Local Anesthetics in Special Populations — MCQs
The anesthetic agent which can cause massive hepatic necrosis?
What is the main barrier for the diffusion of local anesthetic?
Most common cause of maternal mortality in spinal anesthesia is ?
A patient presented with rigidity, tremors, and trismus after being administered an anesthetic agent. Which anesthetic agent is most likely to have been administered?
What is the percentage of halothane that is metabolized in the human body?
Which of the following inhalational anesthetic agents is contraindicated in liver disease?
In a 2 months old infant undergoing surgery for biliary atresia, you would avoid one of the following anaesthetic -
Methemoglobinemia is associated with:
What is the maximum dose of plain lignocaine (in mg) for adults?
A drug is more likely to cause toxicity in elderly patients due to all of the following reasons except which of the following?
Local Anesthetics in Special Populations Indian Medical PG Practice Questions and MCQs
Question 1: The anesthetic agent which can cause massive hepatic necrosis?
- A. N 2 O
- B. Halothane (Correct Answer)
- C. Methoxyflurane
- D. Isoflurane
Explanation: ***Halothane*** - Halothane can be metabolized into toxic intermediates through oxidative pathways, leading to **halothane hepatitis** or fulminant hepatic necrosis. - This idiosyncratic reaction is more likely after repeated exposures and presents as severe liver injury, possibly due to **immune-mediated mechanisms** triggered by trifluoroacetylated proteins. *N 2 O* - **Nitrous oxide** (N2O) is generally considered very safe regarding hepatic effects and does not cause massive hepatic necrosis. - Its primary metabolism involves no significant liver pathways that would generate toxic metabolites affecting hepatocytes. *Methoxyflurane* - Methoxyflurane is known to cause **nephrotoxicity** due to its metabolism to fluoride ions, which can impair renal concentrating ability. - While it can be hepatotoxic, its effects are generally less severe and less common than halothane-induced necrosis, with **renal toxicity** being its most prominent adverse effect. *Isoflurane* - Isoflurane is a commonly used volatile anesthetic with a **very low incidence of hepatotoxicity** compared to halothane. - It undergoes minimal metabolism, reducing the likelihood of producing toxic metabolites that could harm the liver.
Question 2: What is the main barrier for the diffusion of local anesthetic?
- A. Epineurium
- B. Endoneurium
- C. Perineurium (Correct Answer)
- D. None of the options.
Explanation: **Perineurium** - The **perineurium** is the main barrier to the diffusion of local anesthetics, forming a tight sheath that surrounds fascicles of nerve fibers. - Its **tight junctions** between cells create a blood-nerve barrier, restricting the passage of substances into the nerve. *Epineurium* - The **epineurium** is the outermost connective tissue layer covering the entire nerve, which is relatively loose and offers little resistance to anesthetic diffusion. - Its main function is to provide **protection** and cushioning to the nerve, rather than acting as a diffusion barrier. *Endoneurium* - The **endoneurium** is the delicate connective tissue that surrounds individual nerve fibers within a fascicle. - While it provides structural support, it is **highly permeable** and does not significantly impede the diffusion of local anesthetics. *None of the options.* - This option is incorrect because the **perineurium** is a well-established anatomical barrier for local anesthetic diffusion.
Question 3: Most common cause of maternal mortality in spinal anesthesia is ?
- A. Allergy to local anesthesia
- B. Nerve injury
- C. Hypotension (Correct Answer)
- D. High block
Explanation: ***Hypotension*** - **Profound hypotension** due to sympathetic blockade is the most common cause of maternal mortality in spinal anesthesia. - This can lead to **decreased placental perfusion**, fetal distress, and maternal cardiovascular collapse if not promptly managed. *Allergy to local anesthesia* - True allergic reactions to local anesthetics are **extremely rare**, especially to ester-type anesthetics used in spinal anesthesia. - While possible, it is not the most common cause of maternal mortality. *Nerve injury* - **Direct nerve injury** during spinal anesthesia is a rare complication, usually resulting in localized neurological deficits rather than mortality. - It does not represent the primary cause of maternal death. *High block* - A **high spinal block** can cause severe hypotension and respiratory compromise, which can lead to mortality. - However, the underlying mechanism for the life-threatening aspects of a high block is often **severe hypotension** and subsequent cardiovascular collapse.
