Review of the Use and Diagnostic Accuracy of the RUSH Exam for Internal Medicine

Sargis Manukyan, Akash Desai

Point-of-care ultrasound (POCUS) is an important tool for today’s practitioners. Studies have supported the use of POCUS in many clinical decision-making scenarios compared solely to standard examinations and other imaging modalities¹. Its integration in the emergency medicine (EM) setting has been pivotal and is now gaining momentum for implementation in internal medicine (IM).¹

POCUS differs from formal radiological US assessments in that it is a fast, dynamic bedside tool that both performed and interpreted by the sonographer-physician.² A recent systematic review demonstrated that in the hospital setting, integration of POCUS in clinical decision making helped change the primary diagnosis in up to 18% of patients, added a relevant diagnosis in up to 24% of cases, and had an impact on the management plan in 37% to 52% of the participants.³ Its use in trauma settings has been shown to reduce mortality and time to operative intervention.⁴ A recent quality improvement study found its use in internal medicine wards led to reduced hospital length of stay, with direct cost savings of $751,537 in a timespan of 6 months.⁵ Multiple groups have recognized the utility of POCUS in IM and have advocated for its integration into IM residency training, as well as created a collaborative model of EM and IM fellow training in POCUS.^6-8

One promising POCUS application in IM is in assessing patients with undifferentiated hypotension or shock. The Rapid Ultrasound for Shock and Hypotension (RUSH) exam introduced a standardized assessment of patients presenting with hypotension or shock. It includes evaluations of the heart, inferior vena cava (IVC), Extended Focused Assessment by Sonography in Trauma (E-FAST) abdominal views, and aorta. This can be remembered with the HI-MAP mnemonic, which stands for Heart, IVC, Morrison’s (the FAST exam), Aorta and Pneumothorax, and helps providers not miss steps in the sequence.⁹

The purpose of the RUSH exam is to assess the likely etiology of shock through evaluation of the pump (heart), the tank (volume), and the pipes (systemic vascular resistance).¹⁰ The four broad categories of shock include hypovolemic, obstructive, cardiogenic, and distributive. Different combinations of findings allow the physician to match the patient in front of them to a shock phenotype. For example, the presence of a hypercontractile heart with small collapsing chambers, a flat IVC, and the presence of peritoneal/pleural fluid in the setting of trauma argues for hypovolemic shock and should prompt appropriate volume resuscitation and concomitant source control. On the other hand, a hypocontractile or dilated heart, distended IVC, and presence of B-lines/pulmonary edema argue for cardiogenic shock and likely diuresis and consideration of vasoactive medications. Findings of pericardial effusion with tamponade physiology, RV strain, or absent unilateral lung sliding, all support a diagnosis of obstructive shock. Finally, hyperdynamic (early sepsis) or hypodynamic (late sepsis) heart contractility, variable IVC, and the appropriate laboratory correlates and infectious source argue for distributive shock.¹⁰

A prospective study showed that the RUSH exam had a sensitivity of 88% and specificity of 98% for identifying the type of shock with almost-perfect agreement between RUSH-based shock classification and the final clinical diagnosis (kappa of 0.84).¹¹ Furthermore, a meta-analysis of five articles looking into the diagnostic accuracy of RUSH showed high sensitivity and specificity of 87% and 98%, respectively, for detecting etiologies of shock.¹²

In evaluating the heart (pump), the examiner assesses left ventricular ejection fraction (LVEF), the presence or absence of pericardial effusion (Figure 1), and size of the ventricles relative to each other. Cardiac standard views include the parasternal long and short axes, apical four chamber, and subcostal four chamber views, which allow for appropriate characterization of these assessments.¹³ In assessing LVEF, visual estimation using POCUS has been shown to have a high accuracy when compared to gold standard transthoracic echocardiogram (TTE).¹⁴ IM residents with limited ultrasound training were able to detect ejection fraction (EF) <40% with 94% sensitivity and 94% specificity, even while using a lower fidelity hand-held POCUS device.¹⁵ After a 27-hour training, significant (5-fold) increase in positive likelihood ratio and decrease in negative likelihood ratio was seen for POCUS detection of left ventricular systolic dysfunction, severe mitral regurgitation, and moderate or large pericardial effusion.¹⁶ Pericardial effusion has been detected with a sensitivity of 96%, specificity of 98%, and overall accuracy of 97.5% by ED physicians using POCUS.¹⁷ An observational study showed that emergency department physicians could detect RV dilation with a high inter-rater agreement of 89%, which has been shown to have 50% sensitivity and 98% specificity of detecting pulmonary embolism (PE).^18,19

