthetic gas from the alveoli into the systemic circulation more rapidly, preventing the buildup of alveolar partial pressure. Consequently, the ratio of $P_A/P_I$ rises slowly, delaying induction. Conversely, in shock states (low CO), induction is much faster. ### Explanation of Other Options * **Low Blood-Gas Solubility (A):** Agents like Sevoflurane or Desflurane do not dissolve easily in blood. Since the blood "reservoir" doesn't need to be filled first, the alveolar partial pressure rises rapidly, leading to **faster induction**. * **Second Gas Effect (C):** When a high concentration of a fast-absorbing gas (like $N_2O$) is given with a potent volatile anesthetic, the rapid uptake of $N_2O$ creates a vacuum that "sucks" in more of the second gas, **speeding up its induction**. * **High Alveolar Ventilation (D):** Increased ventilation replaces the gas taken up by the blood more quickly, maintaining a high concentration gradient and **accelerating induction**. ### High-Yield Clinical Pearls for NEET-PG * **Solubility Rule:** The lower the Blood-Gas Partition Coefficient, the faster the induction (e.g., Desflurane is the fastest). * **Concentration Effect:** Higher inspired concentrations lead to faster induction. * **Ventilation-Perfusion:** Ventilation affects insoluble agents more; Cardiac Output affects soluble agents (like Halothane) more.

Question 394: Which of the following is the muscle relaxant of choice in renal failure?

A. Rapacurium
B. Pancuronium
C. Atracurium (Correct Answer)
D. Rocuronium

Explanation: **Explanation:** The muscle relaxant of choice in renal failure is **Atracurium** (or its isomer, Cisatracurium). **1. Why Atracurium is the Correct Choice:** Most neuromuscular blocking agents (NMBAs) rely on renal or hepatic excretion for clearance. In renal failure, these drugs accumulate, leading to prolonged paralysis. Atracurium is unique because it undergoes **Hofmann Elimination**—a spontaneous, non-enzymatic degradation at physiological pH and temperature—and ester hydrolysis. Since its metabolism is independent of organ function, its duration of action remains unchanged in patients with end-stage renal disease (ESRD). **2. Why the Other Options are Incorrect:** * **Pancuronium:** This is a long-acting NMBA primarily excreted by the kidneys (approx. 80%). It is strictly contraindicated in renal failure due to the high risk of profound, prolonged neuromuscular blockade. * **Rocuronium:** It is primarily eliminated by the liver, but a significant portion (up to 30%) is excreted unchanged in the urine. Its duration of action is unpredictable and often prolonged in renal failure. * **Rapacurium:** This was a rapid-onset agent withdrawn from the market worldwide due to a high incidence of severe bronchospasm. **Clinical Pearls for NEET-PG:** * **Cisatracurium** is more potent than atracurium and is often preferred because it produces less **laudanosine** (a metabolite that can cause seizures) and does not cause histamine release. * **Vecuronium** is mostly biliary-excreted but has an active metabolite (3-desacetyl vecuronium) that accumulates in renal failure. * **Sugammadex** (a reversal agent) is generally avoided in severe renal impairment because the sugammadex-rocuronium complex is cleared renally.

Question 395: Which of the following statements regarding halothane is incorrect?

A. It is generally considered unsuitable for the pediatric population. (Correct Answer)
B. It potentiates the effects of competitive neuromuscular blockers.
C. Hepatitis is a known potential adverse effect.
D. It is contraindicated in patients with certain cardiac arrhythmias.

Explanation: **Explanation:** The correct answer is **A**, as the statement is incorrect. Halothane has historically been the **agent of choice for pediatric inhalation induction**. This is because it is non-pungent, has a pleasant odor, and does not irritate the airways, leading to a smooth induction with a low incidence of laryngospasm or coughing. In contrast, it is less preferred in adults due to the higher risk of halothane-induced hepatitis. **Analysis of other options:** * **Option B:** Halothane, like all volatile anesthetics, **potentiates** both depolarizing and non-depolarizing (competitive) neuromuscular blockers by acting on the nicotinic acetylcholine receptors at the neuromuscular junction. * **Option C:** **Halothane Hepatitis** is a rare but severe immune-mediated hepatotoxicity caused by the metabolite trifluoroacetyl chloride. It occurs more frequently in adults, especially with repeated exposure. * **Option D:** Halothane **sensitizes the myocardium to catecholamines**, which can trigger ventricular arrhythmias. It is contraindicated in patients with pre-existing arrhythmias or those receiving exogenous adrenaline. **High-Yield NEET-PG Pearls:** * **Blood-Gas Partition Coefficient:** 2.4 (High solubility leads to slow induction/recovery). * **Metabolism:** Approximately 20% is metabolized in the liver (highest among common volatiles). * **Preservative:** Contains **Thymol**, which can cause vaporizer valves to stick. * **Uterine Effect:** Causes significant uterine relaxation, making it useful for version but risky for postpartum hemorrhage. * **Malignant Hyperthermia:** Like all volatile agents, it is a known trigger.

