Truncal Blocks — MCQs
In doing phrenic nerve block, it is best to infiltrate
Retrobulbar injection of xylocaine blocks all of the following except:
Which local anesthetic is considered the most cardiotoxic?
"Triangle of Petit" is a landmark for which block?
During abdominal surgery under local anesthesia, the patient suddenly felt pain due to
Which block is described as regional anesthesia of the arm:-
A young male was administered regional anesthesia with 0.25% bupivacaine. The patient became unresponsive, and the pulse became unrecordable. What is the best management in this situation?
Which of the following is correct about the EMLA patch shown in the image below?
Which nerve is targeted in the nasociliary nerve block?
What is the maximum concentration allowed for epidural block?
Truncal Blocks Indian Medical PG Practice Questions and MCQs
Question 1: In doing phrenic nerve block, it is best to infiltrate
- A. Scalenus anterior
- B. Scalenus posterior
- C. Anterior border of sternomastoid
- D. Posterior border of sternomastoid (Correct Answer)
Explanation: Posterior border of sternomastoid - The phrenic nerve (C3-C5) descends on the anterior surface of the scalenus anterior muscle through the neck. - To block the phrenic nerve as it emerges from the brachial plexus roots, local anesthetic is ideally infiltrated at the posterior border of the sternomastoid muscle at the level of the cricoid cartilage (C6 vertebral level). Scalenus anterior - While the phrenic nerve rests on the anterior surface of the scalenus anterior, infiltrating this muscle directly might not be as effective for a complete block, as the nerve is relatively superficial at the posterior border of the sternomastoid. - Infiltration within the scalenus anterior could potentially lead to a less targeted block or hit other structures within the muscle. Scalenus posterior - The scalenus posterior muscle is located deeper and more laterally in the neck compared to the scalenus anterior. - The phrenic nerve does not have a direct anatomical relationship with the scalenus posterior that would make this an optimal site for a block. Anterior border of sternomastoid - The anterior border of the sternomastoid muscle provides an anatomical landmark for other neck structures, but the phrenic nerve is not readily accessible for blockade at this specific location. - Infiltrating here would be too anterior and medial to where the phrenic nerve emerges from the brachial plexus components.
Question 2: Retrobulbar injection of xylocaine blocks all of the following except:
- A. 3rd cranial nerve
- B. 4th cranial nerve (Correct Answer)
- C. 6th cranial nerve
- D. Ciliary nerves and ciliary ganglion
Explanation: ***4th cranial nerve*** - The **trochlear nerve (CN IV)** innervates the **superior oblique muscle** and has a unique superior and anterior course in the orbit, making it less accessible to retrobulbar injections. - Its location relative to the muscle cone and globe means a retrobulbar injection, which typically aims to block nerves within the muscle cone, often misses it. *3rd cranial nerve* - The **oculomotor nerve (CN III)** supplies most of the extraocular muscles and travels within the **muscle cone**, where retrobulbar anesthetic is deposited. - It is reliably blocked by a retrobulbar injection, causing akinesia of the muscles it innervates. *6th cranial nerve* - The **abducens nerve (CN VI)** innervates the **lateral rectus muscle** and is located within the **muscle cone**, making it susceptible to retrobulbar block. - Anesthetic diffusion within the cone effectively blocks this nerve, leading to paralysis of the lateral rectus. *Ciliary nerves and ciliary ganglion* - The **short ciliary nerves** and **ciliary ganglion** are located in the retrobulbar space, typically within the muscle cone or close to it. - Anesthetic solution injected retrobulbarly readily diffuses to these structures, blocking sensory input from the cornea and iris, as well as parasympathetic innervation to the pupil and ciliary body.
Question 3: Which local anesthetic is considered the most cardiotoxic?
- A. Procaine
- B. Prilocaine
- C. Ropivacaine
- D. Bupivacaine (Correct Answer)
Explanation: ***Bupivacaine*** - **Bupivacaine** is an amide-type local anesthetic associated with significant **cardiotoxicity** due to its high lipid solubility and slow dissociation from cardiac sodium channels. - This can lead to severe **arrhythmias** and myocardial depression, making it particularly dangerous in systemic overdose. *Procaine* - **Procaine** is an ester-type local anesthetic with a relatively low potential for cardiotoxicity. - Its rapid metabolism by **plasma pseudocholinesterase** limits systemic exposure and reduces the risk of cardiac effects. *Prilocaine* - **Prilocaine** is an amide-type local anesthetic that is generally less cardiotoxic than bupivacaine. - Its primary concern is the potential to cause **methemoglobinemia** at higher doses, a side effect not directly related to cardiotoxicity. *Ropivacaine* - **Ropivacaine** is an amide-type local anesthetic developed as an alternative to bupivacaine with a reduced cardiotoxicity profile. - It exhibits a more favorable **therapeutic index** for cardiac effects due to its chemical structure and faster dissociation from cardiac sodium channels.
Question 4: "Triangle of Petit" is a landmark for which block?
