In drip feed units, it is a virtual requirement that there be a constant flow or drip into the patient. This ensures that the patient is under a constant state of medication. If the rate of medication is not uniform, and if drugs are used which have a short half life, then quite often the patient is placed in a condition of alternatively being over treated and under treated, and often with the consequences of over treatment having side effects and undesirable reactions.
One form of drip device is the use of a bottle or bag which is held in an elevated position, and wherein the flow is regulated by an adjustable clamp on the hose to the cannula in the patient's vein. The flow of such a unit varies due to the varying pressure head of the liquid, the flow decreasing as the liquid falls in level in the reservoir or bag or bottle.
Sophisticated units are available, these including electrically driven units, but with any electrical device, severe insulation requirements have to be met to prevent even small current leakages measured in micro-amps which could be detrimental to a patient's heart.
Other forms of devices are known, such as disclosed in U.S. Pat. Nos. 3,895,741, 4,033,479 and West German Pat. No. 2,731,448 in which the liquid to be dispensed is provided in a pliant bag, and a pressure applying means in the form of a piston or diaphragm pressurizes the liquid to dispense the liquid to be infused into the patient.
However, during the infusion of drugs or any liquid into a patient, it is essential that not only must the rate of infusion be closely monitored, but also the total dose be carefully controlled. Also it is essential that no air be infused at any time.