Regional Anesthesia Practice Questions

Q: In general, which is the last muscle to be rendered akinetic with a retrobulbar anesthetic block?

Superior oblique. **Explanation:** The goal of a retrobulbar block is to achieve anesthesia and akinesia of the globe by injecting local anesthetic into the muscle cone. The **Superior Oblique** is typically the last muscle to be rendered akinetic because of its unique anatomical position. **Why Superior Oblique is the correct answer:** The retrobulbar block targets the nerves within the retrobulbar cone (ciliary nerves and Cranial Nerves III and VI). However, the **Trochlear nerve (CN IV)**, which supplies the Superior Oblique, is the only motor nerve to the extraocular muscles that remains **outside the muscle cone**. Because the local anesthetic must diffuse from the intraconal space to the extraconal space to reach CN IV, the Superior Oblique is the last to be paralyzed. **Analysis of Incorrect Options:** * **Superior Rectus & Inferior Oblique:** These are supplied by the Superior and Inferior divisions of the Oculomotor nerve (CN III), respectively. Since CN III enters the orbit through the tendinous ring *inside* the muscle cone, these muscles are blocked rapidly. * **Levator palpebrae superioris:** Also supplied by the Superior division of CN III within the cone. While it is responsible for ptosis after a block, it is not the last muscle affected. **High-Yield Clinical Pearls for NEET-PG:** * **The "Classic" Retrobulbar Block:** Provides excellent anesthesia and akinesia but carries risks like retrobulbar hemorrhage or optic nerve injury. * **Nerves outside the cone:** Trochlear (IV), Lacrimal, Frontal, and Nasociliary (though Nasociliary eventually enters). * **Safety Note:** If a patient can still look "down and in" after a block, the Superior Oblique (CN IV) is still functioning. * **Alternative:** Peribulbar blocks are safer as the needle remains extraconal, though they require a larger volume of anesthetic and have a slower onset.

Q: What is the concentration of Xylocaine heavy in the subarachnoid space?

5%. **Explanation:** The correct answer is **5% (Option D)**. In spinal anesthesia (subarachnoid block), the baricity of the local anesthetic determines its spread within the cerebrospinal fluid (CSF). **Xylocaine Heavy** (Lignocaine/Lidocaine) is formulated as a **5% concentration** mixed with **7.5% Dextrose**. The addition of dextrose increases the specific gravity of the solution (making it "heavy" or hyperbaric) relative to the CSF (specific gravity ~1.003–1.008). This allows the clinician to control the level of the block using gravity by tilting the patient. **Analysis of Options:** * **A (1%):** This concentration is commonly used for local infiltration or minor nerve blocks, but it is too dilute for a standard hyperbaric spinal block. * **B (2%):** This is the standard concentration for **Epidural Anesthesia** and peripheral nerve blocks. It provides excellent sensory and motor blockade in the epidural space but is not the standard "heavy" preparation for spinal use. * **C (3%):** This is not a standard commercial concentration for Xylocaine in regional anesthesia. * **D (5%):** This is the gold-standard concentration for hyperbaric Lignocaine used in the subarachnoid space. **High-Yield Clinical Pearls for NEET-PG:** * **Transient Neurological Symptoms (TNS):** 5% Lignocaine has fallen out of favor in many centers due to a high incidence of TNS (radicular pain/dysesthesia post-operatively), especially when used for spinal anesthesia in the lithotomy position. * **Bupivacaine (Sensorcaine/Marcaine):** Currently the most common drug for spinal anesthesia, used as a **0.5% heavy** solution (with 8% dextrose). * **Specific Gravity:** Hyperbaric solutions have a specific gravity >1.008; Isobaric = 1.008; Hypobaric < 1.008. * **Lignocaine Metabolism:** It is an amide-linked local anesthetic metabolized in the liver by cytochrome P450 enzymes.

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

Infraclavicular. 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.

Q: 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?

Posterior tibial nerve. ### 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).

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

All of the above. 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 1

What are the physiological effects of spinal anesthesia primarily due to the blockage of?

Accepted Answer

Sympathetic nerve roots

Answer

Afferent motor nerves

Answer

Sensory fibres

Answer

Efferent motor nerves

Question 2

In general, which is the last muscle to be rendered akinetic with a retrobulbar anesthetic block?

Accepted Answer

Superior oblique

Answer

Superior rectus

Answer

Inferior oblique

Answer

Levator palpebrae superioris

Question 3

What is the concentration of Xylocaine heavy in the subarachnoid space?

Accepted Answer

5%

Answer

1%

Answer

2%

Answer

3%

Question 4

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

Accepted Answer

Infraclavicular

Answer

Supraclavicular

Answer

Axillary

Answer

All

Question 5

What is the most common side effect of neuraxial opioids?

Accepted Answer

Pruritus

Answer

Nausea and vomiting

Answer

Urinary retention

Answer

Sedation

Question 6

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?

Accepted Answer

Posterior tibial nerve

Answer

Saphenous nerve

Answer

Sural nerve

Answer

Superficial peroneal nerve

Question 7

Epidural anesthesia is associated with a decreased risk of which of the following complications?

Accepted Answer

Headache, Arachnoiditis, and Hypotension

Answer

Headache, Hypotension, and Meningitis

Answer

Headache and Arachnoiditis

Answer

Hypotension and Meningitis

Question 8

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

Accepted Answer

Spinal anesthesia is administered below the L3 level in children.

Answer

The spinal cord ends at S1 in adults.

Answer

The dural sac extends up to S2 in children.

Answer

The spinal cord ends at the lower border of L1 in children.

Question 9

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

Accepted Answer

All of the above

Answer

Loss of resistance sign

Answer

Negative pressure sign

Answer

Mackintosh extradural space indicator

Question 10

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

Accepted Answer

Sensory, autonomic, and motor nerves

Answer

Motor and sensory nerves only

Answer

Sensory and autonomic nerves only

Answer

Sensory nerves only

Regional Anesthesia — MCQs

Regional Anesthesia — MCQs

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