A lines, B lines, Consolidation… the ABCs of Lung Ultrasound

But what do they really mean?

Here we attempt a #tweetorial presenting a way of thinking about common patterns seen on lung ultrasound.

See table here for a summary, and thread below for details


We will start with a hypothetical case for illustration
65 y/o f w HFpEF, COPD admitted 4 days ago with acute pancreatitis (now resolved). You are prepping her for discharge but she is now short of breath/hypoxic requiring 4 L O2.

Reportedly coughed a lot after dinner yesterday. Has not gotten any inhalers or antiHTN meds this hosp stay.
Net positive 4L. HR 88 SpO2 90% 4L BP 165/90 RR 22 T 99.8. WBC 22 (from 12 a day ago).
JVP not seen RRR, +S1/S2, 2/6 SEM
Bibasilar crackles, No LE edema. BNP 150.

You are considering the following on your differential
-COPD exacerbation
-Fluid overload with cardiogenic pulmonary edema
-ARDS from pancreatitis
-Aspiration pneumonitis
-Hospital acquired PNA

CXR would of course be very helpful. But for the sake of the exercise we will perform lung ultrasound to help narrow the differential.

A-lines everywhere would point toward which of the following causes (poll)
C) Aspiration, PNA, Atelectasis
D) CHF, ARDS, interstitial PNA

B-lines could be consistent with which of the following causes (poll)
B) CHF only
C) Aspiration, PNA Atelectasis
D) CHF, ARDS, interstitial PNA

Consolidation would point toward which of the following causes
C) Aspiration, PNA, Atelectasis
D) CHF, ARDS, interstitial PNA

Now let’s back up and talk about Lung US. It was originally thought that lung US would not be useful since the lung is full of air. But in pathologic states, the lung US pattern changes. A key reason is the air-fluid ratio. As the ratio changes, the ultrasound pattern changes.
When the chest is air-filled (normal lung, COPD, PTX), beams are reflected from the pleural surface creating an A-line pattern from reverberation artifact.

When the interstitium thickens, B lines form. The mechanism is not entirely understood. Either
1) Tetrahedral structure created at the pleural surface continuously reflects
2) Some waves are able to pass through the lung

When the alveoli fill (or collapse), the lung conducts ultrasound waves like tissue, creating a “tissue-like” appearance AKA hepatization AKA consolidation.

Few other tips
-O-lines AKA Non-A non-B pattern - non-diagnostic, may be due to non-perpendicular probe angle to the pleura. Change probe angle to make perpendicular.
-Z-lines AKA false B-lines - “devoid of meaning”.

See thread on B vs Z lines:

In summary
-A: air filled chest (ex: normal, COPD, PE, PTX, or non-pulmonary)
-B: interstitial edema or thickening (ex: CHF, ARDS, interstitial PNA, fibrosis)
-C: filled or collapsed alveoli (ex: PNA, aspiration, atelectasis, and more)
-O: Non-A non-B pattern: non-diagnostic

As with all POCUS, there are limitations/caveats/complicating factors, but this is meant to provide a framework for understanding why we see different patterns on lung ultrasound, and how to apply clinically.

Interested to hear other thoughts from #POCUS twitter on this!

@DRsonosRD @SonoInternist @G2Disrupt @buckeye_sanjay @msenussiMD @MFleshner301 @FoxStevenW @collinflan @trobertson8 @karthi8913 @jelevenson @siddharth_dugar @msiuba @MedEdPGH @NephroP @hraza222 @cameron_baston Apologies, there seem to be some technical issues with the polls (not showing up). Feel free to quiz yourself with the questions in the thread considering there is no actual poll.
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