IWhy is the bottle of IV fluids elevated when administered to patients?

Question

Why is the bottle elevated when administered to patients and by what factors would the flow rate change if the height of the bottle above the patient is doubled, with other factors constant.

Answer 1

IV bags are elevated to use gravity to administer fluids to a patient. Raising the height of the bag would increase the gravitational potential energy, but would not affect flow rate. The accerleration due to gravity is constant and the flow rate would be the same regardless of the height as long as it was elevated.

Two things that might change flow rate are changing the thickness of the tubes or changing the pressure of the bag. Normally, a full bag would exert more pressure than a nearly empty one, but IV's have pressure regulators. (The thing that drips from the bag to the tube) This is to keep the full high pressure bags from emptying out too quickly into the person.

So really the only thing that would affect flow rate is changing the thickness of the tube or removing the thing that dripped.

Answer 2

In the old days, intravenous fluid administration depended on gravity to overcome the venous pressure. I don't remember the average venous pressure, but it wasn't too high, measured in centimeters of water. Flow could be regulated by height of the bottle or by an adjustable clip on the iv tubing. The rate was determined by counting the drops per minute.There were 20 drops per milliliter in adult set-ups and 60 drops per ml in pediatric set-ups. They could go out of adjustment easily.

In most hospitals since the 1980's or so, iv fluids are adjusted via a pump that measures the flow rate and has digital read-outs and can be adjusted by the push of a button or two. Like every other piece of electronic equipment, it has to be calibrated periodically. But it is far more accurate, and the height of the bottle is less important, but it still needs to be placed above the pump.

In real life, other factors are never constant. Sometimes you cannot find a satisfactory vein to insert the needle. If a patient is markedly dehydrated, the flow rate has to be relatively fast. If he is in renal failure, fluids are administered very slowly. In severe diabetic ketoacidosis they have to be monitored very carefully. Sometimes you're damned if you give fluids too rapidly, othertimes you're damned if you give them too slowly.

Answer 3

It is elevated so that the fluid drains into you. The flow rate does not change if the height was doubled. There is a clip on the IV that controls flow rate.

Answer 4

the bottle is elevated so staff don't have to bend down to administer or adjust the drip.
as you know, water doesn't compress .. so the rate of flow is mostly determined by the size of the sphincter.

Answer 5

Gravity fed, there is a restrictor by the needle that will allow only so much Saline fluid in at a time.

Answer 6

So gravity can do the work of delivering it.

The rest of your questions sound like homework questions, so I'll pass.