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Lung Ultrasound

We must keep in mind that LUS [Lung Ultrasound] is more affected by lack of specificity than lack of sensitivity. A LUS pattern showing absent lung sliding or multiple B-lines or a lung consolidation may be not enough to establish a specific diagnosis, since it can be linked to different pathologic conditions. Indeed, this limitation in specificity is a common feature of several diagnostic tools that we routinely interpret in daily clinical practice, from physical examination to EKG, from chest X-ray to more sophisticated instrumental findings. The power of these tools resides in the interpretation of signs when combined with each other at bedside, together with a consideration of the overall clinical picture. *How I do it: Lung ultrasound, 2014

Luna Gargani & Giovanni Volpicelli

Objectives

To reach the objectives for this module read the following text, watch the videos and finish the QUIZ.

Objectives LUS

  • Understanding the indication for focused exams when looking for hydronefrosis, gallstones/cholecystitis, and small bowel obstruction
  • Learning to orient the probe with the patient lying on their back on the stretcher according to the 8-zone exam protocol
  • Being able to evaluate pleural effusion and differentiate it from lung consolidation
  • Having basic knowledge about the sensitivity and specificity of different LUS findings and diagnosis

1. Introduction Lung Ultrasound (LUS)

Historically lung ultrasound (LUS) was a neglected area given perceived notions about the (non-)utility of the modality on air-filled structures. That has all changed in the last decades as Daniel A. Lichtenstein among others have shown that LUS is not only useful but also, a better adjunct than the stethoscope and (for certain diagnosis) the CXR exam with greater sensitivity as a diagnostic tool.

In this module we will cover the basic of lung ultrasound (LUS) and it’s application in the clinical setting.

As previously mentioned, the probe we use for assessing pleural effusion usually needs higher (in adults) depth thus excluding the linear probe, while the examining of lung parenchyma can be done with any of the probes, with the high frequency linear probe providing the best resolution and detail.

Lichtenstein’s own favourite (and many radiologists would agree with him) when it comes to probe choice is the microconvex probe: a mix between the phased array and curvilinear probe, it has a small footprint similar to the phased array optimal for navigating in between ribs while picture quality is similar to the curvilinear probe. Since most emergency departments (in Stockholm) do not provide ultrasound machines that come equipped with microconvex probes, for the intentions of this course the focus will be on how to do the exams with the three most common probes: the curvilinear, phased array, and linear probe.

LUS is, compared to the FAST exam, easier to learn when it comes to obtaining the different views as the RUQ and LUQ views are the same as in the fast exam and the rest is basically just looking at the space between two ribs. But it is, however, more difficult when it comes to understanding and evaluating pathological findings as many of the different signs we will address have a high sensitivity but lower specificity. Improvement in clinical interpretation of the signs takes experience and time, with high volumes of pathological patient exams needed for clinical improvement in LUS skills.

2. Zones & Orientation

For the purposes of this course we will focus our LUS on the patient in the emergency room lying with their back on the stretcher, when the patient is in this position it excludes partially some of the posterior sides of the lungs from the exam.

With the patient lying on their back on the stretcher our baseline LUS exam will include 8 zones (see B on the image above), four on each side: two windows on either side of the sternum, with the probe held at 90 degrees against the patient with the probe pointed towards the patients head (in a long-axis position), and two more posterior windows towards the stretcher obtaining the more cranial part of the RUQ and LUQ views on either side, and then moving further cranially just below the axilla of the patient (window 3 & 7 on the eight zone image above).

3. Vicki Noble LUS Lecture (42 min)

Lung ultrasound is a visual sport – looking at pathological findings in the clinical setting and building a memory palace of what looks like and defines A/B-lines, consolidations, and pleural effusions is the best way to learn the theoretical aspects of LUS for the starting bedside-ultrasound practitioner. For the purposes of this course we recommend that you start with the following two YouTube clips of a Vicki Noble lecture (2012) on LUS. Vicki Noble is, in our opinion, one of the best and most instructive teachers when it comes to Point of Care Ultrasound. The following lecture have been picked by us, among many, since Vicki gives, in approximately 42 minutes, the best foundation and emphasise the most important things to understand and keep track off for LUS beginners.

