By Alice Chao, MD and Laleh Gharahbaghian, MD
In recent years, point-of-care (POC) lung ultrasound (US) has gained significant popularity as a diagnostic tool in the acutely dyspneic patient. Several studies have shown the efficacy of lung US in diagnosing pulmonary pathology, with increased sensitivity compared to that of chest x-ray in many cases. Numerous pathologies can be detected at the bedside with POC lung US. The sensitivity of US for diagnosis of pulmonary edema approaches 94% with a specificity of 92%.(1) Diagnoses of COPD, asthma, pulmonary embolism, pneumothorax, and pneumonia can also be made with POC lung US with a positive predictive value ranging from 83% to 100%.(2)
By evaluating 8 zones of the chest (picture 1) – 4 on each side (2 anterior and 2 lateral) – an assessment for various pathologies by examining the pleural line (sliding, thickness, regularity), the subpleural regions (presence or absence of echogenic changes), and whether there are A lines or B lines present (with the amount and location [focal versus diffuse] of B Lines assessed).
Figure 1 depicts a simple lung US flowchart.
Using the phased array probe at a screen depth of 16cm, and placing it in each of those 8 zones with small circular movements, the assessment of A lines and B lines can be done:
- Multiple repeating horizontal lines that are parallel and equidistant from the pleura (Fig 2_A Lines)
- This can be a normal finding in the healthy patient
- A lines may also be prominent in patients with atelectasis, asthma, COPD (positive lung sliding at pleural line), and pneumothorax (negative lung sliding at pleural line)
Figure 2 Figure 3
- Transient, hyperechoic vertical lines that extend from the pleura to the bottom of the screen at a depth of 16cm (Fig 3_ B line)
- Amount: Less than 2 B lines in any given region can be a normal finding; 3 or more B lines in any given region is pathologic
- Location: focal B lines may suggest pneumonia, whereas diffuse B lines in 3 or more zones on both sides of the chest suggests a diffuse alveolar interstitial syndrome such as pulmonary edema or ARDS
- Spared areas: With focal or diffuse B lines with spared regions of the pleura that lack B lines, a focal or bilateral pneumonia may be present or there could be signs of pulmonary embolism (focal, hypoechoic subpleural region) or cancer (focal or diffuse; hyperechoic)
Using the high frequency linear probe, the pleura may be evaluated for various pathologies:
- A thick pleural line may suggest findings such as pneumonia, ARDS, or fibrosis
- In addition, an irregular pleural line is pathologic and may suggest pulmonary fibrosis or pneumonia (Fig 4a,b)
- Subpleural region: (sub-pleural hypoechoic versus hyperechoic areas) Pulmonary contusion may exhibit pathology within the lung parenchyma (hyperechoic), but will usually have a normal appearing thin pleural line (Fig 5); Pneumonia will have a thickened pleural line (hypoechoic subpleura) (Fig 4b).
- Described initially in 2003 by Lichtenstein, et al., the lung pulse is characterized by absent lung sliding with the detection of underlying cardiac pulsation (Fig 6)
- This finding is a sign of complete atelectasis and can be observed before findings will be seen on chest x-ray
For the Emergency Physician (EP), bedside US can help to narrow the differential diagnosis in the acutely dyspneic patient who is too unstable to leave the department for further testing. It can also assess for fluid overload and whether a patient is fluid tolerant for resuscitative measures. Bedside lung US is easy to perform and can provide a wealth of information for the EP.
- Deeb MA, Barbic S, Featherstone R, et al. Point-of-care ultrasonography for the diagnosis of acute cardiogenic pulmonary edema in patients presenting with acute dyspnea: a systematic review and meta-analysis. Acad Emerg Med. 2014; 21(8):844-52.
- Lichtenstein DA, Meziere G. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: The BLUE Protocol. Chest. 2008;134(1):117-25.
- Lichtenstein DA. BLUE-Protocol and FALLS-Protocol: Two Applications of Lung Ultrasound in the Critically Ill. Chest. 2015;147(6):1659-70. doi: 10.1378/chest.14-1313. PubMed PMID: 26033127.
- Lichtenstein DA, Lascols N, Prin S, et al. The “lung pulse”: an early ultrasound sign of complete atelectasis. Intensive Care Med. 2003;29(12):2187-92.
- Manson W, Hafez NM. The Rapid Assessment of Dyspnea with Ultrasound: RADiUS. Ultrasound Clinics. 2011;6(2):261 – 276.
- Volpicelli G, Mussa A, Garofalo G, et al. Bedside lung ultrasound in the assessment of alveolar-interstitial syndrome. Am J Emerg Med. 2006;24(6):689-96.
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