Regional Anesthesia — MCQs

Regional Anesthesia Indian Medical PG Practice Questions and MCQs

Question 21: For an extraoral maxillary nerve block, what is the target area?

A. Anterior to the lateral pterygoid plate (Correct Answer)
B. Posterior to the lateral pterygoid plate
C. Pterygomandibular fossa
D. Pterygomandibular fissure

Explanation: **Explanation:** The **Maxillary Nerve (V2)** is a purely sensory nerve that exits the skull via the *foramen rotundum* and enters the **pterygopalatine fossa**. In the extraoral approach (specifically the lateral approach), the needle is passed through the sigmoid notch of the mandible to reach this fossa. **1. Why Option A is Correct:** The **lateral pterygoid plate** serves as the primary anatomical landmark for this block. To reach the pterygopalatine fossa where the maxillary nerve resides, the needle must be directed **anterior** to the lateral pterygoid plate. If the needle hits the plate, it is slightly withdrawn and redirected anteriorly (superiorly and medially) to enter the fossa. **2. Why Other Options are Incorrect:** * **Option B:** The area **posterior** to the lateral pterygoid plate contains the mandibular nerve (V3) and the middle meningeal artery. Directing the needle here would result in a mandibular block or potential vascular injury. * **Option C:** The **pterygomandibular fossa** (or space) is the target for an Inferior Alveolar Nerve block (V3), not the maxillary nerve. * **Option D:** The **pterygomandibular fissure** is a clinical distractor; the relevant fissure is the *pterygomaxillary fissure*, which serves as the lateral entrance to the pterygopalatine fossa. **Clinical Pearls for NEET-PG:** * **Landmarks:** The midpoint of the zygomatic arch and the coronoid process. * **Depth:** The lateral pterygoid plate is usually encountered at a depth of **4–5 cm**. * **Complications:** High risk of **hematoma** due to the proximity of the maxillary artery and the pterygoid venous plexus. * **Indications:** Extensive maxillary surgery, midface trauma, or trigeminal neuralgia involving the V2 distribution.

Question 22: Arrange the following structures as pierced by a spinal needle during a spinal block, from outside to inside: Interspinous ligaments, Ligamentum flavum, Supraspinous ligament, Epidural space.

A. Interspinous ligaments, Ligamentum flavum, Supraspinous ligament, Epidural space
B. Ligamentum flavum, Epidural space, Interspinous ligaments, Supraspinous ligament
C. Supraspinous ligament, Interspinous ligaments, Ligamentum flavum, Epidural space (Correct Answer)
D. Ligamentum flavum, Supraspinous ligament, Interspinous ligaments, Epidural space

Explanation: ### Explanation To perform a spinal block (Subarachnoid Block) via the **midline approach**, the needle must traverse several anatomical layers to reach the cerebrospinal fluid. The sequence follows a specific posterior-to-anterior trajectory based on the anatomy of the vertebral column. **1. Why Option C is Correct:** The correct anatomical sequence from superficial to deep is: * **Skin and Subcutaneous tissue:** The initial barrier. * **Supraspinous Ligament:** A strong fibrous cord connecting the tips of the spinous processes. * **Interspinous Ligament:** A thin, membranous structure between the spinous processes. * **Ligamentum Flavum:** A thick, elastic "yellow ligament" that offers a characteristic "pop" or "give" upon penetration. * **Epidural Space:** The space containing fat and internal vertebral venous plexuses, located just outside the dura mater. * *(Following this, the needle would pierce the Dura mater and Arachnoid mater to enter the Subarachnoid space).* **2. Why Other Options are Incorrect:** * **Options A, B, and D** are incorrect because they misplace the **Supraspinous ligament**. It is the most posterior (superficial) ligamentous structure. Any sequence that places the Interspinous ligament or Ligamentum flavum before the Supraspinous ligament is anatomically impossible in a midline approach. **3. NEET-PG High-Yield Clinical Pearls:** * **The "Pop" Sensation:** The most significant resistance is felt at the **Ligamentum Flavum**, followed by a sudden loss of resistance (the "pop") as the needle enters the epidural space and then the dura. * **Paramedian Approach:** If using the paramedian approach, the needle **bypasses** the Supraspinous and Interspinous ligaments, entering the Ligamentum flavum directly after passing through the paraspinous muscles. * **Order of Blockade:** Remember the sequence of nerve fiber inhibition: **B** (Autonomic) → **A-delta & C** (Pain/Temp) → **A-gamma** (Muscle spindle) → **A-beta** (Touch/Pressure) → **A-alpha** (Motor).

