5 Place the Ultrasound on Shallowest Depth for the Vascular Probe
The peripheral veins regularly targeted for ED catheter placement are often superficial. There will be times when the only available vein runs deeper. It is important to remember that the deeper the targeted vein, the lower your success rate for placing an intravenous catheter. A 2010 observational study in The Journal of Emergency Medicine found that success rates were significantly higher for veins of moderate depth between 0.3 cm and 1.5 cm.7 In the same study, the authors found that depth was not the only measurement that predicted success rates of intravenous catheter insertion. Successful cannulation also vastly improved when the targeted vein diameter was greater than or equal to 0.4 cm2. Figure 5 shows a vessel within the parameters for optimal depth and width based on this study. Placing the ultrasound on the shallowest depth not only encompasses this range, it also narrows the field to those veins with higher success rates. The shallow depth with the vascular probe also allows for an expanded view of the targeted area, allowing for better visualization of the beveled edge of the catheter. When inserting the catheter through the patient’s skin, be sure to keep the bevel tip facing up to allow the ultrasound beam to strike the beveled edge. When the ultrasound beam strikes the beveled edge, it creates artifact that allows for easier visualization of the tip as you cannulate the vein.
6 Short Axis Versus Long Axis Approach
The ultrasound probe for intravenous catheter placement can be positioned on two axes, short or long. There are no studies to support greater success with one axis over another, but familiarity with both approaches may help to improve your visualization in real time. In short axis (see Figure 6), a trick to improve visualization of the catheter as you advance through the soft tissue toward the targeted vein is the “tilt to follow” method. Once the target vein is located, tilt the probe so the sonographic beams are angled toward the catheter at initial insertion. Then follow the catheter toward the vein, tilting the probe away from you toward the direction of the catheter as it passes beneath your initial position to a position distal to where the catheter will penetrate the venous wall. Using the “tilt to follow” method will limit the likelihood of advancing the catheter through the posterior venous wall, causing extravasation (see Figure 7). Another approach using the long axis gives you a longitudinal view of the entire length of the targeted vessel (see Figure 8). The sonographic beam is narrow, so you will need to place the catheter tip adjacent to the probe and advance the catheter in the same direction as the probe to be able to follow the beveled tip into the targeted vein.