The anesthesia workstation (system) was examined by our field service engineer.No fault was found.The nozzle units in the gas modules were replaced as a precaution.The system was returned back for clinical use and no further issues have been reported.The returned nozzle units were subject to simulated use testing in a reference system.A successful system checkout (sco) was performed and thereafter a ventilation test, with the given parameter settings as during the event, was started.Ventilation test was ongoing for 3 days without any deviation in the performance noticed.The reported deviation between set and delivered volume was not reproduced and no alarms for high pressure were generated.Evaluation of the event log shows that several treatment periods have been performed.A few alarms for expiratory minute volume high and airway pressure high were generated in the treatment periods.The log shows that successful sco's have been performed before treatment start and there is no technical error in the log to indicate a system malfunction.It cannot from the log be determined if the generated alarms for expiratory minute volume high and airway pressure high were caused of an increase in tidal volume.Our conclusion, even though no fault was reproduced during simulated use testing, is that one of the nozzle units caused an oscillation in one of the gas modules.Oscillations may result in an extra flow delivered from the gas module.Alarms will be activated if the set alarm limits are exceeded.
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