Final answer:
A tourniquet is applied above the venipuncture site to engorge the veins, making them easier to access. For IV placement, the height must be calculated to overcome the venous blood pressure, ensuring that the fluid will enter the vein with the help of gravitational force.
Step-by-step explanation:
A tourniquet is applied 3-4 inches above the intended venipuncture site to facilitate the process of venous engorgement. By applying a tourniquet, blood flow out of the area is restricted while still allowing arterial flow into the limb. This leads to the veins becoming more filled with blood, and therefore more prominent, making it easier for the healthcare provider to locate and puncture the vein successfully. As for the calculation of the height at which an IV bag should be placed, it involves understanding the effects of gravitational force and blood pressure within the veins.
Calculating the Height for an IV Bag Placement
Intravenous infusions rely on gravitational force to administer fluid. If the fluid's density is 1.00 g/ml, to overcome a venous blood pressure that is 18 mm Hg above atmospheric pressure, one first needs to convert this pressure to SI units. Since 1.0 mm Hg equals 133 Pa, we can calculate the height that will provide sufficient pressure. The pressure exerted by the fluid column must be greater than the venous pressure to ensure that the fluid will enter the vein. This is particularly important when dealing with a collapsible IV bag, as any height set for the bag must account for the lack of additional pressure that would come from an inflexible container.