Lung ultrasound for evaluation of dyspnea

Abstract

However, in the emergency setup, time is a crucial commodity. One of the principles of LUCI states that life-threatening disorders usually have an extensive projection. On this premise, Lichtenstein [1] defined six BLUE-points, much like the standard electrode placement in electrocardiogram (ECG), allowing a simplified, quick and standardized technique for evaluating a critically ill patient at the bedside. There are three BLUE-points (Figure 3), 2 on the anterior chest wall (upper & lower BLUE point) and 1 located semi posteriorly (posterolateral alveolar and/or pleural syndrome [PLAPS] point). This allows the detection of PLAPS, i.e., consolidation and/or pleural effusion. Although these points are standardized, the protocol allows for operator flexibility. The first step in performing lung ultrasound is localizing the “bat-sign” (Figure 4) [1]. This is an important landmark and must be visualized before analyzing any artifacts.

Figure 3. Localizing the bedside lung ultrasound in emeregency (BLUE) points [7]. (A) The radiologist first compares their hands with the patient's and places one hand just below the clavicle with fingertips at the midline. The “upper BLUE point” is located at the root of the middle and ring fingers. The other hand is applied just below the upper one, excluding the thumb. The “lower BLUE point” is located in the middle of the palm of the lower hand with the inferior edge of the little finger indicating the “phrenic line.” (B) The “posterolateral alveolar and/or pleural syndrome (PLAPS) point” which lies at the intersection of the posterior continuation of lower BLUE point and posterior axillary line, is used to scan the posterior lung zones in a critically ill patient in supine/semi-recumbent position. It is best performed with a small footprint probe (C, D) which is held like a tennis racket, placed perpendicular to the PLAPS point, and directed as cranially as possible for a wider scanning window.

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The BLUE protocol [1] provides lung ultrasound profiles with an algorithmic approach to assist in diagnosis of 6 common acute conditions causing dyspnea: pneumothorax (A’ profile), pneumonia (C profile, AB profile, B’ profile and A-no V-PLAPS profile), pulmonary edema (B profile), acute exacerbation of chronic obstructive pulmonary disease (COPD)/asthma (A-no V-no PLAPS profile), and pulmonary embolism (A-V profile).

The A-profile is defined by the presence of both lung sliding and A-lines on anterior scans, bilaterally. Sometimes one or two B-lines with lung sliding may also be seen and are also included under A-profile. The pleural line is a hyperechoic, nearly horizontal line visualized <1 cm deep to the ribs. It is constituted by the parietal and visceral pleura which are not normally seen separately and indicates the interface between the soft tissues of the chest wall and the lungs. The normal physiological movement of the lungs results in sliding of the visceral pleura against the motionless parietal pleura resulting in a twinkling, to-and-fro motion called “lung sliding” [8]. On M-mode, the “seashore” [8] sign is demonstrated (Figure 5).

The A-profile can be used to diagnose three etiologies of dyspnea (Figure 6). Pulmonary embolism, pneumonia, and COPD/asthma. Firstly, history and clinical examination findings are taken into account while performing a sequential venous analysis to look for thrombosis. If thrombosed veins are visualized, a diagnosis of pulmonary embolism can be suggested. The presence of subpleural consolidations adds to the diagnostic value. If veins are not thrombosed, the PLAPS point is assessed. If pleural effusion and/or consolidation are detected, a diagnosis of pneumonia can be made. In absence of PLAPS, the most likely diagnosis is an acute exacerbation of COPD/asthma (Figure 7).

The presence of three or more B-lines in one longitudinal scan, disseminated to the anterior chest wall bilaterally with preserved lung sliding is called the B-profile. One must carefully assess a vertical artifact before calling it a B-line. The following are the features of a B-lines (Figure 8) as described by Lichtenstein [7]: (1) B-line is a comet tail artifact. (2) It always arises from the pleural line. (3) Always moves in synchrony with lung sliding. (4) Almost always long, spreading out without fading to edge of the screen. (5) Almost always erases A-lines. (6) Almost always hyperechoic.

