These are clots in transit. They are occasionally seen in the setting of pulmonary embolism (4-18% of cases). In this case they were visualized traversing the tricuspid valve from right atrium to right ventricle.
How does this finding affect prognosis?
This is a poor prognostic factor. The mortality of patients with PE without RV thrombus ranges between 11-16% whereas the presence of clot in transit raises mortality to at least 44%.
Name 2 other signs of RV strain seen in the images above.
Dilated RV. Note the RV:LV ratio even in this parasternal short axis view is >1:1.
Interventricular septal dependence. In the parasternal short axis view, this is also called the “D sign” where the left ventricle forms the shape of the letter “D” due to elevated right ventricle pressures combined with lower left ventricle pressures due to the obstructive physiology proximal to the pulmonary arteries.
What are some treatment options available other than anticoagulation or systemic thrombolysis?
Although more research is needed in regards to treatments such as endovascular therapy, options include: catheter-directed thrombolysis, surgical embolectomy, mechanical thrombectomy, suction thrombectomy, and IVC filter.
How would you dose alteplase in the setting of massive pulmonary embolism? What about in the setting of cardiac arrest?
Numerous dosing regimens have been implemented. The most common method is Alteplase 100 mg (full dose) or 50 mg (half dose) IV administered over 2 hours. In cardiac arrest, you can give Alteplase 50 mg IV administered over 60 seconds. It is recommended to continue CPR for at least another 15 minutes if not longer (some guidelines suggest 30-60 minutes) to allow thrombolysis time to work. Be sure to familiarize yourself with the thrombolytic contraindications.
What are the four primary sonographic signs of cardiac tamponade?
Pericardial effusion. Measure the largest pocket during diastole. Large is >2.0 cm. Moderate is 1.0 – 2.0 cm. Small is <1.0 cm. Trivial is only visible during systole. Important to remember that the rate of accumulation is more important than the actual size in developing tamponade.
Right-sided chamber collapse. In normal physiology, the right ventricle contracts during systole and the right atrium contracts during diastole. As an effusion accumulates, the intrapericardial pressure may overwhelm the intracardiac pressure. This will first lead to right atrial systolic collapse and may progress to the later finding of right ventricular diastolic collapse.
Plethoric IVC. As with any obstructive cardiac process, there will be loss of respiratory variation of the IVC.
Doppler surrogate of pulsus paradoxus. This can be assessed by measuring the inflow velocities of the mitral and/or tricuspid valve. The concept of pulsus paradoxus is that there is an exaggeration of the normal respiratory variation of blood pressure during tamponade physiology when intracardiac volume competes for space with the pericardial sac. This ventricular interdependence during inspiration will cause a decrease in mitral inflow velocity variation >25% and an increase in tricuspid inflow variation >40%.
What intervals are represented by labels “A” and “B”?
The Y-axis of M-mode corresponds to depth, thus A represents the right ventricle with layer of pericardial effusion and B represents left ventricle with mitral valve.
Which phases of the cardiac cycle are represented by labels “C” and “D”?
The X-axis of M-mode corresponds to time, thus C represents ventricular diastole where the first spike is the E-wave (early diastolic filling) and the second smaller spike is the A-wave (atrial kick). D represents the period of ventricular systole. It is important to recognize labels A-D because you can observe the variation in RV size during diastole to determine if there is true RV diastolic collapse. In this case, there is some RV collapse, however it is primarily in systole and does not overlap significantly with diastole.
In the clinical setting of cardiac tamponade, how much variation throughout the respiratory cycle would you expect to see on the structure labeled “E”?
This represents the IVC and you would expect it to be plethoric with minimal to no respiratory variation. This carries a 95-97% sensitivity for cardiac tamponade.
What is being measured in the diagram labeled “F”? Does this represent cardiac tamponade?
This is how the measurement of mitral inflow variation is performed. Note the doppler gate in the left ventricle near the mitral valve on the apical-4 view. The velocities of the tallest and shortest E-waves are measured. The percent decrease between 102 cm/s and 83 cm/s is approximately 20%, which is less than 25% and not quite suggestive of cardiac tamponade.
Name the structures indicated by labels “A, B, C, D, and E.”
A – Diaphragm
B – Liver
C – Spleen
D – Rib with posterior shadowing
E – Pleura
What is indicated by label “F”? What type of artifact causes this? What does it signify?
