The Subcostal Window
©Walter Rasmussen, R.D.C.S.
The subcostal window is located at the mid, upper abdomen, usually directly below the xyphoid process and the inferior border of the left ribcage. For imaging the heart, the transducer is pointed superiorly toward the left lower thorax at a shallow angle. For the liver, inferior vena cava, hepatic veins and abdominal aorta, the transducer is placed at the midline and perpendicular to the abdominal wall, with the index mark pointing cephalically.
The patient should be positioned in the supine position for the subcostal views. It can be helpful to have the patient bend their legs at the knees and place their feet flat on the table, thus relaxing the abdomen and making it more yielding to the probe. Palpate the border of the ribcage in order to locate the xyphoid process, a sharp, bony prominence, upon which direct probe pressure should be avoided.
It is almost always necessary to direct the patient to inhale to some degree and hold their breath in order to obtain the best quality images from this view. If the image is still faint with inhalation, better penetration and signal strength can be obtained by increasing the gain and/or lowering the transducer frequency.
Since the heart is usually at a greater distance from this transducer position, it will often be necessary to move the focal zone to the area of interest. It can make a considerable difference to visual perception to adjust the TGC tabs for an evenly-lit image because the near field tends to be much brighter than the far field.
After a good overall image of the heart is recorded, it is usually necessary to pay individual attention to the right heart, the tricuspid valve, the inter-ventricular septum, the left heart, the mitral valve, and the interatrial septum. Color Doppler can greatly aid in finding the IVC, hepatic vein, and the abdominal aorta when they are small in diameter or when the image is of poor quality. Due to the increased distance, it is often necessary to increase color Doppler gain in order to obtain adequate images.
If the patient is pregnant, no more than minimal pressure should be applied to the abdomen and the patient should not be asked to hold her breath or strain in any way. If a good subcostal view cannot be obtained without applying more than minimal pressure on a pregnant patient, it is advisable accept the sub-optimal quality. Furthermore, if there is discomfort from pressure applied to the probe for any patient, that is enough reason for limiting or omitting the view from the study.
For ergonomic reasons, the sonographer should assume a standing position for all of the subcostal and suprasternal views because a sitting position requires the arm and hand to be in a prolonged unnatural position and increases the possibilty to acquire cumulative strain of the shoulder, hand and wrist. If the bed is adjustable, lower or raise it so that as little tension as possible is developed in the lower spine, elbow and shoulder. Not all sonographers injure themselves by performing ultrasound exams nor are the injuries all the same, but the sonographer should pay attention to positions which tend to stress or strain an area of their body and take steps to limit them if chronic pain develops.
As stated in the opening chapters of the guide, patients who have had abdominal surgery, who are obese or who have bandages covering the abdomen, present some technical challenges to imaging from the subcostal window.