Author: Melanie Willimann 

Secondary Author: Mark Bromley 

Reviewer(s): Nicholas Packer, Emma Burns 

 

**To continue through to the course, make sure to select the “Mark as Completed” button below, and at the end of each lesson page that follows.

Summary

Point-of-care ultrasound can allow physicians to quickly, safely and accurately determine the presence of free fluid in the peritoneal cavity at the bedside.

In trauma, ultrasound is most useful in identifying intra abdominal hemorrhage in hemodynamically unstable patients and may be used to guide their immediate management and disposition. PoCUS has limitations as a stand-alone test for intra-abdominal injuries in stable patients. Despite its ability to detect small amounts of free fluid, the sensitivity of PoCUS is limited by patients presenting early, late or in those patients with solid organ injuries that are unaccompanied by intraperitoneal bleeding. In addition, hollow viscus and retroperitoneal injuries are not reliably detected using this technique. This limits the utility of PoCUS as a rule out test for intraperitoneal hemorrhage. However, while understanding these limitations, it is clear that PoCUS can be used to improve the quality and efficiency of emergent care in the pediatric trauma patient.

The suprapubic view

The pelvis is the most dependent area in the supine patient and the most sensitive view to identify free fluid in the abdomen. In this view, the bladder is used as a window to identify free fluid. It is important to view the pelvis in 2 planes to maximize sensitivity.

 

Technique (figure 7)

Figure 7: Pelvic scanning technique (remember to scan in two views: transverse and longitudinal)

1. Positioning is critical. It is important that the patient remains supine in a flat or slight Trendelenburg position to ensure any fluid collects in dependent areas.
2. Place the probe just superior to the pubic symphysis with the probe indicator toward the patient’s right.
3. Center the bladder on the screen and fan the entire bladder cranial to caudal.
4. Rotate the probe so the indicator points to the patients’ head.
5. Fan through the entire bladder from left to right.

 

Tips

• Remember to fan slowly in both planes paying attention to the area of interest.
• Ensure you allow for adequate depth to view down to the pelvic brim.
• Decrease gain in the far field to account for posterior acoustic enhancement from the bladder in order not to miss anechoic fluid deep to the bladder.

 

What am I looking at?

When placing the probe in the suprapubic view you are using the bladder as an acoustic window to get transverse and longitudinal cross sections of the patient’s pelvis (figure 8). Fluid often collects in the recto vesicular space in males and in the rectouterine space (pouch of Douglas in females) but a complete investigation involves looking anterior, lateral and posterior to the bladder to ensure that small amounts of free fluid are not missed.

 

Figure 8: When scanning suprapubic area in the transverse orientation, one is using the bladder as an acoustic window to the bladder, reproductive organs and pelvic brim.

 

Figure 9: When scanning the suprapubic area in the longitudinal orientation, the bladder is used as an acoustic window to view the reproductive organs and pelvic brim.

 

What is normal?

Most superficially the bladder is easily identified. Deep to the bladder the reproductive organs are visible: the uterus and cervix in females, and the prostate and seminal vesicles in males. Deep to that lies the rectum and finally the pelvic rim.

 

Figure 10: Normal suprapubic sonoanatomy, with the bladder highlighted in blue and uterus in green. Areas of interest include the recto vesicular space (1) and posterolateral borders (2) of the bladder and well as the pouch of Douglas in women (3).

 

Video 6: Pelvis, normal transverse

 

Video 7: Pelvis, normal sagittal

 

What is not normal?

Fluid often collects in the recto vesicular space in males and in the rectouterine space (pouch of Douglas in females) but a complete investigation involves looking anterior, lateral and posterior to the bladder and reproductive organs in all directions to ensure small amounts of free fluid are not missed (video8). The pelvis is the most common area for free fluid to collect in supine pediatric patients [11].

Video 8: Pelvis, free fluid

 

The left upper quadrant

The left upper quadrant view uses the spleen as a window to identify free fluid within the abdominal cavity.

 

Technique (figure 4)

Figure 4: LUQ scanning technique

1. Positioning is critical. It is important that the patient remains supine in a flat or slight Trendelenburg position to ensure any fluid collects in dependent areas.
2. Place the probe on the patient’s left posterior-axillary line at the level of the xyphoid.
3. Probe indicator toward the patient’s head.
4. Center the splenorenal interface on the screen by moving up or down an intercostal space as needed.
5. Fan slowly from anterior to posterior and back again looking for fluid around the superior and inferior poles of the spleen as well as in the splenorenal interface.
6. Fluid appears as anechoic (black) on the screen

 

Tips

• The spleen is smaller and lies more posterosuperior within a patient necessitating adjustment of probe placement accordingly. This is particularly true when dealing with a gaseous stomach.
• The spleen is not bound by ligaments like the liver thus the full area around the spleen must be investigated: superior, perirenal and inferiorly.
• The diaphragm (superior portion) can be tricky to assess due to the proximity of the air-filled lung base. It may be helpful to slide the probe anteriorly and then tip the probe posteriorly to optimize this view.
• Remember to fan slowly from posterior to anterior and back, visualising each area of interest in its entirety.
• It is common to have to fan in multiple rib spaces to ensure a view of the whole hepatorenal interface and caudal liver edge.
• If struggling with rib shadows, consider angling the probe to be in line with the intercostal space.

