Pharmacology of Inhalational Anesthetics — MCQs
Which of the following statements about Nitrous Oxide (N2O) is true?
Which of the following inhalational agents sensitizes myocardium to catecholamines?
Which inhalational anesthetic is most commonly used for induction in general anesthesia?
What is the preferred concentration range of lidocaine for topical anesthesia?
Which of the following inhalational agent is contraindicated in a patient with history of epilepsy -
Malignant hyperthermia is a rare complication of the use of the following anaesthetic:
Which of the following is most cardio depressant
Which of the following inhalation anesthetic agents is hepatotoxic?
A patient with mitral stenosis is having surgery tomorrow. There is some liver compromise. Which of the following inhalational agents is preferred?
Which of the following inhalation anesthetics should be avoided in middle ear surgery?
Pharmacology of Inhalational Anesthetics Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following statements about Nitrous Oxide (N2O) is true?
- A. Least potent inhalational anesthetic (Correct Answer)
- B. Lighter than air
- C. Effective muscle relaxant
- D. Does not cause diffusion hypoxia
Explanation: **Least potent inhalational anesthetic** - Nitrous oxide has a **high Minimum Alveolar Concentration (MAC)** of approximately 104%, making it the least potent of the commonly used inhalational anesthetics. - Its high MAC means a very high concentration is required to achieve surgical anesthesia, which is why it is typically used as an adjunct to more potent agents. *Lighter than air* - The molecular weight of nitrous oxide (N2O) is 44, which is **heavier than air** (average molecular weight approximately 29 g/mol). - Its density is greater than air, meaning it would tend to sink rather than rise. *Effective muscle relaxant* - Nitrous oxide provides **minimal to no skeletal muscle relaxation** benefits. - If muscle relaxation is required, a neuromuscular blocking agent must be administered separately. *Does not cause diffusion hypoxia* - Nitrous oxide rapidly diffuses out of the blood into the alveoli during emergence, diluting the oxygen and carbon dioxide there. - This rapid diffusion can lead to **diffusion hypoxia** (also known as the "second gas effect"), necessitating the administration of 100% oxygen during recovery to prevent this complication.
Question 2: Which of the following inhalational agents sensitizes myocardium to catecholamines?
- A. Ether
- B. Isoflurane
- C. Sevoflurane
- D. Halothane (Correct Answer)
Explanation: ***Halothane*** - **Halothane** significantly sensitizes the myocardium to the dysrhythmogenic effects of **exogenous and endogenous catecholamines**, leading to an increased risk of ventricular arrhythmias. - This effect is due to its interaction with myocardial ion channels and adrenergic receptors, making the heart more susceptible to the arrhythmogenic actions of **norepinephrine** and **epinephrine**. *Ether* - **Diethylether** does not significantly sensitize the myocardium to catecholamines; in fact, it tends to have a more stable cardiovascular profile in this regard. - While it can cause some sympathetic stimulation, its arrhythmogenic potential with catecholamines is much lower compared to halothane. *Isoflurane* - **Isoflurane** has a minimal effect on myocardial sensitization to catecholamines, making it a safer option for patients with pre-existing cardiac conditions or those requiring exogenous catecholamine administration. - It maintains cardiac rhythm stability much better than halothane in the presence of adrenergic stimulation. *Sevoflurane* - **Sevoflurane**, similar to isoflurane, causes very little myocardial sensitization to catecholamines and is considered to be a **cardiac-friendly** inhalational agent. - It maintains **hemodynamic stability** and has a low incidence of arrhythmias even with concurrent use of epinephrine.
Question 3: Which inhalational anesthetic is most commonly used for induction in general anesthesia?
- A. Sevoflurane (Correct Answer)
- B. Desflurane
- C. Enflurane
- D. Nitrous oxide
Explanation: ***Sevoflurane*** - **Sevoflurane** is preferred for inhalational induction due to its **low pungency** and **rapid onset** and offset of action. - Its favorable pharmacokinetic profile makes it suitable for patients of all ages, including children, for quick and smooth induction without airway irritation. *Desflurane* - **Desflurane** has a **very low blood-gas solubility**, leading to rapid onset and offset, but it is **too pungent** for inhalational induction. - Its high pungency often causes **coughing, salivation, and laryngospasm**, making it unsuitable forawake induction *Enflurane* - **Enflurane** is an older inhalational anesthetic that is **rarely used today** due to its side effects, including the potential for **seizures** and **arrhythmias**. - Its slower onset and higher incidence of adverse effects make it inferior to newer agents for induction. *Nitrous oxide* - **Nitrous oxide** is a weak anesthetic and is typically used as an adjunct to other more potent inhalational agents, not as a primary induction agent. - It has a high **MAC (Minimum Alveolar Concentration)**, meaning it cannot produce surgical anesthesia on its own.
