A four-point lung survey run end to end on a handheld probe — pleural sliding, A-lines, B-lines and the curtain sign at the base — with every point timestamped, the settings read off the device screen, and the whole recording transcribed.
Acerca de la Dra. Mariz
I am Dr. Fernando Mariz, a gynecology and pelvic surgery physician practicing in New York City. Before my medical career, I served in the U.S. Marine Corps, where I developed the discipline, focus, and steadiness that continue to shape the way I care for patients today. At Maiden Lane Medical, my work covers women’s health, preventive care, sonography, pelvic pain, abnormal uterine bleeding, and minimally invasive gynecologic procedures.
Acerca del Dr. Ávila
I am Dr. Jailyn Avila, an emergency medicine physician, educator, and digital health innovator based in Southern California. My clinical work is rooted in emergency care, while my teaching focuses on point-of-care ultrasound, residency education, and practical training for physicians. Through my roles with Emergent Medical Associates, UHS SoCal MEC Emergency Medicine Residency, Core Ultrasound, and FemInEM, I work at the intersection of patient care, medical education, and accessible digital learning.
Respuesta rápida
B-lines are vertical, laser-like artifacts that rise from the pleural line, run to the bottom of the screen without fading, and mean there is fluid in the lung at that window. A-lines are their opposite number: horizontal repeats of the pleural line, the signature of air-filled lung, and present in a healthy chest and in a pneumothorax alike, which is why they never settle a question on their own. One or two B-lines in a single intercostal space can be normal, particularly low down and in older patients; three or more in one space is interstitial syndrome at that window, and the conditions behind it are pulmonary oedema, pneumonia, ARDS and interstitial lung disease. The walkthrough on this page runs a four-point survey on a handheld probe and finds none of them — every window comes back A-lines plus sliding, which is exactly what a normal lung looks like, and the B-line, effusion and consolidation pictures are shown as reference images at 2:28 and 2:43 rather than acquired live. That is the honest shape of the recording, and it is still the fastest way I know to learn the finding: you cannot recognise a wet lung until you know precisely what a dry one looks like at 10 MHz. Start at 5:36 if you want the scanning, at 0:43 if you want the pictures.
Looking for a device rather than the exam? The pulmonology hub covers the models used for chest work, and the D3Ultra product page carries the full specification and current price.
The four points
Where the probe goes, and what each point settles
The four windows in the order they are scanned, with the question each one is there to answer and the findings called out loud at it. Click any point to jump the video to it.
01Anterior upper zoneSecond intercostal spaceIs the pleura sliding, and are the lines A or B?A-linesseashore sign5:3602Anterior lower zoneFifth to sixth ribSame question, better window — this is where sliding was easiest to call.pleural slidingseashore sign6:3203Lateral zoneLateral chest wallSliding again, and a deliberate check that no B-lines have appeared.pleural slidingno B-lines7:0704Dependent cornerPLAPS — posterolateral inferiorThe corner where fluid collects. Effusion, consolidation, curtain sign.curtain signlung–liver interface7:38
0:00Teaching, reference images and the protocol argument5:36The four points, scanned live8:52Cerrar
teaching, reference images and the protocol argumentthe four points, scanned liveclose
The BLUE protocol proper is a three-point examination. The four-point survey demonstrated here is the presenting clinician’s own extension of it, and he says so at 0:00. He also recommends adding posterior points whenever the patient can sit forward, on the grounds that the back is easier to reach than the front and consolidation shows there anyway; those points are argued for from 3:36 but are not scanned on camera.
