Abstract
It is unknown whether and to what extent the penetration depth of lung ultrasound (LUS) influences the accuracy of LUS findings. The current study evaluated and compared the LUS aeration score and two frequently used B-line scores with focal lung aeration assessed by chest computed tomography (CT) at different levels of depth in invasively ventilated intensive care unit (ICU) patients. In this prospective observational study, patients with a clinical indication for chest CT underwent a 12-region LUS examination shortly before CT scanning. LUS images were compared with corresponding regions on the chest CT scan at different subpleural depths. For each LUS image, the LUS aeration score was calculated. LUS images with B-lines were scored as the number of separately spaced B-lines (B-line count score) and the percentage of the screen covered by B-lines divided by 10 (B-line percentage score). The fixed-effect correlation coefficient (β) was presented per 100 Hounsfield units. A total of 40 patients were included, and 372 regions were analyzed. The best association between the LUS aeration score and CT was found at a subpleural depth of 5 cm for all LUS patterns (β = 0.30, p < 0.001), 1 cm for A- and B1-patterns (β = 0.10, p < 0.001), 6 cm for B1- and B2-patterns (β = 0.11, p < 0.001) and 4 cm for B2- and C-patterns (β = 0.07, p = 0.001). The B-line percentage score was associated with CT (β = 0.46, p = 0.001), while the B-line count score was not (β = 0.07, p = 0.305). In conclusion, the subpleural penetration depth of ultrasound increased with decreased aeration reflected by the LUS pattern. The LUS aeration score and the B-line percentage score accurately reflect lung aeration in ICU patients, but should be interpreted while accounting for the subpleural penetration depth of ultrasound.
Highlights
Monitoring of lung aeration in intensive care unit (ICU) patients under invasive ventilation is important in understanding the nature of respiratory failure, its evolutionUltrasound in Medicine & BiologyVolume 47, Number 9, 2021 estimation (Gattinoni et al 2001)
Combining all Lung ultrasound (LUS) patterns revealed that the highest association between the LUS aeration score and focal lung aeration measured by computed tomography (CT) was at a subpleural depth of 5 cm with a probe footprint of 160%
For subgroups based on LUS patterns, the highest association between the LUS aeration score and focal lung aeration measured by CT was found at a depth of 1 cm with a probe footprint of 100% for A- and B1- patterns (b = 0.10 per 100 Hounsfield units (HU) [95% confidence interval (CI): 0.06À0.13], p < 0.001), a depth of 6 cm with a probe footprint of 120% for B1- and B2- patterns (b = 0.11 per 100 HU [95% CI: 0.05À0.17], p < 0.001) and a depth of 4 cm with a probe footprint of 160% for B2- and C-patterns
Summary
Monitoring of lung aeration in intensive care unit (ICU) patients under invasive ventilation is important in understanding the nature of respiratory failure, its evolutionUltrasound in Medicine & BiologyVolume 47, Number 9, 2021 estimation (Gattinoni et al 2001). Monitoring of lung aeration in intensive care unit (ICU) patients under invasive ventilation is important in understanding the nature of respiratory failure, its evolution. Performing a CT scan in ICU patients under invasive ventilation poses important challenges, including risks associated with transport to the CT scanner and exposure to radiation (Baldi et al 2013). Lung ultrasound (LUS) has gained popularity for monitoring and diagnosing pulmonary complications in mechanically ventilated ICU patients, as it is a radiationfree technique and can be repeated often (Bouhemad et al 2010; Shyamsundar et al 2013; Mongodi et al 2016). Density of lung tissue underneath the probe can be semiquantified using the LUS aeration score, which relies on specific ultrasound patterns. In case of complete loss of aeration, the lung is observed as an anatomical image of partial or lobar consolidation (Lichtenstein and Meziere 2008)
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