Question 4: What is the preferred concentration range of lidocaine for topical anesthesia?
- A. 2-4% (Correct Answer)
- B. 7-12%
- C. 12-15%
- D. <2%
Explanation: ***Correct Option: 2-4%*** - **Lidocaine** is an **amide-type local anesthetic** commonly used for topical anesthesia to numb localized areas before minor procedures. - The **preferred concentration range for topical application is 2-4%**, which provides effective anesthesia with an acceptable safety profile. - **2% lidocaine gel/cream** is commonly used for skin and genital mucosa. - **4% lidocaine** is standard for oral and respiratory mucous membranes. - **5% lidocaine patches** are used for post-herpetic neuralgia. - This concentration range balances **clinical efficacy** with **minimal systemic toxicity risk**. *Incorrect Option: <2%* - Concentrations below **2%** are generally **suboptimal** for achieving significant topical anesthesia. - These lower concentrations result in **insufficient pain relief** or require longer application times. - While 0.5-1% solutions exist, they are primarily used for infiltration anesthesia, not topical application. *Incorrect Option: 7-12%* - Concentrations in the **7-12%** range are **too high** for routine topical use and increase the risk of **systemic toxicity**. - These concentrations are not standard in clinical practice for general topical anesthesia. - Higher concentrations increase absorption without proportional improvement in efficacy. *Incorrect Option: 12-15%* - Concentrations in the **12-15%** range are **excessively high** and pose substantial **risk of systemic absorption and toxicity**. - Such high concentrations are **not recommended** for topical anesthesia in clinical practice. - Even 10% sprays (used for oropharyngeal anesthesia) require strict dose limitations to prevent toxicity.
Question 5: Which of the following inhalational agent is contraindicated in a patient with history of epilepsy -
- A. Enflurane (Correct Answer)
- B. Isoflurane
- C. Sevoflurane
- D. Halothane
Explanation: ***Enflurane*** - **Enflurane** is known to cause **epileptiform EEG changes** and seizures, especially at high concentrations or in the presence of hypocarbia. - This proconvulsant effect makes it contraindicated in patients with a history of **epilepsy** due to the risk of inducing or exacerbating seizure activity. *Isoflurane* - **Isoflurane** is generally considered safe in patients with epilepsy as it has **minimal proconvulsant activity** and can even have anticonvulsant properties. - It does not typically produce epileptiform EEG patterns or clinical seizures. *Sevoflurane* - **Sevoflurane** is also considered safe in epileptic patients and is widely used for induction and maintenance of anesthesia. - While there have been reports of seizure-like activity during **Sevoflurane** induction, these are rare and usually resolve quickly without long-term complications. *Halothane* - **Halothane** is largely historical and not commonly used today due to its association with **hepatotoxicity** and cardiac dysrhythmias. - It does not typically induce seizures and historically was not contraindicated in patients with epilepsy based on seizure risk.
Question 6: Malignant hyperthermia is a rare complication of the use of the following anaesthetic:
- A. Thiopentone sodium
- B. Halothane (Correct Answer)
- C. Ether
- D. Ketamine
Explanation: **Halothane** - **Halothane** is a potent volatile anesthetic and a classic trigger for **malignant hyperthermia** due to its effect on ryanodine receptors, leading to excessive calcium release from the sarcoplasmic reticulum. - While its use has declined, it remains a critical example of an anesthetic agent known to induce this life-threatening genetic disorder. *Thiopentone Sodium* - **Thiopentone sodium** is an intravenous barbiturate anesthetic and is **not associated** with triggering malignant hyperthermia. - It is often used for induction of anesthesia and has a different mechanism of action involving GABA receptors. *Ether* - **Diethyl ether** was one of the earliest general anesthetics but is **not a trigger** for malignant hyperthermia. - Its use has largely been discontinued due to its flammability and adverse side effects, but it doesn't cause MH. *Ketamine* - **Ketamine** is a dissociative anesthetic that acts as an NMDA receptor antagonist and is **not a trigger** for malignant hyperthermia. - It is often used for its analgesic and sedative properties and is considered safe in patients susceptible to MH.