Diffuse interstitial syndrome (Figure 9) is an ultrasound diagnosis defined by presence of multiple (three or more) B-lines in more than one scanning zone in the anterolateral chest wall, bilaterally [10]. In the critically ill, diffuse interstitial syndrome is almost always due to pulmonary edema, either hemodynamic (fluid overload or cardiogenic) and permeability induced (acute respiratory distress syndrome [ARDS]/post-infectious, etc.). The utility of B-lines in diagnosis and follow up of Interstitial lung diseases has been established in studies by several authors including Reissig and Kroegel [11], Gargani et al. [12], and Copetti et al. [13]. Reissig and Copetti [14] stated that appearance of the pleural line can be used as a criterion to differentiate pulmonary edema from Interstitial lung disease, with a regular pleural line seen in pulmonary edema. Buda et al. [15] defined several criteria for pulmonary fibrosis on lung ultrasound based on pleural line abnormalities including irregularity, tightening, fragmentary nature, blurring and thickening of the pleura line. Furthermore, Gargani [16] described the utility of lung ultrasound in differentiating pulmonary edema from ARDS on the basis of distribution of B-lines—homogenous, diffuse distribution is seen in pulmonary edema in contrast to non-homogenous distribution with areas of sparing noted in ARDS/acute lung injury. The latter also included additional sonographic findings like pleural alterations and consolidations of varying sizes.

After establishing the A’ profile, the next step to confirm the diagnosis of pneumothorax is to detect the “lung point” sign (Figure 10) [19], which occurs at the border of pneumothorax due to the sliding lung intermittently coming into contact with the chest wall during inspiration. This is the confirmatory sign for establishing a diagnosis of pneumothorax (Figure 11) and helps in determining its size, which is important for clinical decision-making, as larger pneumothoraces are more likely to require thoracostomy. On M-mode, this sign is translated as alternating “seashore” and “stratosphere” patterns appearing over time when the probe is kept at a particular location. The more lateral or posterior the “lung-point sign” is identified, the larger the pneumothorax. According to Lichtenstein [1], the “Lung-point sign” is 100% specific for pneumothorax but with a relatively low sensitivity of 66% and is not seen in cases of total lung collapse. Various authors [20-22] have found that lung sliding is absent in many cases other than pneumothorax, including pleural effusions, ARDS, large consolidations, pulmonary fibrosis, pleural adhesions, atelectasis, right mainstem intubation, and phrenic nerve paralysis. Thus, lung sliding when used alone has a low specificity.

PLAPS (A-No V-PLAPS Profile) & Pneumonia (C, A/B & B’ Profile)

In the BLUE protocol, the terms used for lung consolidation are “Pneumonia” for anterior consolidation and posterolateral alveolar/pleural syndrome (PLAPS) for consolidation and/or pleural effusion in posterolateral lung zones. In the BLUE protocol [1], pneumonia is diagnosed by four profiles (Figure 12), namely C profile, AB profile, B’ profile and A-no V-PLAPS profile. Anterior consolidation is designated a “C-profile” (Figure 13) while posterolateral consolidation in a patient showing A-profile (lung sliding and A-lines) anteriorly is designated a “A-no V-PLAPS” profile (Figure 14). Unilateral lung-rockets are designated “A/B profile.” Diffuse, bilateral B-lines with loss of lung sliding is designated a “B’ profile.”

Four patterns of consolidation were described by Lichtenstein [1] to diagnose pneumonia. These included “non-translobar consolidation,” “translobar consolidation,” small subpleural consolidation identified by “C-line” and unilateral lung rocket pattern. To identify the “non-translobar” type of consolidation (Figure 15), presence of associated pleural effusion is first looked for by evidence of a regular lung line. This is done to avoid misdiagnosing a consolidation for an effusion. Traditionally, the diagnosis of pleural effusion is based on visualizing an anechoic/hypoechoic collection. This criterion is not advocated by the BLUE protocol, especially in critically ill patients with life-threatening collections like hemothorax and pyothorax and in challenging cases where difficulty in examination might create “parasite echoes” as described by Lichtenstein [7]. In the BLUE protocol, Lichtenstein [1] described the “lung line”, “quad sign” and “sinusoid sign,” as criteria for diagnosis of pleural effusion, disregarding the echogenicity of the collection (Figure 13).

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