Timestamped
Key moments, with the settings
The third column is the part that is normally missing from a scan video: the preset, depth and transmit frequency showing on the device at that moment. What is striking on this recording is that they never change. One preset, one depth, one frequency carry all four points — and that frequency is the ceiling of what this probe’s linear array offers.
| Tiempo | What is on screen | Transducer, preset, depth, frequency |
|---|---|---|
| 0:00 | Four points, and whyteachingThe exam is framed before the probe is picked up: three lobes plus the dependent corner where fluid collects. The BLUE protocol proper uses three points; the four-point survey demonstrated here is the presenting clinician’s own extension of it, and he says so. | Teaching segment · no device panel on screen |
| 0:43 | Pleural sliding — the ants signteachingThe single finding the whole exam turns on. Sliding is described as ants moving along the wall of the cavity; if the pleura is not moving there, the lung is not against the chest wall. | Reference clip on a slide · no device panel on screen |
| 1:03 | A-lines, M-mode, seashore versus barcodeteachingA-lines named as a reverberation artifact that repeats at regular intervals below the pleura, and stated plainly to be present in normal lung and in pneumothorax alike. M-mode is offered as the tie-breaker: a sandy seashore pattern where the lung moves, a flat barcode where it does not. | Reference clip on a slide · B and M mode shown |
| 1:50 | The curtain sign at the lung baseteachingThe lung base, where aerated lung slides across the liver and blocks the view of it. What would replace that on an abnormal scan is spelled out: an anechoic triangle above the diaphragm for effusion, or a lung you can see straight through for consolidation. | Reference clip on a slide · no device panel on screen |
| 2:28 | What effusion and consolidation look like insteadteachingTwo abnormal reference images: a pleural effusion, and a consolidated lung transmitting sound well enough that the spleen or liver is visible through it. | Reference images on a slide · no device panel on screen |
| 2:43 | B-lines, comet tails and confluent B-linesteachingWet lung. Comet-tail artifacts rising from the pleural line raise the suspicion of pneumonia, and when there are enough of them that they merge into one broad band the finding is called out as strongly suggestive. | Reference images on a slide · no device panel on screen |
| 3:05 | How accurate the BLUE protocol isteachingSensitivity and specificity for the BLUE protocol are quoted from a published table on screen as being in the eighties and nineties. | Cited table on a slide · no device panel on screen |
| 3:36 | Why these points, and scanning from the backteachingThe B in BLUE stands for bedside, and that constrains access: a supine patient gives you the front and a little of the side. Sitting the patient up opens the back, which is easier to reach and is where consolidation shows anyway. | Teaching segment · no device panel on screen |
| 4:40 | Let the clinical question drive the lookteachingThe most portable idea in the recording: decide what you are asking before you look. Chasing pneumonia means watching for B-lines; chasing pneumothorax means watching the pleura and nothing else. A normal lung scan in a breathless patient is a reason to go and look at the legs. | Teaching segment · no device panel on screen |
| 5:36 | Point 1 — second intercostal spaceFirst live acquisition. The probe goes between the ribs at the second rib level, the subject takes a breath, M-mode is switched on. An A-line is identified, no comet tails, and the M-mode strip is read as seashore rather than barcode. | Linear · MSK preset · D 60 mm · F H10.0 MHz · GN 105 dB · DR 80 · B + M |
| 6:32 | Point 2 — fifth to sixth ribThe clearest sliding in the recording, and the point where the rule-out logic is stated outright: you cannot have pleural sliding if the lung is not attached to the chest wall, so sliding here settles the question at this window. | Linear · MSK preset · D 60 mm · F H10.0 MHz · GN 105 dB · DR 80 · B + M |
| 7:07 | Point 3 — lateral wallMore gel, arm raised, probe onto the lateral chest wall. Sliding is seen again and B-lines are explicitly excluded at this window. | Linear · MSK preset · D 60 mm · F H10.0 MHz · GN 105 dB · DR 80 · B + M |
| 7:38 | Point 4 — PLAPS, and reading the baseThe posterolateral inferior point, taken down until the bottom of the lung comes into frame. M-mode is switched off. Rib, liver and lung are named on a frozen frame, the curtain sweeping across the liver with the diaphragm, and the abnormal versions of that picture are described. | Linear · MSK preset · D 60 mm · F H10.0 MHz · GN 105 dB · DR 80 · B + M, then B only |
Settings transcribed from the device interface visible in the recording. Depth is the D value on screen; frequency is the F value, harmonic. The first nine rows are taught against slides and reference images rather than scanned live, so no device panel is on screen for most of them. M-mode is switched on at 5:36 and switched off again inside the fourth point.