Question 7: Which of the following is most cardio depressant
- A. Sevoflurane
- B. Halothane (Correct Answer)
- C. Isoflurane
- D. Desflurane
Explanation: ***Halothane*** - **Halothane** is known for causing significant **myocardial depression** by directly reducing myocardial contractility and stroke volume. - It also **sensitizes the myocardium to catecholamines**, increasing the risk of arrhythmias. *Sevoflurane* - **Sevoflurane** causes less **myocardial depression** and is often preferred in patients with compromised cardiac function. - Its effects on heart rate and blood pressure are generally moderate compared to halothane. *Isoflurane* - **Isoflurane** can cause **systemic vasodilation** and a dose-dependent decrease in blood pressure but is generally less cardio-depressant than halothane. - It maintains **cardiac output** better than halothane, sometimes increasing heart rate to compensate for vasodilation. *Desflurane* - **Desflurane** typically causes a **lesser degree of myocardial depression** and tends to preserve cardiac output. - It can, however, lead to transient increases in heart rate and blood pressure upon rapid increases in concentration due to **sympathetic stimulation**.
Question 8: Which of the following inhalation anesthetic agents is hepatotoxic?
- A. Halothane (Correct Answer)
- B. Sevoflurane
- C. Isoflurane
- D. Desflurane
Explanation: ***Halothane*** - **Halothane** is known for its potential to cause **halothane hepatitis**, a severe and sometimes fatal form of liver damage. - This toxicity is typically due to the formation of reactive metabolites during its metabolism, which can lead to immune-mediated liver injury. *Sevoflurane* - **Sevoflurane** is generally considered to have a very low risk of hepatotoxicity. - While it can produce a small amount of inorganic fluoride, which was a concern with older halogenated anesthetics, its metabolic profile makes it much safer for the liver compared to halothane. *Isoflurane* - **Isoflurane** is metabolized to a very small extent (less than 0.2%), significantly reducing the risk of generating toxic metabolites that could harm the liver. - It is commonly used in clinical practice due to its favorable safety profile, including minimal hepatotoxicity. *Desflurane* - **Desflurane** has an even lower metabolism rate than Isoflurane, making it one of the safest inhaled anesthetics in terms of liver toxicity. - Its rapid onset and offset properties, coupled with its minimal metabolism, contribute to its low potential for hepatotoxic effects.
Question 9: A patient with mitral stenosis is having surgery tomorrow. There is some liver compromise. Which of the following inhalational agents is preferred?
- A. Enflurane
- B. Xenon
- C. Sevoflurane (Correct Answer)
- D. Halothane
Explanation: ***Sevoflurane*** - **Sevoflurane** is preferred due to its **minimal hepatic metabolism** and rapid elimination, making it a safer option in patients with **liver compromise**. - It maintains **cardiovascular stability**, which is beneficial in mitral stenosis and avoids the arrhythmogenic potential seen with other agents. *Enflurane* - **Enflurane** is extensively metabolized in the liver, leading to the production of inorganic fluoride ions, which can cause **renal toxicity**. - It can also induce a decrease in **hepatic blood flow**, exacerbating existing liver compromise. *Xenon* - While **Xenon** has excellent cardiovascular stability and minimal metabolism, its **high cost** and **limited availability** make it an impractical choice for routine use. - Its anesthetic potency is relatively low, requiring **higher concentrations** for surgical anesthesia. *Halothane* - **Halothane** is associated with a significant risk of **halothane-induced hepatitis** due to its extensive hepatic metabolism and the production of toxic metabolites. - It can also cause **cardiac depression** and **arrhythmias**, which are undesirable in patients with mitral stenosis.
Question 10: Which of the following inhalation anesthetics should be avoided in middle ear surgery?
- A. Nitrous oxide (Correct Answer)
- B. Isoflurane
- C. Ether
- D. Halothane
Explanation: ***Nitrous oxide*** - **Nitrous oxide** rapidly diffuses into air-containing cavities, such as the middle ear, causing an increase in pressure that can disrupt grafts and ossicles, leading to **hearing loss** or **facial nerve damage**. - Its use during tympanoplasty or stapedectomy can lead to **barotrauma** and potential complications for graft survival and successful middle ear reconstruction. *Ether* - **Ether** is an older anesthetic not commonly used today in developed countries due to its flammability, pungency, and slow onset/offset. - While it doesn't specifically cause middle ear pressure changes like nitrous oxide, its general disadvantages make it an unsuitable choice for modern surgical anesthesia. *Isoflurane* - **Isoflurane** is a volatile anesthetic that does not readily diffuse into air-filled cavities in a manner that would significantly increase middle ear pressure. - It is a commonly used intravenous anesthetic for maintaining general anesthesia and would not typically be avoided for middle ear surgery. *Halothane* - **Halothane** is a potent volatile anesthetic but is rarely used now due to concerns about **hepatotoxicity** (halothane hepatitis). - Like other volatile anesthetics (except nitrous oxide), it does not cause rapid and problematic pressure changes within the middle ear.
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