Local Anesthetics — MCQs

Local Anesthetics Indian Medical PG Practice Questions and MCQs

Question 211: Regarding malignant hyperthermia, which statement about local anesthetics is correct?

A. Local anesthetics are safe to use in malignant hyperthermia-susceptible patients (Correct Answer)
B. Amide local anesthetics can trigger malignant hyperthermia
C. Ester local anesthetics are contraindicated in malignant hyperthermia
D. Local anesthetics should be avoided in patients with family history of malignant hyperthermia

Explanation: ***Local anesthetics are safe to use in malignant hyperthermia-susceptible patients*** - Malignant hyperthermia (**MH**) is primarily triggered by **volatile anesthetic agents** and **succinylcholine**. - Local anesthetics, whether **amide** or **ester** types, do not trigger MH and are considered safe for use in **MH-susceptible individuals**. *Amide local anesthetics can trigger malignant hyperthermia* - This statement is incorrect. **Amide local anesthetics** (e.g., lidocaine, bupivacaine) have **not been implicated** as triggers for malignant hyperthermia. - The mechanism of action of amide local anesthetics differs significantly from that of known MH triggers, which affect **calcium regulation** in muscle cells. *Ester local anesthetics are contraindicated in malignant hyperthermia* - This statement is incorrect. **Ester local anesthetics** (e.g., procaine, tetracaine) are also **safe** to use in patients susceptible to malignant hyperthermia. - Their metabolism and mechanism similarly do not interact with the **ryanodine receptor** or the pathways leading to uncontrolled calcium release characteristic of MH. *Local anesthetics should be avoided in patients with family history of malignant hyperthermia* - This statement is incorrect. A **family history of malignant hyperthermia (MH)** indicates the patient might be MH-susceptible, but local anesthetics are still **safe to use** in these individuals. - Avoiding local anesthetics in such patients would be an **unnecessary restriction** and deny them effective pain management options.

Question 212: An 18 years old woman in the active stage of labour requests an epidural anaesthesia for delivery. Immediately following the epidural injection of 12ml of 2% lidocaine, the patient complains of lip numbness and becomes apprehensive. What is the presumptive diagnosis?

A. Allergy to drug administered
B. Systemic toxicity to drug administered (Correct Answer)
C. Vasovagal shock
D. Drug entered SA space

Explanation: ***Systemic toxicity to drug administered*** - **Lip numbness** and apprehension immediately following epidural lidocaine injection are classic signs of **local anesthetic systemic toxicity (LAST)** due to unintended intravascular injection. - The rapid onset of symptoms suggests direct access to the systemic circulation via a blood vessel, leading to high plasma concentrations of lidocaine. *Allergy to drug administered* - Allergic reactions to local anesthetics are rare and typically involve **urticaria**, **bronchospasm**, or **anaphylaxis**, which are not described here. - Symptoms of allergy usually do not include lip numbness and apprehension as the primary manifestations. *Vasovagal shock* - Vasovagal reactions are characterized by **bradycardia**, **hypotension**, and syncope, usually triggered by pain or anxiety. - While apprehension is present, the specific symptom of lip numbness is not typical of a vasovagal response. *Drug entered SA space* - If the drug had entered the subarachnoid (SA) space, the patient would likely experience a **rapid onset of profound motor and sensory block**, potentially leading to **total spinal anesthesia** and respiratory compromise. - Lip numbness and apprehension are not primary indicators of inadvertent subarachnoid injection; rather, they point to systemic absorption.

Question 213: Which of the following is commonly used as an epidural anesthetic agent?

A. Bupivacaine
B. Chloroprocaine
C. All of the options (Correct Answer)
D. Lidocaine

Explanation: ***All of the options*** - **Bupivacaine**, **chloroprocaine**, and **lidocaine** are all commonly used as epidural anesthetic agents due to their differing onset times, durations of action, and potencies, allowing for tailored anesthetic approaches. - The choice among these agents depends on the surgical procedure, desired duration of action, and patient-specific factors. *Bupivacaine* - **Bupivacaine** is a long-acting amide local anesthetic, frequently chosen for epidural anesthesia when a prolonged duration of action is required, such as in labor analgesia or postoperative pain management. - It is more potent than lidocaine and has a **slower onset** but offers a longer duration of sensory and motor block. *Chloroprocaine* - **Chloroprocaine** is an ester-type local anesthetic known for its very **rapid onset** and short duration of action, primarily used when a quick onset and short-lived block are desired, such as for emergency C-sections or rapid surgical procedures. - It is rapidly metabolized by plasma pseudocholinesterase, leading to a quick offset and lower systemic toxicity compared to amide local anesthetics. *Lidocaine* - **Lidocaine** is an intermediate-acting amide local anesthetic, commonly used for epidural anesthesia when a moderate duration of action is needed, suitable for various surgical procedures. - It offers a **rapid onset** of action and a good balance between motor and sensory block, making it versatile for different clinical scenarios.