Part 1 – Lung Ultrasound with Vicki Noble

(start at 6:20 in, total run time from there: approx 12 min)

Part 2 – Lung Ultrasound with Vicki Noble (approx 30 min)

Once you’ve seen the two clips above you can keep reading the rest of this text and also do the required quiz at the end (mandatory).  There will be less time spent practicing LUS hands-on during the course since there is not much to look at in healthy individuals.

4. Pleural line

The apical positions in LUS are acquired by putting the probe at a 90 degree angle against the patients chest with the marker pointed cranially. The picture you’ll acquire will look something like this:
[Image credit: Abhilash Koratala]

All signs arise from the pleural line.
Lung ultrasound in the critically ill, 2014

Daniel A. Lichtenstein

Closest to the probe (top of image) where the probe connects with the skin, you’ll first se subcutaneous fat below the skin, then the pectoris major muscle, then below the two ribs a white line (marked with an orange arrow in the image above). That white line is the pleural line, and it should be moving with each breath, that movement equals lung-sliding (as covered in the E-FAST exam). The absence of movement could mean that a pneumothorax is present (more on that in the PTX section below).

In the image above the linear probe is used which gives us superior resolution compared to the curvilinear probe, but with a smaller footprint. In each view that we acquire when it comes to the apical LUS-views, we want two ribs to be present in the image if possible. One reason for this is: the pleural line will always be below the ribs, and having the ribs in view helps us with orientation and not mistaking some other line for the pleural line. However, in some individuals due to their anatomy and the space between ribs, and depending on the size of your linear probe, it can be difficult to acquire both ribs in the same image. In these cases the work around is finding one rib and sliding the probe gently in the space between ribs to evaluate that point in the lungs.

Identifying the pleural line is important not just for evaluating the presence of lung-sliding but also for other pathologies, as the quote from Lichtenstein above says: “All signs arise from the pleural line”. The pleura line provides us with so much information, not just if the pleura is moving (sliding) or not. Is the line thick or thin? Is it rugged? Are there b-lines present? Are there sub-pleural consolidations present? We will look closer at all of the mentioned findings in the following sections below.

5. A-lines

A-lines are a reverberation artifacts that arise when the ultrasound waves bounces between the probe and the visceral-parietal pleural interface, causing the lines to appear with equal distance below the pleural line and fatigue with depth. They appear during the insonation of an aerated lung *. A-lines are not a pathological finding and are generally found in healthy and aerated lungs, however note that the absence of A-line does not indicate pathology either as they are not always present. Also note that the presence of A-lines does not rule out a PTX.

6. B-lines

[Image credit: Abhilash Koratala]

B-lines are hyperechoic vertical lines (see image above) arising from the pleural line, extending indefinitely, erasing A-lines (when present), and moving in concert with lung sliding. B-lines are an artefact that appears when patients present with sub-pleural thickened interlobular septa *. B-lines are present in alveolar-interstitial syndromes and absent under normal condition, however few B-lines can be found under normal conditions when the patient is lying on their back on the stretcher due to atelectasis acquired over time.

For B-lines, in any given ultrasound window, to be judged pathological they need to be:

  • ≥ 3 B-lines present
  • Vertical lines that arise from the pleura all the way dow
  • They need to go down at least to (approx) 16 cm dept
  • They should erase the A-lines (when present)

Sometimes shorter horizontal lines can be observed arising form the pleural line, often only a couple of cm at most in depth. These are sometimes called comet tails or Z-lines, and have been described as artifacts without any significance *.

B-line patterns can be present due to the following pathologies:

  • Pulmonary edema
  • Pneumonia
  • Diffuse interstitial lung disease
  • Acute respiratory distress syndrome

B-lines are usually not present in the following pathologies:

  • Reactive airway disease (such as asthma and COPD)

Consolidation

[Image credit: Durant A & Nagdev A, ‘Ultrasound Detection of Lung Hepatization’, 2010.]

