Lung Ultrasound in the COVID-19 Pandemic.

Lung ultrasound (LUS) is one of the most important and innovative applications in emergency and critical care medicine for the management of critically ill patients. Ultrasound has been widely used in the COVID-19 pandemic as an extremely reliable technique and has proved to have a key role in the diagnosis and monitoring of patients with acute respiratory failure. The diagnostic accuracy of LUS is higher than chest X-ray and similar to computed tomography, which is considered the gold standard. COVID-19 pneumonia has some distinctive ultrasonographic signs but not pathognomonic, and LUS significantly improves the management of COVID-19 patients speeding up the diagnostic path. The examination is bedside; reduces the risk of contamination, avoiding mobilization of the patients; cuts down the amount of radioactive exposure; and gives real-time answers to many diagnostic and therapeutic doubts. Finally, the instruments are small and the scanner and the probes can be protected from contamination easily. Copyright:

INTRODUCTION

Lung ultrasound (LUS) is one of the most important and innovative applications in emergency and critical care medicine, and its use has significantly changed the management of critically ill patients.[1234]

Ultrasound has grown more relevant in the last years with the availability of new, small, handheld machines that can be carried to patients' beds and installed in different settings, both in hospital departments (emergency medicine, cardiology, internal medicine, pneumology, geriatric, infectious disease, surgery, and intensive care unit) and out of hospital on ambulances or helicopters.

Ultrasound has been widely used in the COVID-19 pandemic as an extremely reliable technique.[56789] It can be adapted to all settings where patients are managed, gives rapid and clear answers, and is safe and cost-effective.

It reduces the amount of radioactive exposure, permits to monitor the lung lesions, gives real-time answers to specific clinical questions and an important feedback about the effects of pharmacological treatment and ventilation. In addition, the possibility to perform the examination bedside without moving the patient reduces the risk of contamination.

Hence, LUS is considered suitable for an extensive use in the COVID-19 pandemic, according to the original meaning of critical ultrasound: “when there is a dangerous performance gap between the patient status and the resources available for an appropriate decision-making and problem-solving.”[210]

METHODS

The technique could be extremely different according to the clinical conditions, which range from patients without any symptoms to those with severe respiratory insufficiency, and to the setting (emergency department, medical department, and intensive care unit).[13]

Patients with a suspected or confirmed COVID-19 infection are usually placed in a supine position or seated on the bed in order to examine the posterior and basal areas of the lungs.[1112]

Those with severe respiratory distress syndrome or treated with continuous positive airway pressure (CPAP) or a noninvasive ventilation (NIV) are usually placed in a supine position with an elevation of the chest of 30°–45°, reducing the possibility to scan the posterior regions. Collaborative patients can be slightly turned on the right and left sides using a pillow or a rolled-up blanket.

On the other side, the anterior areas are hidden when “the prone swimmer position,” is used for prone position ventilation. The elevation of the shoulder with a pillow, as described by Uglade, forms a space to put the transducer and opens an important window toward the anterior parts of the chest.[13]

In terms of choosing the probe, LUS is usually performed with a 3.5 MHz convex transducer for the identification of the lung profile (A: dry; B: wet[14]), consolidations, and pleural effusions, with a high-frequency linear probe (7.5–12 MHz) for a more precise and accurate evaluation of the pleural line, lung sliding, and subpleural consolidations. Color Doppler function is sometimes useful for better characterization of lung consolidations.[12]

A suitable presetting of the scanner is mandatory, selecting the appropriate lung preset and gain, for the best visualization of the pleura and B-lines. If a lung preset is not available, the abdomen preset should be chosen.

The most comprehensive examination, in a patient with a suspected or confirmed COVID-19 infection, includes the 12-regions technique, which also permits to scan the posterior areas of the lungs [Figure 1].[31112]

Figure 1

The 12-regions technique in patients with suspected COVID-19 pneumonia

One of the methods that has been recently established worldwide[1112] suggests to divide each lung into six regions, which are generated by the intersections of the parasternal line (PSL), anterior axillary line (AAL), posterior axillary line (PAL), and paravertebral line (PVL) with the horizontal intermammillary line: regions 1 and 2 denote the anterior superior and anterior inferior areas; regions 3 and 4 represent the lateral superior and lateral inferior areas; and regions 5 and 6 represent the posterior superior and inferior areas.

The examination usually starts from the PSL searching for the lung sliding longitudinally, moves downward and laterally toward the AAL, PAL, and PVL; then, it is necessary to complete the scan with transversal and oblique scans, to prevent the posterior shadowing of the ribs. This panoramic examination of the chest is called “the lawn mower technique” [Figure 2].[1112]

Figure 2

Lung ultrasound sequence in the 12-regions technique

The operator must pay attention to protect himself/herself from the risk of contamination during the bedside examination of patients with suspected COVID-19 infection: an appropriate separation from the face of the patient must be guaranteed to prevent accidental contact with the infectious droplets that come from sneezes, cough, nebulizer, CPAP, and NIV; the use of individual protection devices is mandatory. Intubated patients might slightly reduce the risk of contamination because the airways are sealed by the endotracheal tube.

Finally, the ultrasound must be adequately prepared by covering both the machine and the probes with disposable protections and cleaned with an appropriate cleanser at the end of the examination.

SEMEIOTICS

COVID-19 pneumonia has some distinctive ultrasonographic patterns but not pathognomonic; these patterns can also be found in many other bacterial or viral pneumonia and in acute respiratory distress syndrome (ARDS) [Table 1].[141516]

Table 1

The ultrasonographic and computed tomography characteristics of COVID-19 pneumonia

Lung ultrasound	CT scan
Irregular or thickened pleural line	Thickened pleura
B-lines (rare, confluent, and multifocal)	Ground-glass aspects
Subpleural consolidations	Subpleural consolidations
Rare pleural effusions	Rare pleural effusions
Bilateral distribution	Bilateral distribution

CT=Computed tomography

The most important features can be sought in three lung landmarks:

Pleural line

Subpleural area

Costophrenic angle.

