US Case of the Month: Ultrasound RUSHes to the Rescue
/The Case:
The patient is an elderly female with a history of small bowel adenocarcinoma, pancreatic cancer, and atrial fibrillation, not on anticoagulation, who presented to the emergency department after being found down with a last known well 45 minutes prior to arrival. Per EMS report, the patient was normoglycemic, but hypotensive to the 80s/40s and tachycardic. She was started on IVF in the ambulance with improvement in her BP en route to 100s/50s. On arrival the patient is awake, alert, and oriented to self and denies any acute complaints. She has a non-focal neurological exam, moist mucous membranes, is tachycardic to the 110s with an irregular rhythm, and hypotensive to 50s/30s. She has clear breath sounds bilaterally, is tachypneic to the low 20s, and is saturating mid 90s on room air. The remainder of her physical exam is unremarkable. The patient was started on additional IVF and a bedside echo was performed.
The echo demonstrates atrial fibrillation, an enlarged right ventricle, and echogenic material in the right atrium consistent with thrombus. CT Chest revealed bilateral lobar and segmental pulmonary emboli with signs of right heart strain.
Ultrasound in Undifferentiated Hypotension
Point of care ultrasound (POCUS) can be a life saving, management changing tool in the care of critically ill patients. Multisystem POCUS can help emergency physicians quickly and accurately identify categories of shock, leading to more timely and more focused treatment(1, 2, 3). A multisystem study can be performed in a matter of minutes and help ED physicians distinguish between cardiogenic, obstructive, hypovolemic, and distributive shock.
While multiple variations of whole body ultrasound in shock have been proposed, The RUSH exam (Rapid Ultrasound for Shock and Hypotension) is commonly used. This includes evaluation of the heart, inferior vena cava (IVC), aorta, FAST abdominal views, and lung sliding (4). It is essentially the medical analog to the FAST exam (Focused abdominal sonography in trauma). The Mnemonic HI-MAP can help you remember the necessary views: Heart, IVC, Morrison’s pouch/FAST views, Aorta, and Pneumothorax. Remember, the goal of these views is to help you determine the category of shock, so that you can rapidly move to targeted treatment.
Which Probe to Use
The original protocol utilizes a linear probe for evaluation of pneumothorax and a phased array for all other views
The curvilinear probe may be used for all views, eliminating the need to switch probes.
The choice should be tailored to what is available at your institution, and which is most appropriate for image optimization in your patient.
Cardiac
At minimum you should obtain a parasternal long axis view, and an apical 4 chamber view. This being said, one view is no view. If you are performing a limited echo during a RUSH exam and believe you are seeing an important finding, go ahead and complete the echo so that you can confirm or deny the finding in multiple views. When a RUSH is too rushed, you can introduce critical errors. There is a critical balance to speed and accuracy.
Start by assessing for a pericardial effusion.
In the parasternal long axis, pericardial effusions are anterior to the descending thoracic aorta (as opposed to pleural effusions which are lateral and posterior to the descending thoracic aorta)
Pericardial fat pads may mimic pericardial effusions. Unlike pericardial effusions, pericardial fat pads move with the myometrium.
Parasternal long Axis demonstrating Pericardial and Pleural effusion
PARasternal Long Axis view, notice how the pericardial effusion is anterior to the descending thoracic aorta
Tamponade
Circumferential effusions can lead to cardiac tamponade, although loculated effusions may also cause focal dysfunction
Cardiac Tamponade is indicated by the following findings:
Right atrial collapse in ventricular systole occurs early in tamponade (RA collapse when valves are closed)
Right ventricular collapse in ventricular diastole occurs in later tamponade (RV collapse when valves are open)
AP4 with Pericardial effusion and Right atrial Collapse indicative of early tamponade physiology
Subcostal view with Pericardial effusion and right ventricular colLapse, indicative of later tamnpoade physiology
Next, assess the left ventricular ejection fraction (LVEF or EF)
A decreased EF suggests at least a component of cardiogenic shock. A hyperdynamic heart suggests distributive, hypovolemic, or obstructive shock.
Fractional shortening estimates the EF by comparing the left ventricular end diastolic diameter (LVEDD) to the end systolic diameter (LVESD). These measurements can be obtained, with the assistance of M Mode, at the level of the papillary muscles in the parasternal long axis view.
Fractional Shortening = ((LVEDD- LVESD)/LVEDD) x100
Fractional shortening < 30% indicates a significantly impaired heart. FS > 90% indicates a hyperdynamic heart.
