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IV Interrogation
In clinical practice we often wonder if the intravenous access that we have at the moment is actually working as it should. Although it may be evident in some cases, in others this is not as simple. Patients have peripheral edema or swollen tissues which may make the clinical signs of infiltration challenging. We do not want to be placing drugs through an intravenous line that is not working. If there is doubt the recommendation is to remove and replace the line. However in some circumstances this may entail a delay in therapy or need of central access. The good news here is that the technology of 2D as well as Color Flow Doppler is able to help us with this differentiation.
Scanning Technique
For optimal interrogation, the linear high frequency probe (7-12 Mhz) should be selected and a shallow depth between 2-3 cm chosen. The probe is held perpendicular to the skin and in a short axis or transverse orientation of the limb of interest as shown in the image. We then recognize the soft tissues structures that are imaged on these planes.
Begin scanning a short distance away from the area of interest to gain an appreciation of the appearance of the normal, uninvolved anatomy. Then the transducer can be slid toward the area of interest.
Soft Tissue Sono Layers
Layers visualized:
1. Skin (the epidermis and dermis cannot be differentiated) is the first hyperechoic layer.
2. Subcutaneous layer. This appears hypoechoic with two components: hypoechoic fat interspersed with hyperechoic linear echoes running mostly parallel to the skin, which represent connective tissue septa. This is where we find superficial veins and our area of interest (V on the image).
3. Fascia. Appears as a linear hyperechoic layer.
4. Muscle. Fascicles as hypoechoic surrounded by a hyperechoic connective tissue.
It may be helpful to view the contralateral side of the patient’s body to obtain information about the normal appearance of structures
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V
Peripheral intravenous line interrogation on 2D
Begin scanning a short distance away from the area of interest to gain an appreciation of the appearance of the normal, uninvolved anatomy. Then the transducer can be slid toward the area of interest.
As you approach the catheter you will see its tip (C) if its located within the walls of the vein (V)
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V
Peripheral IV with Color Flow Doppler
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C
Color Flow Doppler (CFD) may also aid you in the identification of an adequately placed peripheral intra venous line.
Steps:
1. Start by scanning a few centimiters distal to the location of the iv. and scan the limb at an angle and not perpendicular to the skin since CFD works best when the flow of parallel the CFD beam.
2. Turn on the CFD doppler and adjust the nyquist to be in the mid teens. A high nyquist will make it difficult to appreciate changes in flow. A low nyquist will create significant amount of aliasing and will obscure the view.
3. Flush the iv with 5cm of saline. What you should be able to see is:
- Expansion of the vein as the fluid displaces its walls which can be seen in 2D ultrasound
-A change in color in the distal portion of the IV.
Images shown: 2D ultrasound with the presence of the catheter tip on the vein. CFD with a narrow interrogation window displaying color changes indicating a correctly placed peripheral iv.
Color Flow Doppler to Identify Proper Central Line Placement
CFD can also help you identify if you are correctly placing a central line. In the case you are using a catheter to confirm placement in the internal jugular this method can be useful.
Steps :
1. Start by scanning a few cm distal to the location of the catheter and scan the neck at an angle and not perpendicular to the skin since CFD works best when the flow of parallel the CFD beam.
2. Turn on the CFD doppler and adjust the nyquist to be in the mid teens. A high nyquist will make it difficult to appreciate changes in flow. A low nyquist will create significant amount of aliasing and will obscure the view.
3. Flush the iv with 5cm of saline. What you should be able to see is:
-A change in color in the distal portion of the catheter.
Images shown: 2D ultrasound of the internal jugular vein. CFD with a narrow interrogation window displaying color changes indicating a correctly placed central venous catheter.
References.
1.Riveros-Perez E, and all. Utility of color flow Doppler ultrasound to identify peripheral intravenous catheter position in adult surgical patients. SAGE Open Med. 2020;8:2050312120912123. Published 2020 Mar 7. doi:10.1177/2050312120912123