Patient Positioning

Changing patient position can mean the difference between a technically acceptable study and not being able to answer the focused question of interest for your clinical scenario.

Turning the patient into the left lateral decubitus position can facilitate cardiac or gallbladder scanning.

Sitting the patient upright may improve imaging of the gallbladder.

In the trauma abdominal examination, using the Trendelenberg position increases the sensitivity for fluid collections in the hepatorenal space.

Bending the patient’s knees can relax the abdominal wall musculature and facilitate scanning of the aorta and aid in subxiphoid scanning of the heart.

Techniques for Dealing With Tissue Artifacts Various types of tissue artifacts include:

• Air. There are large differences in density between air and soft tissue. When ultrasound waves encounter these large differences, the energy is scattered. Little energy returns to the transducer to be analyzed into an image. An adequate amount of transmission gel placed between the footprint of the probe and the imaging surface will reduce the number of difficult air-filled pockets the waves encounter, such as when scanning over the umbilicus.
• Air, lung. Parasternal windows depend on visualizing the heart through the cardiac notch of the left lung. In patients with hyperinflated lungs from obstructive pulmonary disease or positive pressure ventilation, this window may be obscured. Images can be improved by keeping the probe as close as possible to the left sternal border or placing the patient in a left lateral decubitus position to move the heart closer to the anterior thoracic wall. The subxiphoid view of the heart can be improved by moving the probe a bit to the patient’s right, under the costal margin, and directing the probe toward the patient’s left shoulder. In this way, the liver is used as a sonographic window. Moving the probe to the patient’s left, which may seem more anatomically correct, results in attempting to obtain images through an air-filled stomach or transverse colon.
• Air, bowel. For structures viewed from the right and mid-upper abdomen (such as the proximal aorta, gall bladder, right kidney, and sub­xiphoid view of the heart), the homogeneous, blood-filled liver makes a good acoustic window. A deep inspiration moves the diaphragm and liver caudad, pushing the transverse colon inferiorly to improve visualization of structures beneath. In addition, patient comfort permitting, a process of slow graded compression or a rocking motion may be used to push bowel gas out of the way.
• Bone. When ultrasound waves encounter a highly reflective surface such as bone, the waves are returned right back to the transducer. There is very little energy left to travel to deeper structures and create an image. This hypoechoic area deep to the bone is referred to as shadowing.
• Bone, thorax. Emergency ultrasound of the heart includes evaluation for pericardial effusion and cardiac activity. The heart is encased in the bony thorax, so the ribs cast sonographic shadows. A phased-array cardiac probe (2-4 MHz) or a low-frequency curvilinear probe with a small footprint can be used, which allow the ultrasound waves to be directed between the rib interspaces.
• Bone, upper abdomen (Fig. 8). Using the inferior displacement of the abdominal viscera with a deep inspiration can also bring structures out from beneath rib shadows. If these techniques do not allow for adequate visualization, the patient can be moved into the left lateral decubitus position and the probe placed in the right midaxillary line, scanning toward the patient’s left side. This position can bring structures out from behind the rib cage, and the echogenic liver used as a window to view deeper structures. Similarly, but to a lesser extent, when imaging the left upper abdomen, the spleen can be used for left kidney visualization. Variations in the respiratory cycle can also be used to move the kidneys out from the shadows of overlying ribs.
• Adipose tissue. Abdominal imaging includes evaluation of the aorta, biliary system, focused assessment with sonography for trauma (FAST), and kidneys and bladder.

A low-frequency (2-5 MHz) curvi­linear probe should be used to image abdominal structures.