The ultrasonographic examination by an intensive care physician differs significantly from other clinical disciplines such as cardiology, gastroenterology, or radiology. These specialties generally focus on one organ system in particular, and the examination is done systematically and in great detail. During the evaluation of an acutely and severely ill patient, however, ultrasonography is used to quickly narrow the differential diagnosis list, monitor the disease progress, and assist in difficult procedures. The intensivist uses this diagnostic tool at the bedside to answer specific questions (eg, why is this patient acutely short of breath?) as quickly as possible to tailor the therapy specifically to his patient. The intensivist performs ultrasonography as a part of the overall assessment of the patient, having a “quick look” at specific organs that may cause the acute illness or clinical change. To accomplish this task the intensivist needs an interdisciplinary approach to ultrasonography focusing on basic features/techniques of imaging the heart, lungs and thoracic wall, abdomen, and vascular structures. This chapter focuses on thoracic ultrasonography and echocardiography in the critical care setting.
Until recently ultrasonography of the lungs did not gain widespread acceptance, since its usefulness was questioned given the fact that ultrasound cannot transmit through air-filled spaces or penetrate bony structures. Dr. Lichtenstein and other authors, however, showed that simply evaluating pleural structures and ultrasound artifacts generated at the soft tissue-air interface of the chest wall and pleura may provide important diagnostic information to the clinician. A growing number of scientific papers describe the value of imaging the lung with ultrasonography instead of the conventional studies such as chest x-ray or the thoracic CT scan,1,2 thus avoiding unnecessary exposure to ionizing radiation. Lung ultrasonography is easily performed at the bedside and given the lack of negative effects on the patient, it may be repeatedly used to monitor therapeutic progress in patients with lung pathology.3
Normal Lung Pattern on Ultrasonography
Each intercostal space is visualized by first illustrating the upper and the lower ribs along a longitudinal plane. The proximal rib surface is identified as a bright white (hyperechoic) convex line followed by a clean, black acoustic shadow (Figure 10-1). In between the ribs, the pleura is identified as a hyperechoic line approximately 0.5 to 1 cm deep to the rib surface. During the respiratory cycle a to-and-fro movement of the visceral pleura against the parietal pleura on the chest wall can be seen in the real time or B-mode, and is referred to as the “lung sliding” sign. This finding can only be seen if both pleural sheaths are in direct contact, and thus effectively excludes a pneumothorax at that level.4 If the examiner is unsure about the presence of lung sliding, the time motion mode (M-mode) can be used. With the cursor placed over the pleural line, the “Seashore sign” (Figure 10-2) should become apparent....