(1)
Hôpital Ambroise Paré Service de Réanimation Médicale, Boulogne (Paris-West University), France
Lung ultrasound is a standardized domain. Each of its components is based upon pathophysiological realities. As for any novelty, a new terminology had to be considered. The one used in the BLUE-protocol favors fast communication, in the spirit of aviation language: maximal information in minimal time.
In this quest, a maximal effort has been done for helping memory. Logic and culture were mixed together. As an example, the term “B-line” should spontaneously suggest interstitial syndrome to any physician. Confusions were avoided for the best. The terms A-lines, B-lines, and up to Z-lines have been chosen on purpose with each time a precise idea helping memorization. We checked that the bat sign, seashore sign, lung sliding, quad sign, sinusoid sign, tissue-like sign, shred sign, lung rockets, stratosphere sign, lung point, BLUE-protocol, etc., did not yield confusion in the medical terminology. The standardization of the method is favored by following seven principles:
1.
A simple method is suitable for lung ultrasound. A two-dimensional unit without filters or facilities is the most appropriate.
2.
The thorax is an area where air and water are intimately mingled.
3.
The lung is the largest organ in the human body.
4.
All signs arise from the pleural line.
5.
Lung signs are mainly based on the analysis of the artifacts.
6.
The lung is a vital organ. Most signs are dynamic.
7.
Nearly all acute disorders of the thorax come in contact with the surface. This explains the potential of lung ultrasound, which is paradoxical only at first view.
Development of the First Principle: A Simple Method
Two peculiar points highlight lung ultrasound.
First, sophisticated units – usually devoted for cardiac explorations – are not ideal. The large size of these cardiac units, the image resolution, the start-up time, the probe shape, the complexity of the technology, and the high cost can be hindrances for bedside use devoted to critically ill patients The machine that we use, manufactured in 1992, last (cosmetic) update 2008, is perfect for lung – and whole body – analysis. We provide some figures allowing the reader to compare our 1992 resolution with laptop models from the twenty-first century (see Fig. 2.2). One figure in particular may explain one of the main reasons of the delay of use of lung ultrasound in many ICUs (Fig. 5.1).
Fig. 5.1
Cardiac probes. This figure shows (right image) how lung ultrasound appeared to many intensivists who had standard echocardiography units. One can understand that they were not fully encouraged to go beyond. Compare with our 1992 machine (left)
Second, the pleural line and the normal signs arising from it (A-lines and lung sliding) are the same at any part of the thorax. The lung is a simple organ, unlike the heart, the abdomen (which contains more than 21 organs), or a fetus.
Development of the Second Principle: Understanding the Air-Fluid Ratio and Respecting the Sky-Earth Axis
Air and fluids coexist in the lung. Air rises, fluids sink. Lung ultrasound requires precisions on the patient’s position with respect to the sky-earth axis and the area where the probe is applied. Pneumothorax is nondependent, interstitial syndrome usually nondependent, alveolar consolidation usually dependent, and fluid pleural effusion fully dependent.
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