General Anesthetics — MCQs
Anaesthetic agent causing analgesia?
Arrange the following anesthetic agents based on their potency Nitrous oxide Halothane Isoflurane Methoxyflurane
Which of the following is the most potent trigger of malignant hyperthermia?
Malignant hyperthermia is a rare complication of the use of the following anaesthetic:
Depth of Anesthesia is best measured by:
Which anaesthetic agent has maximum MAC ?
Which of the following antiepileptic drugs is preferred for treating generalized tonic-clonic seizures?
Which anti-epileptic drug marked X will act at the site shown?
Which of the following is NOT considered a 'date rape drug'?
What is the percentage of halothane that is metabolized in the human body?
General Anesthetics Indian Medical PG Practice Questions and MCQs
Question 1: Anaesthetic agent causing analgesia?
- A. Thiopentone
- B. Ketamine (Correct Answer)
- C. Propofol
- D. Etomidate
Explanation: ***Ketamine*** - Ketamine provides excellent **analgesia** by acting as an **NMDA receptor antagonist**, making it unique among commonly used intravenous anesthetics [1]. - It induces a state of **dissociative anesthesia**, where the patient is conscious but detached from painful stimuli, maintaining cardiovascular stability [1]. *Thiopentone* - Thiopentone is a **barbiturate** that causes rapid **induction of anesthesia** and profound **sedation** but has no analgesic properties. - Its primary action is through potentiation of GABA-A receptor activity, leading to central nervous system depression. *Propofol* - Propofol is a widely used intravenous anesthetic known for its rapid onset and short duration of action, but it lacks significant **analgesic effects** [3]. - It primarily works by enhancing GABA-A receptor function, leading to **sedation** and hypnosis. *Etomidate* - Etomidate is an intravenous anesthetic characterized by its minimal cardiovascular depression, making it suitable for patients with **hemodynamic instability**, but it provides **no analgesia** [1], [2]. - Its anesthetic effect is mediated through GABA-A receptor potentiation, resulting in rapid loss of consciousness.
Question 2: Arrange the following anesthetic agents based on their potency Nitrous oxide Halothane Isoflurane Methoxyflurane
- A. Methoxyflurane > Halothane > Isoflurane > Nitrous oxide (Correct Answer)
- B. Methoxyflurane > Nitrous oxide > Halothane > Isoflurane
- C. Methoxyflurane > Isoflurane > Halothane > Nitrous oxide
- D. Halothane > Isoflurane > Nitrous oxide > Methoxyflurane
Explanation: ***Methoxyflurane > Halothane > Isoflurane > Nitrous oxide*** - Anesthetic potency is inversely related to its **MAC (Minimum Alveolar Concentration)** value. A lower MAC value indicates higher potency. - The MAC values for these agents are: Methoxyflurane (0.16%), Halothane (0.75%), Isoflurane (1.15%), and Nitrous oxide (104%), which directly corresponds to this order of potency. *Methoxyflurane > Nitrous oxide > Halothane > Isoflurane* - This order incorrectly places nitrous oxide as more potent than halothane and isoflurane. **Nitrous oxide** has a very high MAC (104%), indicating low potency. - **Halothane** and **isoflurane** have significantly lower MAC values (0.75% and 1.15%, respectively), making them much more potent than nitrous oxide. *Methoxyflurane > Isoflurane > Halothane > Nitrous oxide* - This order incorrectly places **isoflurane** as more potent than halothane. **Halothane** has a MAC of 0.75%, while **isoflurane** has a MAC of 1.15%. - Therefore, halothane is more potent than isoflurane, making this sequence incorrect. *Halothane > Isoflurane > Nitrous oxide > Methoxyflurane* - This order incorrectly places **halothane** as the most potent and **methoxyflurane** as the least potent among the listed agents. - **Methoxyflurane** has the lowest MAC (0.16%), making it the most potent, while **nitrous oxide** has the highest MAC (104%), making it the least potent.
Question 3: Which of the following is the most potent trigger of malignant hyperthermia?
