Areas of investigation and the BLUE-points. Two hands placed this way (size equivalent to the patient’s hands, upper hand touching the clavicle, thumbs excluded) correspond to the location of the lung, and allow three standardized points to be defined. The upper-BLUE-point is at the middle of the upper hand. The lower-BLUE-point is at the middle of the lower palm. The PLAPS-point is defined by the intersection of: a horizontal line at the level of the lower BLUE-point; a vertical line at the posterior axillary line. Small probes, such as this Japanese microconvex one (1992), allow positioning posterior to this line as far as possible in supine patients, providing more sensitive detection of posterolateral alveolar or pleural syndromes (PLAPS). The diaphragm is usually at the lower end of the lower hand. Extract from “Whole body ultrasonography in the critically ill” (2010 Ed, Chapter 14), with kind permission of Springer Science.
Lichtenstein, D.A. Lung ultrasound in the critically ill. Ann. Intensive Care 4, 1 (2014). https://doi.org/10.1186/2110-5820-4-1
The BLUE-protocol decision tree. This decision tree, slightly modified from the original article (Chest 2008;134:117–125), with the permission of Chest, indicates a way proposed for immediate diagnosis of the main causes of acute respiratory failure, using a lung and venous ultrasound approach.
Lichtenstein, D.A. Lung ultrasound in the critically ill. Ann. Intensive Care 4, 1 (2014). https://doi.org/10.1186/2110-5820-4-1
KC C. 雙和急診超音波教學-Lung US & BLUE protocol - POCUS Academy. POCUS Academy - Point-of-care ultrasound is the visual stethoscope in the 21st century. Published December 15, 2023. Accessed August 29, 2025. https://pocusacademy.com/2023/12/15/雙和超音波教學-lung-us-blue-protocol/