Regional Anesthesia — MCQs

Regional Anesthesia Indian Medical PG Practice Questions and MCQs

Question 41: Which anesthetic agent is contraindicated for intrathecal use?

A. Fentanyl
B. Remifentanyl (Correct Answer)
C. Sufentanil
D. Alfentanil

Explanation: **Explanation:** The correct answer is **Remifentanil**. The primary reason Remifentanil is contraindicated for intrathecal (spinal) or epidural administration is its formulation. Remifentanil is buffered with **glycine**, an inhibitory neurotransmitter. When injected into the subarachnoid space, glycine can cause profound **neurotoxicity**, leading to motor dysfunction and potential spinal cord damage. Furthermore, Remifentanil’s unique pharmacokinetic profile—ultra-short duration due to rapid metabolism by non-specific plasma esterases—makes it impractical for regional anesthesia, where a sustained effect is usually desired. **Analysis of Incorrect Options:** * **Fentanyl (Option A):** A highly lipophilic opioid commonly used as an adjuvant in spinal anesthesia. It provides rapid onset of analgesia and reduces the dose requirement of local anesthetics. * **Sufentanil (Option C):** Even more lipophilic than fentanyl, it is frequently used intrathecally, especially in obstetric analgesia, due to its high potency and rapid onset. * **Alfentanil (Option D):** While less common than fentanyl, it is preservative-free and can be used neuraxially without the neurotoxic risks associated with Remifentanil. **High-Yield Clinical Pearls for NEET-PG:** * **The "Glycine" Rule:** Always remember that Remifentanil = Glycine = Neurotoxicity in the CNS. * **Metabolism:** Remifentanil is the only opioid metabolized by **plasma and tissue esterases**, giving it a predictable context-sensitive half-life of ~3–4 minutes, regardless of infusion duration. * **Preservatives:** Many drugs (like certain formulations of Lidocaine or Bupivacaine) are contraindicated intrathecally if they contain preservatives like **methylparaben** or **sodium metabisulfite** due to the risk of arachnoiditis.

Question 42: The dose of which of the following local anesthetics does NOT need to be decreased in patients with deranged liver function?

A. Lignocaine
B. Bupivacaine
C. Cocaine
D. Procaine (Correct Answer)

Explanation: **Explanation:** The metabolism of local anesthetics (LAs) depends entirely on their chemical structure, specifically the linkage between the aromatic ring and the hydrocarbon chain. **1. Why Procaine is Correct:** Local anesthetics are classified into two groups: **Amides** and **Esters**. * **Esters** (e.g., Procaine, Chloroprocaine, Tetracaine) are metabolized by **pseudocholinesterase (plasma cholinesterase)** enzymes in the blood. * Since their metabolism occurs primarily in the plasma and not the liver, their clearance is largely independent of hepatic function. Therefore, the dose of Procaine does not need to be adjusted in patients with liver disease. **2. Why the Other Options are Incorrect:** * **Lignocaine and Bupivacaine (Amides):** Amide LAs (identified by having two "i"s in their name) are metabolized primarily by **hepatic microsomal enzymes** (Cytochrome P450). In patients with deranged liver function or reduced hepatic blood flow (e.g., CHF, cirrhosis), the half-life of these drugs is significantly prolonged, increasing the risk of Systemic Toxicity (LAST). Thus, doses must be decreased. * **Cocaine:** Although an ester, cocaine is unique because it undergoes significant metabolism by **hepatic carboxylesterase** in addition to plasma cholinesterase. Therefore, its clearance can still be affected by liver dysfunction. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic:** Am**i**des have two "i"s (L**i**doca**i**ne, Bup**i**vaca**i**ne, Pr**i**loca**i**ne, Rop**i**vaca**i**ne). Esters have one "i" (Proca**i**ne, Coca**i**ne, Benzoca**i**ne). * **Prilocaine** is associated with **Methemoglobinemia** (due to its metabolite o-toluidine). * **Bupivacaine** is the most **cardiotoxic** LA; Intralipid (20% lipid emulsion) is the specific antidote for toxicity. * **Chloroprocaine** has the shortest duration of action and fastest metabolism among esters.

