In the outpatient setting, the spectrum of pulmonary disease and characteristics of the ultrasound exam are notably different than that seen in the acute inpatient and intensive care unit settings.
The spectrum and severity of pulmonary disease is different in the primary care clinic than in the emergency department or critical care unit where lung ultrasound was originally developed. Clinic patients are usually sub-acutely or chronically ill with cough, mild shortness of breath, or localized chest discomfort. These patients need a careful but efficient evaluation of all lung lobes and sensitive detection of pleural effusions and sub-pleural consolidation. The supine approach sometimes used in the hospital is not optimal for the clinic.
Clinic patients can always be examined in the upright position, which has two advantages for lung ultrasound. The first is that the lungs are more fully expanded in the upright position in all but the most obese patients. The second is that pleural effusions are better detected and quantified in this position. As with the sinus exam, the standard patient position for the lung exam in clinic can be standing. This makes for a quicker and easier exam, particularly for patients with mobility troubles, as long as they can stand for a short while. The sitting patient position on the exam table is certainly fine, but has a longer total exam time without any improvement in imaging.
A curvilinear probe is used with Venue instead of the phased array for the lung exam because more VPPI can be seen with each probe placement, allowing a quicker exam with less probe movement.
With the phased array probe it doesn’t make much difference whether the probe orientation on the lungs is parasagittal or transverse because the probe is close to square. However, with the wider curvilinear probe there is a real advantage to using a transverse, intercostal view. Substantially more VPPI is seen with each probe placement because ribs are not in view.
Here are normal lungs on Venue with the curvilinear probe in the parasagittal orientation in the middle of the posterior chest.
Next is the same location on the patient with the probe in the transverse intercostal orientation. More VPPI is seen with each probe placement.
It is important to remember that the intercostal spaces are mostly horizontal at the cephalad chest but become more obliquely angled in the caudad chest. The probe needs to be subtly rotated to stay intercostal as it is moved on the chest. If rib shadow begins to show, the probe is not optimally positioned.
The default depth should be less than 12 cm for most patients. The default depth for the Lung preset on Venue machines at COC is 10 cm and there are ED experts who use a routine depth of 8 cm. At 8-10 cm, the details of the VPPI can be seen and important B-lines, consolidation, or fluid are never missed. The depth can be increased to further evaluate fluid or consolidation as necessary.
Some advanced IMBUS physicians prefer to begin with the posterior chest where abnormalities are more frequent, but the following description begins with the anterior chest.
Remove the gown from an arm on one side and drape the gown across the breast and under the arm. In almost all women, the lungs can be viewed down to the liver interface without exposing much of the breast. Apply gel over the upper chest.
Have the indicator physician left and move the probe up and down the anterior chest in two passes. It is very important to stop and watch part of a breath with each move. It is wrong to continually slide the probe hoping to spot something on the move. Wipe the gel and repeat the process on the other side.
After the anterior exam, turn the patient so his back is to the physician and place gel over the cephalad chest medial to the scapula and then over the caudad chest below the scapula. Begin the posterior exam caudad of the diaphragm with the probe in a parasagittal orientation, as in the following image.
The probe starts below the diaphragm because this location is very sensitive for finding a pleural effusion. Move the probe cephalad and either a typical lung curtain will be seen or a pleural effusion may appear. The parasagittal probe position helps make quantification of any pleural effusion easier. Here is a moderate pleural effusion that was seen in this location. The depth was moved to 15 cm to more fully see the pleural effusion extent.
After the pleural fluid evaluation, switch the probe to the transverse intercostal orientation and, if needed, restore the depth to 10 cm. Keep the indicator physician left and cover the posterior chest by vertical up and down movement, subtly adjusting probe rotation to remain intercostal as the probe moves cephalad. There is enough gel on the chest to never leave the chest with the probe. Depending on the size of a patient, only two or three vertical passes are needed to cover the posterior chest.
Finally, complete the lateral chest imaging. If possible, the patient needs to put his hand on his head for this part of the exam. Pre-apply gel on the mid-axillary line. First, look for fluid with a coronal probe position and then switch to transverse and go up the intercostal spaces in the mid-axillary line. The gel is then cleared and the process is repeated on the other side.
Below is an image that shows the approximate surface projections of the main lobes of the lung. We document localized findings at COC with “lobe terminology”, such as “posterior, superior, RLL” or “lateral RML” to correlate with radiology reports of the lung. This approach also helps communicate better to non-IMBUS physicians.
SMALL PERIPHERAL (AKA SUB-PLEURAL) CONSOLIDATION
Pulmonary findings of lung sliding, A-lines, B-lines, air bronchograms, and pleural effusion are essential to caring for inpatients with serious disease and are extensively covered in IMBUS Core. However, sub-pleural consolidation is a subtle finding that is often important in the outpatient setting.
Small peripheral (aka sub-pleural) consolidation is caused by inflammation or infiltration of the pleura and in the earliest phase, the VPPI only appears a bit lumpy-bumpy. As sub-pleural consolidation worsens, small hypoechoic spaces appear in the VPPI and any B-lines begin below these hypoechoic areas. The hypoechoic areas can be small, moderate or large. Here is an example of sub-pleural consolidation with small defects.
Diffuse lumpy-bumpy VPPIs were described during a large influenza outbreak and even the addition of very small hypoechoic spaces probably still points to viral disease if the process is bilateral and diffuse. Importantly, this process should not be confused with diffuse interstitial edema of heart failure, which should have linear VPPI.
With bacterial pneumonia, the process is almost always focal and the dividing line between extensive focal sub-pleural consolidation and full consolidation is a judgment call that depends on how deep the process extends below the VPPI and the presence of air bronchograms. It is not necessary to see B-lines with bacterial pneumonia. Moderate-sized hypoechoic gaps, with or without B-lines, were described in a series of pulmonary embolism patients and large gaps were seen with lung metastases.
The following patient was 4 days after an uncomplicated micro-discectomy. Bilateral, migratory chest and shoulder pain was present without dyspnea. Early on there was a sharp inspiratory discomfort in the back, but the pain was not pleuritic at the time of the clinic visit. The PCP thought that PE was lower likelihood, but the IMBUS exam showed multiple moderate-sized sub-pleural lower lobe consolidations, some with B-lines. CT showed multiple, small, bilateral PEs. Here is a clip from the IMBUS exam.
The pulmonary IMBUS exam was critical to making this important diagnosis in a timely fashion.