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, 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.

The ANGMA clinics use a curvilinear probe 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 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. 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 coronal view.

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 not be more than 12 cm for most patients. At this depth, 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.

For a full lung exam, have the patient sitting or standing while facing the examiner and first examine 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 examiner 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 examiner and place gel over the cephald 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 longitudinal 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. 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, if needed, restore the depth to 12 cm. Keep the indicator examiner 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. Look for fluid with a longitudinal probe position and then switch to transverse and go up the intercostal spaces in the mid-axillary line and then come down the anterior 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. Document localized findings with “lobe terminology”, such as “posterior, upper, RLL” or “lateral RML” to correlate with radiograph and CT imaging reports of the lung. This approach is easier than trying to use numbered lung segment terminology and communicates better to non-IMBUS users than zone terminology.