Chapter: Lung

Posterior Screen CVA and Effusion Mid-Axillary Screen Lung Anatomy

Lung

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, and 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, often used in hospitalized patients, is not optimal for the clinic.

Clinic patients can always be examined completely in the sitting position, which has two advantages for lung ultrasound. The first is that the lungs are more fully expanded in the sitting position in all but the most obese patients. The second is that pleural effusions are better detected and quantified in the sitting position.

The ANGMA clinics use the curvilinear C60 probe (2-5 MHz) instead of the P21 phased array (1-5 MHz) for the lung exam. The default ABD exam type and GEN setting on the curvilinear probe give higher resolution than the phased array probe and details of the VPPI are more distinct. The wider C60 probe also allows 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. We see substantially more VPPI with each probe placement because ribs are not in view.

Here are normal lungs with the curvilinear probe in the parasagittal orientation in the middle of the posterior chest.

Next we see the same location on the patient with the probe in the transverse intercostal orientation. In this particular view, 25% more VPPI was seen with the intercostal approach. In the mid-axillary line of this patient, the transverse view saw 50% more VPPI than the parasagittal view. The increased width of the transverse orientation means that the posterior chest can be covered in only three vertical passes and the anterior chest is covered in two passes.

The default depth, as shown on the previous two clips, should not be more than 13 cm for most patients. At this depth, we can see the details of the VPPI well while never missing important B-lines or fluid. We can increase the depth to further evaluate fluid or consolidation as necessary.

For a full lung exam, start with the patient sitting on the end of the exam table and first examine the anterior chest. The gown on one side is dropped to just above the breast. In almost all women, the lungs can be viewed down to the liver interface without exposing much of the breast. Two stripes of ultrasound gel are placed vertically (from top to bottom because the gel tends to drip down anyway) on the anterior chest in the parasternal and anterior axillary lines from the first intercostal space to the likely diaphragm. Then have the patient place his hand on his head.

Have the indicator examiner left and move the probe down one interspace at a time. It is very important to stop and watch a breath with each move. It is wrong to continually slide the probe hoping to spot something on the move. With the width of the curvilinear probe it only takes two vertical passes to complete the anterior chest. Wipe the gel and repeat the process on the other side.

After the anterior exam, the patient turns so his back is to the examiner and gel is placed in the right supra-scapular area and then the right paraspinal, mid-back,  and posterior axillary lines below the scapula (again, apply the gel from top to bottom). Finally, gel the mid-axillary line as well and have the patient return the hand to the top of the head.

The first part of the usual posterior exam is finding the kidney in the costo-vertebral angle with a parasagittal orientation of the probe, as shown in the following image. This is covered in more detail in the kidney chapter.

There are two reasons to do this. First, it makes sure the probe is below the diaphragm, which is important because this location is very sensitive for finding a pleural effusion. Second, it is important to become good and efficient at finding the kidney in this location. This is a nice long axis kidney view that is sometimes better than the coronal long axis view from the sides. Here is an image of the kidney obtained in this area. Notice there are no interfering ribs. The depth was increased to 15 cm to have the kidney fill the sector.

After viewing the kidney, move up one probe width looking for a pleural effusion. The parasagittal orientation easily shows the height of a pleural effusion. Here is a moderate pleural effusion that was seen in this location. The depth was moved to 18 cm to more fully see the pleural effusion.

After the pleural fluid evaluation, switch the probe to the transverse intercostal orientation and restore the depth to 13 cm. Keep the indicator examiner left and cover the posterior chest in 3 vertical passes, plus the suprascapular area. There is enough gel on the chest to never leave the chest with the probe.

Finally, complete the mid-axillary line imaging with a single vertical pass in the intercostal orientation. If pleural effusion is seen at the bottom, switch the probe to parasagittal to see the height of the fluid. The gel is then cleared from the first side of the chest 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. Document localized findings with “lobe terminology”, such as “posterior, superior, RLL” or “lateral RML” to correlate with radiograph and CT imaging reports of the lung. This approach is also easier than trying to use numbered lung segment terminology.