Regional Anesthesia Practice Questions

Q: A 24-year-old woman presents for labor and delivery. Caudal anesthesia is administered to block spinal nerves in the epidural space. Local anesthetic agents are most likely injected through which of the following openings?

Sacral Hiatus. **Explanation:** **Correct Answer: B. Sacral Hiatus** **Concept:** Caudal anesthesia is a type of epidural anesthesia where local anesthetic is injected into the **sacral canal** via the **sacral hiatus**. The sacral hiatus is a U-shaped or V-shaped opening at the distal end of the sacrum, formed by the failure of the fifth sacral laminae to fuse in the midline. It is covered by the sacrococcygeal ligament. This route provides access to the epidural space containing the sacral and coccygeal nerve roots. It is commonly used in pediatric surgery and for obstetric procedures (labor and delivery) to provide analgesia for the "saddle area" (S2–S4). **Analysis of Incorrect Options:** * **A. Intervertebral Foramen:** These are lateral openings between adjacent vertebrae through which spinal nerves exit. They are not the primary site of injection for regional blocks. * **C. Vertebral Canal:** This is the general longitudinal space containing the spinal cord and its coverings. While the sacral canal is a continuation of the vertebral canal, the specific "opening" used for needle entry in caudal blocks is the hiatus. * **D. Dorsal Sacral Foramen:** These are the four pairs of openings on the posterior surface of the sacrum through which the posterior rami of sacral nerves exit. They are used for transsacral nerve blocks but not for caudal epidural anesthesia. **High-Yield NEET-PG Pearls:** * **Landmarks:** The sacral hiatus is located between the **sacral cornua** (bony prominences representing the inferior articular processes of S5). * **Dural Sac:** In adults, the dural sac ends at the level of **S2**. In infants, it ends lower (around S3-S4), increasing the risk of accidental dural puncture during caudal blocks. * **Clinical Use:** Caudal blocks are the most common regional technique in **pediatric anesthesia** for infra-umbilical surgeries.

Q: In epidural anesthesia, where is the local anesthetic drug deposited?

Extradural space. **Explanation:** **1. Why Option B is Correct:** Epidural anesthesia involves the injection of local anesthetic into the **extradural space** (also known as the epidural space). This potential space lies between the **dural mater** (the outermost layer of the meninges) and the **ligamentum flavum**, which lines the vertebral canal. The drug acts primarily on the spinal nerve roots as they exit the dura and pass through the intervertebral foramina. **2. Why Other Options are Incorrect:** * **Option A (Intrathecal space):** This is the subarachnoid space (between the arachnoid and pia mater) containing CSF. Depositing drugs here results in **Spinal Anesthesia**, which requires a much smaller volume of anesthetic compared to epidural anesthesia. * **Option C (Paraspinal space):** This refers to the area alongside the spinal column. While used for paravertebral blocks, it is not the site for central neuraxial blockade like epidural anesthesia. * **Option D (Intervertebral space):** This is an anatomical landmark (the gap between vertebrae) used as a point of entry for the needle, but it is not the physiological space where the drug is deposited to achieve anesthesia. **3. High-Yield Clinical Pearls for NEET-PG:** * **Loss of Resistance (LOR) Technique:** The most common method to identify the epidural space (using air or saline). * **Hanging Drop Method:** Utilizes the negative pressure of the epidural space to identify correct needle placement. * **Site of Action:** The primary site of action is the **spinal nerve roots**; a secondary site is the paravertebral nerves. * **Test Dose:** A small dose of local anesthetic with adrenaline (e.g., 3ml of 1.5% Lignocaine with 1:200,000 adrenaline) is used to rule out accidental intravascular or intrathecal injection. * **Segmental Block:** Unlike spinal anesthesia, epidural anesthesia allows for a "segmental block," where only specific dermatomes are anesthetized.

Q: In epidural analgesia, morphine acts by acting on which structure?

