An automated test system for error simulation in anaesthesia devices

Abstract: Anaesthesia devices are a critical part of the medical equipment in any hospital. Safe operation of these devices is of the highest importance to the lives of the patients. To ensure this, the device has to detect when a component is malfunctioning. During development, the device is tested to insure that possible errors are detected, reported and that the device reacts properly. This thesis was performed at Dräger Medical, in Lübeck, Germany, to analyze and attempt to improve the development of anaesthesia devices. In the anaesthesia device, the gas mixer unit consists of several valves and pressure sensors whose function is to deliver the correct gas mixture to the patient. To verify that any malfunctions in the components are detected correctly, errors are simulated in a laboratory setting. This simulation of malfunctioning valves and pressure sensors is currently done manually at Dräger Medical. This manual procedure is very time-intensive, and limited in terms of complexity and the accuracy. To reliably and cost-effectively test for errors, an automated test procedure would be preferred. Such a procedure is able to perform complex test during extended periods of time. The repeatability and the accuracy can also be higher. A new approach using a computer that controls the simulation hardware was developed. The hardware needs to be able to manipulate the valves and pressure sensors in the mixer and accept commands from a computer to facilitate complex automatic testing. For this purpose, a 32-bit microcontroller with appropriate connectivity was chosen. For sensor manipulation, several modules controlled by the microcontroller were designed and assembled. For communicating with the microcontroller, a graphical user interface was designed in LabVIEW. This offers the operator full manual control over the simulation hardware as well as the possibility to automate the testing procedure through the use of scripts. These scripts are executed by an internal script engine and the results are automatically compiled into a report for documentation purposes. The new system has significantly improved the ability to test anaesthesia devices. Automatic testing can now be done from a normal desktop computer. Compared to the old method of manually testing one signal at a time, the operator is now able to simultaneously manipulate several signals. If no automatic control is necessary, the combination of a computer and microcontroller still offers superior accuracy and flexibility compared to the old method.