Reading the images
What this scan shows
The pleural line is the only structure this exam really needs. It sits a centimetre below the skin, framed between two rib shadows, and it shimmers as the patient breathes. That shimmer is lung sliding, and the whole survey turns on it: if the two pleural layers are still in contact they slide against each other, and a pneumothorax at that window is ruled out. Absent sliding is not by itself a diagnosis — it says only that the lung is not moving against the chest wall there.
Everything below the pleural line is artifact, because air-filled lung reflects almost all the sound that reaches it. A-lines are horizontal echoes of the pleural line repeating at even intervals; they are what dry lung looks like, and they appear in a pneumothorax too. B-lines are the vertical answer: laser-like bands that start at the pleura, run off the bottom of the screen without fading, erase the A-lines they cross, and swing with the breath. They exist only where there is fluid. Three or more in one intercostal space reads as interstitial syndrome at that window; enough of them and they merge into a single broad white band.
M-mode is the tie-breaker when sliding is too subtle to call by eye: a granular seashore below a smooth band where the lung moves, flat parallel lines — the barcode sign — where it does not. The settings matter more than they look. All four points run on the linear array at 10 MHz and 60 mm, the top of this probe’s range and the right choice for a structure a centimetre deep. Take that setting to an effusion ten centimetres down at the base and it will not reach; I would move to the convex array there.
Verbatim
Full transcript
Transcript — 9:28, 18 passages
Transcribed from the recording and edited for readability; square brackets mark an editorial clarification, and every timestamp jumps the video.
Framing the exam
0:00[The presenting clinician introduces himself.] Today we’re going to do a very, very quick sample lung scan using a Suresult D3Ultra handheld ultrasound unit. My version of the exam uses four points. Why do I pick four points? If you look at the lobes, I get this lobe, this lobe, this lobe, and then I pick the bottom corner where fluid is likely to collect. There are many similar protocols. The BLUE protocol uses three points instead of four points, and in general the more points you do, the better. So if you want, you can do the posterior wall; and if you don’t like three, you can pick four, five, six — you can check between every rib if you want.
What you are looking for
0:43Here, just on myself, I wanted some samples of normals to talk about what we are looking for. We’re looking for pleural sliding — it sort of looks like ants moving along the wall of the cavity. If it’s not moving along the wall of the cavity, guess what: you have a pneumothorax. The lung isn’t there, or the lung isn’t moving.
1:03In general, the rest of the appearance of the lung — you don’t really see into the lung, because the lung is full of air. So pneumothorax and regular normal lung look the same. When you get past the pleura you do see something they call an A-line, which is just a reverberation artifact: sound bouncing back and forth here makes this line repeat itself at regular intervals. That is a sign that’s either pneumothorax or normal lung. And then you look for pleural sliding, and if you see pleural sliding you can rule out pneumothorax. Some people like to use M-mode and they look for the seashore sign — this looks like a sandy beach and this looks like the water, and that’s what you should see. And if you see something more that looks like this, like just a barcode, then that’s a sign of a pneumothorax.
1:50And again, just check different locations; we see the same thing. We’re looking for ants crawling across the pleura. And here at that corner, this is called curtain sign, because you can’t see through lungs normally, right? So what we’re seeing is the lung basically move, and it’s covering up — it prevents us from seeing within the liver. If there was fluid we would see a corner of hypoechoic or anechoic fluid, sort of a triangle right here. And if the lungs had pneumonia, were full and solid, we’d be able to see through the lungs.
2:28So here’s just an example of what an effusion would look like. Here’s another case where we have consolidation, so we can basically see through the lungs — we can see the spleen or liver, depending on what side of the body you’re on.