- A. Thiopentone
- B. Isoflurane
- C. Suxamethonium
- D. Halothane (Correct Answer)
Explanation: ***Halothane*** - **Halothane** is a volatile anesthetic agent and the **most potent trigger** of malignant hyperthermia, directly acting on the **ryanodine receptor (RyR1)** to cause massive calcium release from the sarcoplasmic reticulum. - It has extensive historical documentation as the **primary MH trigger** and is used as the reference standard in MH susceptibility testing. *Suxamethonium* - **Suxamethonium** (succinylcholine) is a depolarizing neuromuscular blocking agent that can trigger malignant hyperthermia but is considered a **secondary trigger** compared to volatile anesthetics. - While it can independently cause MH episodes, volatile agents like **halothane** are recognized as more potent and primary triggers in current medical literature. *Thiopentone* - **Thiopentone** (thiopental) is an intravenous barbiturate anesthetic that is **safe** in patients susceptible to malignant hyperthermia. - It does not interact with the **ryanodine receptor (RyR1)** or cause uncontrolled calcium release, making it a preferred induction agent in MH-susceptible patients. *Isoflurane* - **Isoflurane** is a volatile anesthetic agent and a **potent trigger** of malignant hyperthermia, similar to halothane in its mechanism of action. - While equally potent as halothane, **halothane** is considered the classic reference trigger due to its historical significance and extensive research documentation.
Question 4: 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 5: Depth of Anesthesia is best measured by:
- A. TOF
- B. MAC
- C. BIS (Correct Answer)
- D. Post Tetanic Potentiation
Explanation: ***BIS*** - The **BIS (Bispectral Index)** is an EEG-derived parameter that provides a quantitative measure of the patient's level of consciousness or depth of anesthesia. - A typical range for adequate surgical anesthesia is a BIS score between **40 and 60**, indicating a low probability of consciousness and recall. *TOF* - **TOF (Train-of-Four)** monitoring is used to assess the level of neuromuscular blockade, measuring the response of a muscle to a series of four electrical stimuli. - While important for managing **muscle relaxants**, it does not directly measure the depth of anesthesia or consciousness. *MAC* - **MAC (Minimum Alveolar Concentration)** is a measure of the potency of an inhaled anesthetic, defined as the concentration at which 50% of patients do not respond to a surgical stimulus. - It reflects the **ED50 of the anesthetic agent** itself rather than the patient's individual depth of anesthesia at a given moment. *Post Tetanic Potentiation* - **Post Tetanic Potentiation (PTP)** is a phenomenon observed during neuromuscular monitoring where a single twitch response is enhanced following a brief tetanus (rapid series of high-frequency stimuli). - PTP is used to assess **deep neuromuscular blockade** and recovery from paralytics, not the depth of anesthesia.
Question 6: Which anaesthetic agent has maximum MAC ?
- A. Ether
- B. Methoxyfluorane
- C. Halothane
- D. Nitrous Oxide (N2O) (Correct Answer)
Explanation: ***Nitrous Oxide (N2O)*** - **Nitrous Oxide** has the highest **minimum alveolar concentration (MAC)** of all commonly used inhalational anesthetics, approximately 104%. - A high MAC indicates **low potency**, meaning that a large concentration is required to achieve anesthetic effects. *Ether* - **Ether** has a MAC of about 1.92%, which is significantly lower than that of Nitrous Oxide. - Its use has largely been replaced due to its flammability, slow induction, and recovery times. *Methoxyfluorane* - **Methoxyfluorane** is known for having a very low MAC, around 0.16%, making it the most potent inhalational anesthetic. - Due to its high potency and significant nephrotoxicity, its use is now very limited. *Halothane* - **Halothane** has a MAC of approximately 0.75%. - While it was a widely used inhalational anesthetic, it has largely been replaced due to concerns about **halothane hepatitis** and arrhythmogenicity.
Question 7: Which of the following antiepileptic drugs is preferred for treating generalized tonic-clonic seizures?
- A. Ethosuximide
- B. Gabapentin
- C. Valproic acid (Correct Answer)
- D. Carbamazepine
Explanation: ***Valproic acid*** - **Valproic acid** is a broad-spectrum antiepileptic drug effective against various seizure types, including **generalized tonic-clonic seizures**. - It is considered the **gold standard** for generalized seizures because it is effective against all types (absence, myoclonic, and tonic-clonic). - It works by increasing GABA levels, blocking voltage-gated sodium channels, and inhibiting T-type calcium channels. *Ethosuximide* - **Ethosuximide** is specifically used for **absence seizures** (petit mal) and is not effective for generalized tonic-clonic seizures. - It primarily acts by blocking **T-type calcium channels** in the thalamus. *Gabapentin* - **Gabapentin** is primarily used for **focal (partial) seizures** and neuropathic pain, not generalized tonic-clonic seizures. - Its mechanism involves modulating the release of neurotransmitters, possibly by binding to the **α2δ subunit of calcium channels**. *Carbamazepine* - **Carbamazepine** is a first-line treatment for **focal (partial) seizures** and is also effective for **generalized tonic-clonic seizures**, though valproic acid is generally preferred for purely generalized seizures. - It works by blocking voltage-gated sodium channels. - It should be **avoided in absence and myoclonic seizures** as it can worsen these seizure types. - Also used for **trigeminal neuralgia**.
