This week we have a guest blog from Dr. Roland Snijder, Medical Physicist Resident at Haaglanden Medisch Centrum (NL). To obtain his PhD degree at the Utrecht University, Roland worked as a researcher on the multi-infusion project at the department of Medical Technology & Clinical Physics of University Medical Center Utrecht (UMC Utrecht). His research focused on investigating physical causes of dosing errors in multi-infusion systems. In this research flow characteristics of multi-infusion setups were investigated using Bronkhorst Coriolis flow meters. In this blog Roland explains more about his research.
What is infusion?
Most patients admitted to the hospital are treated with medication (pharmaceuticals). Especially in critical care, a substantial amount of patients require intravenous therapy. Intravenous therapy means that a solution of pharmaceuticals are administered directly into the veins. The process of administering pharmaceuticals directly into the veins is called infusion and is done using a vascular access device (e.g. a catheter), which is inserted into the vein.
The importance of an accurate flow
Often patients in critical care, most notably young and premature patients, suffer from conditions that require the intravenous administration of very potent and short acting pharmaceuticals. These pharmaceuticals typically require a very accurate administration where deviations in flow- and thus dosing-rate can easily result in dosing errors. For this reason, infusion or syringe pumps are used.
On top of this, vascular access to the patient is typically limited and therefore many infusion pumps have to co-administer through one catheter (multi-infusion), making the entire pharmaceutical delivery process complex and hard to predict.
Because dosing errors are common in clinical practice, it was clear that more research was required. Many of the results of this research can be found in the PhD-thesis: “Physical Causes of Dosing Errors in Patients Receiving Multi-Infusion Therapy”.
Fig 1. Example of a multi-infusion setup in clinical practice.
Flow measurement with Coriolis flow meter
We conducted a large amount of measurements to learn more about the flow characteristics of multi-infusion setups. These measurements were conducted using Bronkhorst Coriolis flow meters (series mini CORI-FLOW. These flow meters allowed us to measure the flow rate of infusion pumps very accurately, precisely and independent of the density of the solution being measured (although most of the solutions were similar to water).
The flow meters were also chosen because of the suitability for very low flow rates, infusion flow rates may be as low as 0.1 ml/h. Ultimately it is, of course, the dose rate or mass flow rate of the pharmaceutical administered to the patient that is important.
To measure this we used an absorption spectrophotometric setup, which enabled us to measure the concentration of a substance in a solution, i.e. a pharmaceutical or pharmaceutical-analogue. To convert density (e.g. µg/l) to a mass flow rate (e.g. µg/h), the cumulative flow rate (e.g. ml/h) of the infusion setup has to be measured as well.
First we used a precision balance for this but later in the research project we used the mini CORI-FLOW flow meter. The data from the precision balance was rather noisy, whereas the flow meter provided very clean data, which improved our measurements substantially.
However, one point of caution that has to considered is that flow meters do produce a pressure drop resulting in intrinsic flow resistance. The implications of this and how the measurement setup relates to a clinical situation is thoroughly explained in the PhD-thesis.
The research concluded that a wide variety of infusion components all had a particular, usually significant influence and, importantly, medical personnel is usually not aware of the implications this has for infusion therapy. Awareness of the underlying mechanisms of these effects through education and technical innovation were recommended. The Coriolis flow meters from Bronkhorst proved to be very suitable for gaining insight in the different mechanisms of infusion pump system failure.
Further reading: R.A. Snijder - Physical causes of dosing errors in patients receiving multi-infusion therapy (ISBN: 978-94-028-0382-2)
About the author:
Dr. R. A. (Roland) Snijder (1985) is Medical Physicist Resident at Haaglanden Medisch Centrum (NL). He obtained a master’s degree in Biomedical Engineering at the University of Groningen with a specialization curriculum in the area of medical physics (medical instrumentation and imaging). In his master thesis, conducted at the University Medical Center Groningen, he investigated the effects of using computed tomography (CT) for lung cancer screening. After finishing his master thesis in 2012, Roland went on to pursue a PhD degree at the department of Medical Technology and Clinical Physics of University Medical Center Utrecht (UMC Utrecht).
Dr. Roland Snijder (HMC)
Want to learn more about calibration of infusion pumps? Read the blog of Marcel Katerberg, explaining the calibration techniques to improve infusion pump performance.
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)
Learn more about (mini) CORI-FLOW™ instruments combined with a valve or pump and watch the principle of operation of the mini CORI-FLOW Coriolis mass flow meter
This week I felt it would be good to reflect upon some of the blogs that we have put out into the world and share with you some of our most successful work. I cannot define exactly what has made a blog successful but if you have an idea of you would like to see then please let me know.
Below are 5 of our blogs from this year, we look forward to working with you in 2017.
Nils Kupper talks about optimisation of 3D printers
Henk Wassink discusses our work with Machine Builders
Marcel Katerberg on our work to improve Infusion pump calibration techniques
Ric Besseling on the difference between bubbler and Vapour generation systems
Finally, our top 10 tips for installing Mass Flow Meters and Controllers
Happy New Year.