Question 43: What is the drug of choice for Bier's block?

A. Prilocaine
B. Bupivacaine
C. Lidocaine (Correct Answer)
D. None of the above

Explanation: **Explanation:** **Bier’s Block (Intravenous Regional Anesthesia - IVRA)** involves the injection of a local anesthetic into the venous system of an extremity that has been isolated from the systemic circulation using a pneumatic tourniquet. **Why Lidocaine is the Correct Answer:** Lidocaine (0.5%) is the **drug of choice** for Bier’s block due to its excellent safety profile, rapid onset, and moderate duration of action. It provides reliable sensory and motor blockade with a low risk of systemic toxicity once the tourniquet is deflated, as it rapidly redistributes and is metabolized. **Analysis of Incorrect Options:** * **Prilocaine:** While Prilocaine is actually considered the safest drug for IVRA in many international guidelines (due to its high therapeutic index), it is **not** the most commonly used or the standard "textbook" answer in the context of Indian medical exams unless specifically asked for the "safest" drug. Furthermore, it carries a risk of **methemoglobinemia**. * **Bupivacaine:** This is **strictly contraindicated** in Bier’s block. Bupivacaine is highly cardiotoxic; if the tourniquet fails or is released prematurely, the sudden systemic bolus can lead to fatal arrhythmias and cardiac arrest that is notoriously difficult to resuscitate. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** The anesthetic works by diffusing from the vascular bed into adjacent nerve endings and trunks. * **Tourniquet Time:** The tourniquet must remain inflated for at least **20 minutes** to allow for tissue fixation of the drug, preventing a toxic systemic bolus upon release. * **Maximum Time:** Should not exceed 90 minutes to avoid nerve injury and ischemia. * **Chloroprocaine:** Avoided in IVRA due to a high incidence of thrombophlebitis.

Question 44: Which technique is used for a closed mouth mandibular nerve block?

A. Clark and Holmes technique
B. Akinosi-Vazarani technique (Correct Answer)
C. Gow gates technique
D. Angelio Sergenti technique

Explanation: The **Akinosi-Vazirani technique** is the correct answer as it is specifically designed as a **closed-mouth approach** to the mandibular nerve block. ### 1. Why Akinosi-Vazirani is Correct This technique is primarily indicated for patients with **trismus** (limited mouth opening) or when the landmarks for a standard inferior alveolar nerve block (IANB) are obscured. The needle is inserted at the level of the maxillary mucogingival junction, parallel to the occlusal plane, into the pterygomandibular space while the teeth are in occlusion. It anesthetizes the inferior alveolar, lingual, and mylohyoid nerves. ### 2. Analysis of Incorrect Options * **Gow-Gates Technique:** This is an **open-mouth** technique. It is considered a "true" mandibular block because it targets the neck of the mandibular condyle, anesthetizing almost all branches of the mandibular nerve (V3). It has a higher success rate than IANB but requires the patient to open wide. * **Clark and Holmes Technique:** This is a variation of the IANB but is not the standard closed-mouth approach. * **Angelo Sargenti Technique:** This refers to a controversial endodontic method (N2 paste) involving root canal filling materials containing formaldehyde, unrelated to nerve block techniques. ### 3. Clinical Pearls for NEET-PG * **Landmark for Akinosi:** Maxillary tuberosity at the level of the mucogingival junction. * **Landmark for Gow-Gates:** Intertragic notch and the mesiopalatal cusp of the maxillary second molar. * **Highest Success Rate:** Gow-Gates (due to lower anatomical variation at the condyle). * **Highest Aspiration Risk:** Standard IANB (approx. 10–15%). * **Nerves spared in IANB but caught in Gow-Gates:** Buccal nerve and auriculotemporal nerve.

Question 45: Which of the following is true about spinal anesthesia?

