Central Venous Access - Real Time IV Access
Real Time IV Access
In the Vascular Access - Basics Module, we talked about the techniques of both the Short Axis and Long Axis approaches. Here, we shall apply them for central venous access. As a reminder, Real Time US signifies maintaining the needle tip in view during the entire process.
1. Short Axis Approach
2. Long Axis Approach
3. Pitfalls
In the Vascular Access - Basics Module, we talked about the techniques of both the Short Axis and Long Axis approaches. Here, we shall apply them for central venous access. As a reminder, Real Time US signifies maintaining the needle tip in view during the entire process.
1. Short Axis Approach
2. Long Axis Approach
3. Pitfalls
1. Short Axis Approach
The vessel of interest is imaged in its short axis, and the needle is guided into the vascular lumen with this view. The needle, also, is imaged in its short axis as well with this approach. On the monitor, the vessel will be displayed as a circular/ovoid anechoic structure, and the needle tip will be an hyperechoic dot.
The vessel of interest is imaged in its short axis, and the needle is guided into the vascular lumen with this view. The needle, also, is imaged in its short axis as well with this approach. On the monitor, the vessel will be displayed as a circular/ovoid anechoic structure, and the needle tip will be an hyperechoic dot.
a. Staggered Sliding:
- Center the vein
- Introduce the needle
- Look for the hyperechoic dot
- Look for the needle tip
- Advance the probe until the needle tip fades
- Advance the needle forward until the hyperechoic dot reappears
- Repeat until the hyperechoic dot is in the vessel
- Advance the tip until it is in the center of the lumen to ensure the angiocath's sheath is, also, in the lumen
2. Long Axis Approach
The vessel of interest is imaged in its long axis, and the needle is guided into the vascular lumen with this view. The needle, also, is imaged in its long axis as well with this approach. On the monitor, the vessel will be displayed as a tubular anechoic structure, and the needle will be seen along its length.
This is a more challenging technique as most peripheral superficial veins are not straight - it is not easy to find a segment of vein that is straight enough to run across the entire screen. However, if you have a "decent" length of the vein imaged on the screen, it should be doable.
The vessel of interest is imaged in its long axis, and the needle is guided into the vascular lumen with this view. The needle, also, is imaged in its long axis as well with this approach. On the monitor, the vessel will be displayed as a tubular anechoic structure, and the needle will be seen along its length.
This is a more challenging technique as most peripheral superficial veins are not straight - it is not easy to find a segment of vein that is straight enough to run across the entire screen. However, if you have a "decent" length of the vein imaged on the screen, it should be doable.
a. Fixed Imaging
- Image the vein in at its WIDEST diameter in the long axis
- Steady the probe-hand once the ideal image is attained
- Introduce the needle IN PLANE with the probe
- Advance the needle forward until the hyperechoic tip is in the vessel
- Advance the tip until it is in the center of the lumen to ensure the angiocath's sheath is, also, in the lumen
3. Pitfalls
As you know, real time needle guidance is defined by the visualization of the needle tip throughout its trajectory. However, sometimes, it is difficult to see the needle tip. Instead, Vascular Wall Tenting or "Needle Shadowing" is seen. Often these signs are mistaken by the novice as the location of the needle tip. VISUALIZATION OF THESE SIGNS IS NOT REAL TIME US NEEDLE GUIDANCE.
Nevertheless, one may use these signs to INFER the location of the needle (NOT THE TIP) when it is difficult to visualize the needle tip on the monitor.
As you know, real time needle guidance is defined by the visualization of the needle tip throughout its trajectory. However, sometimes, it is difficult to see the needle tip. Instead, Vascular Wall Tenting or "Needle Shadowing" is seen. Often these signs are mistaken by the novice as the location of the needle tip. VISUALIZATION OF THESE SIGNS IS NOT REAL TIME US NEEDLE GUIDANCE.
Nevertheless, one may use these signs to INFER the location of the needle (NOT THE TIP) when it is difficult to visualize the needle tip on the monitor.
Clip i. Vascular Wall Tenting Animation:
This animation illustrates that when the needle is applying pressure on the vascular wall, the wall "bends" (tents) inward into the lumen. Visualization of this tent means a part of the needle (body/tip) is already pressing on (or already pierced into the vascular wall .
Clip ii. Vascular Wall Tenting in situ:
The vascular wall is tenting whenever pressure is applied. However, notice that the hyperechoic dot is not visualized. You may infer from this clip that the needle body/tip is touching the vascular wall and its general location. However, the exact location of the tip is unknown.
Clip iii. "Needle Shadowing":
Sometimes when you are advancing the needle, you may see this vertical shadow along the plane where you are advancing the needle. This shadow is created when the tissue is not in contact with the probe - when downward pressure is applied to the needle, the flesh underneath it may, also, be displaced slightly downwards and lose contact with the probe. Hence, a shadow is created.
To prevent this, slide the probe forward so that it is not so close to the needle insertion point.
To prevent this, slide the probe forward so that it is not so close to the needle insertion point.
Key Messages:
- Real time US demands visualization of the needle TIP during the entire guidance process
- Ensure the needle tip and the angiocath's sheath are in the vascular lumen
- Vascular Wall Tenting and "Needle Shadowing" are NOT real time US guidance techniques