Lung consolidation can be detected by ultrasound and can present as a “hepatization” of the lung, i.e. the lung appears to look like the liver with a relatively hypoechoic heterogeneous echotexture (see image above). Note the “white dots” that are marked in the image above as hyperechoic bronchogram, they are analogous to the same phenomenon seen on chest radiographs, and appear due to air trapped within the consolidation. Air bronchograms can be static or dynamic, the importance of this is disputed but a general rule of thumb is: that dynamic air bronchograms have a high sensitivity and positive predictive value for pneumonia while static air bronchograms tend to represent resorptive atelectasis *. As always the clinical picture is of greater importance than identifying whether the white dots within the hepatized lung are moving or not. Consolidation can be found anywhere in the lung, but is usually most commonly identified in the RUQ/LUQ views with the patient lying with their back against the stretcher.

Sub-plural consolidation

[Image credit: unknown source]
The image above is a medial-apical view on a patient with more severe Covid-19 pneumonia. Observe the pleura line that is irregular, rugged and thickened, and also the small hypoechoic black spaces between the pleural line and the chest wall that represent small subpleural consolidations. They correspond to findings in CT-scans and chest x-rays of of peripheral subpleural consolidations, a common clinical finding in patients with severe Covid-19 pneumonia *.
[Image credit: Pocus Atlas]

Subpleural consolidations can be more discrete with less pronounced hypoechoic spots between the pleura and chest wall and a pleural line that is less irregular/thickened/rugged. They can also be more pronounced as the image above with a larger consolidation containing air bronchograms. Notice that there seems to be, on the image above, both pleural effusion present (the hypoechoic/ black space between the pleural line and chest wall) and lung consolidation (the area below the hypoechoic mass with uneven boundaries containing air bronchograms).

As always with ultrasound the clinical presentation is key in helping you evaluate your ultrasound findings. LUS can be used both as a diagnostic tool as it has higher sensitivity for pneumonia than chest x-ray, but also as a tool for measuring progress over time for admitted patients. Measuring the progress or regression of subpleural consolidations can help assist you when examining the patient bedside. It is an addition to the stethoscope and other clinical adjuncts that you have at your disposal such as lab tests, CT and chest x-ray.

8. Pleural effusion

Pleural effusion and the spine-sign was covered to some extent previously in the E-FAST chapter. In short, when looking at the intersection between diaphragm, spine, and liver/spleen depending on if you’re looking at the patients left or right side you might see the spine extending beyond the diaphragm due to hypoechoic fluid being present. However, spine-sign alone isn’t indicative of pleural effusion. As mentioned above hyperechoic lung consolidation can also visualize the spine in the patients thorax beyond the diaphragm. Similarly the spine-sign can be obtained if a large enough lung tumour is present where there should be aerated lung.

It can be difficult differentiating between lung consolidation and a solid hyperchoic mass such as a tumour. For the bed-side ultrasound practitioner the LUS spine-sign helps in the clinical determination of: if there is an area of non-aerated lung and if that area appears an/hypoechoic (as with fluid) or whether that area appears iso/hyperechoic (as with lung consolidation and/or solid mass of some kind).

9. PTX

We covered the basic when it comes to a pneumothorax (PTX) and lung-sliding in the M2: E-FAST section. In short: the absence of lung-sliding should make you suspect a pneumothorax. If you’re having a difficult time evaluating whether there is lung-sliding present or not, the following steps might help with your evaluation:

  1. Compare with the other side/lung.
    • The advantage of looking for a PTX is that you always have a contralateral side to compare with. This is always the first step when you’re not sure whether lung sliding is present or not. 
  2. Switch to the linear probe (if you are using the curvilinear one).
    • Switching to the linear probe will give you a higher resolution image and could help in your evaluation. Also decreasing the gain (whether you are using a linear or curvilinear probe) can help bring the pleural line into better focus. 
  3. Ask the patient to take a couple of deep breaths.
    • Lung sliding is more notable in correlation with the patient breaths. 
  4. Is there any B-lines present?
    • If there are any B-lines or comet tails present, there can’t be a PTX present since they are artefacts created by the underlying lung tissue.  
  5. Attach heart electrodes to help you determine if lung-pulse is present or not.
    • If you see a correlation of movement with each heart beat at the pleural line, this is due to vibrations from the heart as it pumps, also called a lung-pulse. If a pneumothorax is present there is no connection with the outer pleura and the lungs, and therefor the heart pulse should not be present either.      