A. Onset of analgesia takes about 15 minutes
B. Anesthesia is injected in the subarachnoid space (Correct Answer)
C. Most common complication is post-dural puncture headache (PDPH)
D. May lead to intra-operative tachycardia

Explanation: **Explanation:** **Correct Answer: B. Anesthesia is injected in the subarachnoid space** Spinal anesthesia (Subarachnoid Block) involves the injection of a local anesthetic into the **subarachnoid space** (between the arachnoid mater and pia mater), where it mixes with the cerebrospinal fluid (CSF). This results in a rapid, predictable, and dense sensory and motor blockade by acting directly on the spinal nerve roots. **Analysis of Incorrect Options:** * **Option A:** The onset of spinal anesthesia is very rapid, typically occurring within **2–5 minutes**. A 15-minute onset is more characteristic of epidural anesthesia. * **Option C:** While PDPH is a classic complication, the **most common** complication of spinal anesthesia is **hypotension** (due to sympathetic blockade causing peripheral vasodilation). * **Option D:** Spinal anesthesia typically leads to **bradycardia** (not tachycardia). This occurs due to the blockade of "cardio-accelerator" fibers (T1–T4) and a decrease in venous return (Bainbridge reflex). **High-Yield Clinical Pearls for NEET-PG:** * **Level of Injection:** Usually performed at L3-L4 or L4-L5 to avoid spinal cord injury (the cord ends at **L1** in adults and **L3** in infants). * **PDPH Management:** Characterized by a "postural" headache. Conservative management includes bed rest and hydration; the definitive treatment is an **Epidural Blood Patch**. * **Order of Blockade:** B-fibers (Sympathetic) > A-delta & C fibers (Pain/Temp) > A-gamma (Muscle spindle) > A-beta (Touch/Pressure) > A-alpha (Motor). * **Specific Gravity:** Hyperbaric solutions (dextrose added) are most commonly used to control the spread of the block via gravity.

Question 46: What is the anesthetic of choice for an elderly patient with a fracture of the right hip?

A. Spinal/epidural anesthesia (Correct Answer)
B. General anesthesia
C. Local infiltration anesthesia
D. None of the above

Explanation: **Explanation** **1. Why Spinal/Epidural Anesthesia is Correct:** Neuraxial anesthesia (Spinal or Epidural) is the preferred choice for hip fracture surgeries in the elderly. It provides superior postoperative analgesia and significantly reduces the risk of **Deep Vein Thrombosis (DVT)** and pulmonary embolism by improving lower limb blood flow. Furthermore, neuraxial blocks minimize the "stress response" to surgery and reduce the incidence of **Postoperative Cognitive Dysfunction (POCD)** and delirium, which are common complications in geriatric patients undergoing general anesthesia. **2. Why Other Options are Incorrect:** * **General Anesthesia (GA):** While frequently used, GA is associated with a higher risk of respiratory complications (atelectasis, pneumonia) and a greater incidence of postoperative confusion in the elderly. It also lacks the inherent thromboembolic protection provided by regional techniques. * **Local Infiltration:** This is insufficient for hip surgery as it cannot provide the deep muscle relaxation or the dense sensory block required for manipulating a fractured femur and performing internal fixation or arthroplasty. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mortality:** Studies (like the Cochrane review) suggest a slight reduction in 30-day mortality and a significant reduction in DVT risk with regional vs. general anesthesia for hip fractures. * **Positioning:** The main challenge for spinal anesthesia in these patients is pain during positioning (sitting/lateral). A **Fascia Iliaca Compartment Block (FICB)** or a **Femoral Nerve Block** is often performed *before* the spinal to provide analgesia for positioning. * **Contraindications:** Always check for anticoagulation status (common in elderly cardiac patients) before performing neuraxial blocks to avoid spinal hematoma.

Question 47: Which cranial nerves are NOT involved in spinal anesthesia?