Mitral Valve E-Point Septal Separation
Obtain a parasternal long axis view and place the M mode indicator at the distal end of the anterior mitral valve leaflet. The resulting image will depict the movement of the anterior mitral valve leaflet throughout the cardiac cycle in relation to the interventricular septum. Measure the distance from the interventricular septum to the mitral valve waveform e point (the peak point of the first opening of the mitral valve in diastole).
EPSS < 7mm indicates normal LVEF, EPSS > 7mm indicates depressed LVEF
EF can also be calculated using MVEPSS (5) EF = 75.5 – 2.5 x EPSS
While objective measures as described above can be used to assess EF, numerous studies have demonstrated that emergency physicians are able to accurately assess EF with visual estimation alone (6, 7, 8).
Minimally depresses EF by MVEPSS
SevereLY DEpressed EF by MVEPSS
Assess for RV Strain
RV strain can be caused by RV infarction, pulmonary hypertension, and several other causes. However, in an acutely hypotensive patient, RV strain is concerning for a massive pulmonary embolism leading to obstructive shock.
Enlarged Right Ventricle
RV dimensions are typically discussed in relation to the LV. A normal RV to LV ratio is 0.6 or less.
One study showed that an RV to LV EDD ratio > 0.7 was the most accurate echocardiographic predictor of PE (sensitivity 66%, specificity 77%) (9).
Comparative measures should be obtained at the maximal diameter of each ventricle in an apical 4 chamber view.
D Sign
Elevated RV pressure causes flattening of the normally rounded interventricular septum. This causes the LV to take on a “D” shape as opposed to it’s normal rounded shape. This is most easily appreciated in the parasternal short view.
McConnell’s Sign
McConnell’s sign describes RV free wall akinesis with sparing of the apex, most easily appreciated in the apical 4 chamber view.
McConnell’s sign is though to be more specific for acute right heart strain.
Although poorly sensitive, McConnell’s sign is thought to be highly specific (96%) for PE (9).
Dilated RA and RV with incidental PAcer LEAD
Interventricular flattening causing a D Sign
RA and RV dilation with Mcconnell’s sign
IVC
Measurement of the IVC can provide clues as to the patient’s central venous pressure, volume status, and predicted fluid responsiveness.
The IVC (maximal) width and variation with respiration should be measure 2 cm inferior to the atriocaval junction. M Mode can assist in measuring the variability.
In spontaneously breathing patients, the IVC collapses with inspiration.
% Collapsibility = ((IVCmax-IVCmin)/(IVCmax)) x 100
A maximal IVC width < 1.5cm and >50% collapsibility indicates a CVP < 5 and likely fluid responsiveness.
A maximal IVC width > 2.5 cm and < 50% collapsibility suggests a CVP > 15 and that the patient is unlikely to be fluid responsive (10, 11).
In mechanically ventilated patients, the IVC distends with inspiration and collapses with expiration.
For IVC measurements to be meaningful in ventilated patients, the patient should be sedated enough that they are not participating in respiration, and their tidal volume should be set to 10ml/kg (at least for the duration of the study).
% Distensibility = ((IVCmax-IVCmin)/(IVCmin)) x 100
Patients with >18% distensibility are predicted to be fluid responsive (12).
Collapsible IVC
Plethoric IVC with minimal respiratory variation
Morrison’s Pouch, Splenorenal Space, Pelvic Space
Just as in the FAST exam, the purpose of obtaining these views in a RUSH exam is to evaluate for intraperitoneal and pelvic free fluid
The differential for free fluid in a non-traumatic hypotensive patient may include diagnoses such as ruptured AAA (hypovolemic), ruptured ectopic pregnancy (hypovolemic), ruptured hemorrhagic cyst (hypovolemic), intra-abdominal infection (distributive), or bacterial peritonitis (distributive).
One study demonstrated that in patients with a suspected ectopic pregnancy, the finding of free fluid in Morrison’s pouch had a positive likelihood ratio of 112 that they would require operative intervention (13).
In a patient with free fluid and a high suspicion for ectopic pregnancy, further pelvic ultrasound may allow you to locate the rupture ectopic pregnancy.
Aorta
Obtain infra-cardiac, suprarenal, infra-renal, and bifurcation views of the aorta in at least a transverse orientation. The aorta should be measure in the transverse plane at each of these points.
Obtaining these views in one continuous scan (from xiphoid to umbilicus) allows you to visualize a larger proportion of the aorta, and may improve visualization by displacing bowel gas.