2:43This reverberation artifact is considered normal or pneumothorax. If you get something called B-lines or comet-tail artifacts, that means the lungs are wet; it increases your suspicion for pneumonia. And if you get something that looks like this — basically these lines, there’s so many of them that they sort of bunch up into just one giant line — that is also very indicative of pneumonia.
How good it is
Why these points
3:36So my protocol for the lung exam is basically the BLUE protocol, and the B in BLUE stands for bed, or bedside. So basically if someone’s lying down, you only have access to the front and maybe a bit of the side, and that’s it. If you have access — let’s say if they’re sitting like this — well, you have access to the back. In fact you have easier access to the back than the front, so you can add on more points. Or let’s say you have a woman, and there are breasts and bras in the way: you can still check a lot of the lung from the back instead of the front. And if you’re looking for something like pneumonia or consolidation, you’re going to see that on the back as well as the front, so don’t worry about missing the two front parts when you have access to the back.
4:21The reason why this is my recommended protocol is because it’s just a few points, and the BLUE protocol is a validated set of points to check. So if I follow that, that means your exam is at least as good as the BLUE protocol, which is, you know, 80 to 90-some percent accurate at finding things like pneumonia and pneumothorax.
4:40And that raises another point. Based on your clinical intuition — what exactly are you looking for? You might be looking for different things in the images. If you’re looking for pneumonia, then you don’t really care about the pleura sliding around; you just care about those B-lines or the C-lines. If you care about a pneumothorax, then you’re really looking at that pleura and you’re just going point to point, really focusing on that pleura. Again, if you have time, I guess you can always look at everything, but you want to answer your clinical question. Is there pneumothorax? If that’s your only clinical question, then you’re just looking: is the pleura sliding, are there A-lines — A-lines for a pneumothorax or for a normal lung. And if you find nothing, if you follow that BLUE protocol and you find nothing, normal lung — and they have lung symptoms — well, maybe check for a DVT. Maybe it’s a pulmonary embolism, in which case the lung scan shows normal but they still have trouble breathing.
Point 1
5:36So I’m going to turn on M-mode, because some people like M-mode for looking for seashore sign versus barcode sign. I don’t really pay attention to that myself; I’m just going to be looking at the pleura, looking for those ants moving across. I’m looking for: are they A-lines, B-lines or C-lines. So around second rib, let’s take a look here. So between the ribs, and take a breath. And we can see we have an A-line here. We’re not getting comet-tail type artifacts like B-lines, so we have basically an A-line, and we do get a little bit of motion across, and we do get more of a seashore sign instead of the barcode sign.
Point 2
6:32And let’s go to the next point. So normally around, I don’t know, like fifth, sixth rib. Now this one I can really, really see it. The first one, honestly, I didn’t see the pleural sliding that clearly; this one you can really see the pleural sliding here. Remember, if you can see the pleura sliding, that rules out — virtually 100% rules out — a pneumothorax, because you can’t have pleural sliding if the lung isn’t attached to the wall of the thoracic cavity. So if you’re missing pleural sliding, well, it could be other things; but if you have pleural sliding that rules out pneumothorax. So we have pleural sliding, so I definitely don’t have pneumothorax.
Point 3
7:07So I added more gel, and the next point is over here. And again, we can very clearly see pleural sliding. So that’s great. And again we’re not seeing these B-lines or anything that looks like that, so no pneumonia for me.
Point 4
7:38And if I move down, now this is posterolateral, inferior. I go down until I hit the bottom of the lungs. In fact, I’m going to turn off M-mode now.
7:57Okay, so what are we looking at? Well, particularly if we can go through a few frames here, we have the liver here, and we have — we have rib, we have liver, and we have the lung. This is called the curtain sign. The lung is covering, because we can’t see through a lung, so it’s covering the liver; and as I breathe the lung is — well, the diaphragm is moving up and down, and so the lung is moving, and so we see this curtain come across the liver and prevent us from seeing anything. So this is normal.