A. 1st and 10th (Correct Answer)
B. 3rd and 6th
C. 2nd and 4th
D. 7th and 8th

Explanation: **Explanation:** Spinal anesthesia involves the injection of local anesthetics into the subarachnoid space, typically at the lumbar level. The "level" of the block depends on the cephalad spread of the drug. While spinal anesthesia primarily targets spinal nerves, it can occasionally involve cranial nerves due to high cephalad spread or secondary physiological changes. **Why Option A is Correct:** * **1st Cranial Nerve (Olfactory):** This nerve is purely sensory and located high within the anterior cranial fossa. It has no anatomical or physiological connection to the subarachnoid space affected by spinal anesthesia. * **10th Cranial Nerve (Vagus):** The Vagus nerve originates in the medulla and exits the skull via the jugular foramen. Crucially, it provides parasympathetic innervation to the heart and abdominal viscera **independently** of the spinal cord. Spinal anesthesia causes a "sympathectomy," leading to **unopposed vagal tone**, but the nerve itself is not blocked or inhibited by the anesthetic. **Why Other Options are Incorrect:** * **Options B, C, and D:** These involve nerves (3rd, 4th, 6th for ocular movement; 2nd for vision; 7th/8th for facial/vestibulocochlear) that can be affected by **Post-Dural Puncture Headache (PDPH)**. A decrease in CSF pressure causes "sagging" of the brain, leading to traction on these cranial nerves. The **6th cranial nerve (Abducens)** is the most commonly affected due to its long intracranial course, leading to diplopia. **NEET-PG High-Yield Pearls:** 1. **Most common CN palsy post-spinal:** 6th Cranial Nerve (Abducens) due to traction from low CSF pressure. 2. **Bradycardia in Spinal:** Occurs due to blockade of T1-T4 cardioaccelerator fibers and unopposed vagal activity (not vagal block). 3. **Total Spinal:** If the anesthetic reaches the brainstem, it can cause respiratory arrest (medullary depression) and unconsciousness.

Question 48: What is the most common complication of spinal anesthesia?

A. Hypotension (Correct Answer)
B. Headache
C. Meningitis
D. Arrhythmia

Explanation: **Explanation:** **Hypotension** is the most common complication of spinal anesthesia, occurring in approximately 25–35% of patients. The underlying mechanism is the **blockade of preganglionic sympathetic fibers** (T1–L2). This leads to arterial vasodilation (decreasing systemic vascular resistance) and venous pooling (decreasing venous return and cardiac output). If the block reaches high thoracic levels (T1–T4), the cardioaccelerator fibers are inhibited, leading to bradycardia, further exacerbating the drop in blood pressure. **Analysis of Incorrect Options:** * **B. Headache:** Post-Dural Puncture Headache (PDPH) is a well-known complication caused by CSF leakage through the dural hole. While high-yield, its incidence has significantly decreased (to <1%) with the use of smaller, non-cutting needles (e.g., Whitacre or Sprotte). * **C. Meningitis:** This is a rare but severe infective complication. It is usually caused by a breach in aseptic technique or the introduction of skin flora (e.g., *Streptococcus viridans*). * **D. Arrhythmia:** While bradycardia can occur due to sympathetic blockade or the Bezold-Jarisch reflex, generalized arrhythmias are not a common primary complication of spinal anesthesia. **High-Yield Clinical Pearls for NEET-PG:** * **Management of Hypotension:** Initial treatment includes left uterine displacement (in obstetric cases), IV fluid bolus (pre-loading or co-loading), and vasopressors (Phenylephrine is currently the drug of choice; Ephedrine is an alternative). * **Order of Nerve Block:** B-fibers (Sympathetic) > A-delta & C-fibers (Pain/Temp) > A-gamma (Muscle spindle) > A-beta (Touch/Pressure) > A-alpha (Motor). * **Level of Block:** Sympathetic block is usually 2–3 segments higher than the sensory block, which is 2 segments higher than the motor block.

Question 49: Inferior alveolar nerve block alone can be used in which of the following procedures?

