Undifferentiated shock is a common patient presentation, but it can be difficult to narrow down the etiology of this life-threatening and time-sensitive emergency. Conventional laboratory testing and imaging are time-consuming and may not be helpful in distinguishing between the different types of shock (cardiogenic, hypovolemic, obstructive, and distributive).
The implementation of bedside ultrasound, however, allows a quick evaluation of the hemodynamic status of the patient. Specifically, The “RUSH Exam” (Rapid Ultrasound for Shock and Hypotension), first introduced by Weingart et al in 2006, is designed to provide a quick bedside assessment of a patient with undifferentiated shock. With the use of the RUSH protocol, the potential etiologies of shock can be quickly narrowed down.
A common question that comes up is what is the difference between the RUSH Exam vs the FAST/eFAST Exam. The FAST Scan is used in the trauma setting to figure out where a patient may be hemorrhaging from. The RUSH Exam on the other hand is a more broad ultrasound protocol used on any patient with undifferentiated hypotension.
Simply put, this protocol addresses the components of the cardiopulmonary system, summarized in the RUSH Exam mnemonic HI MAP (See below). When a patient has a “low MAP,” we want to fix the problem and get them to a “HI MAP.” So, we will be using this mnemonic to serve as a helpful tool for quick recall when assessing patients.
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Table of Contents
The HI MAP Mnemonic
The main indication of the RUSH Ultrasound Exam is to quickly assess any patient with undifferentiated Shock and Hypotension.
Here is a simple to table that summarizes the pathology that may be encountered using the HI MAP Mnemonic of the RUSH Exam Ultrasound Protocol.
It is important to remember that the RUSH exam is not a comprehensive assessment of every component listed, but rather a quick evaluation for the major pathologies that can cause hypotension (and shock) in a patient. Once practiced, this exam can be completed in as little as 2-5 minutes.
Limitations faced by this protocol are those faced by any ultrasound examination: body habitus, patient positioning, and physical constraints that make ideal imaging difficult.
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RUSH Ultrasound Exam Preparation
The RUSH Ultrasound Exam is usually performed when the patient is supine.
Transducer: The phased array probe will be the mainstay of the RUSH protocol (Some authors have advocated the use of the curvilinear probe, contingent on machine capability). If a DVT examination is indicated, a switch to the linear probe is required.
Preset: eFAST Exam or Abdominal Exam Mode will be sufficient.
Placement: Place the ultrasound machine on the patient’s right when possible. This allows your right hand to maneuver the probe and your left hand to adjust settings.
Step-By-Step RUSH Exam protocol
Step 1: Heart
First, we look at the heart. In the setting of hypotension, we want to know how well the heart is squeezing and ejecting. Is the heart the problem or is it trying to compensate for a problem somewhere else? The primary pathologies to assess are systolic heart failure, pericardial effusion & tamponade, and right ventricular strain for pulmonary embolism.
There are four primary cardiac views including the Parasternal Long Axis View, Parasternal Short Axis View, Apical 4 Chamber view, and Subxiphoid View. It is important to learn all of these views since the body habitus between patients can vary greatly.
POCUS 101 Note: Remember, using the eFAST or abdominal preset will have the orientation marker on the left side of the screen instead of the right side like in the cardiac preset. This will require you to flip your probe indicator 180 degrees on your probe to obtain the appropriate cardiac views.
Ejection Fraction Assessment
- Observe the left ventricle throughout the cardiac cycle. Is it hyperdynamic or hypodynamic? Does it squeeze uniformly?
- Next, note the anterior leaflet of the mitral valve. Does it move freely and approach the interventricular septum with each diastolic filling? If not, the heart’s contractile function may be impaired and the patient may be experiencing an exacerbation of systolic heart failure resulting in hypotension.
- If the heart appears hyperdynamic, the source of hypotension may be related to hypovolemia or sepsis. This can be determined by continuing to evaluate the patient using the rest of the RUSH exam.
Here are cardiac ultrasound (echo) images of patients with different degrees of ejection fraction from hyperdynamic to severely reduced:
Right Ventricular Strain – Pulmonary Embolism
- The RV chamber normally size should be about ⅔ the size of the LV chamber. If you notice an increase in this ratio, or bowing of the interventricular septum towards the left side of the heart, this may indicate RV strain (i.e. the right heart is having trouble ejecting, so as pressure builds the RV chamber enlarges and encroaches on the LV).
- Look out for McConnell’s Sign which is hypokinesis of the right ventricular free wall with sparing of the Apex.
- You can also look for the “D Sign” on the parasternal short axis view and occurs when the increased pressure of the RV pushes the interventricular septum into the LV. Click HERE to learn more about the “D Sign.”
- Note that the presence of any of the above-mentioned findings is suggestive of RV strain and not specific to PE.