8:28If we can see through the lungs, that’s bad. That means there’s consolidation and the lungs are full of fluid and junk. If there is a large hypoechoic or anechoic collection of fluid here — here we see it’s often just this triangle, black triangle — then we would have a lung effusion, which could be a hemothorax, for example. And that’s it. Pretty quick.
Cerrar
8:52[Sponsor segment omitted, 8:52–9:28.]
Hardware
Device and settings
One probe, one setting, the whole survey. The left column is the published specification; the right column is what the device interface actually showed while this exam was being run, and that second column is the one I would work from if you are reproducing it. For chest work the linear array at 10 MHz is the right default, because the pleura is superficial and resolution beats penetration there. If your lung work is mostly deep effusions and consolidation at the base, a linear-only setup is not a good fit: the convex array is the one that matters there, and this is the wrong setting to copy.
Published specification
Suresult D3Ultra
One head, three arrays — $2,976
- Lineal7.5 and 10 MHz · depth steps of 20, 40, 60 and 100 mm · 40 mm footprint — the array this exam runs on
- Convexo3.2 and 5.0 MHz · 90 to 300 mm · 45° — the one to reach a deep basal effusion
- Por fases3.2 and 5.0 MHz · 90 to 300 mm · 60°
- Modes used hereB, and B+M for the seashore strip; Color, Power and PW Doppler also available
- Gane30 to 105 dB — this scan sits at the ceiling of that range
- Dynamic range40 to 110, in ten steps
- Array192 elements · 64 channels · 256 grey levels
- Body156 × 65 × 20 mm · 263 g · 2 h continuous scanning
Read off the screen in this recording
- ArrayLinear · MSK preset, unchanged at all four points
- ProfundidadD 60 mm · the middle of the linear array’s four steps
- FrecuenciaF H10.0 MHz, harmonic · the top of the linear range
- GaneGN 105 dB · the top of the published range
- Dynamic rangeDR 80
- ProcessingENH 0 · Compound OFF
- OutputMI 0.9 · TIS 0.2
- ModosB throughout · B+M from 5:36 until M-mode is switched off inside the fourth point
Same device, other windows
Related scans
14:09eFAST trauma exam on the same handheld probeThe thoracic windows of this lung survey inside a full trauma study — pericardium, both upper quadrants and the pelvis, in one pass.Read the walkthrough →
1:23DVT: the three-point compression scanThe scan to run when the lungs are normal and the patient is still breathless: common femoral, femoral and popliteal veins, compressed in sequence.Watch in the Library →
6:42POCUS for rib fracture detectionThe other high-frequency chest-wall exam — a linear survey of the rib cortex, and what a cortical step-off looks like on screen.Watch in the Library →All the clinical clips, filterable by anatomy and probe, are in the Scan Library.
Asked on this search
B-line questions
What do B-lines on ultrasound mean?
B-lines mean fluid in the lung. They are vertical, laser-like reverberation artifacts that start at the pleural line, run to the bottom of the screen without fading, erase the A-lines they cross, and move with the breath. The conditions that increase them are the ones that put fluid or thickening into the interstitium: pulmonary oedema, pneumonia, ARDS and interstitial lung disease. In the walkthrough above they are called comet-tail artifacts, and the point is made that when enough of them appear they merge into one broad band. What I check first is simply whether they are there at all: their presence or absence at a window moves the differential further than their exact number does.
Source: POCUS Certification Academy — A-lines and B-lines. Accessed September 5, 2026.
What is the difference between A-lines and B-lines?
A-lines are horizontal and B-lines are vertical, and they mean opposite things. A-lines repeat below the pleural line at regular intervals because sound is bouncing between the probe and the pleura; they are what aerated lung looks like, which is why they appear in a healthy lung and in a pneumothorax alike and cannot settle the question on their own. B-lines rise from the pleural line and run down the screen, and they only exist where there is fluid in the lung. So A-lines plus lung sliding is a normal anterior scan; B-lines say the lung is wet at that window.