B-Lines which are caused by a type of reverberation artifact. This typically signifies thickened or fluid-filled interlobular septa. While occasional B-Lines in the lung bases can sometimes be a normal finding (especially in elderly populations), 3 or more per lung field is usually pathological and consistent with an interstitial syndrome. This can be seen in almost any interstitial process such as pulmonary edema, pneumonia, lung contusions, and masses, for example.
What sign is label “H” and what does it mean?
Spine sign. In normal lung, vertebral bodies on ultrasound should terminate at the level of the diaphragm and not be visualized above due to the inability of ultrasound waves to transmit through air. The presence of a fluid collection in the lung, however, will act as an acoustic medium for the transmission of ultrasound waves allowing visualization of the spine above the diaphragm as seen in the images above. This is non-specific for determining the type of fluid collection, as this can be seen with pleural effusions, hemothorax, and even consolidations.
What is indicated by label “G” and what are the two different types?
Air bronchograms. They are air-filled areas of the bronchial tree which are visualized in the presence of fluid-filled alveoli which act as an effective acoustic window. There are 2 types of sonographic air bronchograms:
Static – These will remain fixed in position during the respiratory cycle. This indicates air trapped in small bronchi caused by complete bronchial obstruction from atelectasis.
Dynamic – These will exhibit small movements with respiration indicating partial bronchial obstruction from fluid mixed with air. This finding typically represents pneumonia.
Name four sonographic lung findings that suggest pneumonia as the diagnosis.
B-Lines – often seen with small areas of subpleural consolidation. In early stages of pneumonia, only some alveoli will be fluid-filled and can lead to a patch of focal B-Lines.
Hepatization – this refers to the solid “liver-like” sonographic appearance of lung as it becomes inflamed and filled with purulent fluid. This can be seen in consolidation or atelectasis.
Shred sign – this appears as an irregularity of the pleural interface in the setting of small areas of consolidated lung. These areas abut the pleural surface causing the “shredded” appearance on ultrasound.
Dynamic air bronchograms – as discussed in question 4, this finding has been shown to have a 94% specificity and 97% positive predictive value for pneumonia as the cause of the consolidation.
Color doppler can also be used which would demonstrate the pulmonary vasculature in areas of consolidation. A concomitant parapneumonic effusion with echogenic debris can suggest empyema.
18 y/o M p/w chest and abdominal pain s/p fall from motorcycle the night prior
Which FAST exam view above does NOT contain free fluid?
The Subxiphoid view does NOT contain free fluid. All three other views are positive.
The primary survey of ATLS follows the “ABCDE” protocol. Which part of the primary survey does the FAST exam further assess: A, B, C, D, or E?
C – Circulation. An Extended-FAST (E-FAST) would also further assess B – Breathing.
Can you accurately name what each arrow is depicting in the images above labeled A-L?
A – Liver
B – Free fluid in Morrison’s Pouch
C – Rib shadow artifact
D – Spleen
E – Left subdiaphragmatic free fluid
F – Left hemidiaphragm
G – Urinary bladder in sagittal view
H – Pelvic free fluid
I – Intestines
J – Right ventricle
K – Left ventricle
L – Pericardium
What is the minimum amount of free fluid that the literature suggests can be detected on a FAST exam?
It was suggested that a minimum of 500 mL of free fluid could be detected on a FAST exam. However, as ultrasound imaging technology and operator technique improves, newer literature suggests that as little as 100 mL of free fluid can be detected.
If the patient in the above scenario had unstable vital signs, do ATLS guidelines recommend the next step to obtain a CT scan or to activate the OR? What if the patient had stable vital signs?
As per ATLS, an unstable patient with a traumatic mechanism of injury and a positive FAST exam should go directly to the OR for laparotomy. A stable patient with a traumatic mechanism of injury and a positive FAST exam should receive a CT scan.
Does a positive FAST exam differentiate what type of fluid is present?
No. Ascites and blood, for example, may have a similar appearance on ultrasound. In certain settings, such as trauma or an unstable patient, the fluid should be assumed to be blood until proven otherwise.
Does a positive FAST exam reliably identify the source of bleeding?
No. Free fluid in any quadrant can represent blood that has pooled from a different area.
Where does free fluid tend to initially accumulate in the RUQ view? What about in the LUQ view?
In the RUQ view, free fluid most often will be initially visible in the paracolic gutter (liver tip and inferior pole of kidney). In the LUQ view, free fluid most often will be initially visible in the subdiaphragmatic space above the spleen. Be sure to include everywhere from diaphragm to paracolic gutter in both views because free fluid can hide in variable locations.