General Anesthesia — MCQs

General Anesthesia Indian Medical PG Practice Questions and MCQs

Question 581: Which of the following inhalational anesthetic agents is known to cross the blood-brain barrier most effectively?

A. Methoxyflurane
B. Sevoflurane
C. Desflurane (Correct Answer)
D. Nitrous oxide

Explanation: ***Desflurane*** - **Desflurane** has a **low blood-gas partition coefficient (0.42)**, meaning it is poorly soluble in blood. - This low solubility facilitates its rapid uptake into the brain and quick elimination, making it cross the **blood-brain barrier** very effectively and leading to a rapid onset and offset of anesthesia. *Methoxyflurane* - **Methoxyflurane** has a **high blood-gas partition coefficient (12.0)**, leading to slow induction and emergence from anesthesia. - Its high solubility in blood means it poorly crosses the **blood-brain barrier** compared to less soluble agents. *Sevoflurane* - **Sevoflurane** has a **moderate blood-gas partition coefficient (0.69)**, allowing for relatively rapid induction and emergence, but not as rapid as desflurane. - While it effectively crosses the **blood-brain barrier**, its solubility is higher than desflurane, making it slightly less effective in this regard. *Nitrous oxide* - **Nitrous oxide** has a very low blood-gas partition coefficient (0.46), leading to an extremely rapid onset and offset. - However, its **low potency (high MAC)** means it cannot achieve deep anesthetic states on its own, and its primary mechanism involves displacement of nitrogen from air-filled cavities, which differs from direct BBB crossing for maintenance of anesthesia.

Question 582: Ether was first used as an anesthetic by?

A. Morton (Correct Answer)
B. Wells
C. Simpson
D. Priestly

Explanation: ***Morton*** - **William T.G. Morton**, a dentist, publicly demonstrated the use of **ether as a surgical anesthetic** in 1846 during a tooth extraction at Massachusetts General Hospital. - This event marked a pivotal moment in medicine, revolutionizing surgical practices by providing effective pain relief. *Priestly* - **Joseph Priestley** was an 18th-century chemist who discovered several gases, including **oxygen**, but was not involved in the anesthetic use of ether. - His work was foundational to understanding the composition of air but did not extend to surgical applications of inhaled substances. *Wells* - **Horace Wells**, an American dentist, was an early pioneer in anesthesia who experimented with **nitrous oxide** as an anesthetic for tooth extractions. - While significant, his work predated and differed from Morton's successful public demonstration and widespread adoption of ether. *Simpson* - **James Young Simpson**, a Scottish obstetrician, is credited with pioneering the use of **chloroform** as an anesthetic, particularly in childbirth. - His contributions were later than Morton's use of ether and involved a different anesthetic agent.

Question 583: The anaesthesia of choice in renal disease is which one of the following:

A. Atracurium
B. Cisatracurium (Correct Answer)
C. Vecuronium
D. Rocuronium

Explanation: ***Cisatracurium*** - **Cisatracurium** is preferred in renal disease because it undergoes **Hofmann elimination**, a chemical breakdown independent of renal or hepatic function. - Its metabolism generates **laudanosine**, a metabolite that can accumulate in renal failure but has minimal clinical significance at typical doses. *Atracurium* - **Atracurium** also undergoes **Hofmann elimination** and ester hydrolysis, making it suitable for renal patients, but it produces more **laudanosine** than cisatracurium. - Higher levels of **laudanosine** can potentially cause central nervous system excitation (seizures) with prolonged use or in very high doses, although this is rare in clinical practice. *Vecuronium* - **Vecuronium** is primarily eliminated by the **liver** and, to a lesser extent, by the kidneys, so its duration of action can be prolonged in renal failure. - Its active metabolites, particularly **3-desacetylvecuronium**, accumulate significantly in renal insufficiency, leading to prolonged neuromuscular blockade. *Rocuronium* - **Rocuronium** is mainly eliminated by the **liver** (approximately 70-80%), with a smaller portion excreted renally. - In patients with renal failure, its duration of action can be significantly prolonged due to reduced renal clearance and potential alterations in hepatic elimination.

Question 584: What effect does Propofol have on the EEG?