Question 4: A patient presented with rigidity, tremors, and trismus after being administered an anesthetic agent. Which anesthetic agent is most likely to have been administered?
- A. Halothane (Correct Answer)
- B. Nitrous Oxide (N2O)
- C. Thiopentone sodium
- D. Etomidate
Explanation: ***Halothane*** - The combination of **rigidity**, **tremors**, and **trismus** after an anesthetic agent suggests **malignant hyperthermia (MH)**, a rare but life-threatening inherited condition. - **Halothane (and other volatile anesthetics)**, along with succinylcholine, are known triggers for malignant hyperthermia. *Nitrous Oxide (N2O)* - While an anesthetic agent, **nitrous oxide** is not a known trigger for **malignant hyperthermia**. - It works by modulating **NMDA receptors** and does not typically cause rigidity, tremors, or trismus as a side effect. *Thiopentone sodium* - **Thiopentone sodium** is a **barbiturate** anesthetic and is not associated with triggering **malignant hyperthermia**. - Its effects primarily involve potentiation of **GABA-A receptors**, leading to sedation and hypnosis. *Etomidate* - **Etomidate** is a short-acting intravenous anesthetic that is not a known trigger for **malignant hyperthermia**. - It is typically associated with minimal cardiovascular depression but can cause **adrenocortical suppression** with prolonged use.
Question 5: 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.
Question 6: Which of the following inhalational anesthetic agents is contraindicated in liver disease?
- A. Methoxyflurane
- B. Isoflurane
- C. Ether
- D. Halothane (Correct Answer)
Explanation: ***Halothane*** - **Halothane** is metabolized in the liver, and approximately 20% undergoes **oxidative metabolism**, sometimes leading to the formation of reactive intermediates. - In susceptible individuals, these metabolites can cause **immune-mediated hepatotoxicity**, known as **halothane hepatitis**, making it contraindicated in pre-existing liver disease. *Methoxyflurane* - While **methoxyflurane** is extensively metabolized by the liver, its primary concern is **nephrotoxicity** due to the release of fluoride ions, not direct hepatotoxicity that would contraindicate it in liver disease. - It is rarely used clinically today because of its significant renal side effects. *Ether* - **Ether** is minimally metabolized by the liver; most of it is eliminated unchanged via the lungs. - It is not associated with significant hepatotoxicity and is therefore not contraindicated in liver disease. *Isoflurane* - **Isoflurane** undergoes very little metabolism (less than 1%) in the liver, making it one of the safest inhalational agents for patients with liver disease. - Its low metabolic conversion means a negligible risk of producing toxic metabolites that could harm the liver.
Question 7: In a 2 months old infant undergoing surgery for biliary atresia, you would avoid one of the following anaesthetic -
- A. Propofol
- B. Halothane (Correct Answer)
- C. Thiopentone
- D. Sevoflurane
Explanation: ***Halothane*** - **Halothane** is a potent hepatotoxic agent and should be avoided in patients with **biliary atresia** or other liver conditions. - Its metabolism can lead to the formation of **toxic metabolites** that can worsen pre-existing liver dysfunction. *Propofol* - **Propofol** is primarily metabolized by the liver, but its hepatic clearance is generally **high** and less dependent on liver function than some other anesthetics. - It is often used for induction and maintenance of anesthesia in patients with liver disease, with **dose adjustments** as needed. *Thiopentone* - **Thiopentone** (thiopental) is an ultra-short-acting barbiturate primarily eliminated by **hepatic metabolism**. - While it has a good safety profile for liver disease compared to halothane, careful **dose titration** is needed due to potential for prolonged effects with severe hepatic impairment. *Sevoflurane* - **Sevoflurane** is an inhalation anesthetic with minimal hepatic metabolism and a low potential for hepatotoxicity. - It is often considered a **preferred agent** in patients with liver disease due to its favorable metabolic profile.
