Reliability Assessment of Clinical Ventilators.

System Reliability, Medical Technology, Environmental Testing

A Ventilator in the environmental testing lab. A combination of an electrodynamic shaker and a climate chamber simulates the environmental stress of the control panels during usage, storage and transport. (© Fraunhofer LBF)

While automation and digitization are becoming more and more part of our daily lives, they have long become indispensable in medical technology. When, after an accident or in the course of an illness, methods such as artificial respiration are required to support the vital functions of patients, we want to be able to rely on state-of-the-art technical equipment. In their use in hospitals, these devices are not only exposed to the stresses of their actual use. Especially during transport and storage, loads such as shocks, vibration, humidity, and extreme temperatures occur. These external influences must at no time impair the condition or operation of such equipment.

Methodical System Analysis and Reliability Assessment

Dräger is an internationally leading company in the fields of medical and safety technology. The reliability requirements for ventilators such as those used for intensive care in hospitals are particularly high. In addition, these are complex mechatronic systems that require a perfect interplay of all associated hardware and software components under various environmental influences. In recent years, a strategic partnership has developed between Dräger and the Fraunhofer Institute for Structural Durability and System Reliability LBF aiming to further increase the reliability and quality of medical devices. The aim of this project was the reliability analysis of the control display of the ventilators. Reliability targets were defined in close cooperation with Dräger and its suppliers. Subsequently Failure Mode and Effects Analyses (FMEA) were carried out and merged with data sets from existing FMEAs. From material parameters to manufacturing tolerances to functional properties, all important system contexts were precisely and methodically analyzed and evaluated.

On the Test Bench

Based on the previous methodical considerations and research, Fraunhofer scientists developed an experimental test plan. The aim was to apply all mechanical, thermal and climatic stresses that occurs during the service life of a device within one year and to record and prove the most important functionalities qualitatively and quantitatively. Data from relevant standards were used as a basis for determining the load profiles for the various tests. These were combined with data from measurements of different use cases in clinical use to form a customized test program. Custom test benches were developed and set up at Fraunhofer LBF to observe and characterize functions such as the usability of the integrated touch display or the consistent performance of an acoustic alarm system of the devices. For example, the touch displays were regularly operated by a pressure-sensitive touch robot with different sized artificial fingers to ensure its consistent usability. Between the test cycles, the devices were exposed to different partially combined climatic and vibrational loads in a climate chamber, to simulate the loads in use, during transport, and storage.

In addition to the hardware components examined, the underlying software activities were also closely monitored. In this way, the long-term tests could also help to make bug fixes and improvements in the firmware and software of the devices.

“The LBF helped to shape the reliability-oriented development process for this product. We intend to include the LBF as a partner in the following development projects.” Martin Meyer, Reliability Engineer, Drägerwerk