Question 8: Which anti-epileptic drug marked X will act at the site shown?
- A. Tiagabine (Correct Answer)
- B. Vigabatrin
- C. Gabapentin
- D. Rufinamide
Explanation: ***Tiagabine*** - The image shows site 'X' as a **GABA reuptake transporter** that actively removes GABA from the synaptic cleft back into the presynaptic neuron or glial cells - **Tiagabine** specifically inhibits **GABA reuptake transporters (GAT-1)**, thereby increasing GABA concentration in the synaptic cleft and enhancing its inhibitory effect - This is the mechanism directly targeting the site shown in the diagram *Vigabatrin* - Irreversible inhibitor of **GABA transaminase (GABA-T)**, the enzyme responsible for catabolizing GABA - Acts intracellularly to prevent GABA breakdown, not at the synaptic reuptake transporter shown - Different mechanism from the site depicted *Gabapentin* - GABA analog but does not bind to GABA receptors or interfere with GABA reuptake - Primary mechanism involves modulating **voltage-gated calcium channels (α2δ subunit)**, reducing excitatory neurotransmitter release - Does not act at GABA transporters *Rufinamide* - Prolongs the inactive state of **voltage-dependent sodium channels**, reducing neuronal excitability - Mechanism is distinct from GABA reuptake or metabolism - Does not act at the site shown in the diagram
Question 9: Which of the following is NOT considered a 'date rape drug'?
- A. Rohypnol
- B. Ketamine
- C. Gamma hydroxyl butyrate
- D. Propofol (Correct Answer)
Explanation: ***Propofol*** - **Propofol** is an **intravenous anesthetic** and sedative primarily used in medical settings for induction and maintenance of anesthesia or for sedation in critical care. - While it can cause sedation and amnesia, it is not commonly associated with or used as a **'date rape drug'** due to its rapid onset and short duration of action, requiring medical administration. *Rohypnol* - **Rohypnol** (flunitrazepam) is a potent **benzodiazepine** known for its sedative-hypnotic effects and is commonly explicitly referred to as a **'date rape drug'**. - It can cause **amnesia**, muscle relaxation, and impaired judgment, making victims vulnerable and unable to recall events. *Ketamine* - **Ketamine** is a **dissociative anesthetic** that causes a trance-like state, pain relief, sedation, and amnesia, and is also known as a **'date rape drug'**. - At lower doses, it can produce **hallucinations** and a sense of detachment, impairing a person's ability to resist or remember. *Gamma hydroxyl butyrate* - **Gamma-hydroxybutyrate (GHB)** is a **central nervous system depressant** that has been widely implicated as a **'date rape drug'**. - It rapidly induces **sedation**, euphoria, and amnesia, with effects often lasting for several hours.
Question 10: What is the percentage of halothane that is metabolized in the human body?
- A. 50%
- B. 5%
- C. 2.50%
- D. 25% (Correct Answer)
Explanation: **Correct: 25%** - Approximately **25%** of administered halothane is metabolized in the liver, which is a relatively high percentage compared to other volatile anesthetics. - This extensive metabolism can lead to the formation of reactive intermediates, contributing to its potential for **hepatotoxicity** (halothane hepatitis). *Incorrect: 50%* - **50%** metabolism is significantly higher than what is observed for halothane and would imply even greater risk of significant metabolic byproduct accumulation and toxicity. - Most volatile anesthetics are metabolized to a much lesser extent, with desflurane having the least metabolism (<0.02%). *Incorrect: 5%* - **5%** metabolism is too low for halothane; while some volatile anesthetics like isoflurane fall into this range (~0.2-2%), halothane is known for its considerably higher metabolic rate. - A 5% metabolism rate would result in less concern for and incidence of **halothane hepatitis**. *Incorrect: 2.50%* - **2.50%** metabolism is an underestimation of halothane's metabolic activity within the body. - Anesthetic agents such as **enflurane** have a metabolism rate closer to this value (~2-5%), whereas halothane is much higher.
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