The purpose of the Pre-scan is to survey the underlying vessels and confirm the target vessel appropriately (Figure 19-8). For internal jugular vein cannulation, three structures should be seen during the pre-scan: thyroid gland, internal jugular vein, and carotid artery. Generally, all three structures should be visualized before proceeding. The internal jugular vein can be easily compressed, especially in volume-depleted patients; confirming its presence in relationship to the other structures will ensure verification of the proper target vessel. When standing at the head of the bed, the position marker should be pointed toward the patient's left side. This will ensure the proper relationship of the underlying anatomy to the ultrasound image anatomy. For example, when cannulating the patient's right internal jugular vein, the thyroid, carotid artery, and internal jugular vein will be from left to right anatomically as well as on the ultrasound monitor. Thus, when moving the needle more medially, or to the left, it will move left on the monitor. When moving the needle more lateral, or to the right, it will move to the right on the monitor.