Final answer:
The venous needle should be placed at a height that allows the IV bag to create pressure greater than the venous blood pressure, thus ensuring the fluid infuses correctly into the vein.
Step-by-step explanation:
The placement of the venous needle for intravenous therapy should be determined by the necessary pressure required to infuse the fluid into the vein. For the fluid to just enter the vein, the pressure at the entry point must exceed the blood pressure within the vein. If we assume that the blood pressure in the vein is 18 mm Hg above atmospheric pressure, and given that the density of the fluid being administered is 1.00 g/ml, we must first convert the pressure from mm Hg to SI units, where 1.0 mm Hg is equivalent to 133 Pascal (Pa).
After the conversion, the height at which the IV bag should be placed can be calculated to create the necessary pressure head. The IV bag typically is placed at a height sufficient to create a pressure that is greater than the venous pressure to allow the fluid to infuse into the bloodstream without any issue.