We are glad of having had the opportunity to enrich the discovery of Dénier and all founders of ultrasound [1, 2], for studying, since 1985, an unexplored field: critical ultrasound [3]. We remind that critical ultrasound was defined as diagnoses or procedures done in critical targets in the critically ill (echocardiography, then lung ultrasound, optic nerve, venous cannulation etc.), by the first-line physician on-site 24/7/365. This way to practice ultrasound was not a copy-paste of the radiologic culture, with some applications (aortic aneurism, biliary tract disorders, etc.) just transferred from the radiology department to the emergency room, nor from the cardiological cultures (heart function, a.m.o.). In this field, our main target was to define a simple unit and simple rules.

Critical ultrasound was a silent volcano, which began to rumble since the early 1990s. Some pioneers tried to show during years to those who wanted to listen how to wake up this sleepy giant.

The prehistorical period ranged from the year 1946 (the birth) to 1982. The pioneers who created medical ultrasound were internists like Dénier [1] or surgeons like Wild [2]. Cardiologists and obstetricians immediately saw the interest and self-appropriated the method. The rest of the medical community did not move a lot. Why? How could intensivists not see the huge range of this weapon, this will remain a mystery (they are no longer here today for answering)? Since the tool provided images, it was given into the hands of the experts of medical imaging. They used their skills for creating a sophisticated discipline, immune to the non-initiated. Meanwhile, the frontline physicians (intensive care, emergency dept) did not see the interest of ultrasound but used their hands, X-rays, central venous pressures, etc. We have the absolute proof that with antique machines before the era of real-time (1974), it was possible to do lung ultrasound in the critically ill.

Ultrasound came on age, with the advent of the real time (1974, Henry & Griffith), but this was a discrete revolution which was not, once again, noticed by the critical care physicians – nor by some academicians whose work is to acknowledge the real innovations in medicine and biology.

In the 1980s, pioneering ICU teams developed the cardiac part [4].

A really weird period ranged from 1989 to 2001. We had the opportunity to work since 1989 in a prestigious ICU, equipped with ultrasound, the first to our knowledge [4]. It is with the simple unit present there that we could define the whole field of critical ultrasound [3]. The intensivists around us were able to see its utility, but little happened. Human factors are unfathomable; intensive care (especially medical) is a prestigious discipline, and maybe these elites mastered their duty and did not feel the need to be better than excellent. When we used noncardiac ultrasound (an unusual image in 1989, fully inappropriate in this profession), and in addition pointing out that the most important to develop was the lung ultrasound, we can easily imagine what happened in the minds of doctors having been educated in the opposite way (ultrasound? “Not for us”. Lung ultrasound?? “Impossible”).

Therefore, the immediate change we were able to note was a complete standstillness (rather familiar in medicine), which resulted in an efficient stoppage of its widespread use.

Among incredible comments, one told us he would believe in lung ultrasound when the radiologists would give their endorsement. We guess the guy is still waiting.

During this time, other colleagues around us, less academic, learned immediately and use it today daily (Gilbert Mezière, Agnès Gepner, Philippe Biderman, Mohammad Siyam, Olivier Axler, and some others, efficient but discrete physicians). The university colleagues were less enterprising. We were “kings” of the night, but “outlaws” at daylight. Thus, we had to make a critical choice: devoting 100 % of time submitting in first priority the less known, i.e., lung ultrasound, instead of promoting “easy” fields (blood in the peritoneum). The period of these endless submissions took years and years (and is far from finished).

In no other field of medicine did we see so many dogmas. Let us select a few.

The whole next section will show why this technological development was unnecessary.

One could also speak of oxymoron. Since this misconception originated the full textbook you now have in hands, we won’t spoil space for arguing this. Now, this debate is completely obsolete.

Especially when the medicolegal rules will be inverted, in 50 years or maybe tomorrow, physicians checking for the absence of a pneumothorax using the irradiating (and costly) CT may have to explain their choice to medicolegal experts. We humbly suggest them to anticipate this and take basic courses of LUCI.

The word “ECHO,” a bit confusing but let us admit, is an abbreviation of expert echocardiography-Doppler US, popular in the US. The usual cardiologists were not especially trained to answering questions regarding shock, critically ill patients. As a striking example, they need standardized views, like policemen require strict front and profile ID views. Yet anyone is able to recognize a familiar face by any incidence, even not strictly frontal. First deep misconception. During decades, “ECHO” in the critically ill was a copy-paste of this culture: they were called at the bedside and used their science for providing advices in a field they ignored.

Little by little, intensivists have acquired their independency [4]. What we could see is that in some (but prestigious) ICUs, ultrasound is still today restricted to the heart and just the heart. “ECHO” is of high interest, and we fully understand that those who invested huge energy in this tool want to use it intensively. As a sign of respect to the heart, we published in 1992 a simple approach [3].

There are now four ways to use echocardiography. The regular one is done by cardiologists ever since. The ECHO is performed by intensivists of today (with Doppler TTE and TEE). The numerous simple protocols are recently developed such as FATE, RACE, and FOCUS and the CEURF approach, i.e., another simple to use but different approach, since it is fully coupled with lung ultrasound and venous ultrasound (BLUE-protocol, FALLS-protocol, etc.).