Question 23: What is the landmark for superior laryngeal nerve block?

A. Angle of mandible
B. C7 transverse process
C. Cricoid cartilage
D. Greater cornu of hyoid bone (Correct Answer)

Explanation: ### Explanation The **Superior Laryngeal Nerve (SLN)** is a branch of the Vagus nerve (CN X) that provides sensory innervation to the larynx above the vocal cords. Blocking this nerve is a crucial component of "awake intubation" to abolish the cough reflex. **Why the Greater Cornu of the Hyoid Bone is correct:** The SLN divides into internal and external branches near the hyoid bone. The **internal branch**, which provides sensory supply to the glottic and supraglottic mucosa, pierces the **thyrohyoid membrane** just inferior to the **greater cornu of the hyoid bone**. To perform the block, the hyoid bone is displaced toward the side of injection, and the needle is walked off the greater cornu inferiorly into the thyrohyoid membrane. **Analysis of Incorrect Options:** * **Angle of mandible:** This is a landmark for the **Glossopharyngeal nerve block** (specifically the intraoral or peristyloid approach), which provides anesthesia to the posterior third of the tongue and oropharynx. * **C7 transverse process:** This is the landmark for a **Stellate Ganglion block** (specifically the Chassaignac’s tubercle at C6 is preferred, but C7 is anatomically related to the ganglion itself). * **Cricoid cartilage:** This is the landmark for a **Recurrent Laryngeal Nerve block** (via the transtracheal approach) to anesthetize the airway below the vocal cords. **High-Yield Clinical Pearls for NEET-PG:** * **Innervation Rule:** The SLN (internal branch) supplies sensory above the vocal cords; the Recurrent Laryngeal Nerve (RLN) supplies sensory below the vocal cords. * **Motor Supply:** All intrinsic muscles of the larynx are supplied by the RLN **except** the **Cricothyroid muscle**, which is supplied by the **external branch of the SLN**. * **Airway Blocks:** A complete "awake intubation" block requires: 1. Glossopharyngeal block (base of tongue/gag reflex). 2. Superior Laryngeal block (supraglottic/vallecula). 3. Transtracheal/RLN block (subglottic/trachea).

Question 24: Hematoma formation is more frequent with which of the following nerve blocks?

A. Inferior alveolar nerve block
B. Posterior superior alveolar nerve block (Correct Answer)
C. Greater palatine nerve block
D. Infraorbital nerve block

Explanation: The **Posterior Superior Alveolar (PSA) nerve block** is associated with the highest incidence of hematoma formation among dental nerve blocks due to the specific anatomy of the infratemporal fossa. ### Why PSA Nerve Block is the Correct Answer: The PSA nerve block requires the needle to be inserted near the maxillary tuberosity. This area contains a dense network of veins known as the **Pterygoid Plexus of veins** and the **maxillary artery**. If the needle is inserted too far posteriorly or superiorly into the infratemporal fossa, it can easily puncture these thin-walled vessels. Because this space is relatively large and contains loose connective tissue, a significant amount of blood can accumulate rapidly, leading to a visible extraoral swelling (hematoma) within minutes. ### Explanation of Incorrect Options: * **Inferior Alveolar Nerve Block (IANB):** While it has the second-highest frequency of hematoma, it is usually intraoral and less clinically dramatic than the PSA block. * **Greater Palatine Nerve Block:** The palatal mucosa is very dense and firmly attached to the bone, which limits the space for blood to accumulate, making hematoma rare. * **Infraorbital Nerve Block:** While vessels are present, the anatomy allows for easier digital pressure to be applied against the bone to prevent bleeding post-injection. ### NEET-PG High-Yield Pearls: * **Management:** If a hematoma occurs during a PSA block, apply **digital pressure** over the site (mucobuccal fold) as far posteriorly as possible. * **Prevention:** Use a short needle and avoid over-penetration (depth should not exceed 16mm) to stay away from the pterygoid plexus. * **Clinical Sign:** A PSA hematoma typically manifests as a rapidly progressing swelling of the cheek.