The most important finding in the COVID-19 pneumonia is the “B-line,” which may appear as isolated and nonhomogeneous vertical artifacts or as a storm of aggregated and fused lines in the “white lung” pattern; in the middle, there are all the intermediate clinical pictures of the interstitial syndrome [Figure 3].[41415]

Figure 3

Confluent B-lines in COVID-19 pneumonia

They start from the pleural line or from lung consolidations, in a way that resembles other interstitial pneumonia. Nevertheless, in COVID-19 pneumonia, a wide and bright B-line has been often observed, which looks like a “light beam” that switches on and off when the patient breaths.[9] Areas of a normal lung are usually next to pathological findings, and the “light beam” sign represents an early manifestation of a lung lesion [Figure 4].

Figure 4

The “light beam” effect

Pleural line is often irregular and thickened, and even short interruptions of the line are observed in correspondence with lung consolidations [Figures 5 and 6]. The distribution of these findings is irregular, patchy, and not homogeneous, and they should be scanned and studied with a high-frequency linear probe.[41415]

Figure 5

Irregular pleural line in COVID-19 interstitial syndrome

Figure 6

Interstitial syndrome with multiple B-lines, irregular pleural line, and subpleural mini-consolidations

Subpleural consolidations are another important pathological feature of COVID-19 pneumonia: they are mainly small, hypoechoic consolidations, located under the pleural line; they are usually identified in both lungs, have different shapes (triangular, circular, and stretched), and do not have any color-Doppler echo [Figures 5–7].[41415]

Figure 7

Subpleural consolidation with an interrupted pleural line

Larger consolidations are the ultrasonographic sign of pneumonia, which are often observed in the posterior areas, in severe and advanced lung disease, and caused by the high local inflammation. These lesions have nonhomogeneous echogenicity, B-line artifacts at the far-field margin, and both air and fluid bronchograms [Figures 8 and 9].[41517]

Figure 8

Subpleural consolidation with air bronchograms

Figure 9

Thickened and irregular pleural line with small subpleural consolidation

Small and thin pleural effusions can be found next to the lung consolidations, whereas either moderate or severe pleural effusions are not usually observed in COVID-19 pneumonia [Figure 10].[4141517]

Figure 10

Small pleural fluid collection

DIAGNOSIS, MONITORING, AND STRATIFICATION

LUS is an important and adaptable tool, and it represents the first step of the instrumental evaluation in a patient suspected of having COVID-19 infection. The triad of COVID-19's diagnostic pathway involves chest X-ray, computed tomography (CT) scan, and ultrasound.

LUS has demonstrated to be relevant and unique to rule in or rule out an interstitial syndrome; it has a high sensitivity and a moderate specificity, and the global accuracy is higher than that of the chest X-ray.[12]

The performance of ultrasound in COVID-19 infection resembles, in many situations and settings, a CT scan of the chest, which is considered the gold standard.

Although COVID-19 infection does not have a pathognomonic lung pattern, resembling other bacterial or viral pneumonia and ARDS, many studies have already demonstrated the capability of ultrasound to identify some typical lung features of COVID-19 pneumonia. The ultrasonographic and CT characteristics of COVID-19 pneumonia are described in Table 1.[141516]

On the other hand, COVID-19 has some lung characteristics that are completely different from those observed in a cardiogenic pulmonary edema, and the differences are summarized in Table 2.[12]

Table 2

Lung ultrasound differences between cardiogenic pulmonary edema and COVID-19 pneumonia

Cardiogenic pulmonary edema	COVID-19 pneumonia
Homogeneous interstitial syndrome	Nonhomogeneous interstitial syndrome
No “spared areas”	Spared areas
The absence of the “light beam” sign	The presence of the “light beam” sign
Normal pleural line	Thickened and irregular pleural line
Normal sliding	Normal sliding/reduced in advanced disease
Absence of consolidations	Small subpleural consolidations
Pleural effusions	Small or no pleural effusions

In addition, a new interesting role of ultrasound is gaining importance: the monitoring of patients and the estimation of prognosis. It can estimate short-term prognosis effectively; in particular, it has a high negative predictive value and it can identify early pleural and lung lesions and can predict worsening of clinical conditions.

When LUS is performed together with point-of-care echocardiography combined with the evaluation of inferior vena cava, it can also be used to monitor patients with COIVD-19 pneumonia in a step-by-step manner. It enables physicians to evaluate the effect of pharmacological and fluid therapy; to set CPAP, NIV, and ventilator properly; to monitor the effect of ventilation on alveolar recruitment; and to guide weaning from mechanical ventilator. This new trend is in tune with the guidelines published by the most important international scientific societies, which consider critical ultrasound a useful diagnostic tool and an efficient instrument for monitoring and guiding the management of critically ill patients.[31819]

In all these settings and situations, LUS maintains a high predictive value when it is strictly connected with all the other information that come from the patient's history, in particular the time related to the onset of the disease, physical examination, and laboratory and radiological findings.

CONCLUSIONS

LUS has all the features that make it a perfect, reliable, and adaptable instrument during the COVID-19 pandemic:

Cost-effective

High sensitivity

Good specificity

No radioactive exposure

Bedside

Reduced diagnostic time

Reduced patient movements, thereby lowering the risk of contamination

Prognostic capabilities

Bedside monitoring.

LUS has become a modern and effective operative example that can be exploited in the management of a major global emergency, like the COVID-19 pandemic, where there is a gap between the current needs and the available resources.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.