Question 396: Which is the most potent analgesic agent among the following?

A. Nitrous oxide (Correct Answer)
B. Nitric oxide
C. Carbon dioxide
D. Oxygen

Explanation: **Explanation:** **Nitrous Oxide (N₂O)**, also known as "laughing gas," is the correct answer because it is the only agent among the options that possesses significant anesthetic and analgesic properties. While it is a weak anesthetic (MAC of 104%), it is a **potent analgesic**. Inhalation of 20% N₂O is equivalent to the analgesic efficacy of 10–15 mg of morphine. Its analgesic effect is primarily mediated through the release of endogenous opioid peptides (endorphins) and the activation of opioid receptors and descending inhibitory pathways in the spinal cord. **Why other options are incorrect:** * **Nitric Oxide (NO):** This is a potent endogenous vasodilator used clinically in inhaled form to treat pulmonary hypertension. It has no analgesic or anesthetic properties. * **Carbon Dioxide (CO₂):** This is a metabolic byproduct. While high levels can cause narcosis (CO₂ narcosis), it is not used as an analgesic and is respiratory-stimulant at lower concentrations. * **Oxygen (O₂):** This is essential for life and aerobic metabolism. While hyperbaric oxygen has specific medical uses, it possesses no intrinsic analgesic properties. **High-Yield Clinical Pearls for NEET-PG:** * **Second Gas Effect:** N₂O accelerates the uptake of a concurrently administered volatile anesthetic. * **Diffusion Hypoxia (Fink Effect):** Occurs during recovery when N₂O rapidly diffuses from blood to alveoli, diluting oxygen. Prevention: Administer 100% O₂ for 5–10 minutes after stopping N₂O. * **Contraindications:** Avoid in closed-space pathologies (e.g., pneumothorax, intestinal obstruction, air embolism, middle ear surgery) because N₂O is 34 times more soluble than nitrogen and expands these spaces. * **Toxicity:** Chronic exposure can lead to Vitamin B12 deficiency (megaloblastic anemia) by oxidizing the cobalt atom in methionine synthase.

Question 397: What is the duration of action of flumazenil?

A. 10 minutes
B. 20 minutes
C. 30 minutes
D. 40 minutes (Correct Answer)

Explanation: **Explanation:** **Flumazenil** is a specific competitive antagonist at the benzodiazepine receptor. It is used to reverse the sedative and respiratory-depressant effects of benzodiazepines (like Midazolam or Diazepam). **Why Option D is Correct:** The duration of action of flumazenil is approximately **30 to 60 minutes** (with a mean clinical effect of roughly **40 minutes**). This is significantly shorter than the half-life of most benzodiazepines it is intended to reverse. Because it is rapidly cleared by the liver, its antagonistic effect wears off quickly. **Why Other Options are Incorrect:** * **Options A & B (10-20 mins):** While the onset of action is rapid (1–2 minutes), the clinical duration is longer than 20 minutes. * **Option C (30 mins):** While 30 minutes is the lower end of the range, 40 minutes is the standard textbook value cited in major anesthesia references (like Miller’s) and frequently tested in NEET-PG as the definitive duration. **Clinical Pearls & High-Yield Facts:** 1. **Resedation (Recurarization):** Because flumazenil’s duration (40 mins) is shorter than that of benzodiazepines (e.g., Diazepam lasts hours), patients may experience "resedation" once the flumazenil wears off. Monitoring for at least 2 hours is essential. 2. **Seizure Risk:** Flumazenil can precipitate acute withdrawal or seizures in patients on long-term benzodiazepine therapy or in cases of mixed tricyclic antidepressant overdose. 3. **Metabolism:** It is metabolized exclusively by the liver (high hepatic extraction ratio). 4. **Dose:** Typically administered in increments of 0.2 mg IV, up to a total of 1 mg.

Question 398: Which of the following agents can be used for anaesthesia in dogs?

