Table 1 How pleural effusion with ultrasound is measured, according to different formulas

Vignon et al. [35]

Measured the maximal perpendicular interpleural distance (the distance between the lung and posterior chest wall) at the apex and the lung base and compared the maximal distance with the drained volume

Roch et al. [36]

Mean of 3 distances measured between lung and diaphragm, lung and posterior chest wall at the base, lung and posterior chest wall at the fifth intercostal space

Balik et al. [37]

Measured the maximal interpleural distance (D) at lung base and used the formula Volume (ml) = 16 × D (mm)

Usta et al. in patients after cardiac surgery [38]

Measured the maximal distance between the mid-height of the diaphragm and the visceral pleura in the sitting position while spontaneously breathing

Remérand et al. [39]

Identified the lower and upper intercostal spaces where pleural effusion is visible in supine patients; the distance between these two points was drawn on the patient's skin to establish pleural effusion paravertebral length. The pleural effusion cross-sectional area is manually delineated at the half way point with LUS. The volume of pleural effusion is obtained by multiplying LUS by the cross-section area