## 3 Measurement Results  
### Tests of Medical Devices  
#### 3.1.1 Syringe Pump  
Smaller quantities of drugs are administered via syringe pumps. The operating principle is that a pusher block on a threaded rod is driven by an electronically controlled stepper motor. The pusher block (plusher holder) moves the plunger, or more precisely, the thumb rest, and thus delivers the desired amount of volume drug per unit of time. Most syringe pumps have a pressure sensor built into the plunger holder. If a set pressure (occlusion pressure) value is exceeded during the advance of the syringe plunger, the syringe pump stops, and an alarm is triggered. At that moment, the plunger retracts slightly to release the pressure. The BBraun Space is a modular infusion system. The BBraun Perfusor Space syringe pump is designed for intermittent or continuous administration of parenteral fluids, enteral fluids, medications, blood and blood products in adults, children and neonates. For the tests, a pump was used that had been modified by the manufacturer in terms of software, so that it was possible to measure at \(0.01\,\mathrm{mL}\,\mathrm{h}^{-1}\). Normally, the smallest possible flow rate value is limited to \(0.10\,\mathrm{mL}\,\mathrm{h}^{-1}\).  
Figure 7 shows the measurements with the BBraun Perfusor Space syringe infusion pump at a set flow rate of \(0.01\,\mathrm{mL}\,\mathrm{h}^{-1}\) and a measurement period of about 3 days. The syringe used was a BBraun Omnifix \(10\,\mathrm{mL}\), which is probably too large for this low flow rate. From these measurements, the performance of the syringe pump at extremely low flow rates can be derived. The manufacturer specifies a flow rate accuracy of \(\pm 2\%\) according to IEC/ISO 60601-2-24 [11]. Added to this is the uncertainty of the \(10\,\mathrm{mL}\) disposable syringe used, which according to standard ISO 7886-2:2020 [25] results in a maximum permissible tolerance for the ID of \(\pm 1\%\), leading to a tolerance of \(\pm 2\%\) for the flow rate. The measurement deviation obtained with this configuration were within the manufacturer's specifications. In addition, the figure shows a typical measurement as required for the analysis of the short-term variability of the flow rate. Furthermore, such a measurement can be used for the analysis of the short-term variability of the flow rate according to standard IEC/ISO 60601-2-24 (trumpet curve) or the AAMI technical information report (TIR) TIR101:2021 [16] (PK-CV curve). Both methods are similar but different. While the trumpet curve focuses on the variation of the pump flow rate, the CV-PK describes the drug consumption of a patient in a simplified way using a single-compartment pharmacokinetic (PK) model. The result is thus the variation (coefficient of variation, CV) of the drug level in the patient's body.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Flow Rate** & **Measurement Uncertainty** \\  & **U(\(k=2\))** \\ \hline \(5\,\mathrm{nL}\,\mathrm{min}^{-1}\) & \(5.0\,\mathrm{\char 37}\) \\ \hline \(20\,\mathrm{nL}\,\mathrm{min}^{-1}\) & \(2.5\,\mathrm{\char 37}\) \\ \hline \(100\,\mathrm{nL}\,\mathrm{min}^{-1}\) & \(1.0\,\mathrm{\char 37}\) \\ \hline \(\mathrm{greater}\) than or & \(0.5\,\mathrm{\char 37}\) \\ equal to \(500\,\mathrm{nL}\,\mathrm{min}^{-1}\) & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Expanded measurement uncertainty U(\(k=2\)) of the Nanoflow test facility at different flow rates.