Substantia gelatinosa. **Explanation:** The correct answer is **Substantia gelatinosa (Option A)**. **Mechanism of Action:** When morphine is administered into the epidural space, it crosses the dura mater and enters the cerebrospinal fluid (CSF) to reach the spinal cord. Its primary site of action is the **Substantia Gelatinosa (Rexed Lamina II)** located in the **dorsal horn** of the spinal cord. Morphine binds to pre-synaptic and post-synaptic **mu (μ) opioid receptors** here, inhibiting the release of excitatory neurotransmitters (like Substance P and Glutamate) from primary afferent nociceptors. This modulates and suppresses the transmission of pain signals before they ascend to the brain. **Analysis of Incorrect Options:** * **B. Axons:** Morphine does not possess local anesthetic properties; it does not block sodium channels or interfere with axonal conduction. * **C. Ventral horn:** The ventral horn is primarily responsible for motor output. Opioids act on the sensory processing areas (dorsal horn), which is why they provide analgesia without causing motor blockade. * **D. Sensory nerve:** While opioids can have minor peripheral effects, the clinical efficacy of epidural morphine is specifically due to its central action on the spinal cord receptors, not the peripheral sensory nerve fibers. **High-Yield Facts for NEET-PG:** * **Lipid Solubility:** Morphine has **low lipid solubility** (hydrophilic). This results in a slow onset, long duration of action, and a risk of **delayed respiratory depression** (6–24 hours) due to the cephalad (upward) spread of the drug in the CSF. * **Site of Action:** Always remember: **Opioids = Dorsal Horn (Substantia Gelatinosa)**; **Local Anesthetics = Nerve Roots/Axons.** * **Side Effects:** Common side effects of neuraxial morphine include pruritus (most common), urinary retention, and nausea.

Q: Sciatic nerve blockade provides sensory loss of which area?

Posterior thigh and majority of the leg below the knee. **Explanation:** The **Sciatic Nerve (L4–S3)** is the largest nerve in the human body. It provides motor innervation to the posterior thigh muscles (hamstrings) and all muscles below the knee. Sensorially, it supplies the **posterior thigh** (via the posterior cutaneous nerve of the thigh, which often travels with it) and the **entire leg below the knee**, with the notable exception of the medial strip. * **Why Option B is correct:** After leaving the pelvis, the sciatic nerve descends the posterior thigh. At the popliteal fossa, it divides into the tibial and common peroneal nerves. Together, these branches provide sensory coverage to the skin of the posterior thigh, the lateral leg, and the entire foot (except the medial arch). * **Why Option A is incorrect:** The **Anterior and Lateral thigh** are supplied by the **Femoral nerve** and the **Lateral Femoral Cutaneous nerve**, respectively (branches of the Lumbar Plexus). * **Why Option C is incorrect:** While the sciatic nerve covers the posterior thigh, the **Medial thigh** is supplied by the **Obturator nerve**. * **Why Option D is incorrect:** The **Medial leg below the knee** (and the medial foot) is supplied by the **Saphenous nerve**, which is the terminal sensory branch of the **Femoral nerve**. This is a classic "trap" in exams. **High-Yield Clinical Pearls for NEET-PG:** 1. **Complete Leg Block:** To achieve complete anesthesia below the knee, a Sciatic nerve block must be combined with a **Saphenous nerve block** to cover the medial leg. 2. **Anatomical Landmark:** The sciatic nerve is most commonly blocked using the **Labat approach** (Classic posterior approach), identifying the greater trochanter and the posterior superior iliac spine (PSIS). 3. **Foot Surgery:** For surgeries involving the foot and ankle, the Sciatic nerve block is the gold standard.

Q: Which of the following local anesthetics should be avoided in spinal anesthesia?

Chlorprocaine. **Explanation:** The correct answer is **Chlorprocaine**. Historically, Chlorprocaine was avoided in spinal anesthesia due to reports of permanent neurological deficits (Cauda Equina Syndrome). This neurotoxicity was primarily attributed to the preservative **sodium bisulfite** and the low pH of the formulation used in the 1980s, rather than the drug itself. While preservative-free formulations are now available and used for short procedures, for the purpose of standard examinations like NEET-PG, Chlorprocaine remains the classic answer for a local anesthetic traditionally avoided/associated with neurotoxicity in the subarachnoid space. **Analysis of Options:** * **Mepivacaine (A):** An intermediate-acting amide used for spinal anesthesia. While it has a higher incidence of Transient Neurological Symptoms (TNS) compared to bupivacaine, it is not contraindicated. * **Prilocaine (B):** Frequently used for short-duration spinal anesthesia in Europe. Its main systemic side effect is methemoglobinemia, but it is safe for spinal use. * **Bupivacaine (C):** The **gold standard** and most commonly used local anesthetic for spinal anesthesia due to its potency, long duration, and minimal sensory-motor dissociation. **High-Yield Clinical Pearls for NEET-PG:** * **Toxicity:** The neurotoxicity of older Chlorprocaine was due to **Sodium Bisulfite**. * **Hyperbaric Solutions:** Most spinal anesthetics (like Bupivacaine 0.5%) are made "heavy" by adding **Dextrose** to control the spread via gravity. * **TNS Risk:** Lidocaine has the highest association with Transient Neurological Symptoms (TNS) after spinal anesthesia. * **Potency:** Bupivacaine > Lidocaine > Procaine.

