Category: 4. Abdominal Aorta Ultrasound Protocol: Long Axis

When an anterior view is difficult to obtain, an alternate approach is to use the patient’s right or left side to obtain long axis views of the aorta.

From the patient’s Right Side, visualize the liver, IVC, and aorta.

• Place your probe, with the indicator facing the patient’s head, in the right mid-axillary line around the 10-11th intercostal space.

From the patient’s Left Side, visualize the spleen and adjacent aorta.

• Place your probe, with the indicator facing the patient’s head, in the left posterior axillary line around the 7th-8th intercostal space.

• Be sure to orient your caliper perpendicular to the aortic wall so you don’t overestimate the diameter.

The Cylinder Tangent Effect

Be careful with underestimating the aortic measurements using the long axis approach. This concept is called the Cylinder Tangent Effect and can be seen below where panel (A) shows an ultrasound measurement through the center of the aorta will provide the maximal anteroposterior diameter, whereas panel (B) shows an ultrasound measurement to the side (tangent) of the aorta and will result in a falsely smaller aortic diameter.

• You should see the celiac trunk and superior mesenteric artery (SMA) branch off the aorta in the long axis view.

We recommend obtaining your short axis views and measurements first, then obtaining your long-axis view.

Step 1. Orient the Probe in the Long Axis/Sagittal Plane

• Return to the short axis, subxiphoid view described above, then rotate your probe 90˚ clockwise, with the indicator towards the patient’s head.
• Tip: center the aorta in the short-axis before rotating. It may be useful to use 2 hands – one to keep your probe centered over the aorta, and the other to rotate the probe.