Question 214: Anesthetic agent with vasoconstrictor is contraindicated in

A. Spinal block
B. Regional anesthesia
C. Digital block (Correct Answer)
D. Epidural block

Explanation: ***Digital block*** - **Vasoconstrictors** in local anesthetics can cause severe **vasoconstriction** in tissues with limited collateral circulation, like digits. - This can lead to **ischemia**, **necrosis**, and even **gangrene** of the affected digit, making it a contraindication. *Spinal block* - **Vasoconstrictors** are sometimes added to local anesthetics for spinal blocks to prolong the duration of action and reduce systemic absorption. - While careful monitoring is needed, it is not an absolute contraindication and can be used cautiously. *Regional anesthesia* - In many forms of **regional anesthesia** (e.g., peripheral nerve blocks), vasoconstrictors like epinephrine are commonly added to prolong the block and reduce systemic toxicity. - This is a standard practice and generally safe outside of specific areas like digits. *Epidural block* - Similar to spinal blocks, **vasoconstrictors** are frequently used in **epidural anesthesia** to improve the quality, duration, and reduce systemic absorption of the local anesthetic. - While dose and patient factors must be considered, it is not a contraindication.

Question 215: The site of action of local anaesthetic in epidural anesthesia is

A. Anterior root of spinal nerve
B. Spinal nerve root (Correct Answer)
C. Epidural neural tissue
D. Spinal cord

Explanation: ***Spinal nerve root*** - Local anesthetics injected into the epidural space primarily act on the **spinal nerve roots** as they exit the spinal cord. - They also affect the **dorsal root ganglia** and the unmyelinated axons within the epidural space. *Anterior root of spinal nerve* - While the **anterior roots containing motor fibers** are affected, the local anesthetic's action isn't limited exclusively to them. - Sensory fibers in the **dorsal roots** are also blocked, contributing significantly to the analgesic effect. *Epidural neural tissue* - "Epidural neural tissue" is a too broad and non-specific term; the primary targets are the **nerve roots** themselves, not just any neural tissue within the epidural space. - This option does not specify which neural structures within the epidural space are the primary site of action. *Spinal cord* - Local anesthetics do not directly act on the **spinal cord parenchyma** in epidural anesthesia, as they do not typically penetrate the meninges to reach the cord in significant concentrations. - The medication exerts its effect outside the dura mater, primarily on the **nerve roots** before they enter the subarachnoid space.

Question 216: True regarding EMLA is

A. used for bilateral nerve block
B. used as general anaesthesia in pediatric use
C. Its mixture of 25 mg/g Lidocaine + 25 mg/g prilocaine used for skin anaesthesia (Correct Answer)
D. None of the above

Explanation: ***Its mixture of 25 mg/g Lidocaine + 25 mg/g prilocaine used for skin anaesthesia*** - **EMLA** (Eutectic Mixture of Local Anesthetics) is a cream containing a 1:1 ratio of **lidocaine** and **prilocaine**. - It is primarily used for **topical anesthesia** of the skin, offering pain relief during superficial procedures like venipuncture or skin biopsies. *used for bilateral nerve block* - **EMLA cream** is a topical anesthetic and is not suitable for **nerve blocks** due to its formulation and limited depth of penetration. - Nerve blocks require injection of local anesthetics directly near nerves. *used as general anaesthesia in pediatric use* - **EMLA cream** provides **local analgesia** and is not formulated or intended for use as a **general anesthetic**. - General anesthesia requires systemic administration of drugs to induce a state of unconsciousness. *None of the above* - This option is incorrect because the third statement accurately describes the composition and primary use of **EMLA cream**.

Question 217: In spinal anesthesia, which local anesthetic has the longest duration of action?

A. Procaine
B. Tetracaine
C. Bupivacaine (Correct Answer)
D. Lidocaine

Explanation: ***Bupivacaine*** - **Bupivacaine** is an amide-type local anesthetic known for its **long duration of action** in spinal anesthesia due to its high lipid solubility and protein binding. - Its prolonged effect is particularly useful for surgical procedures requiring extended periods of **analgesia** and motor blockade. *Procaine* - **Procaine** is an ester-type local anesthetic with a **short duration of action** due to rapid hydrolysis by plasma pseudocholinesterase. - It is rarely used for spinal anesthesia today due to its brief effect and potential for **allergic reactions**. *Tetracaine* - **Tetracaine** is an ester local anesthetic that has a relatively **long duration of action** compared to procaine, but generally shorter than bupivacaine. - While it provides good spinal anesthesia, its use has decreased in favor of amide anesthetics like bupivacaine due to similar but often preferred profiles of efficacy and safety. *Lidocaine* - **Lidocaine** is an amide-type local anesthetic with an **intermediate duration of action** in spinal anesthesia. - It is frequently used for surgical procedures of moderate duration, but its effect is significantly shorter than that of bupivacaine.

Question 218: What is the concentration of adrenaline typically used with local anesthetics?