Q: Transient Bell's palsy during mandibular nerve block after injection of local anesthesia occurs due to needle piercing into which structure?

Parotid gland. **Explanation:** The occurrence of transient Bell’s palsy (facial nerve paralysis) following an inferior alveolar nerve block (mandibular nerve block) is a known complication caused by the **accidental deposition of local anesthetic into the capsule of the parotid gland.** **Why the Parotid Gland is the Correct Answer:** The parotid gland is situated posteriorly to the ramus of the mandible. If the needle is inserted too far posteriorly or if the bony contact with the medial aspect of the ramus is not maintained, the needle can pierce the parotid capsule. The **Facial Nerve (CN VII)** traverses through the substance of the parotid gland. Local anesthetic deposited here diffuses and blocks the motor branches of the facial nerve, leading to temporary ipsilateral facial drooping and inability to close the eyelid. **Analysis of Incorrect Options:** * **Maxillary Artery:** Piercing this would lead to a hematoma or intravascular injection (systemic toxicity), not motor nerve paralysis. * **Buccinator Muscle:** This muscle is pierced during the initial phase of the block; however, it does not contain the facial nerve trunk. * **Temporalis Muscle:** The tendon of the temporalis is a landmark for the injection (coronoid notch), but it is not related to the path of the facial nerve. **Clinical Pearls for NEET-PG:** * **Prevention:** Always ensure the needle tip makes **contact with bone** (medial ramus) before injecting to ensure you are anterior to the parotid gland. * **Management:** The palsy is **transient** and resolves as the anesthetic wears off (usually 1–3 hours). The most critical management step is **eye protection** (patching or manual closure) to prevent corneal drying/abrasion since the patient cannot blink. * **Differential:** If the palsy is permanent or delayed, it may be due to viral reactivation or trauma, rather than simple anesthetic diffusion.

Question 1

Which of the following is NOT a contraindication for combined spinal and epidural anesthesia?

Accepted Answer

Patient on antihypertensive medication

Answer

Platelet count < 50,000

Answer

Patient on clopidogrel

Answer

Local infection

Question 2

For which of the following conditions is epidural analgesia considered suitable?

Accepted Answer

All of the above

Answer

Rib fracture

Answer

Lower abdominal surgery

Answer

Thoracotomy

Question 3

Alkalization of local anesthetic solutions by the addition of sodium bicarbonate has the following benefits, except:

Accepted Answer

Decreases systemic toxicity

Answer

Speeds the onset

Answer

Improves quality

Answer

Decreases pain at the injection site

Question 4

A 24-year-old woman presents for labor and delivery. Caudal anesthesia is administered to block spinal nerves in the epidural space. Local anesthetic agents are most likely injected through which of the following openings?

Accepted Answer

Sacral Hiatus

Answer

Intervertebral Foramen

Answer

Vertebral canal

Answer

Dorsal Sacral Foramen

Question 5

In epidural anesthesia, where is the local anesthetic drug deposited?

Accepted Answer

Extradural space

Answer

Intrathecal space

Answer

Paraspinal space

Answer

Intervertebral space

Question 6

In epidural analgesia, morphine acts by acting on which structure?

Accepted Answer

Substantia gelatinosa

Answer

Axons

Answer

Ventral horn

Answer

Sensory nerve

Question 7

Sciatic nerve blockade provides sensory loss of which area?

Accepted Answer

Posterior thigh and majority of the leg below the knee

Answer

Anterior and lateral thigh

Answer

Medial and posterior thigh

Answer

Medial leg below the knee

Question 8

Which of the following local anesthetics should be avoided in spinal anesthesia?

Accepted Answer

Chlorprocaine

Answer

Mepivacaine

Answer

Prilocaine

Answer

Bupivacaine

Question 9

Intravenous regional anesthesia (IVRA) is contraindicated in which of the following conditions?

Accepted Answer

Coagulopathy

Answer

Cancer of the hematogenous system

Answer

Sickle cell disease

Answer

Hypertension

Question 10

Transient Bell's palsy during mandibular nerve block after injection of local anesthesia occurs due to needle piercing into which structure?

Accepted Answer

Parotid gland

Answer

Maxillary artery

Answer

Buccinator muscle

Answer

Temporalis muscle

Regional Anesthesia — MCQs

Regional Anesthesia — MCQs

On this page

Practice by Chapter

Want unlimited practice?