(1)
Hôpital Ambroise Paré Service de Réanimation Médicale, Boulogne (Paris-West University), France
Electronic supplementary material
The online version of this chapter (doi:10.1007/978-3-319-15371-1_28) contains supplementary material, which is available to authorized users.
Some critically ill patients with massive loss of lung function are not dyspneic, not blue, and have a quiet breathing, just because they are deeply sedated and curarized on occasion and receive pure oxygen. This is mainly the case of ARDS. Lung ultrasound in these patients does not strictly obey to the rules of the BLUE-protocol. This setting was called the Pink-protocol. Not surprisingly in our discipline, the definitions of ARDS changed recently. A homogeneous management is en route, but not fully achieved, with space for discussion [1, 2]. It is peculiar to see that, even if lung ultrasound was of possible use when ARDS was defined [3], in the 2012 definition, this potential was still not fully, deeply integrated (Anecdotal Note 1). Time will correct this. We assume that LUCI will clarify more than confuse, helping in better classifying this multifaceted disease. The lung is a complex organ, and such an injury (ARDS) can complexify the field even more [4, 5]. Hopingly, an intensive use of ultrasound (lung, veins, diaphragm, heart, etc.) may optimize patient’s survival or quicker discharge from the ICU.
This chapter is the opportunity to describe other protocols developed around familiar themes (pulmonary embolism, fever in the ICU, etc.). The reader will find in one chapter elements which made a thick part of our 2010 Edition.
Peculiarities of the Ventilated Patient in the ICU
Because of the quiet breathing with low frequency, the mangrove variant of lung sliding is more marked. Intrications of events will be seen in this battlefield made of victories and defeats, explaining non-frank profiles (that we could maybe call the “Pink profiles”). One finds more b-lines or bb-lines in patients who recover from hemodynamic pulmonary edema, the same with patients initiating ARDS or worsening from nosocomial infections, etc. Apart from ARDS (with B′-profile, C-profile, A/B-profile, etc.), variants of the A-profile will be rather frequent. Venous thromboses are frequent, quite usual once catheters have been inserted. At this step, many patients will have an A-DVT-profile, but it should not be concluded in a pulmonary embolism. The patient is no longer blue; we are not in the BLUE-protocol. PLAPS are quite always present for reasons of gravity; it is true (but we cannot refrain thinking that minor infections and minor infarctions, in addition to gravity atelectases, are possible).
The BLUE-Protocol for Positive Diagnosis of ARDS
ARDS can be assimilated to pneumonia, in the terms of the BLUE-protocol. Massive inflammation, lung consolidation, pleural exudate, etc., create the four profiles of pneumonia: the B′-profile, the C-profile, the A/B-profile, and on occasion the A-no-V-PLAPS profile.
The A/B-profile should here be understood as areas, even in the same side, of lung rockets and A-lines (“spared areas” of some Italian literature).
The C-profile can be reduced to minute alveolar syndrome touching the pleural line, resulting in an irregular pleural line (“thickened, irregular pleural line” of some Italian literature). See Fig. 17.4.
In the patients of the BLUE-protocol who initiated ARDS, these four profiles were found in 86 % of cases. The B-profile was seen in 14 % of them [6]. These data indicate that the BLUE-protocol has a substantial role to play for differentiating ARDS from hemodynamic pulmonary edema.
The pathophysiology explains each profile. Lung sliding is frequently abolished (between 33 and 40 % of cases), mainly because of the inflammatory adhesions. The anterior consolidations are due to inflammation (consolidations from hydrodynamic edema reaching the anterior wall in a supine patient would be highly surprising; see again Fig. 24.1).
The Pink-protocol is more subtle than the BLUE-protocol. The patient is visited more quietly. The scanning is more comprehensive. It includes the lateral wall (not used in the BLUE-protocol). The apex is under analysis (we use the ideal probe for this difficult area).
The Extended BLUE-protocol allows bacteriological diagnosis, when a microorganism is isolated from a thoracentesis, among other procedures of interest (read Chap. 35).
Note: the Pink-protocol can be done in any kind of patient on mechanical ventilation, not especially ARDS.
Lung Ultrasound for Quantitative Assessment of ARDS
Ultrasound allows to understand and evaluate each component of the disease. The main disorders benefit from a qualitative and quantitative approach – helping for an adapted therapy.