Question 8: Methemoglobinemia is associated with:
- A. Aminoester local anesthetic
- B. Prilocaine (Correct Answer)
- C. Bupivacaine
- D. Mepivacaine
Explanation: ***Prilocaine*** - **Prilocaine** is a local anesthetic known to cause **methemoglobinemia** at higher doses due to its metabolite, **o-toluidine**. - This metabolite oxidizes iron in hemoglobin from the ferrous (Fe2+) to the ferric (Fe3+) state, rendering it unable to bind oxygen. *Aminoester local anesthetic* - While some aminoester local anesthetics can cause allergic reactions, they are not typically associated with **methemoglobinemia**. - **Methemoglobinemia** is more commonly linked with aminoamide local anesthetics containing specific chemical structures. *Bupivacaine* - **Bupivacaine** is an aminoamide local anesthetic primarily known for its potential to cause **cardiotoxicity** at high systemic concentrations. - It does not commonly induce **methemoglobinemia**. *Mepivacaine* - **Mepivacaine** is another aminoamide local anesthetic, chemically similar to lidocaine. - While it can cause CNS toxicity and cardiovascular effects at high doses, it is not a significant cause of **methemoglobinemia**.
Question 9: What is the maximum dose of plain lignocaine (in mg) for adults?
- A. 300 (Correct Answer)
- B. 500
- C. 700
- D. 1000
Explanation: ***300 mg*** - The maximum recommended dose of **plain lidocaine** (without epinephrine) for adults is typically **300 mg** or 4.5 mg/kg, whichever is less. - Exceeding this dose can increase the risk of **systemic toxicity**, including central nervous system and cardiovascular effects. *500 mg* - This dose is generally considered the maximum for **lidocaine with epinephrine** in adults, as **epinephrine** causes vasoconstriction and delays systemic absorption of lidocaine. - For **plain lidocaine**, 500 mg would be an overdose and significantly increase the risk of toxicity. *700 mg* - This is well above the recommended maximum dose for both plain lidocaine and lidocaine with epinephrine, posing a **severe risk of toxicity**. - Such a high dose could lead to **seizures**, cardiac arrhythmias, and even **cardiac arrest**. *1000 mg* - This dose is extremely dangerous and far exceeds any recommended maximum for lidocaine, regardless of whether it contains epinephrine. - Administration of 1000 mg of lidocaine would almost certainly result in **severe and potentially fatal toxicity**.
Question 10: A drug is more likely to cause toxicity in elderly patients due to all of the following reasons except which of the following?
- A. decreased renal excretion of drugs
- B. decreased hepatic metabolism
- C. decreased volume of distribution (Correct Answer)
- D. increased receptor sensitivity
Explanation: ***decreased volume of distribution*** - A **decreased volume of distribution** would generally lead to a higher peak plasma concentration for a given dose, potentially increasing drug effect and thus toxicity, particularly for **hydrophilic drugs**. - However, for drugs that primarily distribute into **fat** or have a large volume of distribution, age-related changes in body composition (e.g., increased body fat, decreased total body water) can actually lead to an **increased volume of distribution** for some lipophilic drugs. *decreased renal excretion of drugs* - **Aging** is associated with a decline in **glomerular filtration rate (GFR)** and **renal tubular function**, leading to reduced drug clearance. - This results in a longer **half-life** and accumulation of renally excreted drugs, increasing the risk of **toxicity**. *decreased hepatic metabolism* - Liver size, blood flow, and the activity of some **cytochrome P450 enzymes** may decrease with age. - This leads to reduced **first-pass metabolism** and slower systemic clearance of many hepatically metabolized drugs, increasing their **bioavailability** and plasma concentrations. *increased receptor sensitivity* - Elderly patients often exhibit altered **pharmacodynamic responses**, including **increased sensitivity** to certain drugs. - This means a lower concentration of the drug at the receptor site can produce a greater therapeutic or toxic effect, making them more susceptible to **adverse drug reactions**.
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