Would it be a good idea to check a new development or a re-design in the laboratory, or can you well do without this expense? Opinions differ on this! What is indisputable, though, is that risks can be better estimated and unforeseeable costs avoided through the use of a neutral supervisory authority.

Karl Schnurr AG* specialises in the development, construction and sales of medical devices. The Swiss company is currently working on a new generation of mobile infusion pumps. Weighing almost 1.4 kilos, the "Metering Unit 2030" is not only intended to be 15 percent lighter than the predecessor model, but should also integrate all common interface standards. This is intended to enable flexible use for the most diverse therapeutic tasks as well as connection to external patient data management systems (PDMS), barcode systems or clinical networks.

The infusion pump, which has to have a pumping rate accuracy of ±2 percent according to IEC/EN 60601-2-24 , is operated via a graphical display with background lighting. Its supply is rated at 11...16 V DC and is provided by an external 12 V plug-in power supply. A long-life battery is intended to ensure the safe relocation of intensive care patients for which the device must provide power for at least 17 hours at a pumping rate of 1 ml/h or 14 hours at 20 ml/h. Beyond that, exactly coordinated automatic sequences are designed to avoid handling errors in each phase of the treatment. For example, an integrated piston brake protects against the unwanted dispensing of medicaments or free flow.

Cost explosion through undiscovered errors. Compliance with medical technology standards in the development of the "Metering Unit 2030" are only one side of the coin. The other is the feasibility of this mechatronic solution. Since company founder Karl Schnurr is an advocate of calculable costs and doesn't want to experience any nasty surprises during the development of the infusion pump, he has decided to work with an external laboratory services provider right from the functional model phase - especially since he has been sensitised to this by his entrepreneurial colleagues. One of them had to start again from square one due to an error in a dialysis device discovered during the prototype phase, while his best friend since their days together in kindergarten, who is also involved in medical technology, suffered a far greater blow. In his case it wasn't found out until the pilot lot for the manufacture of a digital blood pressure measuring device that it couldn't be produced as envisaged. The redesign increased the development costs by a factor of 85. The manufacturer of the dialysis devices got off much lighter. The extra costs in his case amounted only to a factor of ten. “Such costs are not included in the calculation and can even threaten a company's existence,” says Mo Aakti from the mechatronics specialist Antrimon AG from Muri. The technical manager says that the extra costs for the rework are only one side of the coin: "The delayed market entry is no less serious." And that applies to all branches of industry, not just medical technology.

Understanding of applications for the provision of good services. But what does a mechatronic laboratory service provider actually do? It sounds banal, but the first task is to gain an understanding of the application. Good development can only be achieved if the application is understood by reading the list of requirements, the performance specification and so on. This understanding even includes taking into account the operator's environment. "In the case of the infusion pump it is assumed that the nursing staff wear latex gloves for reasons of sterility", says Mo Aakti with regard to this attempt to understand an application. "The question that arises for us from that is: does the display react at all under this condition?" In the ideal case the developers will already have determined during the functional model phase that the foreseen touch screen does not react to operation with gloves and will replace it with a functioning display. If this functional error doesn't appear until the construction of the prototype or even later during the pilot lot, then the development costs are increased several times over, as in the cases described for the dialysis device and the digital blood pressure measuring device.

V-model facilitates fault finding.

Understanding of the application is, however, just a small stone in the mosaic of the laboratory service. A large part of this is concentrated on clarifying whether the infusion pump, as designed, works at all and can be manufactured. Further questions may be concerned with the optimisation of the system or compliance with certain standards. Antrimon AG follows the «V-Modell XT» development standard when conducting its tests. "The specific thing about this model is that an entire system can be dismantled down to the individual components and then assembled again", Mo Aakti explains, and he adds: "Since the respective requirement and the associated test lie exactly opposite each other in the V-model, errors in the system architecture can be clearly correlated and eliminated." For example, if it transpires when assembling the "Metering Unit 2030" that the piston cylinder vibrates during movement, this methodical approach allows the precise reason for that to be identified. This approach is ideal in particular for mechatronic applications such as the infusion pump, because with the aid of the V-model a complete system can be disassembled into individual subsystems and these in turn into individual modules.

*Name of company and product changed

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Lars Härtel
Team Leader Test & Technology


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