The A-Profile (Normal Lung Surface): 2) Lung Sliding

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Hôpital Ambroise Paré Service de Réanimation Médicale, Boulogne (Paris-West University), France

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In workshops, the lung sliding of healthy models is rather easy to study. In the critically ill, because either exacerbated but parasited by severe dyspneas or made too subtle by deep sedations, its study needs the consideration of adapted signs.

The normal lung surface is defined by the association of A-lines and lung sliding. At the anterior chest wall in a supine patient, this is the A-profile.

Detecting lung sliding is the first step of the BLUE-protocol. Lung sliding is a physiological phenomenon that anyone can easily detect using appropriate tools. In the critically ill, because either dyspneic or ventilated, different phenomena occur. For describing them scientifically, several points must be specified, and this deserves a full chapter.

Like any vital organ, the lung moves from our birth to our death without interruption. Lung sliding is a kind of dynamic (sparkling, twinkling, glittering, shimmering, and “ant’s walk” are suitable terms too) arising from the pleural line (Fig. 10.1, Video 10.1). The pleural line is built by two layers: the parietal pleura, always motionless, and the visceral pleura, only when the lung is at the chest wall, moving or not. The sliding of the visceral pleura against the parietal pleura creates this sparkling at the pleural line.

Fig. 10.1

The seashore sign. This figure is the continuation of Fig. 8.1 and Fig. 9.1, provided without any arrow. The present figure is crowded with arrows. Left, real-time image. The simple (isolated) vertical arrows show the ribs. The white horizontal arrows show the pleural line, clearly defined by the bat sign. Gray horizontal arrows show some of the numerous horizontal lines which should not be confused with the pleural line. They indicate, from top to bottom, the skin, some aponeuroses, a rib, minor air reflections below the pleural line called sub-A-lines (see Fig. 40.4), and (lower gray arrow) an A-line. Right: M-mode. A marked change appears between Keye’s space, here “quiet” above the black arrows, and the space below, called M-Merlin’s space or again MM-space. The black arrows indicate precisely the pleural line, with no space for confusion. Look at the upper coupled, vertical white arrows, indicating how finely real time and M-mode are tuned together: this allows immediate location of the pleural line in any circumstance, a critical point in extreme emergencies. Compare with Fig. 10.5. Keye’s space displays something like quiet waves. The space below (MM-space) shows a homogeneous, sandy pattern, generated by the lung when sliding against the chest wall. This is the seashore sign. No need for video, this figure allows to identify a lung sliding without any confusion

Lung sliding indicates that, first, the lung is at the chest wall and, second, this lung works.

“Lung sliding” is a euphonic locution; read Anecdotal note 1.

Our 5 MHz microconvex probe is ideal for this part of lung investigation. Using our technique (which can be summarized as withdrawing any kind of filter), it makes a work similar (if not superior) to the usual vascular probes advocated by some.

Lung Sliding: A New Sign, a New Entity in the Respiratory Semiology

Lung sliding indicates a physiological reality, the descent of the lung toward the abdomen. Is it a valuable sign? How to assess it? Not clinically of course; we don’t benefit from any specific sign from the father of lung semiology [ 1 ]. So with what? Fluoroscopy? It is a too imperfect tool. Lung sliding should be considered as a new sign which speaks for itself and does not need any gold standard. Those who denied the reality of lung ultrasound were maybe in lack of a gold standard [2]. Some would have appreciated a tool allowing to better understand the lung physiology [3].

Since when is ultrasound able to detect this fine movement? From our eyes, since at least 1982, but it is obvious that the antique, pantographic systems of the 1960s were able to demonstrate this dynamic, using M-mode.

Normal Lung Sliding in the Healthy Subject, a Relative Dynamic: The Seashore Sign

The lung works like a craniocaudal piston. Lung sliding is more easy to detect using longitudinal scans; this is one of the reasons why we advise them.

We now define lung sliding as a homogeneous sparkling of the whole of the Merlin’s space, i.e., beginning at the very pleural line, not one mm above, not one mm below. This dynamic is relative, a critical notion since a diffuse dynamic of the whole image is unavoidable. First, the patient as well as the doctor are still alive, both generating minute movements. Second, there is a minute background noise. Yet these dynamics are diffuse, whereas lung sliding begins at the very pleural line. The M-mode appears to be insensitive to the background noise; this is why it displays a sandy pattern exactly at and below the pleural line. We called this pattern the seashore sign (Fig. 10.1). The use of the M-mode perfectly highlights the relativity between lung sliding and motionless wall.

The M-mode is useful for understanding lung sliding. The whole of Merlin’s space twinkles, creating this seashore sign. The physicians able to interpret a posteriori a frozen M-mode image prove that they master lung ultrasound. They won’t need videos. Yet one point is of prime importance: the operator’s eye should recognize lung sliding through a real-time image before using M-mode. This must be a habit. One main reason is explained in the SESAME-protocol (cardiac arrest), where there is no time for starting the M-mode.

The M-mode is practical for data recording; it is easier to insert an image in a medical file. In the LUCIFLR project, one image is taken after any thoracic procedure and must show the bat sign at the left, the seashore sign at the right, and a mention where it was taken (e.g., upper BLUE-point, supine patient): this replaces (to advantage!) the chest radiography (Chap. 29).

Lung sliding is suppressed by many conditions (listed in Table 14.1). Apart from them, it is present in eupnea and dyspnea, in spontaneous as well as conventional mechanical ventilation. It is visible in skinny and bariatric patients (see Fig. 33.3). It is present in bronchial emphysema. In giant emphysema bulla, in our observations, a minute lung sliding (or equivalents, see below) is usually detected. Lung sliding is visible at any age, from the first second of extrauterine life to the dying breath.

