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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.
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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:
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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.
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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.
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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