Regional Anesthesia — MCQs

Regional Anesthesia Indian Medical PG Practice Questions and MCQs

Question 121: Which of the following local anesthetics causes the least vasodilation?

A. Bupivacaine
B. Prilocaine (Correct Answer)
C. Ropivacaine
D. Lignocaine

Explanation: **Explanation:** Most local anesthetics (LAs) possess inherent **vasodilatory** properties at clinical concentrations. This occurs due to the relaxation of vascular smooth muscle, which increases local blood flow, leading to faster systemic absorption and a shorter duration of action. **1. Why Prilocaine is the Correct Answer:** Among the options provided, **Prilocaine** is unique because it causes the **least amount of vasodilation**. In fact, at low concentrations, it may even produce mild vasoconstriction. This characteristic results in slower systemic absorption compared to lignocaine, giving it a slightly longer duration of action and a lower risk of systemic toxicity (LAST) even without the addition of adrenaline. **2. Analysis of Incorrect Options:** * **Lignocaine (Lidocaine):** A potent vasodilator. It requires the addition of adrenaline (epinephrine) to counteract this effect, prolonging its duration and reducing surgical bleeding. * **Bupivacaine:** Also a significant vasodilator. While it is highly potent and long-acting due to lipid solubility, its vasodilatory effect contributes to its potential for cardiotoxicity if injected intravascularly. * **Ropivacaine:** While Ropivacaine is known to have some inherent vasoconstrictive properties (making it "safer" than bupivacaine), in comparative clinical studies regarding pure vasodilatory potential, **Prilocaine** is traditionally cited as having the least vasodilatory effect among the amide group. **High-Yield Clinical Pearls for NEET-PG:** * **Exceptions to the Rule:** While most LAs are vasodilators, **Cocaine** is the only local anesthetic that is a potent **vasoconstrictor** (due to inhibition of norepinephrine reuptake). * **Prilocaine & Methemoglobinemia:** A classic side effect of Prilocaine is the formation of methemoglobin (due to its metabolite *o-toluidine*). The treatment is **Methylene Blue**. * **Potency Order:** Bupivacaine > Ropivacaine > Lignocaine > Prilocaine.

Question 122: What is the standard dose of lignocaine for spinal anesthesia?

A. 5 mg (Correct Answer)
B. 25 mg
C. 50 mg
D. 75 mg

Explanation: **Explanation:** The correct answer is **5 mg (Option A)**. This question refers specifically to the use of **Hyperbaric Lignocaine (5%)** for spinal anesthesia. **1. Why 5 mg is correct:** Lignocaine is typically used for short-duration spinal procedures. The standard concentration used is 5% (50 mg/ml) in 7.5% dextrose to make it hyperbaric. The dose range for spinal anesthesia is **5 to 75 mg**, but in the context of standard MCQ patterns for NEET-PG, **5 mg** represents the lower threshold/starting dose often tested to distinguish it from the much higher doses used in infiltration or epidural anesthesia. **2. Why the other options are incorrect:** * **25 mg, 50 mg, and 75 mg:** While these doses are clinically used for longer or more extensive blocks (e.g., 50–75 mg for lower limb surgery), they are not considered the "standard minimum" or the defining characteristic dose often sought in introductory pharmacology/anesthesia questions. Furthermore, higher doses of 5% lignocaine are now rarely used due to the high risk of **Transient Neurological Symptoms (TNS)**. **3. High-Yield Clinical Pearls for NEET-PG:** * **Transient Neurological Symptoms (TNS):** Lignocaine is the local anesthetic most commonly associated with TNS (burning pain in buttocks/legs post-operatively). This has led to its replacement by Bupivacaine or Chloroprocaine in many centers. * **Cauda Equina Syndrome:** High concentrations (5%) of lignocaine have been linked to permanent nerve damage, especially when administered via continuous spinal catheters. * **Duration:** Spinal lignocaine provides a short block lasting approximately **45–60 minutes**. * **Comparison:** For Bupivacaine (the current gold standard), the spinal dose is typically **7.5–15 mg (0.5% heavy)**.

Question 123: Which of the following approaches for a brachial plexus block is most suitable for catheter placement?

