³ remember to image the tip of the needle

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³ Remember to image the tip of the needle. Visualizing the needle shaft is not useful. ³ Be sure to check for depth, compressibility, Doppler flow, and location of nearby arteries. ³ Note how subtle changes in patient positioning, Trendelenburg, and so on impact vessel location and distension. Take some time prior to the procedure to maximize the positioning, using ultrasound as a guide. ³ When using a two-person technique, the more experienced sonogra- pher should hold the probe, and the less experienced one should direct the needle. Pitfalls ³ Keep the vein centered on the screen in the short-axis view. Remember that the needle will be inserted at the center point of the transducer. If the transducer is not centered over the vein, the needle will be directed to the wrong location. ³ After the flash of blood, the procedure is no longer facilitated by ultrasound. At this point, put the probe down and continue the proced- ure as you normally would. ³ Be sure to angle or slide the transducer (in the short-axis technique) to visualize the tip of the needle. If the transducer remains in a static position, it cannot be relied on to demonstrate the needle trajectory accurately. In the short-axis approach, the plane follows the needle tip. ³ In the long-axis approach, the opposite is true. Keep the probe (and plane of the ultrasound beam) steady in the optimal position. If the needle deviates from the plane, the needle (and not the probe) should be redirected. In the long-axis approach, the needle follows the plane. 288 Procedural ultrasound Vascular access
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Cannulation of the subclavian vein The use of ultrasound with the infraclavicular approach to subclavian vein cannulation is limited by the large acoustic shadow created by the clavicle. However, the take-off of the subclavian vein from the internal jugular vein can often be visualized by placing the probe in a supraclavicular position. Using the same basic principles outlined previously, identify the proximal subclavian vein and the internal jugular vein. Cannulation of the external jugular vein Because the external jugular vein is superficial, it is often readily identified by visualization and palpation. However, some cases are limited by a patient’s range of motion or adiposity. In such instances, ultrasound guidance may prove useful. Figure 15.20 demonstrates the sonographic appearance of the external jugular vein, along with the internal jugular vein. The technique of vessel cannulation is identical to that of the internal jugular vein as described previously. Of note, the superficial external jugular vein is easily collapsed with even slight pressure of the transducer on the skin. Peripheral venous cannulation Peripheral venous cannulation can sometimes be unsuccessful after multiple attempts – even with attempts at the relatively larger antecubital veins. In this case, one might consider attempting cannulation of the brachial or cephalic veins. These veins lie deeper in the structures of the upper arm and are not readily palpable. Consequently, these veins are not generally used for
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