Diagnostic Performance of 6-Point Lung Ultrasound in ICU Patients: A Comparison with Chest X-Ray and CT Thorax

Abstract

Objective: To evaluate the diagnostic performance of a rapid bedside 6-point lung ultrasonography (LUS) performed by an intensive care unit (ICU) physician for detection of four common pathological conditions of the lung, such as alveolar consolidation, pleural effusion, interstitial syndrome and pneumothorax, in critically ill patients and its comparison with bedside chest X-ray (CXR) and high-resolution computed tomography (CT) scan of the thorax. Volume of pleural effusion measured by LUS and CT thorax was also compared.

Methods: This was a cross-sectional, observational study of 90 adult patients with an acute lung injury score of ≥1 admitted to the medical-surgical ICU. They were examined by CXR and 6-point LUS as per BLUE protocol at bedside, followed by CT thorax in the radiology department.

Results: The sensitivity of 6-point LUS for detecting alveolar consolidation, pleural effusion, interstitial syndrome and pneumothorax was 76%, 88%, 83% and 89%, respectively, which was remarkably higher than that of CXR. The specificity of LUS was 100% for all pathologies, which was again notably higher than that of CXR except for interstitial syndrome for which it was 88.5%. Measurement of volume of pleural effusion by LUS was comparable and had a strong absolute agreement with CT thorax.

Conclusion: 6-Point LUS can be a useful diagnostic tool and is better than CXR in diagnosing respiratory pathologies in critically ill patients. Owing to the comparable diagnostic performance of LUS and CT scan and with increasing evidence in favour of LUS, the requirement of CT thorax can be reduced. Radiation hazards associated with CXR and CT, as well as potentially risky transfer of patients to CT room, can also be minimised.

Keywords: 6-Point BLUE protocol; CT scan thorax; chest X-ray; lung ultrasound; point of care ultrasound.

Figure 1

CONSORT flow diagram of the study showing reasons for exclusion of patients from study

Figure 2

a,b. (a) Two hands equivalent to the size of patient’s hand were placed over the anterior chest wall in such a manner that the little finger of the upper hand lies just below the clavicle, fingertips at parasternal border, and lower hand was kept adjacent to the upper hand excluding thumbs. The middle point of the upper hand constituted ‘upper BLUE point’, and the middle point of the palm of the lower hand constituted ‘lower BLUE point’ (marked by black circles). (b) A perpendicular line was drawn from lower BLUE point towards posterior axillary line, and the intersection of these two lines was labelled as Postero Lateral Alveolar and/or Pleural Syndrome (PLAPS) point. These points roughly follow the anatomy of the lung and avoid the heart as much as possible. Upper and lower BLUE points are for examination of the anterior surface of the lung, and PLAPS point is for lateral and posterior surfaces of the lungs

Figure 3

USG pattern generated by normal lung. Pleural line (P) is seen between rib shadows (R). Various repetition lines known as A lines (A) can be seen parallel to the pleural line, placed at a regular interval equal to the distance between skin and pleural line. Normal pattern also includes lung sliding, which is the sliding movement of visceral pleura over parietal pleura (not seen here)

Figure 4

a–c (of Patient A). (a) CT thorax of a patient with consolidation of the right and left lower zones (right lower zone consolidation being more extensive than left). (b) LUS in same patient at right PLAPS point showing alveolar consolidation (C) of the right lower zone (seen as isoechoic tissue-like structure) separated from liver (L) by diaphragm (D), caused by loss of lung aeration. (c) Suboptimal CXR due to rotation, showing obscured right costophrenic angle and diffuse haziness in the right lower lung zone, which may either be due to pleural effusion or collapse-consolidation or even due to an enlarged liver pushing up the diaphragm (as it is difficult to differentiate between pleural effusion and consolidation on CXR)

Figure 5

LUS findings in interstitial syndrome; appearance of ‘B lines’ extending downwards from the pleural line (P) up to the bottom of ultrasound screen. Regularly distanced B lines (B) between two adjacent ribs (R), three or maximum of four in number denote interstitial pathology; mean distance between them is 7 mm corresponding to pleural projections of interlobular septa

Figure 6

a–c (of Patient B). (a) Ground glass opacification of lung parenchyma on CT thorax of a patient with alveolar-interstitial syndrome. (b) LUS at lower BLUE point showing >4 B lines (b) between adjacent ribs (R) with unequal distances between them, suggesting an alveolar-interstitial pathology, similar to that of CT thorax in the same patient. (c) Suboptimal CXR with rotation showing haziness in the lower half of lung fields on both sides, favouring the diagnosis of consolidation or pleural effusion (not correlating with CT or LUS findings)

Figure 7

a–c (of Patient C). (a) CT scan of a patient showing large pneumothorax in left hemithorax. (b) M mode across the pleural line (white arrows) with absent lung sliding during LUS at left upper BLUE point, generated ‘Bar code pattern’, in the same patient diagnosing pneumothorax. (c) CXR of the same patient with a rotated film showing blunting of right costophrenic angle but with no evidence of pneumothorax

Figure 8

a–d (of Patient D). (a) CT thorax of a patient showing bilateral pleural effusion with consolidation. (b) LUS at right PLAPS point in the same patient showing pleural effusion (PE) seen as hypoechoic or anechoic homogeneous structure along with hyperechoic shadows of underlying collapsed lung with consolidation (C) above diaphragm (D). (c) LUS at left PLAPS point with pleural effusion and underlying collapsed lung. (d) CXR was suggestive of bilateral lower zone consolidation and right-sided pleural effusion