References

1. Volpicelli et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med (2012) 38:577–591 doi: 10.1007/s00134-012-2513-4
2. Dietrich et al. Lung B-line atrefacts and their use. J Thorac Dis (2016) doi: 10.21037/jtd.2016.04.55
3. Mohamed et al. Frequency of Abnormalities Detected by Point-of-Care Lung Ultrasound in Symptomatic COVID-19 Patients: Systematic Review and Meta-Analysis. Am. J. Trop. Med. Hyg., 103(2), 2020, pp. 815–821 doi:10.4269/ajtmh.20-0371
4. Al Deeb et al. Point of Care Ultrasonography for Diagnosis of Acute Cardiogenic Pulmonary Edema in Patiehs Presenting With Acute Dyspnea: A Systematic Review and Meta-analysis. Acad Em Med (2014) doi: 10.1111/acem.12435
5. Rihal CS, Davis KB. Ward Kennedy J, Gersh BJ. The utility of clinical, electrocardiographic, and roentgenographic variables in the prediction of left ventricularfunction. Am J Cardiol. 1995;75:220–3.
6. Fonseca C, Mota T, Morais H, et al. The value of the electrocardiogram and chest X-ray for confirming or refuting a suspected diagnosis of heart failure in the community. Eur J Heart Fail 2004;6:807–12.
7. Knudsen CW, Omland T, Clopton P, et al. Diagnostic value of B-type natriuretic peptide and chest radiographic findings in patients with acute dyspnea. Am J Med 2004;116:363–8.
8. Martingale, Noble and Liteplo. Diagnosing Pulmonary Edema: lung ultrasound versus chest radiography. EJEM (2013) DOI: 10.1097/MEJ.0b013e32835c2b88
9. Volpicelli et al. Bedside lung ultrasound in the assessment of the alveolar-interstitial syndrome. AJEM (2016) doi:10.1016/j.ajem.2006.02.013
10. Jones BP, Tay ET, Elikashvili I, Sanders JE, Paul AZ, Nelson BP, Spina LA, Tsung JW, Feasibility and Safety of Substituting Lung Ultrasound for Chest X-ray When Diagnosing Pneumonia in Children: A Randomized Controlled Trial, CHEST (2016), doi: 10.1016/j.chest.2016.02.643
11. Volpicelli et al. Lung ultrasound in diagnosing and monitoring pulmonary interstitial fluid. Radiol Med (2011) DOI 10.1007/s11547-012-0852-4

Summary 

• PoCUS is sensitive, specific, and reliable for the detection of interstitial disease
• PoCUS performs better than CXR in the identification of interstitial disease
• LUS findings of interstitial disease are characterized by B-lines which are sharp vertical projections arising from the pleural line, move with respiration and cross A-lines.
• The etiology of B-lines must be interpreted within the clinical context

Pitfalls

Lung ultrasound relies on artefacts generated by the pleural line, so the operator must ensure the probe is positioned perpendicular to the chest and pleural line to maximize visualization of these artefacts. An obliquely oriented probe can obscure the visualization of normal lung artefact.

Small, vertical projections from the pleural line that do not cross A-lines or project to the end of the screen are often seen in normal lung due movement at the visceral-parietal pleural interface. These artefacts are known as z-lines or comet tail artefacts and should not be confused with B-lines (figure 6).

Figure 6:  Z-line or comet tail artefact—small vertical line arising from the pleura that fades quickly and does not cross A-lines

It is also important to note, some areas of lung are difficult to access and image with ultrasound including the supraclavicular, scapular, axillary and peri bronchial areas.

What is NOT normal?

Interstitial syndromes of the lung include a variety of pathologic conditions that involve either localized or diffuse involvement of the lung. The thickened interlobular septa from fibrosis, edema or excess extravascular lung water result in a characteristic appearance on ultrasound.  In these conditions the air-filled alveoli and water-filled interstitium interact to create a reverberation artifact called B-lines. B-lines are characterized as (figure 4):

• Sharp, vertical lines
• Arising from the pleura and extending to the edge of the screen
• Move with respiration
• Erase A-lines

Figure 4:  Sonographic B-line

 

While one or two B-lines can sometimes be seen normally in dependent portions of lung or areas of interlobar fissures, when more than three are seen in one field of view they are considered pathological. In addition, when B-lines are seen diffusely in the chest in multiple fields of view, particularly in non-dependent areas they indicate pathology.

 

Quantifying B-lines

In the acute setting, a qualitative assessment of LUS findings is usually adequate. The number of B-lines on ultrasound correlates well with disease severity as well as response to therapy. In less severe diseases B-lines appear multiple and discrete, as disease progresses, they can become confluent giving a “white out appearance of the lung (figure 5). Studies have shown that B-lines rapidly resolve in response to treatment for heart failure and through the course of dialysis for those with ESRD [11]. In addition, B-lines and other abnormalities found in patients with viral pneumonia, ARDS and bronchiolitis resolve along with their clinical course [1,3].