Lung Sliding
It is for sure correlated with lung compliance, provided factors such as tidal volume and abdominal pressure are under control. Currently, there is no available bedside test such as lung sliding. Since there will not be any practical gold standard, we must accept ultrasound as the gold standard. It is possible to define roughly four stages: normal lung sliding, discrete lung sliding, impaired lung sliding with millimetric amplitude, and complete abolition. Discrete lung sliding is normal near the apex and not normal at the base.
We define normal lung sliding when we see that its amplitude comes, on inspiration at the lower BLUE-point, from the lower end of the upper rib to the upper end of the lower rib (this is, anatomically, roughly 2 cm). B-lines help definitely for a finer assessment. If not, some pleural irregularities may be available. If not, the simplest is to give up with the lung and just take a look to the liver or spleen descent. The usual excursion of the (please choose) podal lung sliding, diaphragmatic cupola, liver, and spleen is roughly 2 cm.
We define discrete lung sliding in between (roughly, 5–10 mm).
We define quite abolished lung sliding as a dynamic reduced to a millimetric move.
Abolished lung sliding is an absent dynamic, even one mm.
Pleural Effusion
Volume Assessment
The BLUE-protocol makes a qualitative estimation: PLAPS or no PLAPS. In the Pink-protocol, intensivists want to know how much fluid is present. We just think that a rough estimation is sufficient: in our practice, the procedure of thoracentesis is so secure that it is quite always done. Withdrawing fluid only when it is >500 cc is not fully satisfactory: patients who have together highly diseased lungs and this restrictive syndrome (even <500 cc) will probably benefit from a procedure. The less the effusion, the more the lung can breathe.
We evaluated several protocols for roughly indicating the volume of the effusion (Accessory Note 1). Different approaches can be consulted [7–11]. We present our most recent approach: the “BLUE-pleural index,” which favors simplicity. It requires inserting the probe at the PLAPS-point and simply measuring the distance between the pleural line and lung line. We measure on expiration (on inspiration, the lung line actively moves toward the pleural line). Care must be done for having a probe as tangential as possible to the chest wall. Each centimeter (of probe length, of body habitus) can be a hindrance, resulting in overestimating the dimensions by simple mathematic distortion.
The PLAPS-point shows all volumes of free pleural effusion. A minimal effusion has a millimetric thickness, which anyway generates frank quad sign and sinusoid sign (Fig. 28.1).
Fig. 28.1
A minute pleural effusion at the PLAPS-point, using the quad and sinusoid sign, between pleural line (upper arrow) and lung line (lower arrow). We expect a 40–80 ml effusion. Asterix, ribs
Care is done to measure from the pleural line to the lung line. Of no sense would be a measurement from the pleural line to the mediastinum, as seen when made too near to the diaphragm: all cases of effusion able to detach the basis of the lung from the cupola will have a standard 10 ± 1 cm depth. Here is a simple rule for beginners: at the PLAPS-point, the BLUE-pleural index can range from 0 to 4, rarely 5, exceptionally 6, and never 7 cm. A 10-cm value invites to question one’s technique. See comment in Fig. 16.5).
One rule must be considered (the principle N°2, of gravity): a quite normal lung should be light like a balloon, allowing pleural effusion to lie dependently. The diagnosis of aerated lung is based, roughly, by the observation of sub-B-lines at the PLAPS-point (see Fig. 16.3). A fully consolidated lung weights and obliges the fluid to spread around. A correction should therefore be made when, below the lung line, the lung is consolidated, not aerated. These rules must be understood as approximate (and, hopingly, sufficient).
And now we can use the BLUE-pleural index. As for consolidations, the BLUE-index is an elementary parameter; the BLUE-volume is an estimated volume, from this index. The following sizes consider adults:
A.
When the underlying lung appears aerated:
Three mm correspond to a BLUE–pleural volume of 15–30 ml.
One centimeter corresponds to 75–150 ml.
Two centimeters correspond to 300–600 ml.
Thirty-five millimeters correspond to 1,250–2,500 ml.
Six cm seem a maximum, and measurements around 10 cm (in our defined conditions) cannot come from a pleural effusion. These numbers are just indicative. This approximation that we use, from simple to double values, is sufficient for clinical practice (has no repercussion on the patient’s safety). This also indicates that the accuracy of such measurement is not a major problem in our habits.
B.