 

What am I looking at?

When placing the probe in the LUQ you are using the spleen as an acoustic window to get a coronal cross section of the patient’s abdomen (figure 5). Unlike the liver, the spleen is mobile and thus the entire area around the spleen must be investigated for fluid, including: (1) the sub-diaphragmatic space (superiorly), (2) the splenorenal interface and (2) the caudal tip of the spleen.

 

Figure 5: When scanning the left upper quadrant, one uses the spleen as an acoustic window to get a coronal view of the spleen, right kidney and splenorenal interface.

 

What is normal?

Superficially, the ribs and chest wall are most easily identified by hypoechoic rib shadows projecting into the abdomen. Deep to the chest wall, the spleen is encountered, followed by the splenorenal interface and left kidney (figure 6, video 4).

 

Figure 6: Normal LUQ sonoanatomy with the spleen highlighted in blue, left kidney in green, diaphragm in red and vertebral bodies in yellow. Areas of interest include the superior pole of the spleen including the subdiaphragmatic space (1), splenorenal interface (2) and the inferior pole of the spleen (3).

Video 4: LUQ, normal view

 

What is not normal?

Free fluid appears as anechoic stripes or collections around the spleen (video 5).

 

Video 5: LUQ, free fluid

 

Pitfalls

Similar to the right upper quadrant, false negative scans are most commonly caused by operator error—due to failing to fully investigate circumferentially around the spleen small amounts of fluid being present or clotted blood. False positives due to perinephric fat and edge artifact also occur in the left upper quadrant. The stomach bubble can also interfere with image interpretation, obscuring free fluid in some cases and mimicking it on others. Differentiating stomach from other structures can be done via anatomic location, appearance of the heterogenous contents and presence of the stomach wall.

The right upper quadrant

The right upper quadrant view uses the liver as an acoustic window to identify free fluid within the abdominal cavity. This is one of the most important views of the abdominal FAST. Free fluid often accumulates in the RUQ as the right paracolic gutter directs fluid from the pelvis to the RUQ and the phrenicocolic ligament and mesentery direct fluid from the LUQ to RUQ.

 

Technique (figure 1)

Figure 1: Scanning technique of the RUQ

1. Positioning is critical. It is important that the patient remains supine in a flat or slight Trendelenburg position to ensure any fluid collects in dependent areas.
2. Place the probe on the patient’s right mid-axillary line along the coronal plane at the level of the xyphoid with the probe indicator toward the patient’s head.
3. Center the hepatorenal interface on the screen by moving up or down an intercostal space as needed.
4. Draw your eye to the area below the diaphragm, hepatorenal interface and caudal liver tip to identify free fluid.
5. Fan slowly from anterior to posterior and back until the kidney disappears in either direction, repeat in each view, as needed, to fully evaluate the subdiaphragmatic space, hepatorenal interface and caudal liver tip.
6. Fluid will appear anechoic (black) on the screen.

 

Tips

• Fan through the area slowly so as not to miss subtle findings, drawing your eyes to the key areas of the hepatorenal interface and the caudal liver tip.
• It is common to have to fan in multiple rib spaces to ensure a view of the whole hepatorenal interface and caudal liver edge.
• If struggling to see between rib shadows, angle the probe slightly to follow the direction of the intercostal spaces to allow you to see between the ribs.

 

What am I looking at?

When placing the probe in the RUQ you are using the liver as an acoustic window to get a coronal cross section of the patient’s abdomen (figure 2).

 

Figure 2: When scanning the right upper quadrant, use the liver as an acoustic window to get a coronal view of the liver, right kidney and hepatorenal interface.

 

What is normal?

Nearest to the probe, the lateral chest wall containing muscle and ribs is easily identified. Often, the hypoechoic rib shadows can be seen projecting into the abdomen. Deep to the chest wall the liver is encountered, followed by the hepatorenal interface and right kidney. The domed diaphragm can be seen cranial to the liver and the vertebral bodies and great vessels can often be identified in the far field deep to the kidney (figure 3, video 1).

 

Figure 3: Normal RUQ sonoanatomy with the liver highlighted in blue, right kidney in green, diaphragm in red and vertebral bodies in yellow. Your areas of interest include the sub-diaphragmatic space (1), Morrison’s pouch (2) and the liver tip (3).

