Perioperative Ultrasound Practice Questions

Q: A 65-year-old patient with BMI 32 kg/m² is scheduled for interscalene block. Ultrasound shows the brachial plexus roots appearing 4 cm deep. Which approach would be most appropriate?

In-plane approach with low-frequency probe. ***In-plane approach with low-frequency probe*** - A **low-frequency probe** (2–5 MHz) is essential for **deeper penetration** (structures >3–4 cm) in obese patients where high-frequency waves would be attenuated. - The **in-plane approach** is preferred for safety as it allows visualization of the **entire needle shaft and tip**, reducing the risk of accidental vascular or pleural puncture at that depth. *Out-of-plane approach with high-frequency probe* - **High-frequency probes** (linear) lack the necessary **tissue penetration** to clearly visualize the brachial plexus at a depth of 4 cm in an obese patient. - The **out-of-plane approach** only shows the needle as a dot, making it difficult to track the **needle tip trajectory** near deep vital structures. *Out-of-plane approach with low-frequency probe* - While the **low-frequency probe** provides the required depth, the **out-of-plane technique** increases the risk of **unintentional needle advancement** beyond the target. - Tracking the **needle tip** is significantly less reliable in the out-of-plane view, which is undesirable when performing deep blocks. *In-plane approach with high-frequency probe* - Although the in-plane technique is generally safer for **needle visualization**, a **high-frequency probe** would result in a poor-quality image due to **ultrasound attenuation**. - At a depth of 4 cm, the **anatomical resolution** of a high-frequency probe is insufficient to accurately identify the **interscalene groove** and nerve roots.

Q: Which ultrasound sign is used to identify the pleura during thoracic paravertebral block?

Bat wing sign. ***Bat wing sign*** - The **bat wing sign** is formed by the hyperechoic **transverse processes** (representing the body) and the **pleura** within the intercostal space (representing the wings). - It is a crucial sonographic landmark used to identify the **paravertebral space** and ensure the needle avoids penetrating the pleura. *Seagull sign* - This sign is typically associated with identifying the **celiac trunk** and its branches (splenic and hepatic arteries) during **abdominal ultrasound**. - It is not used for thoracic regional anesthesia or for identifying the **paravertebral pleura**. *Sliding lung sign* - The **sliding lung sign** confirms the movement of the **visceral pleura** against the **parietal pleura** during respiration. - While it confirms the presence of the pleura, it is a dynamic assessment for **pneumothorax** rather than a primary anatomical landmark for a paravertebral block. *Spine sign* - In thoracic ultrasound, the **spine sign** refers to the visualization of the vertebral bodies above the diaphragm in the presence of **pleural effusion**. - It is an indicator of fluid in the **pleural cavity** and does not characterize the specific bony-pleural relationship used for paravertebral blocks.

Q: What is the optimal ultrasound frequency for performing neuraxial blocks in adults?

2-5 MHz. ***2-5 MHz*** - A **low-frequency curved array transducer** (2-5 MHz) is necessary for neuraxial blocks in adults to provide the **deep tissue penetration** required to visualize the spine. - This frequency range allows the ultrasound beam to reach structures located several centimeters deep, such as the **ligamentum flavum**, **epidural space**, and **vertebral bodies**. *5-10 MHz* - This intermediate frequency lacks the necessary **depth of penetration** to clearly visualize the midline structures of the adult spine in most patients. - It is generally reserved for **musculoskeletal imaging** or neuraxial blocks in very thin patients or **pediatric populations**. *10-15 MHz* - These **high-frequency linear transducers** provide excellent resolution but have very limited **beam penetration**, making them unsuitable for deep neuraxial structures. - They are typically utilized for **superficial nerve blocks**, such as the intercostal or femoral nerve blocks. *15-20 MHz* - Frequencies in this range are used for extremely **superficial structures** and provide high-definition images of the skin and subcutaneous tissues. - The **attenuation** of the signal at this frequency is too high to visualize any osseous landmarks or the **spinal canal** in an adult.

Question 1

During ultrasound-guided internal jugular vein cannulation, you observe the vein collapsing with minimal probe pressure while the artery remains patent. The vein appears enlarged and the artery-to-vein ratio is 1:3. A spontaneously breathing patient shows respiratory variation. Evaluate the most appropriate interpretation and management strategy.

Accepted Answer

This indicates hypovolemia; fluid resuscitation should be considered before central line insertion

Answer

This is normal anatomy; proceed with cannulation using standard technique

Answer

This suggests venous thrombosis; consider alternative site

Answer

This indicates increased central venous pressure; use ultrasound compression technique

Question 2

A 55-year-old patient with previous lumbar spine surgery requires epidural catheter placement for postoperative analgesia. Pre-procedure ultrasound shows loss of normal posterior complex and irregular acoustic shadowing at L3-L4 and L4-L5 levels. The L2-L3 level shows preserved anatomy with a depth of 6 cm to the epidural space. Which technical modification would provide the best success rate?

Accepted Answer

Attempt midline approach at L2-L3 with ultrasound pre-scanning for trajectory

Answer

Use paramedian approach at L3-L4 with fluoroscopy guidance

Answer

Perform caudal epidural with threading of catheter to lumbar level

Answer

Use loss of resistance to saline at L4-L5 with multiple attempts

Question 3

A 65-year-old patient with BMI 32 kg/m² is scheduled for interscalene block. Ultrasound shows the brachial plexus roots appearing 4 cm deep. Which approach would be most appropriate?

Accepted Answer

In-plane approach with low-frequency probe

Answer

Out-of-plane approach with high-frequency probe

Answer

Out-of-plane approach with low-frequency probe

Answer

In-plane approach with high-frequency probe

Question 4

Which ultrasound sign is used to identify the pleura during thoracic paravertebral block?

Accepted Answer

Bat wing sign

Answer

Seagull sign

Answer

Sliding lung sign

Answer

Spine sign

Question 5

What is the optimal ultrasound frequency for performing neuraxial blocks in adults?

Accepted Answer

2-5 MHz

Answer

5-10 MHz

Answer

10-15 MHz

Answer

15-20 MHz

Perioperative Ultrasound — MCQs

Perioperative Ultrasound — MCQs

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