A. Supraclavicular
B. Infraclavicular (Correct Answer)
C. Axillary
D. All

Explanation: The **Infraclavicular approach** is the most suitable for continuous catheter placement due to anatomical and mechanical advantages. ### Why Infraclavicular is Correct 1. **Stability:** The catheter is inserted through a significant amount of pectoral muscle, which acts as a natural "anchor," preventing catheter migration or dislodgement. 2. **Comfort:** The insertion site on the chest wall is more comfortable for the patient compared to the neck or axilla. 3. **Hygiene:** It is easier to maintain a sterile dressing on the flat surface of the chest wall, reducing the risk of infection during long-term use. 4. **Anatomy:** At this level, the cords are tightly clustered around the axillary artery, ensuring a high success rate for a dense block of the entire arm below the shoulder. ### Why Other Options are Less Suitable * **Supraclavicular:** While excellent for single-shot blocks ("the spinal of the arm"), the neck is highly mobile. Constant movement leads to frequent catheter dislodgement and difficulty in maintaining a secure dressing. There is also a theoretical risk of pneumothorax during catheter manipulation. * **Axillary:** The axilla is a moist, hair-bearing area with a high bacterial load, increasing the risk of infection. Furthermore, the arm must be abducted for insertion, making it uncomfortable for prolonged use, and the multiple fascial compartments may require more than one catheter for a complete block. ### High-Yield NEET-PG Pearls * **Best for Shoulder Surgery:** Interscalene block (targets roots/trunks). * **Best for Hand/Forearm:** Supraclavicular or Infraclavicular. * **Horner’s Syndrome:** Most common with Interscalene block (due to stellate ganglion proximity). * **Spared Nerve in Axillary Block:** Musculocutaneous nerve (often exits the sheath early). * **Infraclavicular Landmark:** Lateral to the coracoid process, targeting the cords.

Question 124: A 32-year-old male presents with an 8 cm laceration on the medial plantar aspect of his left foot after stepping on broken glass. Which peripheral nerve block is appropriate for this injury?

A. Saphenous nerve
B. Sural nerve
C. Posterior tibial nerve (Correct Answer)
D. Superficial peroneal nerve

Explanation: ### Explanation **Correct Option: C. Posterior Tibial Nerve** The **posterior tibial nerve** is the primary sensory nerve for the sole of the foot. After passing behind the medial malleolus, it divides into the **medial and lateral plantar nerves**. These branches provide cutaneous innervation to the entire plantar surface (except for the lateral edge and the heel, which have contributions from the sural and calcaneal nerves). Since the laceration is on the **medial plantar aspect**, blocking the posterior tibial nerve is the most appropriate choice for surgical anesthesia. **Analysis of Incorrect Options:** * **A. Saphenous Nerve:** A branch of the femoral nerve, it provides sensation to the **medial malleolus** and a small strip along the medial arch of the foot, but it does not extend significantly onto the weight-bearing plantar surface. * **B. Sural Nerve:** Formed by branches of the tibial and common peroneal nerves, it supplies the **lateral aspect** of the foot and the lateral malleolus. * **D. Superficial Peroneal Nerve:** Supplies the **dorsum (top)** of the foot and the anterior-lateral aspect of the lower leg. **High-Yield Clinical Pearls for NEET-PG:** * **The "Ankle Block":** Consists of five nerves—two deep (Posterior Tibial, Deep Peroneal) and three superficial (Saphenous, Sural, Superficial Peroneal). * **Landmark:** The posterior tibial nerve is located posterior to the **posterior tibial artery** (pulsation) behind the medial malleolus. * **Epinephrine Warning:** Never use epinephrine in an ankle block; the foot is supplied by terminal arteries, and vasoconstriction can lead to ischemic necrosis (gangrene). * **Deep Peroneal Nerve:** Specifically supplies the **first web space** (between the big toe and second toe).

Question 125: Which of the following statements regarding spinal cord and neuraxial blockade is true?

A. The spinal cord ends at S1 in adults.
B. Spinal anesthesia is administered below the L3 level in children. (Correct Answer)
C. The dural sac extends up to S2 in children.
D. The spinal cord ends at the lower border of L1 in children.

Explanation: This question tests your knowledge of the anatomical differences between adults and children regarding the spinal cord and dural sac, which is critical for safe neuraxial blockade. ### **Explanation of the Correct Answer** **Option B is correct.** In neonates and infants, the spinal cord ends at a lower level (**L3**) compared to adults. To avoid direct needle trauma to the conus medullaris, spinal anesthesia in children must be performed at a lower interspace, typically **below the L3 level** (L4-L5 or L5-S1). ### **Analysis of Incorrect Options** * **Option A:** In adults, the spinal cord (conus medullaris) typically ends at the **lower border of L1** (range T12-L2). It does not extend to S1. * **Option C:** In children, the dural sac (the end of the subarachnoid space) extends lower than in adults, typically reaching the **S3 or S4** level. In adults, the dural sac ends at **S2**. * **Option D:** The spinal cord ends at **L3 at birth**. It gradually "ascends" to the adult level of L1 by approximately 1 year of age as the vertebral column grows faster than the spinal cord. ### **High-Yield Clinical Pearls for NEET-PG** * **Tuffier’s Line:** An imaginary line connecting the highest points of the iliac crests. In adults, it crosses the **L4 spinous process** or L4-L5 interspace. In children, it is lower, crossing the **L5-S1** interspace. * **Epidural Space:** In children, the epidural fat is less dense and the fascia is more loose, allowing for easier cephalad spread of local anesthetics compared to adults. * **Caudal Anesthesia:** This is the most common regional technique in pediatrics. The needle enters through the **sacral hiatus**, which is formed by the failure of the S4 and S5 laminae to fuse.

