The purpose of the pre-scan is to survey the underlying vessels, confirm the target vessel appropriately, and optimize patient and machine positions and settings in advance of the actual procedure (Figure 21-8). For internal jugular vein cannulation, observe for three structures during the pre-scan: thyroid gland, internal jugular vein, and carotid artery. Visualize all three structures 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, point the transducer position marker toward the patient's left side and the monitor located at the patient's hip and facing you. This will ensure the proper relationship of the underlying anatomy with 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.