Lung Sliding, Also a Subtle Sign Which Can Be Destroyed by Inappropriate Filters or So-Called Facilities. The Importance of Mastering Dynamics and Bypassing These Facilities

Simple clues will optimize the analysis of lung sliding. We face a dynamic feature. Therefore, the physician must control the dynamic dimension, i.e., suppressing, or understanding, all other dynamics.

A dynamic coming from the physician must be suppressed by any means.

Only the patient is allowed to move. The operator’s hand must be fully standstill (Fig. 10.2). Our small microconvex probe, easy to handle like a pen, favors this standstillness. Ecolight is a non-slippery product, and energy devoted for keeping the probe stable is spared. Once the operator gets the best image of the bat sign, he/she stops any movement and “quietly” watches at the pleural line, like a sniper (see again Fig. 1.1).

Fig. 10.2

Mastery of dynamics. As far as possible (setting permitting), the hand of the operator must be completely motionless and be able to wait for hours, without moving and without fatigue, like a sniper. Nonsteady hand is a key for failure. Only the patient is expected to move

A dynamic impaired by filters must be recognized by any means, and these filters must be suppressed.

All factors making lung ultrasound more difficult must be destroyed. The problem is simple: they have conceived sophisticated programs which slightly improve tissular imaging (a minor benefit for us) and deeply worsen lung imaging, the most critical. See the sections below, widely dealing with this issue.

A dynamic created by the critically ill patient, either exacerbated by dyspnea or decreased by mechanical ventilation.

This dynamic cannot be suppressed; one must work with it. It will generate difficulties. These difficulties will be mastered. This also deserves a special section.

The Various Degrees of Lung Sliding, Considering Caricaturally Opposed States

Lung sliding is naturally weaker at the apex, a kind of starting block. Lung sliding is naturally weaker in quiet ventilation. We can therefore imagine two situations: Studying the lower BLUE-point of a hyperventilating, dyspneic patient will show a frank lung sliding but associated with parasite noise. Studying the upper BLUE-point of a deeply sedated patient will not show any parasite dynamic but will show an extremely weak lung sliding.

Note: one can be very dyspneic on mechanical ventilation.

For mastering lung sliding in these extreme, but daily, situations, we should master the real-time/M-mode harmony, as well as all filters. This proves highly useful when there is too much dynamic or not enough dynamic.

For making all this clear, we will ask a healthy volunteer to show us various degrees of breathing. These experiments will be done just for simplifying the concept, but the whole of the observations can be found in our critically ill patients.

Lung Sliding in the Dyspneic Patient. The Maximal Type. Critical Notions Regarding the Mastery of the B/M-Mode

A severe dyspnea generates uncontrolled movements of the patient, at the highest degree of anxiety. This patient tries to survive by any means, futile such as opening the window, useful such as recruiting the accessory respiratory muscles.

Observing the fine dynamic of lung sliding in such a “messy” environment may appear challenging, an equivalent of shooting from a mobile point toward a mobile target, obeying to the hectic rules of dogfights. All patients of the BLUE-protocol had a severe dyspnea, generating a parasite dynamic above the pleural line that we called muscular sliding on real time. Users may be unable to locate whether the dynamic comes from the pleural line or above. Here, the M-mode has a critical relevance. The rules of lung ultrasound make no space for approximation: a “sand” arising above the pleural line, even a few mm above, does not come from the lung. Any sandy phenomenon which arises above the pleural line cannot be labeled a “seashore sign.”

Dyspnea and the Keyes’ Sign

Take our healthy volunteer and lock him up in a confined room. You create a “pure” dyspnea (on healthy lungs) which gradually worsens (Technical note 1). Then analyze the lower BLUE-point or more caudal, where lung amplitude is maximal. Such a dyspnea will create two conflicting dynamics (apart from the body agitation due to uncontrolled anxiety).

The dyspnea creates an increase of the tidal volume. The amplitude of lung sliding is increased, resulting in a marked seashore sign.

The dyspnea recruits accessory muscles. This generates perturbations above the pleural line.

The real time (bat sign) locates the pleural line in any circumstances, allowing to define Keye’s space on M-mode. A Keye space full of accidents instead of the regular stratified image has the meaning of a severe dyspnea and was coined Keye’s sign (Fig. 10.3) (Video 10.2). Keyes’ sign describes with no space for confusion these parasite dynamic phenomena occurring above the pleural line. And now, we have all elements for defining the seashore sign. The seashore must arise from the pleural line, always, i.e., the lower limit of Keye’s space (defined using real time first, reminder).

Fig. 10.3

Dyspnea and Keye’s sign. Left, real time. The black arrow shows an intermuscular aponeurosis. The white arrow shows the pleural line. R, shadow of ribs. Right, M-mode. This image may appear as a stormy sea. The muscular contraction (indicating major dyspnea) has generated a sandy pattern beginning (from top) at the area of the black horizontal arrow, i.e., above the pleural line. Is this dyspnea due to a pneumothorax? The vertical white arrows (inserted at a distance of the event) clearly display an area of typical seashore sign with a short zone of preserved Keye’s space. This is sufficient. The diagnosis of pneumothorax can be excluded. This 55-year-old lady suffered from a severe asthma. The location of the real-time and M-mode images at the same horizontal level makes easy the distinction between pleural line and muscular lines – in time-dependent settings. Would such an area not be displayed, subtle eyes may observe a fine change when the column of sand arising from the horizontal black arrow crosses the pleural line at the horizontal white arrow: this pattern is opposed to Avicenne’s sign described in Chap. 14. Here, lung sliding has been identified as present

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