Question 25: Which of the following techniques is not considered a type of neuro-axial anesthesia?

A. Spinal block
B. Epidural block
C. Bier's block (Correct Answer)
D. Caudal block

Explanation: **Explanation:** **Neuraxial anesthesia** refers to the placement of local anesthetic drugs in or around the central nervous system (specifically the spinal cord and nerve roots) within the spinal canal. **Why Bier’s Block is the correct answer:** **Bier’s block**, also known as **Intravenous Regional Anesthesia (IVRA)**, is a peripheral anesthetic technique. It involves the intravenous injection of a local anesthetic (typically Lidocaine) into a limb that has been isolated from the systemic circulation using a pneumatic tourniquet. Since the drug acts on peripheral nerve endings and trunks in the extremity rather than the spinal canal, it is **not** a neuraxial technique. **Why the other options are incorrect:** * **Spinal block (Subarachnoid block):** Local anesthetic is injected into the cerebrospinal fluid (CSF) in the subarachnoid space. It is a classic neuraxial technique. * **Epidural block:** Local anesthetic is injected into the epidural space (outside the dura mater). It acts on the spinal nerve roots and is a neuraxial technique. * **Caudal block:** This is essentially an epidural injection performed through the **sacral hiatus**. It is commonly used in pediatric surgery and is considered a form of neuraxial anesthesia. **Clinical Pearls for NEET-PG:** * **Bier’s Block Safety:** **Prilocaine** (0.5%) is often preferred due to its low systemic toxicity, though Lidocaine is commonly used. **Bupivacaine is strictly contraindicated** in Bier’s block due to high cardiotoxicity if the tourniquet fails. * **Neuraxial Landmarks:** The spinal cord ends at **L1** in adults and **L3** in children. Lumbar punctures/spinals are typically performed at the L3-L4 or L4-L5 interspace. * **Caudal Anesthesia:** The landmark for entry is the **sacral hiatus**, which is formed by the failure of the S5 laminae to fuse.

Question 26: Which of the following nerve fibers is most sensitive to inhibition by local anesthetics?

A. B fiber (Correct Answer)
B. Dorsal root
C. A delta fiber
D. A alpha fiber

Explanation: The sensitivity of nerve fibers to local anesthetics (LAs) is determined by fiber diameter, myelination, and the length of the fiber exposed to the drug. **Explanation of the Correct Answer:** **B fibers** are preganglionic autonomic fibers. Although they are slightly larger than C fibers, they are **myelinated**. Myelination makes them highly susceptible to local anesthetics because the drug only needs to block the sodium channels at the Nodes of Ranvier. In clinical practice, B fibers are the first to be blocked during spinal or epidural anesthesia, which explains why **sympathetic blockade** (vasodilation and hypotension) precedes sensory and motor loss. **Analysis of Incorrect Options:** * **A delta fibers:** These are small, myelinated fibers responsible for fast pain and temperature. While sensitive, they are blocked after B fibers. * **A alpha fibers:** These are the largest, heavily myelinated motor and proprioception fibers. Due to their large diameter, they are the **most resistant** to local anesthetics and are the last to be blocked. * **Dorsal root:** This is an anatomical structure containing various fiber types (A delta, C, etc.) rather than a specific fiber classification. **High-Yield Clinical Pearls for NEET-PG:** * **Order of Blockade (Clinical):** Autonomic (B) > Pain/Temperature (Aδ, C) > Touch/Pressure (Aβ) > Motor (Aα). * **The "C-fiber" Paradox:** Although C fibers are the smallest, they are unmyelinated. Myelinated B and Aδ fibers are often blocked faster because the anesthetic concentrates at the nodes. * **Differential Block:** This is the clinical phenomenon where different nerve functions are lost at different concentrations/times. Sympathetic block is typically 2–3 segments higher than sensory block in spinal anesthesia.

Question 27: Maximum safe dose of lignocaine for spinal anesthesia is?

