Pediatric emergency medicine trisk 4514 4514
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Caution must be taken to ensure the probe does not slip from being on top of the
vein to above the artery.
Once the vein is positioned appropriately in the center of the screen, the needle
can be inserted, along the center of the probe. In cross section, the needle appears
as a single bright dot, with or without artifact ( Video 131.25 ). When the
needle encounters the vein, tenting of the vessel wall will be seen and then the
wall will “pop” back after the needle tip punctures it. At this point, blood should
be aspirated, and the ultrasound probe can be set aside as the procedure continues
in normal fashion. Once the wire is threaded into the vein, ultrasound can be used
again to visualize the wire in the vessel prior to dilating the skin and inserting the
catheter (Fig. 131.23 and
Videos 131.25 and 131.26 ).
Pitfalls
While ultrasound can certainly enhance placement of a CV catheter, there are
certain caveats. Puncturing the skin either too close or too far from the transducer
may be problematic. If the needle is inserted too close to the transducer, it will
pass under the probe (i.e., through the plane of sound waves) before encountering
the vessel. The point at which the needle contacts the vessel will not be visualized
unless the probe is repositioned. If the needle is inserted in the skin too far from
the transducer, it will encounter the vessel before being visualized. In the shortaxis view the transducer should always be repositioned in order to follow the tip
of the needle. In the long-axis view, the opposite is true. Once the transducer is
correctly centered over the target vessel, the probe should not move. Moving the
transducer from side to side could lead to cannulation of the artery rather than the
vein.
