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Acute dyspnea is a common symptom in emergency departments (ED), intensive care units (ICU) and internal medicine departments. Usually, the approach to the patient with dyspnea, in addition to the history and physical examination, is based on blood gases, laboratory tests and chest radiography.
The literature shows that approximately 20% of patients presenting in ED with dyspnea are misdiagnosed or receive a wrong diagnosis and inappropriate therapy with negative prognostic consequences: the 30-day mortality rate of these patients is 8%-13%.1,2
Chest X-rays (CXR) is currently the first diagnostic imaging used in patients with acute respiratory symptoms but in this contest, clinical lung ultrasound (LUS) bedside has gained increasing importance.3
Clinical LUS is defined like an ultrasonography performed at the point-of-care from the physician integrated with the patient's physical examination.
It is well demonstrated that this approach, in dyspnoic patients, could rapidly differentiate between “cardiac” and “respiratory” etiologies reducing the need of further diag-nostic tests.4
While the use of clinical LUS at the point-of-care in the last 20 years has attracted the attention thanks to the use of portable machines and pocked sized devices5 up to date its use still does not seem to be defined in a sufficiently systematic way, underestimating its real potential. It still remains underused and this tendency could be explained by the lack of standardized training facilities and the lack of high-quality evidence-based guidelines on this technique.6,7
Clinical LUS has several advantages compared to chest radiography such as efficiency, speed, safety, repeatability, low costs, it is independent of patient's breath-hold limitations, free from ionizing radiation, can be performed in real-time at the bedside, can be used safely in pregnant women, has immediate availability of results.8
Ultrasound is limited in extremely obese patients, in case of subcutaneous emphysema or skin disorders are present. Another limitation of LUS is the observer- dependent nature.
On the other hand, the learning curve is fast.9,10
It represents a valid support to physical examination as shown by D. Lichtenstein et al: chest auscultation performed alone was detected successfully 61% of pleural effusions, 36% of consolidations, and 55% of alveolar-interstitial syndromes.11
LUS seems to be at least as accurate as CXR, with a higher sensitivity for pulmonary edema, pneumothorax, pneumonia, and free pleural effusion.12-14
In a systematic review and meta-analysis, Staub et al15 evaluated 11 017 titles and abstracts screened, involving 25 studies. Fourteen studies assessed pneumonia (n = 1867 patients), 14 assessed acute heart failure (n = 2778 patients), and four studies assessed exacerbation of COPD or asthma (n = 527 patients): in patients suspected for pneumonia, LUS showed high sensitivity and specificity in detecting consolidations. In acutely dyspnoic patients LUS showed sensitivity of 0.90 (95%) and specificity of 0.93 (95%) for acute heart failure, whereas B-profile had sensitivity of 0.93 (95%) and specificity of 0.92 (95%) in detecting modified diffuse interstitial syndrome. The sensitivity of US using B-lines to diagnosis acute cardiogenic pulmonary edema (ACPE) was 94.1% (95%) and the specificity is 92.4% (95%) in patients with a moderate to high pretest probability for ACPE.16
There is a linear correlation between the number of B-lines and the degree of extravascular lung water. Decompensated congestive heart failure can be difficult to differentiate from ACPE and POCUS can play an important role.
Marini et al, to underline the value of LUS, have shown the higher LUS sensitivity and specificity compared to CXR in 4 frequently encountered pathological conditions like: pleural effusion (LUS sensitivity 92% and specificity 93% vs CXR sensitivity 39% and specificity 85%), pneumonia (LUS sensitivity 95% and specificity 90% vs CXR sensitivity 77% and specificity 91%), pneumothorax (LUS sensitivity 87% and specificity 99% vs CXR sensitivity 46% and specificity 100%), pulmonary edema (LUS sensitivity 88% and specificity 90% vs CXR sensitivity 73% and specificity 90%).17
Another study concerning atelectasis, showed a high sensitivity and specificity of lung pulse, respectively 93% and 100%. About pleural effusion, the sensitivity was 94% and specificity 98% compared to CXR (sensitivity 51%, specificity 91%) as previously demonstrated in their meta-analysis.18 In relation to pneumothorax, LUS showed a sensitivity of 78.6% (95%) and a specificity of 98.4% (95%). The absence of lung sliding at a point, followed by the demonstration of the lung point had a sensitivity of 95.3% and a specificity of 91.1% to detect pneumothorax.19
Several ultrasound signs are connected to a high specificity for pulmonary embolism (PE).20 Considering that the proportion of confirmed PE can be expected to be 10% in a low-probability population and 65% in a high-probability population, a hypoechoic pleural-based lesion confirmed from LUS would yield a positive predictive value for the diagnosis of PE of 41.7% and 92.3% respectively.
Moreover, it was demonstrated that LUS is superior to CXR for diagnosing pneumonia in the ICU settings: sonographic consolidation was highly specific but moderately sensitive for pneumonia21; during SARS-CoV-2 pandemic use of LUS underlined its pivotal role.22-24
However, the use of LUS had a limited influence on 30-day and in-hospital mortality and had no relevant effects on the 30-day re-admission rate.25,26
Furthermore, a recent study has emphasized how there are many lung alterations related to heart failure and lung ultrasound is an increasingly widespread tool since it is sensitive, repeatable and safe both for the diagnosis and mana-gement of heart failure.27
Another study showed that in clinical scenarios of decompensated heart failure, LUS and CXR are the most used diagnostic tools and, although LUS does not fully replace CXR, it may be of great help in the emergency setting when a prompt diagnostic evaluation of dyspneic patients is requested and for monitoring clinical evolution too.28
In conclusion the use of an integrated LUS at the point-of-care can shorten the time needed to formulate a diagnosis improving differential diagnosis,29,30reduces the time to treatment with an higher rate of receiving appropriate management in the first hours after arrival at the ED, decreasing length of stay in ICU compared to conventional approaches,31minimizing the number of radiological and laboratory tests and optimizing the use of financial resources, even more so in countries with reduced economic resources.32
This approach should be considered a standard and not only as a supplementary tool when standard diagnostic measures fail.33 It represents a valid extension of the physical examination26 in all patients suffering from acute onset dyspnea. LUS at the point of care34 may represent the first accurate diagnostic approach to the patient with dyspnea in emergency departments, helping stratifying patients who should undergo a second-level diagnostic test.
