Final answer:
The venous needle must be placed against the blood flow for treatments, such as during intravenous (IV) therapy, where the IV bag is usually placed above the entry point in the arm.
Step-by-step explanation:
The venous needle must always be placed against the flow of blood. This is key in facilitating proper circulation and ensuring that the treatment is delivered effectively. For instance, in intravenous (IV) therapy, the IV bag is positioned 0.24 m above the entry point into the arm so that the fluid can enter the arm not by pressure but by gravity.
However, blood collection bags are placed below the donor's arm, which is based on the principle that increasing pressure in the veins increases flow, as veins carry blood back to the heart at lower pressure than arteries. Understanding the pressure dynamics is crucial.
Blood moves from areas of higher pressure to lower pressure, which is why IV bags for therapy are held higher and bags for blood donation are kept lower to facilitate the respective flow directions. Considering all this, when inserting a venous needle for treatments or fluid administration.