A. Causes no significant change in EEG
B. Causes EEG activation
C. Induces EEG depression (Correct Answer)
D. None of the options

Explanation: ***Induces EEG depression*** - Propofol, an intravenous anesthetic, primarily acts as a **GABA-A receptor agonist**, enhancing inhibitory neurotransmission in the brain. - This leads to a dose-dependent reduction in brain electrical activity, characterized by a decrease in the **amplitude and frequency of EEG waves**, effectively causing EEG depression. *Causes no significant change in EEG* - This statement is incorrect because propofol has profound effects on brain electrical activity, as measured by the EEG. - Its anesthetic properties are directly linked to its ability to alter neuronal excitability significantly. *Causes EEG activation* - EEG activation typically involves an increase in fast-frequency, low-amplitude waves, often associated with states of arousal or epileptic activity. - Propofol's primary effect is to depress brain activity, which is the opposite of activation. *None of the options* - This option is incorrect because propofol has a well-documented and significant effect on the EEG, which is precisely EEG depression.

Question 585: Which of the following agents is most commonly used to induce anesthesia?

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

Explanation: ***Propofol*** - **Propofol** is one of the most commonly used intravenous anesthetics for both induction and maintenance due to its rapid onset, short duration of action, and favorable recovery profile with less postoperative nausea and vomiting. - Its mechanism involves potentiation of **GABA-A receptors**, leading to CNS depression and anesthesia. *Thiopentone sodium* - **Thiopentone** is an ultrashort-acting barbiturate that was historically very popular for induction but has largely been replaced by propofol due to a slower recovery profile and higher incidence of cardiovascular depression. - It also acts on **GABA-A receptors**, enhancing chloride influx and hyperpolarizing neurons. *Methohexitone sodium* - **Methohexitone** is another ultrashort-acting barbiturate, similar to thiopentone, used for induction, particularly in electroconvulsive therapy (ECT) due to its lower incidence of post-ictal confusion. - However, it is associated with a higher risk of **muscle twitching** and **hiccups** compared to propofol. *Etomidate* - **Etomidate** is a short-acting intravenous anesthetic known for its excellent **cardiovascular stability**, making it a preferred choice in patients with compromised cardiac function or hemodynamic instability. - A significant drawback is its association with **adrenocortical suppression**, even after a single dose, which limits its widespread use for maintenance.

Question 586: Which of the following drugs produces dissociative anesthesia?

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

Explanation: ***Ketamine*** - **Ketamine** is a **dissociative anesthetic** that causes a trance-like state characterized by profound analgesia, amnesia, and catatonia, with the patient appearing to be awake but unresponsive. - It works by antagonizing the **NMDA receptor**, leading to a functional dissociation between the limbic and cortical systems. *Propofol* - **Propofol** is a short-acting intravenous anesthetic that produces a rapid loss of consciousness and has sedative-hypnotic properties. - It functions primarily by enhancing the activity of the **GABA-A receptor**, leading to central nervous system depression, not dissociation. *Thiopentone* - **Thiopentone** (Thiopental) is a barbiturate that induces rapid anesthesia and is used for induction and short procedures. - Its mechanism involves potentiation of the **GABA-A receptor**, causing global central nervous system depression without dissociative effects. *Enflurane* - **Enflurane** is an inhaled halogenated ether anesthetic that provides excellent muscle relaxation and analgesia. - It primarily acts by enhancing **GABAergic inhibition** and inhibiting excitatory neurotransmission, producing general anesthesia rather than a dissociative state.

Question 587: Which stage of surgical anesthesia is optimal for surgery?

A. Stage I
B. Stage II
C. Stage III (Correct Answer)
D. Stage IV

Explanation: ***Stage III*** - This stage, also known as **surgical anesthesia**, is characterized by stable vital signs, loss of consciousness, and adequate muscle relaxation, making it ideal for performing surgical procedures. - During this stage, the patient's reflexes are suppressed, and pain perception is abolished, ensuring a smooth and pain-free surgical experience. *Stage I* - This is the **analgesia stage**, where the patient is conscious but drowsy and may experience some pain relief. Incisions are typically not made during this stage. - Reflexes are still present, and the patient may be able to communicate, meaning surgical pain would still be experienced. *Stage II* - Often referred to as the **delirium stage** or **excitement stage**, this phase is characterized by involuntary movements, struggling, and potentially vomiting. - It is an undesirable stage for surgery due to the risk of injury to the patient and staff, and the instability of vital signs. *Stage IV* - This stage, known as **medullary depression**, represents an overdose of anesthetic agents, leading to severe depression of respiratory and cardiovascular centers. - It is a life-threatening stage characterized by complete respiratory arrest, cardiovascular collapse, and potential death, requiring immediate intervention.