 

Figure 5:  In severe disease B-lines coalesce and form confluent B-lines resulting in a “white out” appearance of the lung.

 

In non-critical patients a more careful assessment with quantification of B-lines can be useful for assessment and monitoring response to therapy. While beyond the scope of this module there are several techniques described to quantify B-lines.

 

Interpreting B-lines

Sonographic B lines have multiple causes including pulmonary edema, infection, ARDS, contusion, and fibrosis; US interpretation must occur within the clinical context. Focal B-lines with associated pleural line abnormalities or consolidation indicate pneumonia or contusion (video 2).

Video 2: Focal B-lines adjected to pleural irregularity with consolidation in bacterial pneumonia

 

Multifocal but patchy B-lines with spared areas can be seen in bronchiolitis, viral pneumonia, pneumonitis, contusion, ARDS and fibrosis—often along with pleural line abnormalities and/or small subpleural consolidations. Finally diffuse and homogenous B-lines with a regular pleural line is a pattern expected pulmonary edema or fluid overload (video 3) [2]. Generally, the patient’s history and clinical information can help guide the diagnosis improving the sensitivity and specificity of LUS in diagnosing specific etiologies.

 

Video 3: Diffuse and symmetric B-lines with a normal pleural line in a patient with congestive heart failure.

 

What is normal?

In normal lung, the pleura is easily visualized as ultrasound waves are deflected by aerated lung. Reverberation artifacts from the pleural line (secondary to the significant change in acoustic impedance at the pleural-lung interface) generate horizontally arranged artifacts called A-lines (figure 2). Other normal structures visualized are the rib and corresponding rib shadowing below, and at the base of the lung the double line of the diaphragm muscle (figure 3).

 

Figure 2: Normal lung with a-line reverberation artefact

Figure 3:  Normal lung base with the beginning of the diaphgram noted on screen right

What am I looking at?

It is first important to note the following normal anatomic structures and their sonographic appearance (video 1).

Chest wall:

• Most superficial structure
• Hypoechoic with irregular fascial lines

Ribs:

• Oval, hyperechoic periosteum
• Dark shadow behind

Pleural line:

• Hyperechoic horizontal line
• Runs between and deep to the ribs

Lung:

• Deep to the pleural line
• Uniform grey haze

 

Video 1: Normal lung anatomy

Indications

• Dyspnea
• Cough
• Monitoring for volume overload

 

Equipment

• Ultrasound machine
• High frequency linear probe (6-12 MHz) is most used, although a curvilinear may be better especially in older patients. A phased array probe may also be used.
• Gel

 

Technique

1. Position the patient: It is easiest to completely expose the thorax. LUS can be conducted with the patient in any number of positions; in the parent’s arms (helpful for posterior exam), seated on or lying in a stretcher (lateral decubitus can be used to examine the posterior chest).
2. Warm the gel if possible: Younger or sleeping patients may respond better if the gel is warmed. Consider warming the gel between your gloved hands and applying a layer of warmer gel to the chest.
3. Scan the patient:
   1. Set the depth to between 5 – 10 cm, choosing the shallowest depth that gives an appropriate image to maximize resolution.
   2. Orient the probe marker to the patients’ head and identify the pleural line deep to the ribs in the longitudinal orientation. Ensure the probe is perpendicular to the chest wall to give the clearest image of the pleural line possible.
   3. Scan the patient’s chest systematically: this can be done by dividing the chest into anterior and lateral areas and by investigating each zone superiorly and inferiorly (figure 1). Alternatively, you can choose to investigate each rib space by sliding the probe from cranial to caudal until the diaphragm is reached in each zone as you would in pneumonia, including the posterior zone (figure 2).
   4. For any abnormalities detected, the area should be investigated fully by sliding the probe along the rib space or changing the probe to a transverse view to scan in-between the ribs.

 

Figure 1: 8 zone technique for interstitial disease

 

Figure 2: Alternative technique similar to pneumonia

 

Tips:

• It may be easiest to position the child seated in a parents’ arms
• For lateral and posterior views lifting the arm or crossing arms in front of the body can allow greater access to the chest superiorly
• Consider warming the gel
• Consider the size of the patient when selecting a probe
• Consider using the “lung preset” if available on your US machine

Introduction

Point of Care Ultrasound (PoCUS) is the use of portable ultrasonography to answer specific, focused clinical questions at the bedside. It is an extension of both our clinical acumen and physical exam.

