Ultrasound: Assessment of patients in shock

Shock is a state of circulatory dysfunction causing reduced tissue perfusion and metabolic upset. It is commonly encountered in the emergency department and mortality in non-traumatic shock can be as high as 25%.²

Shock can be classified as:¹

• Hypovolaemic or haemorrhagic
• Distributive (sepsis, anaphylaxis, neurogenic)
• Cardiogenic
• Obstructive (pneumothorax, massive pulmonary embolism, cardiac tamponade)

Diagnosing the aetiology of shock in a patient can be challenging, as many causes share a similar clinical picture.

A recent study has shown adding point-of-care ultrasound (POCUS) to the clinical assessment increases diagnostic accuracy for the aetiology of shock from 45% to 89%.²

Another study showed early use of POCUS in patients with hypotension accurately guided diagnosis, significantly reduced diagnostic uncertainty, and substantially changed management and resource utilization in the emergency department.³

The Rapid Ultrasound for Shock and Hypotension (RUSH) protocol is commonly used to assist the emergency physician in diagnosing the aetiology of shock in a rapid but systematic manner.

The RUSH protocol involves a three-part bedside assessment of:

• The Pump (heart)
• The Tank (intravascular volume and free fluid)
• The Pipes (aorta and large veins)

The HIMAP mnemonic describes which parts of the body to scan:

H          Heart

I           IVC

M         Morrison’s pouch and FAST

A         Aorta

P          Pneumothorax

While the whole assessment could be performed using a curvilinear probe, better images are obtained if a phased array probe is used to assess the heart and IVC, and then a curvilinear probe to assess the abdomen, aorta and lung fields.

The first step is to assess the heart, looking to answer the following questions:

• Is there a pericardial effusion?
• Is the left ventricle (LV) contracting normally?
• Is the right ventricle (RV) acutely dilated?

To obtain the best possible images use the phased array probe with a cardiac preset.

How to perform

Parasternal Long Axis view (PLAX)

Probe position: 3^rd or 4^th intercostal space with the probe marker facing the right shoulder. You will see the following structures:

RVOT = right ventricular outflow tract, LV = left ventricle, IVS = interventricular septum, AO = ascending aorta, PMLV = posterior wall left ventricle, MV = mitral valve, LA = left atrium, PCD = pericardium, DA = descending aorta

Parasternal Short Axis view (PSAX)
Probe position: From the PLAX position, rotate the probe 90^o so the probe marker points towards the left shoulder. You will see the following structures:

IVS = interventricular septum, LV = left ventricle, PmP = posteromedial papillary muscle, AlP = anterolateral papillary muscle, IW = inferior wall of left ventricle.

Apical four chamber view (A4C)

Probe position: Apex point (around the 6^th intercostal space), with the probe marker pointing left. You will see the following structures:

IVS = interventricular septum, RV = right ventricle, LV = left ventricle, TVSL = tricuspid valve septal leaflet, TVAL = tricuspid valve anterior leaflet, RA = right atrium, MVAL = mitral valve anterior leaflet, MVPL = mitral valve posterior leaflet, IAS = interatrial septum, LA = left atrium, LIPV = left inferior pulmonic vein, RSPV = right superior pulmonic vein.

Subcostal (subxiphoid) view

Probe position: Subxiphoid with the probe marker pointing left. You will see the following structures:

RA: Right Atrium, RV: Right Ventricle, LA: Left Atrium, LV: Left ventricle

Learning Bite

You need to push the probe down firmly if bowel gas is getting in the way of your images. Or can you gently massage it away? It is always helpful to ask the patient to bend their knees

Assessment

1) Is there a pericardial effusion?

A pericardial effusion forms an anechoic area around the heart.

Remember, not all pericardial effusions cause tamponade. The amount of fluid and how quickly it accumulates are both important factors. However as a general rule, effusions greater than 2cm are considered large and likely to cause tamponade. The earliest and most sensitive finding for tamponade is the diastolic collapse of the right atrium (RA), followed by the RV.

This PLAX view shows a massive pericardial effusion and RV collapse in diastole.

Case courtesy of Dr David Carroll, radiopaedia.org

Is the LV contracting normally?

In a patient with normal cardiac function, the walls of the LV should contract equally towards the middle of the ventricle.

This PLAX view shows globally reduced contractility of the LV. The LV should contract > 30% in systole at the level of the papillary muscles. Hypokinesia may be due to infarction, myopathy or secondary to systemic conditions such as sepsis or toxins.

Case courtesy of Dr David Carroll, radiopaedia.org

Reduced movement (hypokinesia) may be limited to certain areas of the ventricle, suggesting localised ischaemia or damage.

Conversely, if the walls of the ventricles contract > 90% or touch each other at the end of systole, it suggests a hyperdynamic circulation and may indicate hypovolaemia, haemorrhage or sepsis.

Is the RV acutely dilated?

As a rule of thumb, the normal ratio of RV to  LV is < 0.6.

