To assess the inferior vena cava, aka the IVC, sonographically, currently, clinicians use a wide variety of techniques. To address this variability and heterogeneity, this protocol offers a systematic IVC ultrasound image acquisition approach. This technique has built-in safeguards to minimize common pitfalls and prioritizes the least technically challenging views first, allowing the operator the greatest chance of obtaining an adequate exam efficiently.
In patients with shock of unknown etiology, it can be helpful to screen for extremes of IVC size and respirophasic change to narrow the differential diagnosis. However, accurate interpretation of the IVC requires sidestepping important pitfalls in image acquisition, which this protocol is specifically designed to address. New providers often struggle with misidentification of the aorta as the inferior vena cava and misidentification of pseudo collapsibility as true IVC respirophasic change.
These errors can be minimized by consistently obtaining both long and short axis views of the IVC during each exam. For individuals over one year of age, visualize the IVC with any low frequency ultrasound transducer, such as a linear phased array sector arc probe or a curvilinear probe. Set the machine to the cardiology convention using the cardiac preset function, which is present as an indicator on the right of the screen, and confirm that the screen refresh rate is at least 20 hertz.
Then set the mode to B Mode and the depth to 6 to 20 centimeters, depending on the IVC depth in each patient. Apply ultrasound gel to the transducer. To obtain the anterior IVC short axis view, position the patient in the supine position with both hips flexed if tolerated by the patient.
Obtain the lateral IVC short axis view. Place the ultrasound probe centered on the patient's anterior midline, just caudal to the xiphoid process in the coronal plane with the transducer indicator mark pointing toward the patient's left. Adjust the depth so that the IVC and aorta appear in the middle third of the screen and the spine is visible.
To set the axis, fan the ultrasound beam cranially or caudally until the IVC and the abdominal aorta appears in the short axis cross section as rounded structures. Decrease the gain until the blood in the IVC is either completely black or just a few specs of gray are visible. Once all the settings are done, click on Acquire.
Next, obtain the anterior IVC long axis view by positioning the patient and the probe as demonstrated earlier and center the view on the IVC. Then rotate the ultrasound probe 90 degrees counterclockwise without translating the probe such that the probe's indicator faces cranially at the end of the rotation. Adjust the depth so that the IVC appears in the middle third of the screen and the liver tissue is visible deeper than the IVC.
To set the axis, fan the ultrasound beam toward the patient's left or right until the IVC appears rectangular, intrahepatic structure spanning from cranial to caudal. Now decrease the gain until the blood in the IVC is either completely black or just a few specs of gray are visible. Once all the settings are done, click on Acquire.
To quantify the IVC anterior to posterior diameter choose a live optimized image of the IVC, click on Freeze, and click on Caliper or Measure depending on the machine's measurement button. Then move the track ball to the anterior wall of the IVC approximately one to two centimeters caudal from the hepatic vein confluence, and click on Select. Move the track ball to the posterior wall of the IVC such that the line between the two points is roughly perpendicular to the long axis of the IVC.
Click on Select and then click on Acquire. Now obtain the right lateral IVC long axis view by positioning the patient in the supine position with the legs flat and the right arm moved away from the patient's side, either overhead or outstretched laterally, to allow access to the right flank. Place the probe transducer in the coronal plane with the indicator pointing cranially in the sixth or seventh right intercostal space anteriorly to the right midaxillary line.
Adjust the depth so that the IVC appears in the middle third of the screen and the liver tissue is visible deeper than the IVC. To set the axis, fan the ultrasound beam anteriorly or posteriorly until the IVC is visualized as a rectangular intrahepatic structure spanning from cranial to caudal on the screen. Decrease the gain until the blood in the IVC is either completely black or just a few specks of gray are visible.
Click on Acquire. To obtain the right lateral IVC short axis view, position the patient and the probe as demonstrated earlier for the lateral IVC long axis view. Then rotate the probe 90 degrees clockwise so that the probe indicator mark is pointing anteriorly.
Adjust the depth so that the IVC appears in the middle third of the screen and the liver tissue, aorta, and spine are all visible deeper than the IVC. For setting the axis, fan the ultrasound beam cranially or caudally until the IVC and abdominal aorta are visible in the short axis view as rounded structures. Decrease the gain until the blood in the IVC is either completely black or just a few specks of gray are visible.
Click on Acquire. An adequate exam permits the visualization of the IVC. An inadequate exam is one in which the IVC is not visible or the IVC appears to show respirophasic change only in the long axis plane.
Following this procedure, you should document your findings, incorporate them into the clinical context, and decide on any modifications to patient management. The literature on sonographic assessment of the IVC is plagued with conflicting findings. By standardizing image acquisition, this review may help determine whether these conflicts are due to heterogeneity of image acquisition or due to other factors.