The most common initial test for the dyspneic patient is chest x-ray. Recently, growing evidence has shown that PoCUS can reliably detect interstitial edema or thickening with equal, if not better, sensitivity than CXR. While CT scanning provides the best test characteristics, it is impractical and comes with the cost of significant radiation.

Ultrasound images of normal lung show predictable artifacts. These artifacts are disturbed in disease states and can be readily differentiated by ultrasound.

 

Why Ultrasound?

Traditionally, it was the thought was that ultrasound would not be a useful modality for investigating lung pathology because air scatters ultrasound waves. However, lung pathology (i.e. viral pneumonia/pneumonitis, cardiogenic pulmonary edema, contusion, pulmonary fibrosis, ARDS) will often lead to edema and fluid accumulation in the intersitium and alveoli. If this fluid or thickening reaches the pleural line these pathologies can be seen on ultrasound. This is the case in most patients, particularly children who have smaller lungs. This is supported by an ever-growing body of evidence.

International evidence-based guidelines have been published which support the use of point-of-care lung ultrasound in investigating various pulmonary pathologies, including interstitial disease [1]. In fact, LUS far outperforms radiography in the detection of interstitial diseases including viral pneumonia/pneumonitis, pulmonary edema, and pulmonary fibrosis [1,2]. In COVID-19 patients, LUS far outperformed conventional radiography, performing nearly as well as CT while decreasing radiation exposure and patient movement within hospital [3].  A recent meta-analysis looking at the test characteristics of LUS for pulmonary edema found a pooled sensitivity of 94% and specificity of 92% [4]. The test characteristics of LUS are superior to that of CXR in the diagnosis of acute pulmonary edema with the sensitivity of CXR ranging from 14-68% and specificity of 53-96% [5-7]. Also appealing, LUS is easier to interpret than CXR and the inter-reader reliability is consistently higher as well [8]. While these are adult studies and the test characteristics need to be studied in children, it is well proven that LUS performs at least as well in the pediatric population.

Logistically, a typical bedside ultrasound looking for pulmonary edema will take less than 5 minutes [9]. While system implications have not been studied for those with interstitial syndromes, a recent RCT studying the use of PoCUS in the diagnosis of pneumonia showed a 30-60% reduction in the use of CXRs, as well as significantly shorted ED length of stay in those patients’ receiving ultrasound vs. CXR [10].  Similar benefits could be expected in those with interstitial syndromes.

References

1. Patel, G et al. Point-of-Care Cardiac Ultrasound (POCCUS) in the Pediatric Emergency Department. Clinical Pediatric Emergency Medicine. 2018. 19: 323-327. DOI: 10.1016/j.cpem.2018.12.009
2. Lanoix et al. A Preliminary Evaluation of Emergency Ultrasound in the Setting of an Emergency Medicine Training Program. Americal Journal of Emergency Medicine. 2000. 18:41-45. DOI: 10.1016/S0735-6757(00)90046-9
3. Mayron, R et al. Echocardiography Performed by Emergency Physicians: Impact on Diagnosis and Therapy. Annals of Emergency Medicine. 1988. 17: 150-154. DOI: 10.1016/S0196-0644(88)80301-9
4. Plummer, D et al. Emergency Department Echocardiography Improves Outcome in Penetrating Cardiac Injury. Annals of Emergency Medicine. 1992. 21: 709-712. DOI: 10.1016/S0196-0644(05)82784-2
5. Mandavia, D et al. Bedside Echocardiography by Emergency Physicians.  Annals of Emergency Medicine. 2001. 38: 377-382. DOI: 10.1067/mem.2001.118224
6. Ma, J et al. Prospective Analysis of a Rapid Trauma Ultrasound Examination Performed by Emergency Physicians. The Journal of Trauma: Injury, Infection, and Critical Care. 1995. 38: 879-885. http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=reference&D=ovftb&NEWS=N&AN=00005373-199506000-00009
7. Miller AF, Arichai P, Gravel CA, et al. Use of Cardiac Point-of-Care Ultrasound in the Pediatric Emergency Department. Pediatric Emergency Care. 2020 Oct. DOI: 10.1097/pec.0000000000002271. PMID: 33122503.
8. “Pericardial vs Pleural Effusion.” Temple Emergency Ultrasound, Feb 8 2018. https://www.templeemergencyultrasound.com/tips-tricks/2018/2/3/pericardial-vs-pleural-effusion

Summary

• POCUS can easily identify pericardial effusions with good sensitivity and specificity.
• Indications for performing PoCUS looking for pericardial effusion include blunt and penetrating trauma, chest pain, unexplained hemodynamic instability, or dyspnea.
• In the subxiphoid view free fluid is first visualized in the pericardium between the myocardium and liver.
• In the parasternal long axis, a pericardial effusion will be found between the heart and the descending aorta.