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. Historically, there has been far less urgency to use ultrasound to evaluate the medical patient with hypotension or signs of shock. One reason for this discrepancy is the lack of a universally accepted name for the exam, and a standardized sequence of views to obtain. The Rapid Ultrasound for Shock and Hypotension exam (RUSH), first described in 2007, solved this problem with an easy to remember moniker (RUSH) and an acronym (HI-MAP) that serves as a cognitive prompt of the views required.
In 2001, Rose et al. published an ultrasound protocol they had created to evaluate the undifferentiated hypotension patient. (1) A few years later, 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 aggregate all of the various diagnostic ultrasound techniques applicable to these patients into a memorable approach, Weingart et al. created the RUSH exam. (5) RUSH was designed to be rapid and easy to perform with portable machines found in most emergency departments. The components of the exam are views of the: heart, inferior vena cava (IVC), abdomen and thorax as for the extended FAST exam, and of the aorta. These components can be recalled with the mnemonic â€œHI-MAPâ€ which prompts the clinician to scan in sequence the Heart, IVC, Morisonâ€™s (the FAST exam), Aorta and Pneumothorax. We will discuss each of the components in detail below.
The heart portion of the RUSH exam evaluates for pericardial effusion and tamponade, right ventricular failure as a sign of pulmonary embolism and a qualitative assessment of left ventricular function. Of the standard cardiac views, the ones used for the RUSH exam are the parasternal long axis and the four-chamber view.
The parasternal long axis view and apical four chamber view are 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. (6)
If tamponade is diagnosed, ultrasound can be used dynamically to aid in the performance of pericardiocentesis.Â Ideally, a large pocket of fluid with a good amount of space between the pericardium and the heart, without interposed lung will be identified. 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)
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. Signs of acute right ventricular failure will often accompany pulmonary embolism significant enough to cause shock. An enlarged right ventricle on the four-chamber view (see clip 6) points to right ventricular failure (RVF) as one of the contributors to the patientâ€™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 percent of the size of the left ventricle. When the RV size equals or is larger than the LV, RV strain should be suspected. Another sign of RV strain can be flattening or bowing of the interventricular septal wall that can be seen on the apical four-chamber view.Â Increased right-sided pressure will also be seen well on the parasternal short axis view, causing a â€œDâ€ shaped right ventricle. (8)
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 isolated right ventricular failure without associated EKG or left ventricular abnormalities. (9)
Hypodynamic Left Ventricle
In the setting of hypotension, the qualitative assessment of LV function can indicate a cardiogenic cause. Depressed 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. (10)
In parasternal long view, at the level of the papillary muscles, a change in LV chamber size from systole to diastole that is less than 30 percent indicates a severely decreased LV function.
((end diastolic size-end systolic size)/end diastolic size)
In 2002, Moore et al. found that a group of physician that had witnessed a reasonable number of normal and abnormal exams during a brief training could estimate LV function after a few seconds of seeing the heartâ€™s function. (11)
Hyperdynamic Left Ventricle
In the same echocardiographic view just mentioned, if the left ventricular walls change by more than 90 percent 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 IVCÂ 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 if the patient is on mechanical ventilation.
Spontaneously Breathing Patients
The IVC should first be located in longitudinal orientation in the sub-xiphoid area. This view is most easily obtained by first obtaining a subxiphoid four-chamber view of the heart and then with the right atrium centered on the screen, rotating the probe 90 degrees on its axis. Collapsibility of the IVC should be evaluated 2 centimeters below the junction between IVC and right atrium (see clip 11). Both the diameter of the IVC and the response to inspiratory effort 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). (12)
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. (13) 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 ventilator settings after assessing the IVC.
Many studies have evaluated IVC diameter changes as a measurement of response to fluid loading. (14)Unfortunately, these studies calculated their cut-off points using different formulae. The simpler formula is Barbierâ€™s. (15)
((Insp size â€“ Exp Size)/Exp size)
The result is expressed as a percentage; using this formula the cut-off is 18 percent change.Â Values greater than this predict an increase in cardiac output to a fluid challenge.
Morisonâ€™s and the FAST Exam
The FAST examÂ is perhaps the most well recognized use of point of care ultrasound. Imaging for free fluid in the right upper quadrant, left upper quadrant, and suprapubic area can provide a clue to many etiologies of hypotension 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 Morisonâ€™s pouch with the patient in Trendelenberg position is sensitive for significant intraperitoneal blood or fluid. (16)
When performing the upper quadrant views, sliding the probe up to the thorax allows us to image the interface between lung and diaphragm for hypoechoic fluid or blood in either hemithorax. (17)
Scanning the abdominal aortaÂ 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. (18) By sliding the probe down from the xiphoid to the umbilicus, these four views can be obtained in a continuous and rapid fashion (see clip 22). 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 has recently had a procedure such as a central line, pacemaker placement, lung biopsy or thoracentesis. Scan the anterior chest wall of both thoraces with probe held in a parasagittal orientation from the midclavicular second intercostal space to the last rib with a high frequency linear, microconvex or phased array probe. Normally apposed pleural surfaces will appear to slide against one another resulting in a shimmering effect.Â This is normal lung sliding.Â In pneumothorax, the pleura are no longer apposed and this sliding will disappear.Â Pathognomonic for pneumothorax is the transition from normally apposed pleura to pleura separated by the air of a pneumothorax.Â When this â€œlung pointâ€ is found, you will see normal pleural sliding on one side of your screen with loss of sliding on the other.
We have found imaging in M-mode to make for the easiest interpretation. The seashore sign, with static lines above and the granular pattern of normal lung movement below the pleura, reassures that there is no pneumothorax at the location of the probe. If the stratosphere sign (image 28), with static lines above and below the pleura, is observed, then pneumothorax is likely. (19)
One caution in intubated patients: a mainstem bronchus intubation or bronchial obstruction can lead to the false appearance of a pneumothorax over the contralateral chest due to the lack of left lung motion. (20) In these cases, identification of lung pulse indicates that mainstem intubation or bronchial obstruction has resulted in loss of pleural sliding rather than pneumothorax.
This entire exam can be completed in less than 2 minutes using readily available portable machines. The HI-MAPacronym serves as a mnemonic prompt to remind us of the sequence of views
1. Heart: Obtain parasternal long view and then apical four chamber cardiac view, using a phased array cardiac probe or microconvex probe.
2. IVC: switch to a large curvilinear general-purpose probe to obtain dynamic views of the IVC.
3. Morisonâ€™s (and FAST): Obtain Morisonâ€™s and splenorenal views imaging both hemithoraces, and then scan the bladder (transverse and sagittal).
4. Aorta: Increase your depth to find the aorta at the epigastrium, in one motion, scan through entire aorta to bifurcation.
5. Pneumothorax: Scan both sides of the chest for pneumothorax. If unable to image the pleural interface appropriately with large curvilinear probe, switch to a high frequency linear transducer.
The RUSH exam provides a sequenced approach to ultrasound in the critically ill shocked or hypotensive patient. Using the HI-MAP components, we can evaluate for the causes of hypotension and tissue malperfusion and respond appropriately.
The name of the exam, RUSH, ought to inspire the same alacrity to perform ultrasound in the sick medical patients as the ubiquitous FAST has in trauma.
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