Unit for Accurate Measurement of Infusion Rate

Systems for the intravenous infusion of liquid medications into the patient can be divided into two large groups: gravitational infusion systems and infusion systems equipped with some infusion apparatus.

The gravitational infusion system consists of a conduit with the liquid medication, a replaced administration set and an injection needle. The liquid from the conduit passes through the administration set and then enters the patient's body via the needle.

The infusion rate depends on the diameter of the administration set tubing and on the parameters of the liquid, it can not be updated by the operator (the nurse).

The infusion system equipped with an infusion apparatus (usually an infusion pump) consists of the same elements, but administering of the liquid medication is controlled by the sensor that has a feedback with the motor of the pump (Fig. 1).



The nurse preprograms the volume of the infusion dose and either the infusion rate or the duration of the infusion dose. The administration set contains a burette while the burette is equipped with a sensor that controls the infusion rate. The sensor contains a light source (light emitting diode) and a photoelectric cell. Every time a drop falls into the burette, the current through the photoelectric cell changes considerably and the sensor sends a control signal via the feedback line into the microchip of the infusion pump.

The software of the pump counts the number of drops per a minute., i.e. the infusion rate in drops per a minute, and increases the speed of the motor if this measured rate is less than a preprogrammed value or decreases that speed if the measured rate is more than a preprogrammed value.

The problem is only one of evaluation of the rate in ml/min. No technical means of evaluation of the volume of an individual drop has been yet developed. Besides, an important fact is that the drop volume depends on the liquid viscosity, tubing diameter and varies considerably as the conduit devastates.

We offer a new method of the infusion rate precise measurement. The time it takes for a liquid medication to be driven between two fixed levels in the burette of a fixed diameter (i.e. a fixed volume of the liquid medication) is measured. The feedback with the motor of the infusion pump is performed just as in he conventional infusion pumps. The offered method does not require any information about the viscosity or other features of the liquid medication nor about individual drops. The precision of measurement does not depend on the characteristics of the administration set, on the features of the liquid medication, on the liquid medication pressure.