 

Video 1: RUQ, normal

 

What is not normal?

When intraperitoneal free fluid is encountered due to infection, ascites or hemorrhage fluid often collects in right paracolic gutter around the caudal edge of the liver and in morrison’s pouch, or the hepatorenal interface (video 2 & 3). Fluid appears as an anechoic stripe or collection in these areas only bounded by the surrounding anatomical structures. In pediatric patients the second most common area for fluid to collect is in the right paracolic gutter adjacent to the caudal liver edge [11].

Video 2: RUQ, free fluid in Morrison’s pouch

Video 3: RUQ, free fluid around the caudal liver tip

 

Pitfalls

PoCUS for abdominal free fluid is not foolproof.

False negative scans are most commonly caused by operator error. Other causes include patients who only have small amounts of fluid in their abdomen, such as trauma patients presenting early or with minimal hemorrhage. In addition, in trauma patients with delayed presentations, blood can clot which can prevent it from collecting in dependent regions or can make it harder to distinguish on ultrasound (due to the variable echogenicity of clotted blood).

False positives can occur as well, most commonly due to perinephric fat or edge artifact. In the case of perinephric fat, free fluid can often be distinguished as anechoic as opposed to hypoechoic, as fat is. In addition, free fluid is bound only by the organs themselves, while perinephric fat is lined by apparent hyperechoic fascial lines giving a “railroad track” or “marbled” appearance. Edge artifact can sometimes be seen projecting from the edge of a curved structure, usually the kidney; it often is less distinct than free fluid, gets larger as it goes deeper and crosses anatomical boundaries—similar to a rib shadow, whereas free fluid tends to be anechoic, well-defined and narrows to dissect planes and respects anatomic boundaries.

Indications

• Blunt or penetrating thoraco-abdominal trauma
• Multi-system trauma
• The undifferentiated, unstable patient
• Suspected ruptured ectopic pregnancy
• Suspicion of ascites or intraperitoneal free fluid

 

Equipment

• Ultrasound machine
• Curvilinear or phased array probe
• Gel

 

To fully evaluate the peritoneal cavity for free fluid, the abdomen must be scanned systematically in three areas. Studies have shown that while the pelvic view is generally the most sensitive, there are several scenarios such as isolated organ trauma in which fluid can be found in one view but not another. We will discuss each view separately.

 

Introduction

Point of Care Ultrasound (PoCUS) is the use of portable ultrasonography to answer specific, focused clinical questions at the bedside. It is an extension of both our clinical acumen and physical exam. PoCUS is commonly used in adult trauma cases as part of the focused assessment with sonography in trauma (FAST) examination. In undifferentiated and hemodynamically unstable patients, PoCUS can rapidly identify intra-abdominal free fluid which can expedite management and disposition decisions. When ascites is suspected, PoCUS may be used to confirm the diagnosis and guide further management. In recent years, the use of PoCUS has expanded to include pediatric patients as well.

 

Why Ultrasound?

PoCUS is superior to physical exam in detecting intra-abdominal free fluid. In addition, PoCUS can be performed quickly at the bedside without exposure to ionizing radiation. Physical exam alone is a poor test for the detection of peritoneal free fluid, with an overall accuracy of 58% [1]. Studies have shown that as little as 10-50cc of peritoneal free fluid can now be detected with ultrasound. In the hands of emergency doctors, volumes of 100-200 mL of fluid can be routinely detected at the bedside [2,3]. These numbers hold true for trauma patients as well. In 2007, Soyuncu et al. showed emergency physician performed ultrasound detected intraperitoneal hemorrhage with a sensitivity of 86% and specificity of 99% while physical examination reported a sensitivity of 39% and specificity of 90%, respectively [4].

The use of ultrasound in the child who has sustained trauma requires special mention. In the setting of the unstable trauma patient it is critical to identify the cause of decompensation as early as possible as it helps guide and prioritize management decisions, including further diagnostic workup and early disposition from the ER.  The focused abdominal sonography in trauma (FAST) exam is both sensitive and specific in critically ill, hypotensive pediatric trauma patients [5]. It is best used to screen for significant intra-abdominal injuries requiring emergent transfer to the operating room in the unstable patient. In the stable patient, the utility of the FAST is debated and the sensitivities range from 25-80% for the detection of all intra abdominal injuries, though it performs better in those injuries with hemoperitoneum [6]. Performing serial FAST as well as the combining findings with clinical exam and laboratory investigations can increase the sensitivity of the FAST examination [7, 8, 9]. While CT remains the gold standard screening tool for intra-abdominal injuries, the use of the FAST exam may have the ability to decrease CT use in pediatric patients.

The FAST scan can be a challenging scan to master as adequate sonographic windows may be difficult to obtain and multiple areas must be investigated under challenging conditions. Studies show the false negative rate of scans decreases with increasing physician experience. Deliberate practice is key to attaining proficiency [10].

