Single-Use Flow Sensor for Ambulatory Infusion Pumps

New technologies open up room for improvements to existing processes, techniques and equipment. Therefore, therapies and procedures in medical technology can be continuously advanced. The development of the single-use liquid flow sensor represents a new approach to measuring flow rates in the smallest milliliter range, which has been a challenge until now.

Sensors to measure lowest flow rates are required in ambulatory therapy or home care for example. The use of ambulatory infusion pumps offers the advantage of continuous drug delivery over a certain period of time. This has been shown to have a positive pharmacodynamic effect on the efficacy and toxicity of chemotherapy. Ambulatory infusion pumps also have the advantage of shortening hospital stays and thus reducing costs, as well as improving patients' quality of life through the familiar environment.

Systems established to date have a number of weaknesses. The most commonly used elastomeric pumps consist of a pressure reservoir that continuously exerts pressure on the medication, an IV administration set with a flow restrictor, and a IV catheter. They usually have a characteristic concave pressure profile, i.e. the flow rate generated at the end and beginning of therapy is slightly higher than in the middle. The injected flow rates are influenced by the differential pressure between the inlet and outlet as well as by its resistance. While the inlet pressure is determined by the pressure profile of the pump's reservoir, the outlet pressure is affected by several factors: the type of the injection site, the patient's specific vein back pressure, as well as the difference in height between reservoir and injection site. In order to keep the temperature of the solution stable at changing ambient temperatures, manufacturers recommend attaching the flow limiter to the skin with a plaster over the course of the therapy.

The required flow rate accuracy according to international standards is ±15% under very specific conditions. During a typical daily routine, it is challenging for a patient to adhere to the handling instructions that guarantee the specified performance. In consequence the real life flow rates often deviate drastically from the intended values. While higher flow rates lead to an increased toxicity of the therapy, lower flow rates reduce the effectiveness of the treatment.

The exact administration of drugs can therefore have a considerable influence on the outcome of a therapy. The well-being, if not the survival, of the patient depends on reliable and continuous drug delivery (even at extremely low flow rates). At present, the adverse effects described above cannot be monitored. For this reason, many manufacturers of ambulatory infusion pumps are developing intelligent versions of their existing products. One possible solution is the seamless integration of a single-use flow sensor in the infusion set - for example the LD20 sensor from Sensirion.

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