B lines – how best to see them

Thankyou Justin Bowra for this post.

Ultrasound for interstitial lung disease and pulmonary oedema

Key points

• US lets you ‘see the crackles’. The US appearance of crepitations / crackles is called ‘B lines’ (formerly rockets, comets)
• Just like crackles, B lines are found in pulmonary oedema and also in pulmonary fibrosis
• B lines start at the pleural line, move with breathing, are very bright, and reach much further down the screen (more than 10cm) than any other lung artefacts
• It can be tricky learning how to find them- but there are plenty of people who can help you
• But you have to look at the pattern: e.g. bilateral symmetrical crackles suggest cardiogenic pulmonary oedema, while unilateral crackles suggest other pathology such as pneumonia.

Want to find B lines? Here’s how:

1. Select the curved probe (NOT linear probe)
2. Set the depth to 15cm
3. Turn off the ‘filters’ (tissue harmonics and multi beam / compounding) (image 1 ‘B lines with filters on’ and image 2 ‘B lines with filters off’ in the same patient)
4. Move the focal zone to the level of the pleural line (see image 3 ‘incorrect focal zone’ image 4 ‘correct focal zone’ in the same patient)
5. Turning up the far gain can help if you’re not sure (see image 5 ‘far gain not adjusted’ and image 6 ‘far gain turned up’)

  1. Filters on                                                                                           2. Filters off

3. Incorrect focus                                                                                      4. Correct Focus


5.  Far gain not adjusted                                                        6.  Far gain turned up

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