FIGURE 131.23 Wire in vessel When differentiating arteries from veins using compressibility, it should be noted that if the sonographer pushes with extreme pressure, the walls of the artery could touch one another, especially in hypotensive patients Using ultrasound statically should always be performed after the patient has been positioned Repositioning the patient after identification can lead to changes in anatomic relationships and may result in failed attempts at catheterization When inserting the needle, proceduralists need to be cautious about not inserting the needle too slowly If the needle is inserted too slowly, tenting will occur, the walls of the vein will be pushed together and the needle can transverse both walls Furthermore, it is important that the vein and artery are alongside each other in the transverse view If not, and tenting occurs, it is easy to cannulate the underlying artery instead of the vein The proceduralist must pay attention to both the ultrasound image on the screen and the site of the procedure Inexperienced sonographers may focus too heavily on the screen and a flash of blood in the hub will go unnoticed A methodical approach, along with experience, can help minimize this occurrence Although ultrasound-guided catheter placement of the subclavian vein has been described in the literature, it is much more difficult due to the shadows created by