M-mode & PTX

[Image credit: Lobo et al, ‘Thoracic Ultrasound’, 2013.]

The steps mentioned above are usually enough to help determine if lung-sliding is present or not. However, you could also put on the M-mode with the 2d cursor aimed at the middle of the pleura line to help with your evaluation. In a lung without pneumothorax and with lung-sliding present the image should be something that has been described as a “seashore sign”: with the top of the image containing straight lines (depicting the non-moving chest wall) and the bottom half depicting a sand beach looking variance (depicting a moving pleural line). If pneumothorax is present and, therefor, lung-sliding absent, the image should resemble straight lines all the way through, also called the “barcode” sign. See the image above for an illustration of this phenomena. Using M-mode to decide whether lung-sliding is present is used less and less frequently as ultrasound machines have gotten better, and, also, as the other methods mentioned above will usually be sufficient enough. 

Lung Point & PTX

[Image credit: REBELEM]

Lung point is the space where air-filled lung can found in a patient with PTX, usually found when moving the probe down towards the stretcher (lateral/posterior part of the patient), as the air filled PTX rises to the anterior of the chest with the patient lying on their back (see image above). This sign can sometimes be found if the PTX is incomplete and part of the lung is still inflated. The presence of a lung point has been shown to have a sensitivity of 66% to 79% and a specificity of 100% for PTX * *. The best method for locating a lung point is by shifting the linear probe 90 degrees from the usual long axis position to a short axis, and moving it horizontally between the ribs so more of the pleural line can be evaluated. Usually, the larger the (incomplete) PTX, the more lateral/posterior you’ll need to slide with the probe (towards the stretcher).

10. Clinical profiles

Lung ultrasound in combination with basic cardiac bedside ultrasound can help with putting your findings into a diagnostic context. Decreased cardiac function with bilateral b-lines can be indicative for CHF while an isolated window of B-lines in specific lung section can be indicative for pneumonia. There are of course a plethora of other clinical symptoms and adjuncts that we interpret in the emergency room that will help you with making sense of the LUS findings. A more systematic approach to different clinical LUS profiles is described below in the BLUE-protocol.

11. Protocols

[Image credit: Lichtenstein. ‘BLUE-Protocol and FALLS-protocol’, 2015.]
[Image credit: Lichtenstein. ‘BLUE-Protocol and FALLS-protocol’, 2015.]

When it comes to clinical lung ultrasound profiles, there is a flow chart called the BLUE-protocol by Lichtenstein that we won’t cover in length in this course, but that still deserves mentioning. In the BLUE-protocol pathophysiologic “profiles” based on standardised patterns of artifacts are built and a tentative pathophysiologic basis for each kind of acute respiratory failure proposed (se image above). The aim of the BLUE protocol is to suggest a diagnosis with a target overall accuracy of at least 90% or slightly above, when LUS is performed with a relatively simple and cheap ultrasound machine, and needing only a single universal probe (the microconvex probe mentioned earlier).

The different profiles mentioned in the BLUE-protocol are:

  • A-profile: anterior lung-sliding with A-lines
  • A’-profile: A-profile with abolished lung sliding
  • B-profile: anterior lung-sliding with lung rockets
  • B’-profile: B-profile with abolished lung sliding
  • A/B-profile: unilateral B lines, contralateral A-lines
  • C-profile: any anterior lung consolidation (a thick, irregular pleural line is an equivalent)

12. Evidence

The page The POCUS Atlas has created a page were they composed some of the most important studies and reviews when it comes to LUS and the sensitivity and specificity of different diagnosis. Lung ultrasound shows some great numbers when it comes to sensitivity and specificity, especially when compared to CXR, and has the potential to, over time, help increase accuracy and decrease the use of CXR.