A. 5-15 mg
B. 25-100 mg (Correct Answer)
C. 100-200 mg
D. 150-300 mg

Explanation: **Explanation:** The correct answer is **25–100 mg**. In spinal anesthesia (subarachnoid block), the dose of a local anesthetic is determined by the volume and concentration required to achieve a specific dermatomal level, rather than the weight-based systemic toxicity limits used in infiltration or nerve blocks. **Why 25–100 mg is correct:** Lignocaine (Lidocaine) is typically used as a **5% hyperbaric solution**. For a standard spinal block: * **Lower limb/perineal surgery:** 25–50 mg (0.5–1.0 ml) is sufficient. * **Abdominal surgery:** 75–100 mg (1.5–2.0 ml) is required to reach higher dermatomes (T4–T10). Exceeding 100 mg significantly increases the risk of **Transient Neurological Symptoms (TNS)** and Cauda Equina Syndrome, which is why 100 mg is considered the upper clinical safety limit for spinal administration. **Analysis of Incorrect Options:** * **A (5–15 mg):** This dose is too low for lignocaine; it is more characteristic of the dosage range for **Bupivacaine** (e.g., 7.5–15 mg). * **C & D (100–300 mg):** These doses far exceed the capacity of the subarachnoid space for lignocaine. While 300 mg is the max dose for *systemic* infiltration (without adrenaline), injecting this amount into the CSF would cause a "Total Spinal" and severe neurotoxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Hyperbaric Lignocaine (5%):** Has the highest association with **Transient Neurological Symptoms (TNS)** among all local anesthetics. * **Max Systemic Dose (Infiltration):** 3 mg/kg (plain) and 7 mg/kg (with adrenaline). * **Baricity:** Lignocaine 5% in 7.5% dextrose is **hyperbaric** (sinks in CSF), allowing for controlled spread by tilting the patient. * **Onset & Duration:** Lignocaine has a rapid onset (2–5 mins) and short duration (45–90 mins), making it suitable for short procedures.

Question 28: A 30-year-old lady is to undergo surgery under intravenous regional anesthesia for her left trigger finger. Which one of the following should not be used for the patient?

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

Explanation: **Explanation:** The question describes **Intravenous Regional Anesthesia (IVRA)**, also known as a **Bier Block**. This technique involves injecting local anesthetic into the venous system of a limb distal to a double-tourniquet. **Why Bupivacaine is contraindicated (The Correct Answer):** Bupivacaine is strictly contraindicated in IVRA due to its high **cardiotoxicity**. It has a high affinity for myocardial sodium channels and dissociates slowly during diastole ("fast-in, slow-out" kinetics). If the tourniquet fails or is released prematurely, a large bolus of bupivacaine enters the systemic circulation, potentially causing refractory ventricular arrhythmias and cardiac arrest that is notoriously difficult to resuscitate. **Analysis of Incorrect Options:** * **Lignocaine (A):** This is the **gold standard** and most commonly used drug for IVRA (usually 0.5% preservative-free). It has a rapid onset and a safer systemic profile compared to bupivacaine. * **Prilocaine (C):** This is considered the **safest** drug for IVRA due to its high therapeutic index and rapid metabolism. However, in high doses (>600mg), it carries a risk of methemoglobinemia. * **Lignocaine + Ketorolac (D):** Adjuvants are often added to lignocaine in IVRA to improve the quality of the block and provide post-operative analgesia. Ketorolac (an NSAID) is a common and safe additive for this purpose. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** IVRA works by the diffusion of anesthetic from the vascular bed into adjacent nerve endings. * **Tourniquet Time:** Minimum inflation time is **20 minutes** (to prevent systemic toxicity) and maximum is **90 minutes** (to prevent nerve injury/ischemia). * **Chloroprocaine:** Not used in IVRA due to a high incidence of thrombophlebitis. * **Ropivacaine:** Generally avoided in IVRA as it is also associated with potential CNS and cardiac toxicity, though less so than bupivacaine.

Question 29: All of the following procedures can be performed using EMLA cream except?