 

 

Author: Melanie Willimann, MD FRCPC

Secondary Author: Mark Bromley , MD FRCPC

Reviewer(s): Nicholas Packer, MD FRCPC

 

**To continue through to the course, make sure to select the “Mark as Completed” button below, and at the end of each lesson page that follows.

 

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References

1. Valley, V & Stahmer, S. Targeted Musculoarticular Sonography in the Detection of Joint Effusions. Academic Emergency Medicine. 2001. 8:361-367
2. Cruz, C et al. Point-of-care hip ultrasound in a pediatric emergency department. American Journal of Emergency Medicine. 2018. 36:1174-1177. https://doi.org/10.1016/j.ajem.2017.11.059
3. Kane, Balint, & Sturrock. Ultrasonography is superior to clinical examination in the detection and localization of knee joint effusion in rheumatoid arthritis. J Rheumatology. 2001; 30(5):966-971.
4. Zieger, M et al. Ultrasonography of hip joint effusions. Skeletal Radiology. 1987. 16:607-611
5. Tsung, J & Blaivas, M. Emergency Department Diagnosis of Pediatric Hip Effusion and Guided Arthrocentesis Using Point-of-Care Ultrasound. The Journal of Emergency Medicine. 2008. 35:393–399. doi:10.1016/j.jemermed.2007.10.054
6. Shavit, I et al. Sonography of the Hip Joint by the Emergency Physician: Its role in the evaluation of children presenting with acute limp. Pediatric Emergency Care. 2006. 22:570-573.
7. Vieira, R & Levy, J. Bedside Ultrasonography to Identify Hip Effusions in Pediatric Patients. Annals of Emergency Medicine. 2010. 55:284-289. doi:10.1016/j.annemergmed.2009.06.527
8. Adhikari & Blavais. Utility of bedside sonography to distinguish soft tissue abnormalities from joint effusions in the emergency department. J Ultrasound Med. 2010; 29(4):519-526.
9. Deanehan, J et al. Bedside Hip Ultrasonography in the Pediatric Emergency Department: A Tool to Guide Management in Patients Presenting with Limp. Pediatric Emergency Care. 2014. 30:285-287.
10. Alves, T et al. US of the Knee: Scanning Techniques, Pitfalls, and Pathologic Conditions. RadioGraphics. 2016. 36:1759-1775. https://doi.org/10.1148/rg.2016160019
11. Wiler, J et al. Comparison of Ultrasound-Guided and Standard Landmark Techniques for Knee Arthrocentesis. The Journal of Emergency Medicine. Vol 39. No 1. 2010. https://doi.org/10.1016/j.jemermed.2008.05.012
12. Wu, T et al. Ultrasound-guided versus landmark in knee arthrocentesis: A systematic review. Seminars in Arthritis and Rheumatism. 2016. http://dx.doi.org/10.1016/j.semarthrit.2015.10.011
13. Lueders, D, Smith, J, & Sellon, J. Ultrasound-Guided Knee Procedures. Physical Medicine Rehabilitation Clinics of North America. 2016. 27:631-648. http://dx.doi.org/10.1016/j.pmr.2016.04.010]
14. Daniels, J & Williams, D. Basics of musculoskeletal ultrasound. Springer. 2013.
15. Edsonoshare.com

Sonoanatomy Review

Normal skin and soft tissue have many layers (Figure 1). The most superficial structures are the epidermis and dermis, which appear as if one hyperechoic structure. Deep to this, you will find subcutaneous fat, which is hypoechoic and globular. Blood vessels, nerves and lymph nodes are found within the hypodermis, and are varying in their echogenicity. Deep to these structures, the muscle is found beneath a hyperechoic layer of fascia. Muscle is seen as highly organized hypoechoic and striated fibers.

Figure 1: Anatomy of normal skin

 

 

Tendons are visualized as hypoechoic fibrillar organized structures, whereas fat pads are also hypoechoic, but are more homogenous in their appearance (Figure 2). Finally, smooth hyperechoic bone cortex may be seen as the deepest layer.

Figure 2: Anatomy of a normal joint

 

Tip:

Scan with dual screen functionality

In order to facilitate comparing an affected joint with the contralateral side, it can be useful to use the dual screen function on the ultrasound machine.

1. Choose “More Controls” from the main screen, found at the bottom right corner (Figure 3a).Figure 3a: Choose “more controls”
2. Select “Dual” from the options screen (Figure 3b)Figure 3b: Choose “dual”
3. Touch the screen on either side to start scanning. When ready to switch, freeze the area of interest on the screen and then touch the opposite screen to begin scanning the opposite side (Figure 3c).Figure 3c: Toggle between screens by touching the desired side
4. Below is an example of a split screen view (Figure 3d).Figure 3d: Dual screen example