You are reading ARTEFACTS, not anatomy — A-lines mean air, B-lines mean interstitial fluid, and the pattern is the diagnosis.
Orient first
- Normal lung is full of air and reflects almost everything, so lung ultrasound interprets ARTEFACTS rather than structures. That is the conceptual jump, and it is why the images look like nothing until the artefacts are named.
- A-LINES are horizontal repeats of the pleural line and mean air below — normal lung, or a pneumothorax if sliding is absent.
- B-LINES are vertical, laser-like, reach the bottom of the screen, move with sliding and erase A-lines. Three or more in one intercostal space is a positive zone, indicating interstitial fluid.
- The pattern across ZONES is the diagnosis: bilateral symmetric B-lines with a smooth pleural line suggest cardiogenic oedema; patchy B-lines with an irregular thickened pleural line and spared areas suggest pneumonia or ARDS.
- CONSOLIDATION appears as tissue-like ("hepatised") lung, often with air bronchograms; DYNAMIC air bronchograms move with respiration and favour pneumonia over atelectasis.
Acquire the study
- Curvilinear or phased-array probe for depth, linear for detailed pleural assessment.
- Scan a defined ZONE PROTOCOL — anterior, lateral and posterior zones on each side — and use the same zones every time so studies are comparable.
- Scan LONGITUDINALLY across the ribs so the pleural line is seen between two rib shadows: the bat sign confirms you are at the pleura.
- Turn OFF harmonics and any speckle-reduction or multi-beam compounding — those are designed to suppress artefact, and the artefact is the finding.
- Set the depth so B-lines can be seen reaching the far field, and place the focal zone at the pleural line.
The manoeuvre
- Confirm the bat sign and identify the pleural line in each zone.
- Assess LUNG SLIDING in each zone; use M-mode to record the seashore sign, or the barcode sign if sliding is absent.
- Count B-lines per intercostal space and classify each zone as positive or negative.
- Describe the pleural line itself: smooth and thin, or irregular and thickened.
- Look for CONSOLIDATION and, if present, for air bronchograms and whether they are dynamic.
- Assess the dependent zones for effusion, and estimate its depth and whether it is anechoic or septated.
- If pneumothorax is suspected, search for the LUNG POINT, which is the specific sign.
- Summarise the ZONE PATTERN rather than listing findings — the distribution is what carries the diagnosis.
What confirms it
- Three or more B-lines in an intercostal space makes that zone positive; bilateral symmetric positive zones with a smooth pleural line indicate interstitial oedema.
- A lung point is essentially diagnostic of pneumothorax.
What licenses you to exclude it
- Preserved lung sliding at a scanned point excludes pneumothorax AT THAT POINT — state which zones were examined.
- ⚠️ Lung ultrasound cannot assess deep or central lung, and a normal study does not exclude central pathology, a small pulmonary embolus, or a mass behind aerated lung.
- Absent sliding is not specific: it occurs in bullae, adhesions, ARDS, and main-stem intubation as well as pneumothorax.
The classic misread
- Leaving harmonics and compounding on, which suppress the very artefacts being counted.
- Counting B-lines without a defined zone protocol, so studies cannot be compared.
- Calling pneumothorax on absent sliding alone, without a lung point.
- Mistaking the diaphragm and liver for consolidated lung at the bases.