Table 2 Position of the probe and indications on how to measure pleural effusion by ultrasound, according to different studies

Vignon et al. [29]

Along the dorsolateral part of the chest wall, as posteriorly as possible between the mattress and the patient’s back without lifting the hemithorax, in all IC from the base to the apex

Choose the maximal perpendicular interpleural distance from the leading edge of the dependent surface of the lung to the trailing edge of posterior chest wall, at the apex and at the base

Roch et al. [30]

Along the posterior axillary line between the ninth and eleventh ribs to identify the liver on the right side, the spleen on the left side, and the diaphragm

To visualize the effusion, the transducer was advanced cranially and a longitudinal view was chosen

Use the mean of three measurements obtained by distance between:

- Lung and diaphragm

- Lung and posterior chest wall at base

- Lung and posterior chest wall at fifth IC

Balik et al. [31]

Along the posterior axillary line moving the probe cranially, obtaining transverse sections perpendicular to the body axis

Choose the maximal distance between parietal and visceral pleura at lung base (minimum requirement: distance ≥ 10 mm)

Usta et al. [32]

Along mid-scapular line moving cranially (dorsal scanning)

Choose the maximal distance between mid-height of the diaphragm and visceral pleura (minimum requirement: distance ≥ 30 mm)

Remérand et al. [33]

Along each paravertebral intercostal space, slipping the probe between the patient’s back and mattress

The lower and upper intercostal spaces where PLEFF is detected should be drawn on the patient’s skin to establish PLEFF paravertebral length (L_US)

At the half point of L_US the PLEFF area should be manually delineated