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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”.

multi-infusion setup in clinical practice 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.

mini CORI-FLOW mass flow meter

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 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.