Analysis of A-line Patterns Seen on Lung Ultrasound Scans in Healthy Volunteers Following Spontaneous Breathing and High Flow Nasal Cannula Therapy.

Jing Yi Kwan1, Wojciech Wierzejski2, 1University of Manchester, Lancashire Teaching Hospitals NHS Trust, 2Critical Care Unit, Lancashire Teaching Hospitals NHS Trust

A-lines are a type of ultrasonographic artefact seen as horizontal lines arising at regular intervals from the pleural line. The presence of A-lines can either be a variant of normality or pathological conditions like pneumothorax. Currently, there is a lack of guidelines and recommendation about the usage of A-lines analysis in the diagnosis and monitoring of respiratory conditions. This study is designed to determine whether hyperinflation of the lungs results in a difference in the number and echogenicity of A-line artefacts on lung ultrasound scans.

We performed a prospective before-and-after trial on 37 healthy volunteers. Lung ultrasound scans were performed before and right after 15 minutes of high-flow nasal cannula (HFNC) air therapy, which was used to increase the end-expiratory volume of the lungs to create a state of hyperinflation. Two variables were analysed: the number and echogenicity of A-line artefacts.

Changes in the number of A-line artefacts before and after HFNC were analysed using a paired t-test. Out of 37 healthy participants, 28 showed a significant increase in the number of A-lines [1.27, 95% CI 0.82 to 1.72, P< 0.0001] after 15 minutes of HFNC. Conversely, a majority 51.4% of participants (19 participants) showed no changes in echogenicity. However, a two-sided P value of P=0.0127 (P<0.05) obtained using a sign test indicates that if there is any change, it is more likely to be an increase in echogenicity.

Since hyperinflation of the lungs results in an significant increase in the number of A-lines, lung ultrasonography has the potential to be used as a point of care tool for the monitoring of the degree of inflation of the lungs, and thus the severity of Chronic Obstructive Pulmonary Disease (COPD) and asthma attacks. It can also be used in the monitoring of mechanical ventilation and prevention of ventilator-induced lung injury (VILI).

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