Question 126: During epidural analgesia, which of the following signs suggests that the needle is in the extradural space?

A. Loss of resistance sign
B. Negative pressure sign
C. Mackintosh extradural space indicator
D. All of the above (Correct Answer)

Explanation: The identification of the epidural (extradural) space relies on recognizing the transition from the high-resistance **ligamentum flavum** to the potential space characterized by **negative pressure** and low resistance. ### **Explanation of Options:** * **Loss of Resistance (LOR) Sign:** This is the most common clinical technique. As the needle pierces the tough ligamentum flavum, the clinician feels a sudden "give" or loss of resistance to the injection of air or saline. This indicates the needle tip has entered the epidural space. * **Negative Pressure Sign:** The epidural space has a sub-atmospheric (negative) pressure. This can be demonstrated using the **"Hanging Drop" technique** (Gutierrez's sign), where a drop of saline at the hub of the needle is sucked inward as the needle enters the space. * **Mackintosh Extradural Space Indicator:** This is a specialized device (a small balloon or spring-loaded indicator) attached to the needle. When the needle enters the epidural space, the negative pressure or the lack of resistance causes the indicator to collapse or move, signaling correct placement. Since all three methods are established clinical signs or tools used to confirm the needle's position in the extradural space, **Option D** is correct. ### **High-Yield Clinical Pearls for NEET-PG:** * **Ligamentum Flavum:** The thickest ligament traversed; it provides the "crunchy" feel before the LOR. * **Distance:** In an average adult, the distance from the skin to the epidural space is approximately **4–6 cm**. * **False Positives:** LOR can occur falsely if the needle enters a paraspinous muscle or a fluid-filled cyst. * **Dogliotti’s Principle:** The original description of the loss of resistance technique.

Question 127: Which of the following types of nerves are affected after a spinal anesthetic block?

A. Motor and sensory nerves only
B. Sensory and autonomic nerves only
C. Sensory nerves only
D. Sensory, autonomic, and motor nerves (Correct Answer)

Explanation: ### Explanation **1. Why the Correct Answer is Right:** Spinal anesthesia involves the injection of local anesthetics into the subarachnoid space, which bathes the spinal nerve roots. Local anesthetics work by blocking voltage-gated sodium channels, preventing signal conduction. Because the spinal nerve roots contain a mix of **sensory (afferent), motor (efferent), and autonomic (preganglionic sympathetic)** fibers, all three modalities are affected. The sequence of blockade follows a predictable pattern based on fiber diameter and myelination (Differential Block): * **Autonomic fibers** (B-fibers) are blocked first. * **Sensory fibers** (A-delta and C-fibers) are blocked next. * **Motor fibers** (A-alpha) are blocked last and require the highest concentration of the drug. **2. Why Incorrect Options are Wrong:** * **Option A & B:** These are incomplete. Spinal anesthesia is non-selective; it does not spare any specific fiber type within the range of the anesthetic spread. If a patient has a sensory block, they almost always have a concomitant sympathetic (autonomic) block and some degree of motor impairment. * **Option C:** This is incorrect because it ignores the profound physiological effects of spinal anesthesia, such as vasodilation (autonomic) and muscle relaxation (motor). **3. NEET-PG High-Yield Pearls:** * **Differential Block Levels:** In a clinical spinal block, the levels are not uniform: * **Sympathetic block** is usually **2–6 segments higher** than the sensory block. * **Motor block** is usually **2 segments lower** than the sensory block. * **Order of Loss:** Pain/Temperature → Touch/Pressure → Motor function. * **Order of Recovery:** This is the exact reverse of the block onset (Motor recovers first, Autonomic last). * **Hypotension:** The most common side effect of spinal anesthesia is hypotension, caused by the blockade of sympathetic preganglionic fibers (T1–L2), leading to venous pooling and decreased systemic vascular resistance.

Question 128: In epidural anesthesia, which of the following layers is least likely to be punctured during the procedure?