Source: POCUS Certification Academy — A-lines and B-lines. Accessed September 5, 2026.
How many B-lines are normal on ultrasound?
One or two in a single intercostal space can be normal, particularly at the lung bases and particularly in older patients. Three or more B-lines in one intercostal space is an abnormal finding and is read as interstitial syndrome at that window. The count is per space, not per patient, which is why the finding is recorded window by window rather than as a single verdict. My habit when teaching it is to count in one space, write the number down and move on: what you interpret is the pattern across the whole chest, never a single window on its own.
Source: POCUS Certification Academy — A-lines and B-lines. Accessed September 5, 2026.
How accurate is the BLUE protocol?
In the study that defined it, ultrasound profiles gave the correct diagnosis in 90.5% of 260 patients presenting with acute respiratory failure. Multiple anterior B-lines with lung sliding identified pulmonary oedema with 97% sensitivity and 95% specificity; the pneumonia profiles reached 89% and 94%; absent anterior sliding with A-lines and a lung point identified pneumothorax with 81% sensitivity and 100% specificity. That is the basis for the range quoted at 3:05 in the recording above.
Source: Lichtenstein DA, Mezière GA — Chest 2008, the BLUE protocol. Accessed September 5, 2026.
What is the lung point, and does this walkthrough show one?
The lung point is the spot on the chest wall where a partially collapsed lung meets the chest wall again, so sliding appears and disappears in the same image as the patient breathes. In the original BLUE protocol data it is the finding that took the pneumothorax profile to 100% specificity. It is not demonstrated in this recording: the subject’s lungs are normal, sliding is present at every point scanned, and the recording is about recognising the normal picture well enough to know when it is missing.
Source: Lichtenstein DA, Mezière GA — Chest 2008, the BLUE protocol. Accessed September 5, 2026.
Provenance
Fuentes
- Lichtenstein DA, Mezière GA — Chest 2008, the BLUE protocol“Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol.” Chest 2008;134(1):117–125. The three-point protocol, the ultrasound profiles, and the accuracy figures quoted on this page. Accessed September 5, 2026.
- POCUS Certification Academy — A-lines and B-linesPoint-of-Care Ultrasound Certification Academy, Learning Library. Definitions of the pleural line, lung sliding, A-lines and B-lines, and the threshold at which B-lines become an abnormal finding. Accessed September 5, 2026.
- Bhoil R et al. — Signs and lines in lung ultrasoundJournal of Ultrasonography 2021. Reference description of the lung ultrasound artifact set, including the seashore and barcode patterns in M-mode. Accessed September 5, 2026.
- Stanford Medicine 25 — Lung UltrasoundStanford University School of Medicine. Teaching reference for the pleural line, A-lines, B-lines and the curtain sign at the lung base. Accessed September 5, 2026.
- ACEP Sonoguide — LungAmerican College of Emergency Physicians. Scanning technique and findings for the point-of-care lung examination. Accessed September 5, 2026.
- Página del producto Suresult D3UltraThe published attribute table for the device in this recording: the linear and convex frequency ranges, the four linear depth steps, the gain ceiling and dynamic-range steps quoted in the settings column above, and the imaging modes. Accessed September 5, 2026.
- Suresult channel — the video on this page“POCUS Lung Exam Made Easy | BLUE Protocol with Suresult D3Ultra Handheld Ultrasound”, published 12 October 2025. Duration 9:28. The transcript below is drawn from this recording. Accessed September 5, 2026.
Which probe does your chest work actually need?
Lung ultrasound asks two opposite things of a probe. The pleura is a centimetre down and wants the highest frequency you have; an effusion at the base is ten centimetres down and wants the lowest. A three-in-one head covers both from one device, and a dedicated pair covers both better for more money. Tell us the ward and the case mix and you will get a direct recommendation in one conversation — one probe, two, or neither.