The readers may feel surprised to have in hands a textbook on critical ultrasound that does not deal with TEE. We appreciate TEE, a powerful technique providing high-quality imaging. Driving the reader to excellent and respectable textbooks, we recall some drawbacks. The cost makes TEE difficult to afford in most parts of the world. This cost includes that of the probe, scheduled for a limited number of examinations. The technique needs significant learning curve, full installation, long disinfection, etc. The introduction of this probe in the esophagus makes TEE semi-invasive [5, 6]. The user has no choice but to study the heart and only the heart. One last drawback (only our opinion) is the absence of certitude that TEE is the gold standard for hemodynamic assessment – since it can be compared to no gold standard, currently. Aware of the rising place of TEE, not willing to make any fault, we will pay full attention to its value, if ever a gold standard can specify the exact place of each tool. Obviously, trained centers make a good job using TEE.

Now, the image quality of TTE is inferior to that of TEE, but as far as it remains acceptable, it fully pertains to our concept of the optimal compromise; read again Chap. 3. Other authors, and probably all users, are also willing to optimize the noninvasiveness in the first intention [7]. The examination is more democratic (cost, risk, etc.). The problem is now reduced to the interest of cardiac Doppler in the critically ill. See below the detailed (and long) paragraph.

Some believe in the heart (with no lung); we believe in the lung (with simple heart). Emergency cardiac sonography is a simple discipline. The organ is the same, but the user (cardiologist or intensivist) is different. A grand piano can be used for classical music (the cardiologic way) or popular music, as we do. Popular music is less “academic” than classical music, but obeys to extremely rigorous rules regarding harmony, rhythm, and layout. The rules are just different. Those who consider popular music as a precise discipline will be interested by critical ultrasound, which follows the same logic: a same instrument that makes a different music, not requiring the rigid training and scores of the traditional classical music, and a same tool (schematically), a fully different approach but, in both cases, a good music if we dare.

Doppler is interesting. The analysis of the flows provides a physiologic approach of high interest. In critical care, however, its incorporation without adaptation is a passive copy-paste maneuver, keeping the discipline complicated and costly. So what do we win?

Through this textbook (as well as the 1992, 2002, 2005, 2010, and 2011 editions), we took time for explaining the spirit of holistic discipline. In public (not private!) hospitals, the critically ill patients are found. Here, simple alternatives can be used.

The cost was long the main drawback. Out of reach for hospital budgets, the ultrasound units were not bought, keeping critical care doctors blind. A few avant-garde physicians had the conviction that ultrasound was possibly of interest in critical care. Yet they were intoxicated by the radiologic and cardiological culture. This restricted view did not make them immediately aware of the huge potential of simple ultrasound. Therefore, they wanted, candidly, Doppler machines or nothing. This belief that Doppler was mandatory has costed lives. Countless patients died of the absence of a simple visual diagnosis, accessible to real-time ultrasound. In this perspective, Doppler proved to be a silent killer, not Doppler really, but the belief in Doppler. Our 1982 ADR-4000 and our 1992 Hitachi-405, with the unique probe, were easy to purchase, a simple formality – a cheap revolution. With these simple machines in hands, intensivists of the world may have saved countless “dramatic” cases which came in at night and died in the same deep night. All these patients, the “forgotten souls of ultrasound,” are all indirect victims of Doppler. For simplifying the debate, we don’t even evoke the biological side effects of Doppler. Just take into consideration that it is now restricted during pregnancy [8–10].

And let us not forget, the best Doppler machine cannot cross gas (emphysematous lungs hiding the heart, bowel gas).

Inserting color Doppler images would have increased the cost of this textbook. The few color images are here in order not to make a too gray-tone textbook.

So which interesting data may Doppler provide?

A last point: as a researcher (more occupied in research than in politics), we don’t prohibit the use of Doppler (and have no authority for doing so). We just open the minds, pointing out that each physician is free to use Doppler at will. We repeat that we can reconsider our position: we are not opposed to have Doppler on our next machine, provided it makes us happy with our seven requirements (size, image quality, start-up time, flat keyboard, simple conception, the universal probe, cost), and if Doppler inclusion does not create the slightest drawback, see again Chap. 2. The CU (CEURF units) conferred to the existing or upcoming machines are ready to be updated and even give positive points to such a progress (we envisage five points if such a Doppler is included, ten points if this Doppler has high quality).

Ultrasound is gel. This gel is ultrasound, since ever. The gloomy spectacle of a gooey discipline. A kind of sauce, surrounded by amounts of crumpled wipes, it infiltrates everywhere, on the probe, the doctor’s tie…. Sometimes, we see the whacky vision of a patient who was scanned in a haste and was not wiped. Other times, this distressing vision, not really glamour, of some hair stuck on the dried gel over the probe from the previous night. The correct word is “mess.” Patients and colleagues accept this landscape, in view of the utility of ultrasound, but would possibly like to get rid of this nightmare (Fig. 37.1). In addition, this is not only a nightmare: in settings where time is of essence, using gel spoils precious seconds (see Chap. 2, and see its scientific relevance in Chap. 31). Gel? We don’t use it. We long found the substitute for gel (Ecolight^®, soon available). In our world, there is no gel, no wipes, no sticky skin, and no endless hours for (imperfectly) cleaning the skin. This is part of holistic ultrasound.

Only one probe is sufficient in the intensivist’s use, as outlined throughout this book: our microconvex probe, the 0.6–17 cm range one. All others are good for each corresponding specialist, none of them being suitable for the main organ (the lung) and the main discipline (critical care).

See our detailed comments above.

Possibly one day (personal fear), sly manufacturers will propose a liver probe and a splenic probe. We are afraid by such a perspective, quite sure that they will succeed in convincing many that the performances of ultrasound will be enhanced. We advise interested colleagues to refer to doctors with extensive experience, not commercials, when buying a probe.