- A. Epidural block
- B. TAP block (Correct Answer)
- C. Spinal block
- D. Bier's block
Explanation: **TAP block** - The **Triangle of Petit** (or lumbar triangle) is an important anatomical landmark used to approximate the location for a **transversus abdominis plane (TAP) block**. - This triangle is formed by the **latissimus dorsi muscle** posteriorly, the **external oblique muscle** anteriorly, and the **iliac crest** inferiorly. *Epidural block* - An epidural block involves injecting local anesthetic into the **epidural space** surrounding the spinal cord. - Its landmarks are typically based on vertebral palpable structures, not the Triangle of Petit. *Spinal block* - A spinal block (or subarachnoid block) involves injecting local anesthetic into the **subarachnral space**, directly into the cerebrospinal fluid. - Access is gained through the dura and arachnoid membranes, with landmarks again being specific vertebral levels. *Bier's block* - Bier's block, or **intravenous regional anesthesia**, involves isolated limb anesthesia by injecting local anesthetic intravenously after exsanguination and tourniquet application. - It does not involve any specific anatomical surface landmarks like the Triangle of Petit.
Question 5: During abdominal surgery under local anesthesia, the patient suddenly felt pain due to
- A. Liver
- B. Parietal peritoneum (Correct Answer)
- C. Intestines
- D. Visceral peritoneum
Explanation: ***Parietal peritoneum*** - The **parietal peritoneum** is richly innervated by somatic nerves (**spinal nerves**), making it highly sensitive to pain, pressure, and temperature. - When stimulated during surgery, even under local anesthesia which might not completely block deeper somatic nerves or if the local block is inadequate, it can cause the patient to suddenly feel **sharp, localized pain**. *Liver* - The liver itself has very few pain receptors in its parenchyma; pain from the liver typically arises from stretching of its fibrous capsule (**Glisson's capsule**). - This pain is usually dull and poorly localized, not the sudden, sharp pain typically experienced during surgical manipulation. *Intestines* - The intestines are primarily innervated by the **autonomic nervous system** and are sensitive to distension and ischemia, causing visceral pain, which is typically dull, crampy, and poorly localized. - They are generally not sensitive to cutting or burning, which are common surgical manipulations. *Visceral peritoneum* - The **visceral peritoneum** covers abdominal organs and is innervated by the autonomic nervous system, similar to the organs it covers. - Like the intestines, it is sensitive to stretch and ischemia, producing diffuse, poorly localized visceral pain rather than sharp, localized pain from surgical incision or manipulation.
Question 6: Which block is described as regional anesthesia of the arm:-
- A. Interscalene block
- B. Infraclavicular block
- C. Axillary block
- D. Supraclavicular brachial plexus block (Correct Answer)
Explanation: ***Supraclavicular brachial plexus block*** - The **supraclavicular block** targets the **trunks of the brachial plexus** as they exit the scalene muscles, providing comprehensive anesthesia to the entire upper limb, including the shoulder, arm, forearm, and hand. - This block is particularly effective for procedures involving the arm due to its proximal location within the brachial plexus, covering multiple nerve distributions. *Interscalene block* - An **interscalene block** primarily targets the **roots or trunks of the brachial plexus** and is typically used for shoulder and upper arm surgery, but may spare the ulnar nerve. - While it anesthetizes the arm, it is primarily chosen for more proximal procedures and may not provide complete distal arm anesthesia compared to the supraclavicular approach. *Infraclavicular block* - An **infraclavicular block** targets the **cords of the brachial plexus** and is suitable for procedures involving the elbow, forearm, and hand, providing good coverage for these areas. - While it does anesthetize the distal arm, it is more distal than the supraclavicular block and may not provide full coverage for the entire upper arm and shoulder. *Axillary block* - An **axillary block** targets the **terminal branches of the brachial plexus** in the axilla, mainly anesthetizing the forearm and hand. - This block is often used for procedures distal to the elbow and provides less comprehensive coverage for the entire upper arm and shoulder compared to more proximal blocks.
Question 7: A young male was administered regional anesthesia with 0.25% bupivacaine. The patient became unresponsive, and the pulse became unrecordable. What is the best management in this situation?
- A. ECPR with calcium
- B. ECPR with dobutamine
- C. ECPR with 20% intralipid (Correct Answer)
- D. ECPR with sodium bicarbonate
Explanation: ***ECPR with 20% intralipid*** - The scenario describes **Local Anesthetic Systemic Toxicity (LAST)**, likely due to bupivacaine, leading to cardiovascular collapse. - **Intralipid 20%** is the first-line treatment for LAST-induced cardiovascular toxicity, as it acts as a lipid sink for the lipophilic local anesthetic. *ECPR with calcium* - While calcium may be used in certain cardiac arrest scenarios, it is **not the primary treatment for bupivacaine-induced cardiovascular collapse** and LAST. - Calcium might offer some cardiac support but does not directly neutralize the local anesthetic's toxic effects. *ECPR with dobutamine* - **Dobutamine is an inotropic agent** used to improve cardiac contractility but is not indicated as a primary rescue therapy for severe LAST. - It would not address the underlying toxicity caused by bupivacaine and could potentially worsen the situation by increasing myocardial oxygen demand without reversing toxin effects. *ECPR with sodium bicarbonate* - **Sodium bicarbonate** is used to treat metabolic acidosis and can be beneficial in certain drug overdoses to enhance excretion or stabilize cardiac membranes. - However, it is **not the primary or most effective treatment for bupivacaine-induced LAST** and cardiovascular collapse compared to lipid emulsion therapy.
