This concept was first conceived by the authors above in 2006 and discussed in national lectures in 2007 and on. It has been available on emcrit.org since March 2008 and was the first hit on a google search of ‘RUSH Exam’ from this date on. It was published on Emedhome in May 2009.
Rapid Ultrasound for Shock and Hypotension
It is now the standard of care to perform focused assessment using sonography for trauma (FAST) early in the evaluation of a sick trauma patient. There seems to be far less urgency to use ultrasound to evaluate the medical patient with hypotension or signs of shock. We believe that part of the reason for this discrepancy is the lack of an accepted way to refer to the exam and a standardized sequencing. In this paper, we outline the components and rationale for the rapid ultrasound for shock and hypotension (RUSH) exam.
In 2001, Rose et al. reviewed an ultrasound protocol they had created to evaluate the undifferentiated hypotension patient.(1) In 2004, Jones et al. studied the effects of early goal-directed ultrasound for ED patients with hypotension.(2) This study showed reduction in the number of conditions that needed to be ruled out, as well as a quicker time to final diagnosis. Recently, additional articles have discussed the use of focused ultrasound for cardiac arrest (3) and shock patients without obvious etiology.(4)
In an effort to conglomerate all of the various diagnostic ultrasound techniques applicable to these patients into a memorable approach, we created the RUSH exam. The RUSH exam was designed to be rapid and easy to perform with the portable machines found in most emergency departments (ED). The components of the exam are heart, inferior vena cava (IVC), Morison’s/FAST abdominal views with thoracic windows, aorta, and pneumothorax scanning. These components can be recalled with the mnemonic: HI-MAP. This mnemonic also describes the sequencing of the exam. We will discuss each of the components in detail below.
The heart portion of the RUSH exam evaluates for pericardial effusion/tamponade; right ventricular failure, as a sign of pulmonary embolism; and a qualitative assessment of left ventricular function. The echocardiographic views used are the parasternal long axis and the four chamber view. For probe positioning and examples of normal exams, we recommend the Yale Atlas of Echocardiography (Parasternal Long View25, 4-chamber View26)
The parasternal long view is used to assess for pericardial fluid, which is best identified posterior to the left ventricle and anterior to the descending aorta. In the setting of shock and hypotension, more than trace pericardial fluid should increase your suspicion for pericardial tamponade. However, an experienced ultrasonographer can assess for this condition directly. In the same parasternal long view, if there is collapse of the right atrium during diastole (sensitive) and the right ventricle during early diastole (specific), the diagnosis is likely to be tamponade.(5,6)
If tamponade is diagnosed, the ultrasound exam can also aid in the performance of a pericardiocentesis. Ideally, a large pocket of fluid with a good amount of space between the pericardium and the heart, without interposed lung will be indentified. This site may be sub-xiphoid, but more often it is on the anterior chest wall. Ultrasound-guided pericardiocentesis is safer than a blind sub-xiphoid procedure. (7-9)
Right Ventricular Enlargement
Rarely, actual clot can be visualized during transthoracic echocardiography (TTE), but massive pulmonary embolism is more likely to present with only indirect signs. A PE significant enough to cause shock will often be accompanied by signs of acute right ventricular failure. An enlarged right ventricle on the four chamber view points to right ventricular failure (RVF) as one of the contributors to the patient’s shock state. RVF can be caused by many entities, but when it is acute in the setting of shock, the most likely diagnoses are massive pulmonary embolism and right ventricular infarction.
The right ventricle is normally less than 60% the size of the left ventricle. When the RV size equals or is larger than the LV, RV failure should be suspected. Specificity for PE is improved when the McConnell sign is present. This eponym refers to reduction in RV free wall motility with sparing of the apex.(10)
Enlargement of the right ventricle can also occur from right ventricular infarction. This diagnosis will often present with signs of inferior wall infarction on electrocardiogram and may have associated left ventricular dysfunction. However cardiogenic shock can occur from isloated right ventricular failure without associated EKG or left ventricular abnormalities.(11)
Hypodynamic Left Ventricle
In the setting of hypotension, the qualitative assessment of LV function can indicate a cardiogenic cause. The poor LV function can be the result of a primary problem, e.g. infarction or myopathy. Or it can be secondary to conditions such as sepsis or toxins. While more complicated procedures allow a numeric estimate of the ejection fraction, in the setting of hypotension, a visual estimate often suffices. (12)
In parasternal long view, at the level of the papillary muscles, a < 30% difference between the size of the LV in systole and diastole indicates a severely decreased LV function ((end diastolic size-end systolic size)/end diastolic size). After a witnessing a reasonable number of normal and abnormal exams, this estimation can be made after a few seconds of seeing the heart’s function.(13)
Hyperdynamic Left Ventricle
In the same echocardiographic view just mentioned, if the left ventriclular walls change >90% between systole and diastole or if they actually touch at end systole, then the LV is hyperdynamic. This can be seen in hypovolemia, acute blood loss, and often in sepsis prior to the administration of vasopressors. These patients will usually benefit from volume loading.