A. Ketamine
B. Medetomidine hydrochloride
C. Midazolam
D. All of the above (Correct Answer)

Explanation: **Explanation:** In veterinary anesthesia, particularly for dogs, a multimodal approach is used to ensure sedation, analgesia, and muscle relaxation. All three agents listed are standard components of canine anesthetic protocols. 1. **Ketamine (Option A):** A dissociative anesthetic and NMDA receptor antagonist. It provides excellent somatic analgesia and is frequently used in dogs for induction or as part of a "triple drip" (Ketamine-Guaifenesin-Xylazine) to maintain anesthesia. 2. **Medetomidine hydrochloride (Option B):** A potent alpha-2 adrenergic agonist. It is widely used in veterinary medicine for sedation, premedication, and analgesia. It provides reliable chemical restraint in dogs and is often preferred over xylazine due to higher specificity. 3. **Midazolam (Option C):** A short-acting benzodiazepine used for its anxiolytic, anticonvulsant, and muscle-relaxant properties. In dogs, it is commonly used as a pre-anesthetic medication to facilitate smooth induction and reduce the dose of induction agents like Propofol. **Why "All of the above" is correct:** These drugs are often used in combination (e.g., the "Ket-Mid" protocol) to achieve balanced anesthesia, minimizing the side effects of any single agent while ensuring the animal remains unconscious and pain-free. **High-Yield Clinical Pearls for NEET-PG:** * **Ketamine** is unique because it stimulates the sympathetic nervous system (increasing HR and BP), making it useful in hemodynamically unstable patients, though it increases intracranial pressure. * **Atipamezole** is the specific reversal agent for Medetomidine. * **Flumazenil** is the reversal agent for Midazolam. * In veterinary anesthesia, **Xylazine** is another common alpha-2 agonist, but it is highly emetic in cats.

Question 399: Which of the following anesthetic agents are known to cause pain on injection?

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

Explanation: **Explanation:** The sensation of pain during the intravenous injection of anesthetic agents is a common clinical challenge, primarily caused by the **osmolality** of the formulation or the presence of **propylene glycol** as a solvent, which irritates the venous intima. **1. Why Option C is Correct:** * **Propofol:** The most notorious for causing pain (reported in up to 70% of patients). The pain is attributed to the activation of the **kallikrein-kinin system** and the release of bradykinin. * **Etomidate:** Formulated in 35% propylene glycol, which is highly hyperosmolar and irritating to the veins. * **Methohexitone:** An oxybarbiturate that frequently causes pain on injection and is also associated with excitatory phenomena like myoclonus. **2. Why Other Options are Incorrect:** * **Thiopentone (Options B & D):** While highly alkaline (pH ~10.5) and capable of causing tissue necrosis if injected intra-arterially, it typically does **not** cause significant pain when injected into a large, patent vein. * **Ketamine (Option B):** Generally considered painless upon intravenous injection. **Clinical Pearls for NEET-PG:** * **Prevention:** Pain from Propofol can be reduced by using larger veins (antecubital fossa), prior administration of **IV Lidocaine**, or mixing lidocaine with the drug. * **Excitatory Phenomena:** Both Etomidate and Methohexitone are associated with high incidences of **myoclonus** and hiccups. * **Drug of Choice:** Despite the pain, Etomidate remains the drug of choice for induction in **hemodynamically unstable** patients due to its minimal cardiovascular effects. * **Contraindication:** Avoid Methohexitone and Etomidate in patients with a history of **seizures** (though Methohexitone is used to prolong seizures in ECT).

Question 400: Which of the following increases intraocular pressure?

A. Thiopentone
B. Althesin
C. Ketamine (Correct Answer)
D. Barbiturate

Explanation: **Explanation:** **Ketamine** is the correct answer because it is one of the few anesthetic agents that **increases intraocular pressure (IOP)**. The mechanism is attributed to an increase in extraocular muscle tone and a rise in choroidal blood flow due to sympathetic stimulation. Consequently, Ketamine is generally avoided in patients with penetrating eye injuries or glaucoma where a rise in IOP could lead to the expulsion of intraocular contents or optic nerve damage. **Analysis of Incorrect Options:** * **Thiopentone & Barbiturates (Options A & D):** Most intravenous induction agents, particularly barbiturates, significantly **decrease IOP**. They achieve this by depressing the central nervous system, reducing aqueous humor production, and improving its outflow. * **Althesin (Option B):** This is a steroid-based anesthetic (now largely obsolete due to anaphylaxis) that also causes a **decrease in IOP**, similar to the profile of most non-ketamine induction agents. **High-Yield Clinical Pearls for NEET-PG:** * **IOP & Intubation:** While most induction agents (Propofol, Etomidate, Thiopentone) decrease IOP, the act of **Laryngoscopy and Intubation** causes a sharp rise in IOP. * **Muscle Relaxants:** **Succinylcholine** (Suxamethonium) is notorious for increasing IOP (by ~5-10 mmHg) due to prolonged contraction of extraocular muscles. It is contraindicated in open globe injuries. * **Inhalational Agents:** Most volatile anesthetics (e.g., Sevoflurane, Isoflurane) decrease IOP. * **Exceptions:** Only **Ketamine** and **Succinylcholine** are classic "red flags" for increasing intraocular pressure in anesthesia.

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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