Current Advances in Lung Ultrasound in COVID-19 Critically Ill Patients: A Narrative Review

Abstract

Lung ultrasound (LUS) has a relatively recent democratization due to the better availability and training of physicians, especially in intensive care units. LUS is a relatively cheap and easy-to-learn and -use bedside technique that evaluates pulmonary morphology when using simple algorithms. During the global COVID-19 pandemic, LUS was found to be an accurate tool to quickly diagnose, triage and monitor patients with COVID-19 pneumonia. This paper aims to provide a comprehensive review of LUS use during the COVID-19 pandemic. The first section of our work defines the technique, the practical approach and the semeiotic signs of LUS examination. The second section exposed the COVID-19 pattern in LUS examination and the difference between the differential diagnosis patterns and the well-correlation found with computer tomography scan findings. In the third section, we described the utility of LUS in the management of COVID-19 patients, allowing an early diagnosis and triage in the emergency department, as the monitoring of pneumonia course (pneumonia progression, alveolar recruitment, mechanical ventilation weaning) and detection of secondary complications (pneumothorax, superinfection). Moreover, we describe the usefulness of LUS as a marker of the prognosis of COVID-19 pneumonia in the fourth section. Finally, the 5th part is focused on describing the interest of the LUS, as a non-ionized technique, in the management of pregnant COVID-19 women.

Keywords: COVID-19 pneumonia; LUS score; critically ill patients; lung ultrasound.

Figure 1

Scope of lung ultrasound in patients admitted with acute respiratory failure and suspected COVID-19 pneumonia.

Figure 2

Probes used for lung ultrasound examination. (A). Convex probe, low frequency (3–5 Hz), preferred to explore deeper abnormalities. (B). Linear probe, high frequency (8–12 Hz), has a high superficial definition and low penetration capacity and allows better detection of superficial abnormalities with excellent images of the pleura and lung sliding.

Figure 3

BLUE Protocol chest areas. Three areas of interest to explore according to BLUE protocol U: The upper BLUE-areas is at the middle of a virtual hand placed along the clavicula. L: The lower BLUE-areas is at the middle of the palm of another virtual hand placed below the first one. PLAPS: The PLAPS-areas (PosteroLateral Alveolar and Pleural Syndrome) is placed in the horizontal continuation of the lower point in the posterior axillary line.

Figure 4

International Consensus Conference for point-of-care lung ultrasound areas. Four chest areas per side considered for complete eight-zone lung ultrasound examination (modified from Volpicelli et al. [5]). AAL: Anterior Axillary Line; PAL: Posterior Axillary Line; PSL: Parasternal line.

Figure 5

Six areas per hemithorax approach for LUS examination in ICU. Each hemithorax is divided into three areas, using anterior and posterior axillary lines (anterior, lateral and posterior). Each area is divided into two areas: superior and inferior. The LUS score is calculated on a total score of 36 (each area is evaluated as 0 to 3). ANT: Anterior; LAT: Lateral; POST: Posterior; SUP: Superior; INF: Inferior.

Figure 6

LUS score. Each chest area of interest must be evaluated from 0 to 3. The total score ranges from 18 (BLUE protocol, 3 areas of interest per lung) to 24 (ICC, 4 areas of interest per lung) or 36 (six areas per lung approach used preferentially in the ICU).

Figure 7

Basic signs of lung ultrasound in B- and M-mode, normal lung. (A) In B-mode, the red arrow indicates the pleural line (horizontal echogenic line under subcutaneous tissue). The pleural line can be observed moving with respiratory movement. The yellow arrows represents the horizontal A-lines. (B) The M-mode demonstrates normal pleura sliding: subcutaneous tissues above the pleural line do not move away or toward the probe and are represented as straight lines. The pattern below the pleura is an artifact deriving from visceral pleura sliding, as it generates a sandy pattern called the “seashore sign.”

Figure 8

A-lines. A-lines represent horizontal parallel artefacts behind the pleural line at multiples of distance of the probe, indicating a good lung aeration (longitudinal view, linear probe).

Figure 9

B-lines. B-lines appear as vertical hyperechoic line artefacts taking the whole height of the screen crossing the A-lines without decreasing in intensity. B-lines always arising from the pleural line and moving simultaneously with lung sliding and normal lungs can demonstrate up to three B-lines per lung window/intercostal space.

Figure 10

Pneumothorax in M-mode. Parietal pleura visualized below two successive ribs. There was an absence of pleural sliding and seashore signs in M-mode, which indicated the presence of gas effusion. In M-mode, the stratosphere sign and straight horizontal lines above and beneath the pleural line can also be observed, representing the absence of pleural sliding.

Figure 11

Interstitial syndrome with B-pattern in a patient with COVID-19 pneumonia. (A). One isolated B-line (red arrow) visualized on the upper areas bilaterally (longitudinal view, convex probe). (B). In the same patient, multiple coalescent B-lines are visualized in the lower area bilaterally (red arrows) arising from the pleural line and spreading up to the edge of the screen, representing interstitial involvement “B-pattern” (longitudinal view, convex probe). This corresponds to severe impairment in lung aeration resulting from partial filling of alveolar spaces by pulmonary edema.

Figure 12

Thickened pleural lines in a COVID-19 patient. Thickened and irregular pleura (red arrow), suggestive of interstitial lung disease.

Figure 13

Lung consolidation in a COVID-19 patient. Lobar consolidations (translobar) visualized as a tissue-like pattern of the lower lobe. The air bronchograms are visualized as hyperechoic signs within consolidation (air-filled bronchi) (red Asterix). A small pleural effusion is associated (yellow arrow).