A. Pulpotomy of a third molar (Correct Answer)
B. Apicoectomy of a third molar
C. Extraction of a first molar
D. Root resection of a first molar

Explanation: To understand this question, one must distinguish between **pulpal anesthesia** and **soft tissue anesthesia**. ### **Why Pulpotomy of a Third Molar is Correct** The **Inferior Alveolar Nerve (IAN)** provides sensory innervation to the pulp of all mandibular teeth in a quadrant. A **Pulpotomy** involves the removal of the coronal portion of the dental pulp. Since this procedure is confined entirely within the tooth structure (pulp chamber), an IAN block alone is sufficient to achieve complete anesthesia. ### **Why Other Options are Incorrect** * **Extraction of a first molar (C):** Extraction involves the manipulation of the surrounding periodontium and gingiva. While the IAN numbs the tooth, the **Long Buccal Nerve** must also be blocked to anesthetize the buccal soft tissues (gingiva) to prevent pain during forceps application. * **Apicoectomy (B) and Root Resection (D):** These are surgical procedures involving the periapical tissues and alveolar bone. These procedures require reflecting a mucoperiosteal flap, which necessitates anesthesia of the **Long Buccal Nerve** (for buccal access) and sometimes the **Lingual Nerve** (if lingual tissues are involved). ### **High-Yield Clinical Pearls for NEET-PG** * **The "Big Three" in Mandibular Anesthesia:** A standard IAN block typically anesthetizes the IAN and the Lingual nerve (due to proximity), but **never** the Long Buccal nerve. * **Landmark:** The injection is targeted at the **mandibular foramen**, located on the medial aspect of the ramus, protected by the **lingula**. * **Failure Rate:** The IAN block has the highest failure rate of all dental injections (approx. 15-20%) due to anatomical variations like accessory innervation from the **mylohyoid nerve**. * **Aspiration:** Always aspirate before injecting; the inferior alveolar artery and vein run immediately adjacent to the nerve.

Question 50: What is the purpose of adding dextrose to spinal anesthetic drugs?

A. To increase the duration of action.
B. To reduce plasma levels of the local anesthetic and prevent toxicity.
C. To increase the specific gravity. (Correct Answer)
D. To hasten the onset of action.

Explanation: ### Explanation The correct answer is **C. To increase the specific gravity.** **Understanding Baricity and Specific Gravity** The primary reason for adding dextrose (usually 5% to 8%) to local anesthetics like Bupivacaine is to alter their **baricity**. Baricity is the ratio of the density of the anesthetic solution to the density of cerebrospinal fluid (CSF). * **Hyperbaric solutions:** By adding dextrose, the solution becomes "heavier" (higher specific gravity) than CSF. * **Clinical Significance:** Gravity allows the clinician to control the spread of the drug within the subarachnoid space by tilting the patient. For example, in a seated patient, a hyperbaric solution will sink caudally toward the sacral nerves (Saddle Block). **Why the other options are incorrect:** * **Option A:** Duration of action is primarily determined by the drug’s **lipid solubility and protein binding**, or by adding vasoconstrictors like adrenaline. Dextrose does not significantly prolong the block. * **Option B:** Plasma toxicity in spinal anesthesia is rare because the total dose used is very small compared to epidural or peripheral nerve blocks. Dextrose does not affect systemic absorption. * **Option D:** The onset of action is determined by the **pKa** of the drug (which dictates the degree of ionization). Dextrose does not alter the pKa or hasten the onset. **High-Yield NEET-PG Pearls:** * **CSF Specific Gravity:** 1.003 to 1.008. * **Hyperbaric Bupivacaine:** 0.5% Bupivacaine in 8% Dextrose is the most commonly used preparation. * **Hypobaric solutions:** Created by adding sterile water; these "float" upward against gravity. * **Isobaric solutions:** Have a specific gravity equal to CSF (e.g., Plain 0.5% Bupivacaine). These stay localized at the site of injection regardless of patient positioning.

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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