Intravenous, or IV, therapy allows for the fastest transmission of fluid and medicines into the veins. Because of the dangers of gas entering the heart from the veins, causing an air embolism, IV therapy relies on drip chambers which elevate a fluid bag so that only liquid drips as gas rises. Nurses have the responsibility of adjusting the drip rate for the safety and comfort of the patient. They do so by employing basic formulas of pharmacology.

Determine the drip factor, or drop factor, of the tubing. This index of fluid flow is based on the opening-size of the infusion apparatus--the tubing device through which the liquid passes. Most common drip factors are 60, 20, 15 and 10 gtt/ml, where gtt is Latin for "guttae," or drops," and ml stands for millilitres. The drip factor can be found marked on the tubing or on the original packaging.

Determine the volume of the solution in millilitres. Usually a doctor requests the introduction of 3 litres, or another volume, of a certain liquid. Because the drip-rate formula requires the units in millilitres, you must convert the volume to the appropriate dimensions. In this case, 3 L x (1,000ml) / (1 L) = 3,000ml.

Determine the time in minutes of administration. For example, the doctor may request 3 L of a solution to be administered for 16 hours. Then you would convert hour to minute by doing the following: 16 hr x (60 min) / (1 hr) = 960 min.

Determine the drip rate in gtt/ml. Drip rate = V / t x (drip factor), where V = volume in ml and t = time in min. From our example, assuming the drip factor is 60 gtt/ml, the drip rate would be as follows: (3,000ml) / (960 min) x (60 gtt) / (1mL) = 187.5 gtt/min, or 187.5 drops per minute.