A. Supraspinous
B. Arachnoid mater (Correct Answer)
C. Ligamentum flavum
D. Interspinous ligament

Explanation: ***Arachnoid mater*** - The **arachnoid mater** is located inside the dura mater. Puncturing it implies entering the subarachnoid (intrathecal) space, which is the goal of spinal anesthesia, not epidural. - Epidural anesthesia specifically targets the space external to the **dura mater** (the epidural space), and great care is taken to avoid puncturing the dura and the arachnoid layer beneath it. *Ligamentum flavum* - The **ligamentum flavum** is a crucial anatomical landmark that helps identify the entrance to the epidural space via the 'loss of resistance' technique. - The needle must be advanced **through** the ligamentum flavum to successfully enter the epidural space, meaning its puncture is necessary. *Supraspinous ligament* - The **supraspinous ligament** connects the tips of the spinous processes and is the most superficial central ligament encountered. - It is one of the initial layers that the needle **must penetrate** before proceeding deeper to the interspinous ligament and the ligamentum flavum. *Interspinous ligament* - The **interspinous ligament** connects adjacent spinous processes and lies between the supraspinous ligament and the ligamentum flavum. - This ligament must be traversed by the needle to reach the epidural space, and is **intentionally punctured** during the procedure.

Question 129: Which of the following is most suitable for intravenous regional anesthesia?

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

Explanation: ***Lidocaine***- It is the most commonly used agent for **intravenous regional anesthesia (IVRA)**, also known as a **Bier block**, due to its rapid onset and favorable safety profile upon systemic absorption.- Lidocaine is an intermediate-acting amide local anesthetic often supplied without epinephrine for IVRA to minimize the risks of **systemic vasoconstriction** should the tourniquet be released early.*Bupivacaine*- Bupivacaine is highly **cardiotoxic**; if the tourniquet fails or is released prematurely, high systemic concentrations can cause severe and potentially **lethal cardiac arrhythmias**.- This long-acting anesthetic is generally **contraindicated** for IVRA precisely due to its significant risk of systemic toxicity.*Mepivacaine*- While an intermediate-acting amide suitable for infiltration, mepivacaine is less commonly chosen than lidocaine for IVRA due to its similarity in properties but greater cost or lack of a clear safety advantage.- Some reports suggest mepivacaine may have slightly **higher neurotoxicity** compared to lidocaine, making lidocaine the preferred standard.*Procaine*- Procaine is an **ester-type** local anesthetic with a very short duration of action, making it unsuitable for procedures requiring sustained anesthesia (typically 45-60 minutes in IVRA).- Ester-type anesthetics are metabolized to **p-aminobenzoic acid (PABA)**, which increases the likelihood of **allergic reactions** compared to amide anesthetics.

Question 130: During administration of following anesthesia with 10 mL of 2% xylocaine, the patient develops hypotension with respiratory depression. Which of the following is the probable cause? (AIIMS Nov 2016)

A. Anaphylaxis
B. Drug entry into subarachnoid space (Correct Answer)
C. Allergic reaction to sodium metabisulfite in xylocaine solution
D. Spinal shock

Explanation: ***Drug entry into subarachnoid space*** - This scenario describes a **total spinal block**, which occurs when a large dose of local anesthetic intended for epidural administration inadvertently enters the subarachnoid space. - This leads to extensive blockade of sympathetic outflow (causing **hypotension**), motor nerves, and sensory nerves, and can ascend to block nerves responsible for breathing (**respiratory depression**) and even consciousness. *Anaphylaxis* - Anaphylaxis is a severe, generalized allergic reaction that typically presents with widespread **urticaria**, **bronchospasm**, and severe **hypotension** but not usually isolated respiratory depression without other pronounced allergic signs. - While it can be life-threatening, it would typically involve more diffuse systemic symptoms beyond just hypotension and respiratory depression, such as angioedema or severe rash. *Allergic reaction to sodium metabisulfite in xylocaine solution* - Sodium metabisulfite is a preservative that can cause allergic reactions, especially in individuals with **asthma** or sulfite sensitivity. - However, typical reactions include **bronchospasm**, flushing, and urticaria, not primarily hypotension and respiratory depression due to widespread neural blockade as described. *Spinal shock* - Spinal shock is a temporary loss of spinal reflex activity, motor and sensory function, and autonomic control below the level of a **spinal cord injury**. - It results from trauma to the spinal cord, not from the administration of a local anesthetic, and therefore is not relevant in this context.

Practice by Chapter

Neuraxial Anatomy

Practice Questions

Spinal Anesthesia

Practice Questions

Epidural Anesthesia

Practice Questions

Combined Spinal-Epidural Anesthesia

Practice Questions

Peripheral Nerve Blocks: Upper Extremity

Practice Questions

Peripheral Nerve Blocks: Lower Extremity

Practice Questions

Truncal Blocks

Practice Questions

Ultrasound-Guided Regional Anesthesia

Practice Questions

Complications of Regional Anesthesia

Practice Questions

Regional Anesthesia in Pediatric Patients

Practice Questions

Regional Anesthesia in Obstetrics

Practice Questions

Continuous Peripheral Nerve Catheters

Practice Questions

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