It was reported that a technical defect with the involved primus device occurred during anesthetic induction; the device alerted for ¿gas mixer fail¿.The device generated the alarms insp n2o high and insp o2 low accordingly.The patient¿s saturation dropped to 61%.The patient was disconnected from the primus in question and connected to another anesthesia device.By doing this, anesthetic procedure and operation could be continued without further problems, no patient injury was reported.As it was reported additionally, the patient became temporarily blue.
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The investigation was carried out based on the available information, the evaluation of the electronic device logfile and the analysis of the received complaint material in the manufacturer¿s lab.The investigation revealed an open clamping n2o vmix-valve, located between the gas supply block and the mix gas tank, to be the root cause of the reported symptom.In case this valve does not closes correctly, the mix gas tank will be overfilled and the maximum pressure will be exceeded.This results in a high input flow, and exceeding of the maximum differential pressure in the course of the measurement of the input flow as well as a short-term increasing n2o concentration.In this specific case, the primus detected the exceeded maximum pressure in the gas tank right after the beginning of the electronic fresh gas dosage.The device generated the according insp.N2o high and insp.O2 low alarms.Due to the high input flow and the exceeding of the maximum differential pressure, a warm start of the gas mixer was performed.Since the detected deviation could not be remedied by this, an autonomous shutdown of the gas mixer was initiated and the according gas mixer fail alarm was generated.In case of a gas mixer fail, the current ventilation mode remains active and a prompt appears, advising the operator to check the vaporizer setting and set the safety knob for o2 emergency delivery to the required flow.This flow streams through the vaporizer.However, in this specific case, the primus was shut down one minute after the gas mixer fail.Dräger finally concludes that the device responded as specified upon a malfunction of a single component.Replacing the faulty n2o vmix valve on-site has already solved the problem.One case has been reported in which a faulty mounting on the pcb has led to a leakage at the n2o vmix-valve and thus to a gas mixer fail.Nevertheless, this case can be considered as a single event as there are no further cases known where a defect of the valve itself has led to the described symptom.
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