13. LUS Pitfalls

  • For visualizing a crisp pleural line it helps if the probe is angled perpendicularly against the pleura, if the image is not optimal: try fanning the probe gently with small movements to see if the image quality improves.
    If you’re having difficulties visualizing A-lines or
  • B-lines it could be due to software that is optimized for artifact reduction. Try changing to lung-protocol when available, or changing probes.
  • Absence of lung-sliding can be due to other causes than a PTX and further diagnostics might be needed.

14. Summary

Lung ultrasound is a relatively easy exam to learn and perform with high sensitivity for a number of clinical diagnosis. However it takes time to learn to interpret the findings in LUS and, as always, clinical context is important for the clinical assessment of each patient.

15. QUIZ

Question 1


Choice B is correct!
They may rarely occur due to impedance mismatch between the pleura and thickened interlobular septae.

Choice E refers to the A-line artifact.
Choice A: While B-lines can be seen in well-aerated lung, they are associated with increasing pulmonary congestion.
Choice D: The presence of a B-line pattern rules out a pneumothorax at that point. Loss of normal lung sliding and a stratosphere sign on M-mode ultrasound is indicative of pneumothorax.
Choice C: B-lines by consensus definition extend all the way to the edge of the field without fading. Z-lines are similar radially oriented lines which do not extend all the way to the edge of the field.

Choice A is incorrect!
while B-lines can be seen in well-aerated lung, they are associated with increasing pulmonary congestion. 

Choice C is incorrect!
B-lines by consensus definition extend all the way to the edge of the field without fading. Z-lines are similar radially oriented lines which do not extend all the way to the edge of the field.

Choice D is incorrect!
The presence of a B-line pattern rules out a pneumothorax at that point. Loss of normal lung sliding and a stratosphere sign on M-mode ultrasound is indicative of pneumothorax.

Choice E is incorrect!
E refers to the A-line artifact.

 


Question 2

Choice C is correct!
Choice C is correct! In the emergency department, lung ultrasonography has higher clinical accuracy than clinical workup, chest radiography, and natriuretic peptides for differentiating acute decompensated heart failure from other etiologies of acute dyspnea. Source: Meta-Analysis 2016 (57 studies, n=17 893).

Incorrect!
Try again.

 


Question 3

Choice A is correct!
Pulmonary edema, diffuse interstitial lung diseases, acute respiratory distress syndrome, and multifocal pneumonia all produce a B-line pattern, whereas asthma and COPD produce an A-line pattern.

Incorrect!
Try again.

 


Question 4

Choice B is correct!
Well done.

Incorrect!
Try again.

 


Question 5

Choice E is correct!
Well done.

Incorrect!
Try again.

 


Question 6

Choice D is correct!
Well done.

Incorrect!
Try again.

 


Question 7

<img src="https://colligoacademy.se/wp-content/uploads/2022/09/subpleural-effusions.gif"

Choice D is correct!
Well done.

Incorrect!
Try again.

 


Question 8

Choice A is correct!
Well done.

Incorrect!
Try again.

8. Further Reading

Books

  • Noble. ‘Manual of Emergency and Critical Care Ultrasound’. 2nd Edition. 2011.
    • Ch. 9 Respiratory Ultrasound
  • Dawson & Mallin. ‘Introduction to Bedside Ultrasound – Vol 1’. 2013.
    • Ch. 4 Lung
  • Soni et al. ‘Point-of-Care-Ultrasound’. 2nd Edition. 2020
    • Ch. 7 Lungs and Pleura
    • Ch. 8 Lung and Pleural Ultrasound Technique
    • Ch. 9 Lung Ultrasound Interpretation
    • Ch. 10 Pleura and Diaphragm
    • Ch. 11 Lung and Pleural Procedures
    • Ch. 12 Dyspnea and Pulmonary Embolism

Radiopaedia

Web Pages MISC

.

References

[Version 2.0 — Last updated 2022-07-28 — Status: Active]
[Version 2.0, update 2022-07-01: moved QUIZ from google docs to in-page.]