Question 8: Which of the following is correct about the EMLA patch shown in the image below?
- A. Adverse effect is methemoglobinemia
- B. Contains bupivacaine & lignocaine
- C. Eutectic mixture is used (Correct Answer)
- D. 0.5% concentration of lignocaine has 50 mg in 1 gm is used
- E. Requires application for at least 15 minutes for adequate anesthesia
Explanation: ***Eutectic mixture is used*** - EMLA stands for **Eutectic Mixture of Local Anesthetics**, indicating that it uses a mixture of lidocaine and prilocaine to lower their melting points, allowing them to remain liquid at room temperature. - This liquid form enhances skin penetration, providing more effective topical anesthesia compared to individual agents. *Adverse effect is methemoglobinemia* - While methemoglobinemia is a potential side effect of **prilocaine**, which is part of the EMLA cream, it is usually only seen with **excessive doses** or in susceptible individuals (e.g., infants). - Given its topical application and typical dosing, it is not the most common or direct feature associated with correct use of the EMLA patch. *Contains bupivacaine & lignocaine* - The EMLA patch contains **lidocaine (lignocaine)** and **prilocaine**, not bupivacaine. - Bupivacaine is another local anesthetic, but it is not a component of the EMLA formulation. *0.5% concentration of lignocaine has 50 mg in 1 gm is used* - The EMLA patch typically contains a 2.5% concentration of **lidocaine** and 2.5% of **prilocaine**, meaning 25 mg of each per gram of cream. - A 0.5% concentration would be 5 mg per gram, so the stated concentration and amount are incorrect for the EMLA formulation. *Requires application for at least 15 minutes for adequate anesthesia* - EMLA requires a **minimum of 60 minutes** of application time for adequate dermal anesthesia, not 15 minutes. - For procedures on intact skin, the recommended application time is **60-120 minutes** to achieve optimal anesthetic effect.
Question 9: Which nerve is targeted in the nasociliary nerve block?
- A. Greater palatine nerve
- B. Sphenopalatine nerve
- C. Anterior ethmoidal nerve
- D. Nasociliary nerve (Correct Answer)
Explanation: ***Nasociliary nerve*** - A nasociliary nerve block specifically targets the **nasociliary nerve** itself. - This block is used to anesthetize the sensory innervation of structures supplied by the nasociliary nerve, such as parts of the **nasal cavity**, **eyeball**, and **skin of the nose**. *Greater palatine nerve* - The **greater palatine nerve** supplies sensation to the posterior hard palate and is targeted in a **greater palatine nerve block**. - This nerve is a branch of the **maxillary nerve** and is primarily involved in dental and palatal anesthesia. *Sphenopalatine nerve* - The **sphenopalatine nerve**, or pterygopalatine ganglion, contains sensory fibers for the nasal cavity, palate, and pharynx, and its block is distinct from a nasociliary block. - A **sphenopalatine ganglion block** is mainly used for conditions like cluster headaches and facial pain, not for direct eyeball sensation. *Anterior ethmoidal nerve* - The **anterior ethmoidal nerve** is a branch of the nasociliary nerve, but a nasociliary nerve block targets the main trunk, which includes all its branches. - While the anterior ethmoidal nerve supplies the anterior part of the nasal septum and lateral wall, it is a **component** of the nasociliary innervation rather than the sole target.
Question 10: What is the maximum concentration allowed for epidural block?
- A. Chlorprocaine (Correct Answer)
- B. Lidocaine
- C. Ropivacaine
- D. Bupivacaine
Explanation: ***Chlorprocaine*** - **Chlorprocaine** is an ester-type local anesthetic that can be safely used in higher concentrations for epidural blocks up to **3%**, due to its rapid hydrolysis by plasma pseudocholinesterase, leading to a very short half-life and reduced systemic toxicity. - Its rapid metabolism minimizes the risk of accumulation and systemic toxicity, making it a suitable choice when a dense block is needed and a short duration of action is acceptable. *Lidocaine* - **Lidocaine** is an amide-type local anesthetic commonly used in epidural blocks, but its maximum concentration for this application is typically limited to **2%** to avoid systemic toxicity. - Higher concentrations of lidocaine are associated with an increased risk of neurological and cardiovascular adverse effects. *Ropivacaine* - **Ropivacaine** is an amide-type local anesthetic that is less cardiotoxic than bupivacaine, with common concentrations for epidural use ranging from **0.2% to 1%**. - Its maximum concentration is significantly lower than chlorprocaine due to its longer duration of action and potential for systemic toxicity at higher doses. *Bupivacaine* - **Bupivacaine** is a potent amide-type local anesthetic with a high risk of cardiotoxicity, and its maximum concentration for epidural use is generally restricted to **0.5%** or even less for continuous infusions. - Using concentrations above this limit significantly increases the risk of severe cardiovascular complications, including arrhythmias and cardiac arrest.
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