When the underlying lung is consolidated, these values should be increased. Without yet any confirmatory study, these numbers should be considered as a rough indication:
Lung consolidation | Correction factor |
|---|---|
3 cm (roughly 27 cc) | 1,1 |
4 cm (roughly 64 cc) | 1,2 |
5 cm (roughly 125 cc) | 1,4 |
6 cm (roughly 215 cc) | 1,7 |
7 cm (roughly 350 cc) | 2 |
Thoracentesis for Pleural Fluid Withdrawal
For the diagnostic thoracentesis, please refer to Chap. 35 on the Extended BLUE-protocol.
We use this potential of ultrasound to allow safe thoracentesis in ventilated patients, even with PEEP [12]. Fluid withdrawal improves the respiratory parameters [7, 8, 13–15]. The technique for withdrawing fluid is exactly the same than for analyzing some ml. We use the safety criteria explained in Chap. 35. We never use ultrasound during the puncture. Ultrasound just tells us where the needle should be inserted.
Technical Notes
We avoid large tubes, too aggressive, and use a system we have developed with a 16-gauge, 60-mm-long catheter (see Fig. 34.2). Since this multipurpose catheter has no lateral hole, the lung will come into frontal contact with the distal hole, blocking the aspiration in the syringe. The operator should just withdraw the catheter mm by mm and go on aspiration, until this catheter comes out of the pleural cavity.
Using a 60-ml syringe, the fluid is withdrawn with an average output of 1 ml/s, i.e., 20 min for a 1,200 ml effusion. It seems slow but the overall time is decreased: the catheter is withdrawn at the end, a simple family dressing is applied on the skin; this system has the advantages of simplicity, no loss of time, no infectious risk generated by the large tubes (needing dissection of the wall, large wound, the need for making a pouch), no pain, and limited costs. The very limited dressing (1 × 3 cm) allows to make easy post-procedure ultrasound. The procedure can be repeated at will. As described, it aims at simplicity more than 100 % fluid withdrawal (some ml can stay on site).
Lung Consolidation: Volume Assessment (During Recruitment)
Many intensivists worry about the volume of the consolidated lung [16]. Some try to make it disappear using PEEP. We will not open the debate on the usefulness of these maneuvers (not in terms of saved respiration but in terms of lost circulation, with potential outcomes on the multiorgan dysfunction) [17]. We just consider, for those who want to monitor this alveolar part, that a simple ruler is sufficient (Fig. 28.2). In other words, we use simplicity as a guide for this assessment (Accessory Note 1).
Fig. 28.2
Four different volumes of lung consolidation. It is easy to see that, if occurring in the same patient, it would mean, from bottom to top, an improvement or, from top to bottom, a worsening. No need of sophisticated approaches for this. Each red mark indicates one measurement. The principle of the Pink-protocol, trying to import simplicity in the field of ARDS, is to consider this sole dimension as representative of the consolidation volume. Note that the tool in the cartouche (upper right), easy to find in any general shop, was of use twice. Here, it allows to measure lung consolidations in a basic way. Measurements are not emotions. They demonstrated in Chap. 2 that the ultrasound revolution was possible using machines smaller than laptops, far before, more suitable
Sophisticated ways of measurement, as developed by some teams, will give very precise numbers, but is it a true dimension? Critical care teaches us to be cautious if using precise data in a not exact discipline (take the example of the cardiac output measured by the Swan-Ganz catheter). The more precise the measurement, the bigger the risk to be wrong. We have defined a BLUE-consolidation index according to this and two other remarkable points. First, our microconvex probe has the advantage of a sectorial view. Second, observation shows that most lung consolidations behave like compact masses. The three dimensions are roughly the same. Considering two of them – and even one – is sufficient for estimating the other(s), therefore the volume. The BLUE-consolidation index considers the area at the most speaking dimension and assimilates it roughly as one side of a cube. Some would correct this, considering more a sphere than a cube. This may complicate the design, and mostly, the iceberg effect (as we call this) yields underestimations of the volume: massive deep gas collections (air bronchograms usually) can stop the beam, hiding deeper information. The BLUE-consolidation index is expressed in the figures of Chaps. 17 and 35.
Very simply, a BLUE-consolidation index of 1 cm should correspond to a BLUE–consolidation volume of 1 ml (2 cm–8 ml, 3 cm–27 ml, etc.).
Note that even if this index is not 100 % exact, its variations should indicate worsening or healing of the disease.
