CLUE Protocol – Cardiopulmonary US

The CLUE protocol is a quick and rough assessment of the heart and lungs in a patient with hypoxemia and/or shock.  It is performed in as little as 60 seconds with 5 basic views moving against the flow of blood to assess the LV->LA->lungs->RV/pericardium->IVC.  This provides a basic assessment of cardiac function, lung pathology and fluid responsiveness/overload:

1. Parasternal long axis – assess general LV systolic function (nml, moderate or severely reduced EF) and wall motion abnormalities based on inward movement and thickening of the LV walls.  Then look at the size of the LA.  It may be enlarged if it is greater than the diameter of the LVOT.
PSLA

How to obtain view: https://www.youtube.com/watch?v=CIJewMLUQkU

2. Anterior lung apices

Quick intro to lung U/S

US waves do not penetrate air and are instead reflected/dispersed.  Thus, healthy, well aerated lungs are very poorly visualized.  For the most part we use artifacts to assess what might be going on in the lungs because they cannot be directly visualized unless there is pathology.

Lung sliding = No air or fluid in the pleural space at the site of the probe.  Identify rib spaces above and below the probe (left and right of the screen), the bright white line connecting them is the pleural line.  Look for a twinkling or ‘marching ants’ to identify ‘lung sliding’.  This represents the parietal and visceral pleura sliding against each other.  Sensitivity improves with more views
Movie: Lung point, demonstrating pneumothorax – UpToDate.com

A lines = healthy lung or pneumothorax –  They represent the parietal-visceral pleural interface which is as far as the US waves can penetrate before being reflected by aerated lung.  These waves reverberate back and forth between the probe and pleura, making repeated artificial lines at multiples of the distance from the probe to the pleura.

Lung sliding
Movie: A-Lines with lung sliding – UpToDate.com

B lines = pathology in the alveoli or interstitia – These are vertical rays that obliterate A lines.  They extend from the pleural line to the bottom of the screen and move with the sliding pleura during respirations. They represent fluid or tissue in the alveoli or septa where US waves are able to penetrate. 

B lines
Movie: Lung Sliding and B-lines – UpToDate.com

Review of interpretation of lung findings: 
– If there is no lung sliding and A lines then there is a pneumothorax or inflammation of the pleura preventing sliding.
– If there is lung sliding and A lines the lung is normal in that particular view
– If there are B lines there is pathology either in the alveoli or parenchyma

3. Lateral lung bases – Visualize the diaphram in the middle of the screen and assess for fluid around the lung (pleural effusion) or hepatization/consolidation of the lung (pneumonia).

4. Subcostal cardiac view – Compare relative sizes of R and L ventricles and pericardium.
Subcostal
How to obtain: https://www.youtube.com/watch?v=oMwgUo6sbyY

5. IVC
– If the IVC is >2.5cm and collapses by <50% this suggests volume overload
– If the IVC is <1.5cm and collapses by >50% this suggests volume responsiveness in a hypotensive patient (this is most validated in ventilated patients)

correllations IVC
How to obtain: https://www.youtube.com/watch?v=oMwgUo6sbyY

Figure 1. CLUE with normal findings (Upper) and abnormal findings (Lower) for each view (see text for “quick-look” diagnostic criteria). Probe positions seen within insets (black bars). Parasternal long-axis view (Left) shown in mid-diastole and demonstrates LV systolic dysfunction and LA enlargement. Longitudinal subcostal view (Center) shown in end-inspiration and demonstrates IVC. Lung apical view (Right) shown at end-expiration and demonstrates 3 normal horizontal reverberation artifacts compared to ULC examination with 3 vertical linear artifacts.
Figure 1. CLUE with normal findings (Upper) and abnormal findings (Lower) for each view (see text for “quick-look” diagnostic criteria). Probe positions
seen within insets (black bars). Parasternal long-axis view (Left) shown in mid-diastole and demonstrates LV systolic dysfunction and LA enlargement.
Longitudinal subcostal view (Center) shown in end-inspiration and demonstrates IVC. Lung apical view (Right) shown at end-expiration and demonstrates
3 normal horizontal reverberation artifacts compared to ULC examination with 3 vertical linear artifacts.

Example video of CLUE:

Cases – thanks to Cameron Bass and Amy Morris

Original CLUE article:
CLUE protocol

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