There are many causes of RV enlargement, but in the setting of acute shock, consider pulmonary embolism (PE) and right ventricle infarct.

Other features of acute RV overload are:

The D sign

The D sign is seen on the PSAX view. The LV looks like a D instead of its usual round shape, due to paradoxical flattening of the interventricular septum in systole, when the RV pressure exceeds that of the LV.
This PSAX view shows the D sign in a patient with massive PE.

Case courtesy of Dr David Carroll, radiopaedia.org

McConnell’s sign

This is seen in the A4C view. McConnell’s sign is akinesia of the mid-section of the lateral wall of the RV, with normal or hyperkinetic movement of the apex. This is highly suggestive (in the correct clinical picture) for massive PE.

This A4C view shows RV dilatation and denting in the hyperactive apex of the RV (McConnell’s sign).

Case courtesy of Allam Harfoush, radiopaedia.org

Clot in-transit

The presence of a clot in-transit suggests emboli are likely to pass to the lungs imminently which may cause massive PE and collapse.
This A4C view shows a dilated RA with mobile echogenic material in a patient with chest pain and acute shortness of breath.

Image courtesy of Dr William Scheels: thepocusatlas.com

Pitfall

Patients with chronic pulmonary hypertension will have a dilated RA on cardiac ultrasound, so POCUS findings must be applied in the right context. One way to differentiate chronic pulmonary hypertension from acute RV overload is that in chronic pulmonary hypertension, the LV takes a D shape even in diastole. 

There are more advanced assessments for right heart dysfunction inclusing TAPSE, and the 60/60 sign, but these are beyond the scope of RUSH protocol.

Learning bite

The pump part of the RUSH protocol looks at three important questions: 

• Is there a pericardial effusion?
• Is the left ventricle contracting normally?
• Is the right ventricle acutely dilated?

Inferior Vena Cava (IVC)

How to perform

The tank is assessed in two sections. First the inferior vena cava (IVC) is assessed with the phased array probe. Then the abdomen and lung apices are assessed with the curvilinear probe, in the same way as an extended Focused Assessment with Sonography in Trauma (eFAST) scan.

Inferior Vena Cava (IVC)

Probe position: With the probe in the subcostal position, rotate 90 ^o  so the marker now looks to the patient’s head. This image shows the IVC collapsing in inspiration

Image: authors own

Pitfall

The aorta can be mistaken for the IVC in the above view. The easiest way to avoid this mistake is to visualise the RA and follow the hepatic vein draining into the IVC.

Abdomen including Morrison’s pouch

Probe position: A detailed review of how to perform a FAST scan is available in the RCEM Learning Session FAST Scan. You should obtain RUQ, LUQ and pelvic views for the RUSH protocol assessment, looking for free fluid in the peritoneal or pleural cavities, or B lines which suggest pulmonary oedema.

Bilateral apical Lung views

Probe position: The apical region of each hemithorax with the probe marker pointing towards the patient’s head. You should visualise two rib spaces and the pleura between them.

Learning bite

If time allows, the linear array probe will give better resolution when assessing the lung fields.

Assessment

Is the tank full?

The diameter of the IVC gives an estimate of volume status and central venous pressure.

How the IVC collapses in inspiration can predict whether fluids will be useful. The collapsibility or caval index (CI) can be calculated by:

CI = 100 x (IVC expiratory diameter – IVC inspiratory diameter)/IVC expiratory diameter

A “flat” IVC < 1.5cm with a CI > 50% suggests a low CVP and a response to volume.

A “fat” IVC > 2.5cm with a CI close to 0% suggests a raised CVP.

Pitfall

The CI in intubated patients is not of clinical value.

Is the tank leaking or overloaded?

Look for free fluid, ascites, pleural effusion or B-lines that suggest third spacing or overload.

Ascites

This RUQ view shows ascites around a cirrhotic liver.

Image courtesy of Renato Tambeli thepocusatlas.com

Pleural effusion

This view shows a large pleural effusion around a collapsed lung.

Image courtesy of Renato Tambeli: thepocusatlas.com

B lines

B lines are sonographic artefacts which are seen with interstitial oedema. They can be seen in pulmonary oedema, pneumonia and Covid pneumonitis.

This image shows an abundance of B lines (white lines extending to the bottom of the screen) in a patient with pulmonary oedema.

Image courtesy of Dr Justin Bowra et al: thepocusatlas.com

Is the tank compromised?

A pneumothorax is suggested by the loss of normal lung sliding on the apical lung view.

This view shows the Batwing sign, formed by the rib shadows as the bat wings and the lung sliding between them. This rules out pneumothorax.

Image: authors own

This view shows the loss of lung sliding in a patient with a pneumothorax.

Image courtesy of Dr Stacey Frisch, Dr John F Kilpatrick : thepocusatlas.com

Pitfall

A loss of lung sliding, although highly suggestive, is not 100% specific for the presence of a pneumothorax.