To evaluate the tank, examiner assesses central venous pressure using the IVC as a proxy. The probe is typically placed in the subxiphoid region with dynamic assessment of the IVC with respiration. Additional assessment of the lungs, pleural cavity, and abdominal cavity should be performed to identify findings of pulmonary edema (B-lines), pleural effusion (figure 2), or free intraperitoneal fluid.¹⁰ In assessing for cardiogenic pulmonary edema, presence of bilateral B-lines on lung ultrasound has been shown to be a strong indicator of interstitial pulmonary edema.²⁰ Furthermore, POCUS has demonstrated higher diagnostic accuracy of detecting pleural effusions compared to chest x-ray (sensitivity of 95% vs 68%, respectively and specificity of 97% vs 85%, respectively).²¹ This multi-pronged sonographic assessment can help determine if a patient is likely to be fluid-tolerant or fluid-intolerant, and has demonstrated better test characteristics than the use of physical exam alone in assessing volume status.^{22, 23}  

The final portion of RUSH evaluates the pipes. During this portion, the examiner assesses the patient’s arteries and veins. On the arterial side, detecting the presence of vascular catastrophes such as abdominal aortic aneurysm (AAA) rupture and aortic dissection is crucial, as these can be rapidly fatal causes of hypotension and shock.¹⁰

To assess the abdominal aorta, examiner should scan along its course, especially infrarenally where most AAAs occur. AAA is diagnosed when the aortic diameter is greater than 3 cm, measured in short axis from outer wall to outer wall, including any thrombus within the vessel.¹⁰ A systematic review demonstrated a pooled sensitivity and specificity of 99% and 98%, respectively, for detecting AAA by ED POCUS. Given only 50% of patients with AAA present with the classic triad of hypotension, back pain, and pulsatile abdominal mass on history, the application of POCUS may help with early diagnosis and treatment of this life-threatening disease.²⁴

The aortic root on parasternal long-axis cardiac view should also be assessed for dilation, or presence of an intimal flap which would aortic dissection. The abdominal aorta can be scanned for extension of a dissection flap.¹⁰ POCUS has been supported as useful triage tool for identifying high-risk patients who need urgent confirmatory imaging or intervention in acute type A aortic dissection.²⁵

The venous side of the pipes assessment focuses on IVC which has already been discussed, and deep venous thrombosis (DVT) (Figure 3). Compression ultrasound of the lower extremity veins can be used to identify DVT, with non-compressibility of the vein suggesting thrombus.¹⁰ A multicenter prospective cohort study demonstrated that hospital medicine providers can perform compression-only POCUS for DVT on hospitalized patients with a sensitivity of 100% and specificity of 95.8%, positive predictive value of 61% and negative predictive value of 100%, but, more importantly, with a significantly shorter median time to completion when compared to radiology-performed ultrasound (5.8 vs 11.5 hours).²⁶ In the setting of shock, the presence of DVT can support the diagnosis of obstructive shock from pulmonary embolism, especially when combined with other RUSH findings.¹⁰

Although the RUSH protocol is helpful in assessment of shock and hypotension, notable limitations exist. First, POCUS is operator and training-dependent with associated risk for false positive and false negative interpretations. Additionally, studies have yet to show mortality benefit with the use of POCUS in shock.² A systematic review comparing positive likelihood ratios across shock subtypes showed that RUSH was most accurate for detecting obstructive shock, with wide confidence intervals for hypovolemic, distributive, and mixed-etiology shock.²⁷ In addition, much of the evidence supporting RUSH comes from emergency department studies, so its diagnostic performance may not fully generalize to all hospitalized internal medicine patients.

Overall, POCUS has become an increasingly important tool in internal medicine, especially for evaluating patients with hypotension or shock. The RUSH exam provides a structured approach to identifying etiology of shock by assessing the pump, tank, and pipes. By rapidly evaluating cardiac function, volume status, lung findings, arteries, and presence of DVTs, RUSH can help clinicians narrow the differential diagnosis and initiate timely management. As with any other diagnostic study, findings must always be interpreted in the context of the patient’s history, physical exam, labs, and additional imaging. With appropriate training, RUSH can serve as a valuable addition to the assessment of hospitalized patients in internal medicine.

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