The probe must be as perpendicular as possible to the chest wall for having standardized, consistent measurements. Therefore, just the distance between the pleural line and the end of the consolidation should be measured (if not perpendicular, ultrasound overestimates the consolidation dimension; if you measure a sheet of paper on a table, it can be 0.1 or 300 mm, depending how your tool is oriented). The mediastinal line sign (showing always the same dimension: 10–11 cm) indicates major volume.
A very small consolidation, visible between two ribs, has been called C-line (for Centimetric Cupuliform Consolidation) (see Fig. 17.3).
Teams increasingly use prone positioning. Anticipating many rejections, and years of lost time, we confide the principle of our study in progress, for the benefit of the patients. If diffuse interstitial syndrome is not associated with substantial posterior lung consolidation (in a supine patient), this heavy maneuver may not be beneficial. Lobar patients (assuming A-profile plus PLAPS) may benefit from it. In a prone patient, ultrasound remains feasible; the “prone points” can be used (see Fig. 6.7). Even a trans-scapular lung approach is fully possible: see Fig. 28.3, which atomizes two dogmas.
Fig. 28.3
Two dogmas. This single figure invalidates two dogmas, which stipulate that air and bone are insuperable obstacles to ultrasound. On top of the image, the scapula (large upper arrows). The intermediate arrows indicate the ribs. The lower, smaller arrows indicate the pleural line. Arising from the pleural line, a lung consolidation, with a shred sign, is perfectly identified (vertical arrows). Even measurements can be done: this piece of consolidation is 12 mm thick (or the BLUE-consolidation volume is roughly 1.4 cc). ARDS in a 35-year-old patient in the prone positioning
Pneumothorax
In the Pink-protocol, i.e., in ARDS mainly, extensive adhesions, responsible for abolition of lung sliding, may theoretically prevent from pneumothorax, by sticking the lung to the wall. Yet complex pneumothoraces can be seen in these patients. Here, as a rule, lung sliding is abolished everywhere, i.e., in the areas of pneumothorax and in the areas of adherences. Lung rockets and lung pulse help in recognizing the non-detached areas. When there is no B-line nor lung pulse, distinguishing pneumothorax from adhesions is too challenging. This is why the lung point is required for the diagnosis. Knowing the limitations of ultrasound, the physician will not harm the patient. But radiographies can be useful here. If we consider only these cases with large areas of abolished lung sliding with A-lines, associated with radiographies not showing the pneumothorax, CT should answer the question (if clinically relevant). This wise request for CT is fully integrated in the spirit of the LUCIFLR project (next chapter).
How to Evaluate the Volume of a Pneumothorax
This makes no difficulty, yet this raises academical and ethical problems.
Ethical: if we use CT as a gold standard, whereas radiography has already shown specific signs (even with poor appraisal of the volume), the issue is now ethical: useless irradiation. Any research must bear these heavy limitations in mind. We made a correlation only for radio-occult cases, i.e., cases where CT was the only definite proof [23], showing that 1/3 of patients with radio-occult pneumothorax needed a chest tube, which again shows the poor value of the radiography. Subsequent studies with large use of CT confirmed these results [24].
In our study, the lung point location was correlated with the volume, using one simple criterion: the clinical need of the managing team to insert a chest tube. The chest tube was indicated in 8 % of cases when the lung point was anterior, versus 90 % of cases when it was lateral [23]. The more lateral the lung point, the more substantial the pneumothorax. Major pneumothorax yields very posterior – or even absent – lung point. Anterior lung point is correlated with minimal and generally radio-occult pneumothorax [23].
We must define what a “minute” pneumothorax is. A sheet of A4 paper has a minute thickness (0.1 mm) but an extensive surface (21 × 29 cm). This explains why even “minute” cases are easily detected using the standardized BLUE-points.
Can One Monitor the Volume of a Pneumothorax?
Nothing is more easy. One just has to locate the lung point (if present) and see its evolution. No need for irradiating studies for this.
Related posts:
The Excluded Patients of the BLUE-Protocol: Who Are They? Did Their Exclusion Limit Its Value?
Glossary
The Ultrasound Approach of an Acute Respiratory Failure: The BLUE-Protocol
Lung Ultrasound Outside the Intensive Care Unit
The BLUE-Points: Three Points Allowing Standardization of a BLUE-Protocol
The Extended-BLUE-Protocol
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