Barcode sign

Loss of lung sliding can be further assessed in M-mode if time allows. The presence of the barcode sign is highly suggestive of a pneumothorax.

This image shows the barcode sign in a patient with pneumothorax.

Image courtesy of Dr Stacey Frisch, Dr John F Kilpatrick : thepocusatlas.com

Lung point

The presence of a lung point is 100% specific for the presence of pneumothorax. A lung point is where a pneumothorax meets the normal pleura, i.e. where the non-sliding part meets the sliding part.

This view shows a lung point in a patient with a pneumothorax. Note the sliding pleura, which comes to the middle of the screen with every breath.

Image courtesy of Dr. Stenberg thepocusatlas.com

Learning bite

Ultrasound is more sensitive and specific for the diagnosis of pneumothorax than chest X ray.

Assessment of the tank is focused to answer the following questions

Is the tank full?

• Is the tank leaking or overloaded?
• Is the tank compromised?

How to perform

DVT

The final part of the Rush protocol is the assessment of the “big vessels”; looking at the abdominal aorta for aneurysm or dissection, and at the femoral and popliteal veins for deep vein thrombosis (DVT), using the curvilinear probe.

The assessment of the pipes looks to answer the following questions? 

• Is there an aortic aneurysm or dissection?
• Is there a DVT in a large vein?

Abdominal Aorta Aneurysm (AAA)

A detailed review of how to perform a AAA assessment is available in the RCEM Learning Session Abdominal Aorta Aneurysm assessment

The recommended scanning style for the RUSH protocol is to sweep down from the xiphoid to the bifurcation of the aorta.

DVT

An addition to the original RUSH protocol is a limited two-point compression scan to look for DVT at:

• Common femoral vein in the inguinal canal
• Popliteal vein in the popliteal region

Learning bite

The presence of echogenic material in the vein, or the lack of collapsibility of the vein on applying pressure is indicative of DVT.

Examples

Is there an aortic aneurysm or dissection?

This image shows a 10cm abdominal aortic aneurysm with “echogenic smoke” produced by the passing blood cells and platelets.

Image courtesy of Brian Toston : thepocusatlas.com

Is there a DVT in a large vein?

This image shows a left common femoral vein which is not fully compressible confirming DVT.

Image courtesy of Dr Justin Bowra et al : thepocusatlas.com

The findings from the RUSH protocol assessment can be used to narrow down the differential diagnosis.

	Hypovolaemic Shock	Cardiogenic Shock	Obstructive Shock	Distributive Shock
Pump	Small underfilled chambers give the LV “kissing” sign Hyperdynamic state	Dilated heart Reduced global contractility Reduced ejection fraction	Evidence of tamponade RV strain and dilatation Thrombus in-situ	Hyperdynamic heart in early sepsis Hypodynamic in late sepsis
Tank	Flat IVC with high collapsibility index Third spacing with pleural or peritoneal fluid present	Distended IVC with low collapsibility index B lines, pleural effusions or peritoneal fluid	Distended IVC with low collapsibility index Absent lung sliding and barcode sign (pneumothorax)	Normal or flat IVC in early sepsis with high collapsibility index Peritoneal or pleural fluid as source of sepsis
Pipes	Aneurysm Dissection	Normal	DVT	Normal

Table 1- Rush protocol diagnostic strategy, adapted from Perera, P. et al. “The RUSH Exam.

IFEM approach (SHOc)

Performing the full RUSH protocol can take time. To help streamline the bedside scan, the International Federation for Emergency Medicine (IFEM) has produced a consensus statement for Sonography in Hypotension and Cardiac arrest (SHoC).

A review of international data found LV dynamic changes, IVC abnormalities and pericardial effusion were the most common findings on ultrasound in patients who presented with undifferentiated shock.

Finding	Frequency
LV dynamic change	43%
IVC abnormalities	27%
Pericardial effusion	16%
Pleural fluid	8%
Peritoneal fluid	5%
AAA	2%

Table 2- International Data for Prevalence of Findings in Undifferentiated Hypotension, adapted from Milne, James et al.

The SHoC statement recommends the 4F approach to assess:

• Fluid
• Form
• Function
• Filling

Summary target style graphic for the combined SHoC protocols: Atkinson P et al: IFEM SHoC Protocol Consensus Statement⁹

The 4 Fs can be assessed with the 4 core views:

1. Subcostal cardiac view – assess for pericardial fluid, cardiac form and ventricular function.
2. PLAX cardiac view – assess for pericardial fluid, cardiac form and ventricular function.
3. Apical lung views – assess for pleural fluid and B-lines for filling status
4. IVC view – assess filling status

Supplementary views which provide further information are the PSAX and A4C cardiac views.

Additional views are then performed when clinically indicated, including AAA, FAST and DVT imaging.

Learning bite

Performing the four core views (subcostal cardiac view, PLAX cardiac view, apical lung views and IVC imaging) would cover more than 80% of the pathologies seen in patients with shock.

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