Working in flow, specifically low flow solutions, brings you into contact with applications and challenges that can be quite surprising. This week we discuss an opportunity for new calibration techniques to prove infusion pump performance.
Infusion pumps are well-known in medical applications. They come in multiple operating principles for pumping various fluids. • Volumetric pumps are usually used for food and hydration at higher flow rates up to 1L/h. • Syringe pumps are mostly used for accurately dosing low flow rates of down to 1ml/h or even lower.
We learned from users that the readout of a syringe pump shows the set point flow but it gives no feedback on the actual flow. Because of this lack of feedback on the actual flow being delivered, it is an area that should require regular accuracy checks. A regular programme of checks at a pre-determined flow rate or range is essential for ensuring that the delivery of fluid from the pump matches the expectations of the user. This is also an excellent opportunity to data log the performance of the pump for future reference and assists management purposes.
Moreover, we learned from medical engineering groups that there are currently two main calibrating techniques available for infusion pumps;
Volumetric measuring principle
The first uses volumetric measuring principles. This method usually needs a significant flow rate and minimum volume for achieving a reasonable accuracy within an acceptable period of time. This limits the ability to quickly check syringe pumps at the lowest flow rates and in critical applications. This creates a potentially inaccurate and time consuming calibration process.
Distance measuring principle
The second technique is to measure distance that the plunger travels over a pre-determined period of time and use that figure to extrapolate a figure for accept/reject. This technique is usually determined by the manufacturers of the instruments and carries with it a high degree of inaccuracy when adding together the manual method of measuring, the inaccuracy of the ruler, stopwatch and pump.
Improving response time and accuracy of infusion pump calibrations
Recognizing some of the flaws in the techniques above, and having talked to several professional working groups that use syringe pump calibration systems, we were excited to begin new research In these studies we test new sensor technology and techniques that could benefit the response time and accuracy of infusion pump calibrations.
To define the value of this study we identified together with the working groups potential applications in which accurate dosing is a critical process parameter. Below you will find the applications as identified: • The use in pediatrics where patients are extra sensitive and vulnerable for wrong medicine dosage. • Medication dosage at low rates where it is difficult to obtain a relative accurate and stable flow. • Medication with a small therapeutic band in which a high accuracy is even more important. • Multi infusion systems where multiple pumps are connected to a single cannula. In these systems the compliance of the used syringes and tubing can cause major errors in the actual dosage.
Low flow Coriolis sensor
We defined the hypothesis that the characteristics of a low flow Coriolis sensor could support the scope to improve the accuracy and response time of calibration systems used to calibrate syringe pumps. We demonstrated the validity of this hypothesis during an in-house study and at a hospital in the Netherlands. The Coriolis principle was chosen due to its proven accuracy and long term stability. Furthermore, due to their small internal volume and little pressure drop these instruments can be used in line to test complex multi infusion systems.
Surpassing the accuracy and response time
We bench marked the Coriolis sensor technique against an electronic analytical balance in house. The set-up of this experiment was approved by the Dutch Accreditation Council. Furthermore, we performed a bench mark study against an infusion calibration system at a hospital in the Netherlands.
The results of this study confirmed that the Coriolis sensor techniques can surpass the accuracy and response time of the incumbent measurement principles used in calibration systems.
Read about how Mandy Westhoff explains a typical day at Bronkhorst’s flow meter Calibration Centre (BCC)