A normal aorta tapers distally
An abdominal aorta > 3m is indicative of an abdominal aortic aneurysms
Pearls and Pitfalls
The aorta should be measured outer wall to outer wall (including mural thrombus if one exists)
Be sure that the ultrasound is perpendicular to the aorta, oblique images can over or under estimate aortic diameter.
An abdominal aortic dissection may have a normal diameter
Ultrasound frequently cannot distinguish between a ruptured and intact AAA
Pathologic aortas may display a intramural thrombus, a dissection flap, or periaortic fluid but this is not always the case. For this reason, in a hypotensive patient, any aorta >3 cm should be presumed to be a ruptured AAA until proven otherwise.
Abdominal Aortic Aneurysm
Trans Abdominal Aortic Aneurysm with Clot
Trans Abdominal Aorta with Dissection Flap
On the right hand side we see lung sliding, on the left there is an absence of Lung sliding, the transition point is called a Long point and demonstrates a transition from Pneumothorax to normal lung
Pneumothorax/Pulmonary
The original RUSH protocol evaluated the bilateral hemi-thoraces for pneumothorax. However with increasing understanding of lung ultrasound, a more comprehensive pulmonary exam can provide additional clues as to the etiology of hypotension.
Pneumothorax
Non-Traumatic pneumothorax can be seen in medical patients as a result of central line placement, recent thoracic instrumentation, or barotrauma from positive pressure ventilation.
Remember, a pneumothorax will move to the most anti-dependent portion of the chest. While a pneumothorax large enough to cause tension should be easily visualized in numerous rib spaces, it would be wise to start at the apices in an upright patient, and intercostal spaces 4-6 in a supine patient.
Diffuse B Lines
Irregular Border Of the lung indicative of consolidation
Large Pleural Effusion
B Lines
If bilateral or diffuse, these are suggestive of pulmonary edema and may increase suspicion of cardiogenic shock.
If unilateral or focal, may be suggestive of a pneumonia and be concerning for distributive/septic shock.
Consolidation
May suggest pneumonia, concerning for distributive/septic shock.
Pleural Effusions
Bilateral effusions may be suggestive of volume overload and cardiac congestion concerning for cardiogenic shock
Parapneumonic effusions, like consolidations, may be concerning for septic shock
Unilateral effusions could be concerning for hemothorax and hypovolemic shock.
Iatrogenic perforation in patients who had recent thoracic instrumentation (thoracostomy, EGD, central line placement).
Thoracic aortic dissection, spontaneous bleed of intrathoracic malignancy, catamenial hemopneumothorax (could cause hypovolemic and obstructive shock, yikes!).
The sensitivity of lung ultrasound is increased by scanning in multiple locations.
Including the diaphragm and inferior pleural space in you RUQ and LUQ FAST views can provide a more thorough lung evaluation without significantly prolonging the exam.
Extras
Non Compressible FEmoral Vein, notice how the vein does collapse but we are unable to touch wall to wall with compression. Additionally a Clot can be visualized in the Lumen
Although not a part of the original RUSH protocol, some providers advocate expanding the exam to include evaluation of the lower extremity veins for DVT, as their presence may further support a massive pulmonary embolism.
In a patient in which you have high suspicion for pulmonary embolism, it may be reasonable to perform a consolidated DVT evaluation.
With a linear probe, start at the inguinal ligament and scan along the common femoral artery, through the bifurcation of the common femoral vein and deep femoral vein, down to the popliteal trifurcation, compressing periodically along the way.
Summary
Multisystem ultrasound is a useful tool in the diagnosis and treatment of undifferentiated hypotensive patients. Studies have shown that protocols like the RUSH exam can be performed in a matter of minutes and can drastically help emergency physicians narrow their differential diagnosis, allowing them to provide early targeted treatment.
Post by Dr. Meaghan Frederick
Dr. Frederick is a PGY-3 in Emergency Medicine at the University of Cincinnati and section editor of Ultrasound of the Month
Editing by Dr. Lori Stolz
Dr. Stolz is an Attending and Ultrasound Director in Emergency Medicine at the University of Cincinnati.
References
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Keikha, M., Salehi-Marzijarani, M., Nejat, R. S., Vahedi, H. S. M., & Mirrezaie, S. M. (2018). Diagnostic Accuracy of Rapid Ultrasound in Shock (RUSH) Exam; A systematic review and meta-analysis. Bulletin of Emergency & Trauma, 6(4), 271.
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