Inferior Vena Cava
The evaluation of the IVC can give an estimate of the volume status of the patient. The exam outlined below is a dynamic evaluation of filling pressures based on respiration. The exam is conducted differently depending on whether the patient is spontaneously breathing or receiving mandatory breaths from a ventilator.
Spontaneously Breathing Patients
The IVC should first be located in longitudinal orientation in the sub-xiphoid area. By placing the probe just under the xiphoid and sliding 1-2 cm to the patient’s right, the IVC should be easily located. The exam concentrates on the IVC superior to the influx of the hepatic veins. Both the diameter of the IVC and the response to patient inspiration are examined. The latter is often best assessed using M-mode ultrasonography.
The IVC portion of the exam allows both an estimation of the central venous pressure (CVP) and predicts a beneficial response to fluid bolus. An IVC diameter of <1.5 cm with complete inspiratory collapse is associated with a response to volume loading and these findings are associated with a low CVP (<5).(14-16)
Conversely, an IVC diameter of >2.5 cm with no inspiratory collapse represents a high CVP (> 20) and the patient is unlikely to increase their cardiac output in response to fluid loading.(14,16,17) If the patient is intravascularly depleted in this setting, they will need agents to increase their inotropy or decrease their afterload before fluids will be helpful.
Mechanically Ventilated Patients
In contrast to spontaneously breathing patients, mechanical inspiration causes the IVC to enlarge. The difference between the inspiratory and expiratory size of the IVC can be used to gauge the need for fluid loading. In order to accurately assess the IVC in ventilated patients, they must be sedated enough to not be taking spontaneous breaths during the time of measurement. In addition, the ventilator should be adjusted to deliver 10 ml/kg of tidal volume. Even in patients with acute lung injury, placing a patient on this tidal volume for the ~20 seconds of measurement will cause no ill effects. The patient should be returned to their previous ventilatory settings after assessing the IVC.
Many studies have evaluated IVC diameter changes as a measurement of response to fluid loading.(18,19) Unfortunately, these studies calculated their cut-off points using different formulae. The simpler formula is ((Insp size – Exp Size)/Exp size).(18) The result is expressed as a percentage; using this formula the cut-off is 18% change. Values greater than this predict an increase in cardiac output to a fluid challenge.
Morison’s and the FAST Exam Views with Hemothorax Windows
Emergency physicians are familiar with the views of the FAST exam. Imaging for free fluid in the right upper quadrant, left upper quadrant, and suprapubic area can provide a clue to many diagnoses such as, ectopic pregnancy, massive ascites, ruptured viscus, spontaneous intraabdominal bleeding, intraperitoneal rupture of an AAA, etc. If there is not time to complete all of these views, an image of Morison’s pouch with the patient in Trendelenberg position is sensitive for significant intraperitoneal blood or fluid.(21)
When performing the upper quadrant views, tilting the probe towards the chest to image the diaphragm/lung interface reveals the presence of fluid or blood in either hemithorax.(20)
Scanning the abdominal aorta for aneurysm (AAA) is one of the key emergency ultrasound modalities. We prefer to scan the aorta in transverse orientation at four levels: just below the heart, suprarenal, infrarenal, and just before the iliac bifurcation.(22,23) By sliding the probe down from the xiphoid to the umblicus, these four views can be obtained in a continuous and rapid fashion. If the Aorta is > 5 cm in any of these views and the patient is in shock, the diagnosis is a ruptured AAA until proven otherwise.
Though far more likely in trauma, tension pneumothorax can be a cause of shock in medical patients as well, especially if the patient recently had a procedure such as a central line, pacemaker placement, or thoracentesis. Scan longitudinally in the anterior 3rd intercostal space on both thoraces with a high frequency probe.(20) We have found imaging in M-mode to make for the easiest interpretation. The ocean/beach or seashore sign reassures that there is no pneumothorax at the location of the probe.(20) If a continuous ocean pattern (stratosphere sign) is observed, then a pneumothorax is likely.(20) One caution in intubated patients: a right mainstem bronchus intubation can lead to the false appearance of a pneumothorax over the left chest due to the lack of left lung motion.(24)
This entire exam can be completed in less than 2 minutes using readily available portable machines. We go in the order of the HI-MAP acronym.
1. Heart: Parasternal long and then 4 chamber cardiac views, with the general purpose or cardiac probe
2. IVC view with the same probe
3. If not already using it, switch to general purpose abdominal probe and scan Morison’s and splenorenal views with thorax images and then examine the bladder window.
4. Increase your depth and find the aorta above and below the renal artery with four views.
5. Scan both sides of the chest for pneumothorax. It may be beneficial to switch to a small-parts, high frequency transducer, but the general purpose probe will often supply sufficient views of the pleural interface.
In conclusion, the RUSH exam provides a sequenced approach to ultrasound in the medical shock patient. Using the HI-MAP components, we can evaluate for the causes and potential responses to treatements of hypotension and tissue malperfusion. Hopefully, it will inspire the same alactrity to perform ultrasound in sick non-trauma patients as the FAST exam has in traumatic instability.
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26. Yale Atlas of Echocardiography. Accessed 2/13/2009.