Pleural ultrasonography has great utility for the intensivist. As early as 1967, it was apparent that ultrasound was ideally suited for the detection of pleural effusions.1 In addition to permitting imaging of pleural effusions, thoracic ultrasonography can also detect less common pleural pathology and is ideally suited to guide thoracentesis and other pleural procedures.
Ultrasound examination of the pleura is influenced by the surrounding structures. The ribs completely absorb ultrasound waves and prevent deeper structures from being visualized. In contrast, air reflects ultrasound. The surface of aerated lung will reflect most of the ultrasound waves. The point of reflection is immediately below the pleura. However, if the lung is consolidated or atelectatic, it can be readily visualized.
In addition to the artifacts seen in other aspects of medical ultrasonography, there are specific artifacts, such as rib shadowing, that are found commonly in pleural ultrasound. Air reverberation artifacts, which originate below the pleura, are another artifact type that can be commonly observed by clinicians (see Chapter 22). Translational artifacts, due to patient breathing or mechanical ventilation, may also confuse the examiner.2
Obesity and subcutaneous edema can degrade image quality. Significant edema may also present problems in judging the depth for procedures. The presence of subcutaneous air will make visualization of deeper structures problematic. The use of firm pressure on the skin and the use of a coupling medium will reduce some artifacts. Artifacts are often visible in only one scanning plane, so changing the probe angle may cause artifacts to disappear. Furthermore, artifacts usually will not move with the respiratory cycle. The observation of an image throughout several respiratory cycles often clarifies the issue.
Pleural ultrasonography can be performed with many different types of two-dimensional ultrasound machines. Doppler capability is not needed. A probe with a small enough “footprint” to easily fit between rib spaces should be used. The preferred ultrasound probe is a sector or curved-array transducer with a frequency of 2–5 MHz (typically 3.5 MHz). Probes with higher frequencies can visualize the pleural surface but lack adequate penetration for most clinical applications.
In order to enhance one's knowledge of pleural ultrasonography, the use of a uniform probe orientation and screen marker is suggested. This allows easy comparison of images with those found in the literature. Furthermore, the recording and reporting of images will be standardized. The machine should be prepared so that the image marker on the screen is in the upper left corner of the screen. In longitudinal scanning, the probe should be oriented with the marker positioned cephalad. If this orientation is maintained, the cephalad projection will always be on the left of the screen.
Before making any clinical judgments, the clinician should set the gain and depth on the machine. The gain should be set so that images of the pleural surface and chest wall are optimized. Additionally, gain should be adjusted ...