- If any evidence of right heart strain is found, the exam should proceed directly to the evaluation of the legs to scan for a possible deep vein thrombosis by looking for a noncompressible vein. Findings of DVT in the setting of RV strain will greatly increase the chances the patient has a significant pulmonary embolism. Click HERE to learn about how to diagnose DVT using POCUS.
Pericardial Effusion and Tamponade
- Pericardial effusion with Tamponade is another cardiac pathology you should screen for in the RUSH Protocol.
- Look at the border of the heart. Is there a significant anechoic border surrounding it? If so, a pericardial effusion is likely.
- Be sure to distinguish a pericardial effusion from a pleural effusion by identifying the location of the fluid with help from the descending aorta. Anechoic fluid anterior to the descending aorta is a pericardial effusion, whereas fluid posterior to the descending aorta is a pleural effusion.
- Note that a pericardial fat pad can mimic a pleural effusion so it is important to distinguish between the two. Fat is usually more anterior, less mobile, and more echogenic than the fluid of an effusion.
- A pericardial effusion can lead to cardiac tamponade when the pressure from the effusion becomes high enough to impair cardiac filling of the right ventricle. It is important to remember that it is not the absolute size of the pericardial effusion but the rate of fluid accmulation that poses the greatest risk for cardiac tamponade.
- To distinguish between an effusion and tamponade on the RUSH Exam look for two signs: right atrial systolic collapse and right ventricular diastolic collapse.
- These are difficult to capture in real time, so freeze your image and scroll through the frame at a slower rate to determine when systole and diastole are occurring.
- Right atrial collapse is the earliest and the most sensitive finding.
- Right ventricular diastolic collapse is a later and more specific finding.
Cardiac Output Assesment
You can also measure the patient’s cardiac output during the RUSH Exam to help determine the type of Shock a patient is in.
This is a more advanced technique and can be done by measuring the Left Ventricular Outflow Tract Diameter and the Velocity Time Integral (VTI) to calculate the cardiac output.
Measuring the cardiac output helps you differentiate the different types of shock, especially when you combine it with ejection fraction and IVC Measurements as you can see below:
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Step 2: IVC
The next part of the RUSH Exam, we look at the Inferior Vena Cava (IVC) to assess the patient’s central venous pressure (or right atrial pressure). Is there a leak somewhere causing hypotension? Is there fluid overload that is causing the heart to not pump adequately? In the context of shock, we also want to know whether CVP is high or low. This will further categorize the likely type of shock.
The IVC measurement is mostly used to assess fluid tolerance rather than fluid responsiveness. Using the IVC collapsibility Index (below), the diameter and collapsibility during inspiration or with a sniff test can be used to estimate CVP. Limitations include body habitus, increased intraabdominal pressure, etc.
- A high CVP suggested by a dilated and noncollapsible IVC may hint towards an obstructive or cardiogenic etiology.
- A low CVP suggested by a small and collapsible IVC may hint towards a distributive or hypovolemic etiology.
Once again here is an easy way to integrate LV ejection fraction, Cardiac Output, and IVC measurements:
Step 3: Morison’s Pouch/eFAST Exam
The “M” in HIMAP of the RUSH Exam stand’s for Morison’s Pouch but essentially you will be performing an eFAST scan of the RUQ, LUQ, and pelvic views. We are looking for a leak into the abdomen (hemoperitoneum) or thorax (hemothorax) as the source of the patient’s hypotension.
For a complete tutorial on the eFAST Exam Click HERE.
Right Upper Quadrant (RUQ) – Hemoperitoneum
The three common locations for free fluid to accumulate in the RUQ of the eFAST scan are the:
- Hepatorenal Space or “Morison’s Pouch”
- Caudal Tip of the Liver
- Suprahepatic Space
Left Upper Quadrant (LUQ) – Hemoperitoneum
We will evaluate the LUQ in the eFAST for free fluid in the following places:
- Perisplenic Space
- Spleen Tip
- Splenorenal Recess
POCUS 101 TIP: It is important to note that in the LUQ the most common area to find fluid is in the perisplenic space, NOT between the spleen and the left kidney. This is because there is a splenorenal ligament that attaches the spleen and the left kidney preventing a significant amount of fluid to accumulate there unless the ligament is ruptured.
Male Pelvis – Hemoperitoneum
In the male pelvis, you can find free fluid in the rectovesical pouch/space.
Female Pelvis – Hemoperitoneum
In the female pelvis, you can find free fluid in the Pouch of Douglas (Rectouterine Pouch).
After evaluating the RUQ or LUQ, move the probe superiorly one or two rib spaces to evaluate the thorax for fluid accumulation.
A normal lung will have a Mirror Image Artifact and you will be unable to see the spine going above the diaphragm since all of the ultrasound waves will be reflected back by the aerated lung.
