Vascular Access

With few exceptions, vascular access is required to perform an anesthetic.  As the patient population continues to age and the number of comorbidities in these patients increase, obtaining adequate vascular access can be very challenging.

When properly used, studies show ultrasound-guided vascular access improves success rates, while reducing iatrogenic injury, the number of needle passes and infection rates.  The Agency for Healthcare Research and Quality, and the National Institute for Clinical Excellence support the use of ultrasound in the placement of central venous catheters.  In 2012, the American Institute for Ultrasound in Medicine (AIUM) collaborated with many professional medical societies to develop evidence-based recommendations and guidelines for ultrasound-guided vascular access.

Ultrasound Vascular A&P

A thorough understanding of vascular anatomy is prerequisite for performing any vascular access procedure.  Now, let’s examine the ultrasound characteristics of arteries and veins, comparing and contrasting their appearance.

Arteries

Arteries are thick, muscular vessels that allow blood to flow under high pressure. In cross-section, arteries appear round, and in longitudinal view they are tube-like. If slight pressure is applied with the transducer, pulsation is visible. While arteries are more difficult to compress than veins, it is possible, especially in individuals who are dehydrated, or had severe blood loss. Arteries display color when Doppler is applied.

Veins

Veins are thin-walled capacitance vessels. They are easily compressible, often just the weight of the transducer on the skin will flatten them. Similar to arteries, veins are round in cross-section and tube-like in longitudinal view, and they will show color when Doppler is applied. The most obvious difference between arteries and veins are the valves located throughout the venous system. If you scan proximal and distal, you will eventually find them (identified by the white arrows in the image.)

This video is a cross-sectional image of the brachial artery and veins in the antecubital fossa of the arm. Note the median nerve, which appears as group of small circles directly above the artery in the middle of the screen. During the video, slight pressure is applied with the transducer, showing the compressibility of the veins while the artery remains open. This is a normal finding with ultrasound. However, if the veins are distended and not compressible, the likely cause is a a deep vein thrombosis.

This video is a cross-sectional view of the brachial artery and veins in the antecubital fossa with Doppler applied to the BMode image. While both vessels appear pulsatile with color-flow Doppler, note the difference in pulsatility between the artery (red) and vein (blue).


References

Aldrich JE. Basic physics of ultrasound imaging. Crit Care Med. 2007; 35: S131-7.

Falyar CR. Ultrasound in anesthesia: applying scientific principles to clinical practice. AANA J. 2010; 78: 332-40.

J Ultrasound Med. AIUM practice guide for the use of ultrasound to guide vascular access procedures. 2013; 32: 191-215.

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