Question 588: Which inducing agent is associated with the highest incidence of postoperative vomiting?

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

Explanation: ***Ketamine*** - While **ketamine** is a valuable anesthetic, it is associated with a higher incidence of **postoperative nausea and vomiting (PONV)** due to its effects on the central nervous system. - This is particularly noted in adult patients undergoing procedures where ketamine is used as the primary inducing agent or for maintenance. *Etomidate* - **Etomidate** is known for its **hemodynamic stability**, making it a good choice for patients with cardiovascular disease. - It has a moderate incidence of **PONV**, generally considered lower than ketamine but higher than propofol. *Thiopentone* - **Thiopentone** (now less commonly used) was a traditional barbiturate inducing agent. - Its incidence of **PONV** is generally considered moderate and not the highest among common inducing agents. *Propofol* - **Propofol** is well-known for its **antiemetic properties**, which contribute to a significantly lower incidence of **PONV**. - It is often favored in patients at high risk for PONV precisely because of this beneficial side effect.

Question 589: Nitrous oxide alone is not used as a general anaesthetic agent because of

A. Cost and exposure hazards
B. Potential adverse effects on liver function
C. Inability to maintain adequate depth of anesthesia (Correct Answer)
D. Rapid onset and offset leading to unstable anesthesia

Explanation: ***Inability to maintain adequate depth of anesthesia*** - **Nitrous oxide** has a relatively **high minimum alveolar concentration (MAC)** (104%), meaning it cannot achieve surgical depths of anesthesia when administered alone (even at 100% concentration, which would be hypoxic). - Its **low potency** necessitates co-administration with more potent inhalational agents or intravenous anesthetics to ensure appropriate analgesia and muscular relaxation for surgical procedures. *Cost and exposure hazards* - While prolonged exposure to **nitrous oxide** can pose an occupational hazard to healthcare workers and it is an environmental pollutant, these are not the primary reasons it is unsuitable as a sole general anesthetic. - The cost of **nitrous oxide** itself is generally moderate and not prohibitive for its use, especially in combination. *Potential adverse effects on liver function* - **Nitrous oxide** is primarily eliminated by the lungs and undergoes minimal metabolism, making **hepatic toxicity** not a significant concern. - Hepatic adverse effects are more commonly associated with other halogenated anesthetics like halothane. *Rapid onset and offset leading to unstable anesthesia* - The **rapid onset and offset** of **nitrous oxide** are actually advantageous in many clinical situations, contributing to rapid induction and recovery from anesthesia. - While it has a rapid effect, this characteristic does not inherently lead to "unstable anesthesia" in the context of its overall suitability as a sole agent; rather, its low potency is the limiting factor.

Question 590: Propofol and thiopentone are:

A. Anesthesia maintenance agents
B. Anesthesia reversal agents
C. Local anesthetics
D. Anesthesia induction agents (Correct Answer)

Explanation: ***Anesthesia induction agents*** - Propofol and thiopentone are **intravenous anesthetic agents** primarily used to rapidly induce a state of unconsciousness for surgery and other medical procedures. - They produce a **quick onset of action** allowing for a smooth and controlled intubation if needed, initiating the anesthetic process. *Anesthesia maintenance agents* - While propofol can be used for maintenance as a continuous infusion, its primary role, as well as that of thiopentone, is **induction due to their rapid onset and short duration** when given as a bolus. - Anesthesia maintenance typically involves volatile anesthetics (e.g., sevoflurane, isoflurane) or continuous infusions of drugs like propofol or remifentanil. *Anesthesia reversal agents* - Reversal agents are used to **counteract the effects of muscle relaxants** (e.g., neostigmine, sugammadex) or benzodiazepines (e.g., flumazenil) used during anesthesia. - Propofol and thiopentone do not have a role in reversing general anesthesia; their effects simply wear off as they are metabolized. *Local anesthetics* - Local anesthetics (e.g., lidocaine, bupivacaine) block nerve conduction in a **specific region of the body** without affecting consciousness. - Propofol and thiopentone are **general anesthetics** that induce a state of unconsciousness, affecting the entire central nervous system.

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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