Visualizing the patient’s spine above the diaphragm implies that there is free fluid (e.g. blood) in the thorax since ultrasound waves can easily pass through the free fluid in the chest cavity, allowing you to see the spine. This is referred to as a Positive Spine Sign (click here for a more in-depth explanation of the spine sign).
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Step 4: Aorta
The next step is to evaluate for Abdominal Aortic Aneurysm (AAA) or Aortic Dissection as sources of hypotension in the RUSH Exam.
Abdominal Aortic Aneurysm (AAA)
A ruptured abdominal AAA can lead to severe hypotension, especially in elderly patients presenting with acute abdominal pain. A ruptured AAA has a very high mortality.
A normal aorta is usually ~2.0cm in diameter. An abdominal aortic aneurysm is defined as: (Mokashi)
- ≥ 3cm diameter for the abdominal aorta or a > 50% increase in the aortic diameter.
- ≥ 1.5cm diameter for the iliac arteries.
- Anytime a patient presents with a AAA of >/= 5cm and hypotension, assume a rupture until proven otherwise.
- Be sure to measure Outer wall to Outer wall for accurate aorta measurements.
Aortic dissections also have a very high mortality rate. The difficulty with diagnosing aortic dissections is that clinically, they can present with a wide array of symptoms including chest pain, abdominal pain, back pain, stroke-like symptoms, or even just generalized malaise.
Transthoracic Echocardiography (TTE) can be used to try to detect dissections and are specific but not very sensitive.
If there is a high clinical suspicion for aortic dissection and the TTE is negative, you may need to proceed with Transesophageal Echocardiography (TEE) or a CT angiogram (it patient is stable enough).
An aortic dissection may present as a free flap in the aortic lumen of either the descending abdominal aorta, ascending aorta, and/or the aortic arch. Aortic dissections in the ascending aorta can also cause aortic regurgitation and a diastolic murmur. Below are some examples of aortic dissections in multiple different views.
Step 5: Pulmonary
For the last step of the RUSH exam, we look at the lungs or pulmonary system as a cause of hypotension/shock. Although we may have already identified pleural effusion or hemothorax on our RUQ/LUQ exam, this part of the lung exam will evaluate for a potential tension pneumothorax.
Here are three important steps to evaluating for pneumothorax:
First, if lung sliding is present, you can rule out pneumothorax with 100% accuracy at that ultrasound point (Husain LF).
Remember that presence of lung sliding only rules out pneumothorax at that specific point you are scanning. Make sure to maximize your sensitivity by scanning multiple points on the chest.
You can look for lung sliding with B-mode or M-mode:
Second, if lung sliding is ABSENT, you should not automatically assume pneumothorax.
Recall other causes of reduced/absent lung sliding: severe consolidation, chemical pleurodesis, acute infectious or inflammatory states, fibrotic lung diseases, acute respiratory distress syndrome, or mainstem intubation.
Third, if a lung point is present, you can rule in pneumothorax with 100% accuracy (Chan S).
To confirm the presence of a pneumothorax, you should look for the “Lung Point Sign.“
The lung point is when you can see the transition between normal lung sliding and the absence of lung sliding. This is the transition point between the collapsed lung and normal lung. If you see this you can definitively rule in a pneumothorax. The Lung point sign also helps you quantify how large a pneumothorax is.
If you think you may have found a lung point but are not sure, use M-Mode and place your cursor at the intersection where you think lung sliding starts and stops. If you see a normal seashore sign that turns into an abnormal barcode sign, then you have located the lung point with M-Mode.
And that’s it for the RUSH Exam Ultrasound Protocol! Let us know what you think in the comments section.
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- Mokashi, S.A., Svensson, L.G. Guidelines for the management of thoracic aortic disease in 2017. Gen Thorac Cardiovasc Surg 67, 59–65 (2019). https://0-doi-org.catalog.llu.edu/10.1007/s11748-017-0831-8
- Estoos E, Nakitende D. Diagnostic Ultrasound Use In Undifferentiated Hypotension. [Updated 2020 May 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK499955/
- Ghane MR, Gharib MH, Ebrahimi A, Samimi K, Rezaee M, Rasouli HR, Kazemi HM. Accuracy of Rapid Ultrasound in Shock (RUSH) Exam for Diagnosis of Shock in Critically Ill Patients. Trauma Mon. 2015 Feb;20(1):e20095. doi: 10.5812/traumamon.20095. Epub 2015 Feb 20. PMID: 25825696; PMCID: PMC4362031.
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- Armstrong, W.F., et al., Diastolic collapse of the right ventricle with cardiac tamponade: an echocardiographic study.Circulation, 1982. 65(7): p. 1491-6
- Yildizdas D, Aslan N. Ultrasonographic inferior vena cava collapsibility and distensibility indices for detecting the volume status of critically ill pediatric patients. J Ultrason. 2020;20(82):e205-e209. doi:10.15557/JoU.2020.0034
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