A. 1:100,000
B. 1:200,000 (Correct Answer)
C. 1:10,000
D. 1:20,000

Explanation: ***1:200,000*** - This concentration of **adrenaline** (epinephrine) is commonly used with local anesthetics to prolong their duration of action and reduce systemic absorption. - It provides a good balance between efficacy in vasoconstriction and minimizing potential systemic side effects. *1:100,000* - While also used, this concentration provides a higher dose of **adrenaline**, which is often reserved for situations requiring more profound vasoconstriction or when a longer duration of action is critical. - It carries a slightly higher risk of systemic **epinephrine** effects compared to 1:200,000. *1:10,000* - This is a very high concentration of **adrenaline**, typically used for resuscitation in medical emergencies like **cardiac arrest** or **anaphylaxis**, not as an additive to local anesthetics for routine procedures due to significant risk of systemic toxicity. - Using such a high concentration would lead to severe vasoconstriction and a high likelihood of adverse cardiovascular events. *1:20,000* - This concentration is also very high for use with local anesthetics, although less concentrated than 1:10,000. It would still significantly increase the risk of systemic side effects. - It is not a standard concentration for routine local anesthetic admixture.

Question 219: A 45-year-old man undergoing surgery suddenly becomes unresponsive, and his pulse is unrecordable after receiving regional anesthesia with 0.25% bupivacaine. What is the best immediate management?

A. CPCR with 20% Intralipid (Correct Answer)
B. CPCR with sodium bicarbonate
C. CPCR with dobutamine
D. CPCR with calcium

Explanation: ***CPCR with 20% Intralipid*** - The sudden unresponsiveness and unrecordable pulse after regional anesthesia with bupivacaine suggest **local anesthetic systemic toxicity (LAST)**. - **20% Intralipid** (lipid emulsion) is the cornerstone of treatment for severe LAST because it acts as a **lipid sink**, binding to lipophilic local anesthetics like bupivacaine and sequestering them from target organs. *CPCR with sodium bicarbonate* - While sodium bicarbonate is used in some resuscitation scenarios, particularly for severe metabolic acidosis or tricyclic antidepressant overdose, it is **not the primary or most effective treatment for bupivacaine-induced cardiac arrest**. - Its use in LAST is supportive, mainly for treating **acidosis** that can worsen local anesthetic toxicity, but it does not directly counteract the systemic effects of the local anesthetic. *CPCR with dobutamine* - **Dobutamine** is an inotropic agent used to increase myocardial contractility and heart rate in cases of cardiac decompensation. - It is **not indicated as a first-line treatment for cardiac arrest** secondary to LAST; direct reversal of the anesthetic's effects is paramount. *CPCR with calcium* - Administering **calcium** is primarily indicated for cardiac arrest caused by **hyperkalemia** or **calcium channel blocker overdose**. - It is **not effective in reversing the cardiotoxic effects of bupivacaine** and is not part of the standard resuscitation protocol for LAST.

Question 220: Which local anesthetic is associated with the lowest risk of cardiotoxicity?

A. Bupivacaine
B. Ropivacaine (Correct Answer)
C. Lidocaine
D. Mepivacaine

Explanation: ***Ropivacaine*** - **Ropivacaine** is an **amide-type local anesthetic** known for its **lower cardiotoxicity** compared to bupivacaine. - This is attributed to its **reduced lipid solubility** and **faster dissociation from cardiac sodium channels**, leading to less potent cardiac effects. *Bupivacaine* - **Bupivacaine** is associated with a **higher risk of cardiotoxicity**, particularly **ventricular arrhythmias** and **cardiac arrest**, especially with accidental intravascular injection. - Its **high lipid solubility** and **tight binding to cardiac sodium channels** contribute to its potent cardiodepressant effects, making resuscitation difficult. *Lidocaine* - While generally considered safer than bupivacaine, **lidocaine** can still cause **cardiovascular depression** and **arrhythmias** at high plasma concentrations. - Its shorter duration of action and **less potent cardiotoxicity** make it a common choice, but it is not the local anesthetic with the lowest cardiotoxicity profile among the options. *Mepivacaine* - **Mepivacaine** has a similar cardiotoxicity profile to lidocaine and is considered to have **intermediate cardiotoxicity**. - It is **not the safest** option regarding cardiotoxicity when compared to ropivacaine, especially at higher doses or with accidental intravascular administration.

Practice by Chapter

Chemistry and Mechanism of Action

Practice Questions

Pharmacokinetics of Local Anesthetics

Practice Questions

Amide Local Anesthetics

Practice Questions

Ester Local Anesthetics

Practice Questions

Clinical Uses of Local Anesthetics

Practice Questions

Toxicity of Local Anesthetics

Practice Questions

Management of Local Anesthetic Systemic Toxicity

Practice Questions

Adjuvants to Local Anesthetics

Practice Questions

Maximum Safe Doses

Practice Questions

Local Anesthetics in Special Populations

Practice Questions

Allergic Reactions to Local Anesthetics

Practice Questions

Future Developments in Local Anesthetics

Practice Questions

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