A. Split thickness skin graft harvesting
B. Laser removal of port-wine stain
C. Lithotripsy
D. Intubation (Correct Answer)

Explanation: **Explanation:** **EMLA (Eutectic Mixture of Local Anesthetics)** is a 1:1 oil-in-water emulsion of **2.5% Lidocaine and 2.5% Prilocaine**. Its primary purpose is to provide topical anesthesia to **intact skin** by penetrating the keratinized layer, which standard local anesthetics cannot do. **Why Intubation is the Correct Answer:** Intubation requires anesthesia of the **mucous membranes** of the airway (oropharynx, larynx, and trachea). EMLA is specifically designed for **intact skin** and requires a significant application time (60 minutes) under an occlusive dressing to be effective. For intubation, rapid-acting topical sprays (like 10% Lidocaine spray) or nerve blocks are used. Furthermore, EMLA is not recommended for use on mucous membranes due to faster systemic absorption and potential toxicity. **Analysis of Other Options:** * **Split thickness skin graft (STSG) harvesting:** EMLA applied under occlusion for 2–5 hours provides sufficient depth of anesthesia for harvesting thin skin grafts. * **Laser removal of port-wine stain:** This is a common pediatric and cosmetic indication where EMLA prevents the pain of laser pulses on the skin. * **Lithotripsy:** EMLA is frequently used to provide cutaneous anesthesia at the site where Extracorporeal Shock Wave Lithotripsy (ESWL) probes contact the skin, reducing the need for systemic analgesics. **High-Yield Clinical Pearls for NEET-PG:** * **Composition:** 2.5% Lidocaine + 2.5% Prilocaine. The melting point of the mixture is lower than either drug alone (18°C), allowing it to exist as an oil at room temperature. * **Application Time:** Minimum 60 minutes for superficial procedures; 2 hours for deeper procedures (e.g., STSG). * **Contraindication:** Should not be used in infants <1 month or those with **Methemoglobinemia**, as the Prilocaine metabolite (o-toluidine) can worsen the condition. * **Depth:** Penetrates approximately 3–5 mm into the dermis.

Question 30: Which of the following statements about Bupivacaine is FALSE?

A. It is more cardiotoxic than Lignocaine.
B. 0.25% concentration is effective for sensory block.
C. It is a long-acting local anesthetic.
D. It produces methaemoglobinaemia. (Correct Answer)

Explanation: **Explanation:** The correct answer is **D**. **Methaemoglobinaemia** is a classic side effect associated with **Prilocaine** and **Benzocaine**, not Bupivacaine. Prilocaine is metabolized into *o-toluidine*, which oxidizes hemoglobin to methemoglobin, reducing the oxygen-carrying capacity of the blood. The treatment of choice for this condition is intravenous Methylene Blue. **Analysis of other options:** * **Option A (More cardiotoxic than Lignocaine):** This is **True**. Bupivacaine has a high affinity for voltage-gated sodium channels in the myocardium and dissociates slowly during diastole ("fast-in, slow-out" kinetics). This makes Bupivacaine-induced arrhythmias (like Ventricular Fibrillation) particularly difficult to treat. * **Option B (0.25% for sensory block):** This is **True**. Bupivacaine exhibits **sensory-motor dissociation**. At lower concentrations (0.125%–0.25%), it provides excellent sensory analgesia with minimal motor blockade, making it ideal for labor analgesia and postoperative pain relief. * **Option C (Long-acting):** This is **True**. Due to its high protein binding (approx. 95%), Bupivacaine has a prolonged duration of action (3–6 hours) compared to intermediate-acting agents like Lignocaine. **High-Yield Clinical Pearls for NEET-PG:** * **Levobupivacaine and Ropivacaine** are S-enantiomers developed to provide similar potency to Bupivacaine but with significantly **reduced cardiotoxicity**. * **Intralipid (20% Lipid Emulsion)** is the specific antidote for Bupivacaine-induced systemic toxicity (LAST). * **Maximum Dose:** The maximum dose of Bupivacaine is **2 mg/kg**. * **Contraindication:** Bupivacaine is strictly contraindicated in **Bier’s Block** (Intravenous Regional Anesthesia) due to the high risk of cardiac arrest upon cuff deflation.

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

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Continuous Peripheral Nerve Catheters

Practice Questions

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