Ultrasound needle guidance is the skill of accurate steering of the needle tip towards a target when looking at the screen

Ultrasound guided vascular access (UGVA) is the skill of accurately steering the needle into blood vessels guided by visual feedback

The biggest advantage of ultrasound needle guidance is the possibility of steering the needle tip accurately in real time into the centre of even small caliber vessels ensuring correct final catheter positioning

Another advantage is that an entire peripheral venous catheter can be advanced into the target vessel guided by real time visualisation ensuring correct final catheter positioning

The diameter and depth of a vein below the skin surface is easy to gauge using the depth indicator at the lateral border of the ultrasound screen

The majority of ultrasound systems have built-in caliber software for accurate on-screen measurements; however, for practical purposes, it is sufficient to “eyeball” the diameter and depth below skin surface of a vein using the on-screen depth indicator

Use this technique to estimate the venous diameter and depth below skin surface:
– Locate the vein
– Diameter: compare the diameter of the vein with the depth indicator at the lateral side of the screen
– Depth: compare the distance from the surface of the skin to the centre of the vein with the depth indicator at the lateral side of the screen

It is more difficult to insert a venous catheter into a small caliber vein compared to a large caliber vein. The critical diameter of a vessel is approx. 4 mm.

Also it is more difficult to insert a catheter into superficial or very deep

As some catheter length is used for traversing subcutaneous tissue before entering the vessel, long catheters are preferred. If possible, use catheters > 45mm

The length of the catheter placed within the target vessel should not be less than 30mm

For that reason, it is very important that the diameter of the vein as well as the depth of the vein below the skin surface is estimated correctly

Whether you see one or two or more blood vessels on the ultrasound screen depends on the number of vessels in the tissue underneath the probe

The number and the location of the vessels in the tissue will change if the position or orientation of the probe is changed

Veins collapse when pressure is applied by the probe on the skin above the vein

Arteries pulsate and this pulsation is sonographically visible. The pulsation is amplified when the transducer pressure on the skin is increased

In hypovolemic and hypotensive patients arteries can collapse as well as the veins, thereby mimicking veins; however, very gentle, light pressure will also amplify the pulsation of the arteries in this patient group

Veins with thrombosis, including superficial veins, do not collapse even when high pressure is applied. Such veins should not be mistaken for arteries

Compression of the vessels with the transducer can be used to distinguish between veins and arteries

Veins are compressed proportionally to transducer pressure

It is also evident how the arterial pulsation is amplified proportionally to transducer pressure

Arterial vascular access is performed

Blood vessels are hypo-echogic (black) on the ultrasound screen

Blood vessels in the longitudinal, long axis view (LAX) are seen as uniform black, tubular structures in the tissue between the skin and the deeper located muscles

Blood vessels in the cross-sectional view are seen as round, black structures

Only techniques using the cross-sectional view is used in this course

A linear probe is always preferred for vascular access

A high frequency linear transducer ensures a high resolution image at the expense of penetration in terms of reduced depth