The Probe
(continued)
The probe may be positioned either parallel along the length of the vessel (longitudinal view) or perpendicular across the vessel (transverse view). In the longitudinal view, the vessel appears as a long tube, and the echogenic portion of the needle is visualized in its entire length. In the transverse view, arteries and veins appear as dark circles and the echogenic portion of the needle appears as a small point (35).

The probe should be held so that as the needle is inserted, the tip is visible throughout its entire approach toward the vessel. It is important to maintain visual contact with the needle and vein at all times to ensure the needle passes directly into the selected access vein. Once blood is aspirated, the probe can be removed but can be used later to ensure the guide wire is within the lumen (31).

The Ultrasound Unit

There are several adjustable controls on the ultrasound unit. These include:

• Brightness
• Contrast
• Gain
• Depth of field

Making adjustments to these settings allows the user to optimize the images displayed on the screen. In simple terms, adjusting brightness, contrast, gain, and depth of field allows the user to center the image you want to see and make it as big and as clear as possible. Doing so enhances the user the ability to make a more precise interpretation of the object being viewed.

Holding the Probe

Hold the probe by supporting the side closest to you with your thumb and the opposite side with your index and middle finger. The remaining fingers and lateral aspect of your hand form the "base" and rest on the patient's arm providing support. You may also want to support your forearm to avoid shoulder fatigue and reduce probe movement. A hand holding a probe in a free floating fashion causes hand fatigue and uneven pressure on the skin. Keep as much of the probe face flat to the surface of the skin as possible without pushing down too hard. Applying too much pressure with the probe compresses veins making accurate visualization difficult.

Cable management is another aspect of probe control. If not positioned effectively, the weight of the cable can pull on the probe causing it to tilt and slide off the vein. The cable can be rested over the unit, across the bed, over the shoulder or wherever the weight is best supported based on where the ultrasound unit is placed. Simply transfer the weight of the cord to something else so it does not pull on the probe.