Unexpected deposits in the anesthetic circuit: a possible cause of PEEP/Pmax valve malfunction

PEEP is regulated by the internal PEEP/maximum peak inspiratory pressure limit (Pmax) valve. Malfunctioning of the PEEP/Pmax valve can result in the creation of unintentional or unstable PEEP, and a reduction of inspired tidal volume. Some of our Dräger Fabius® anesthesia machines were noted to exhibit changes in expiratory waveforms and unstable PEEP during general anesthesia. We considered that the cause was associated with PEEP/Pmax valve malfunction, and then investigated the problems in collaboration with the manufacturer. Seven of the 22 Dräger Fabius® anesthesia workstations at our department exhibited problems with their PEEP/Pmax valves. We replaced the PEEP membrane and sealing washers in these seven anesthesia machines, and the problems were temporarily resolved. After a short interval, however, one of the seven machines began to show a similar phenomenon. We then asked the manufacturer to overhaul the PEEP/Pmax valve and the entire breathing circuit of the machine. On close investigation, we found that the valve components and the internal surface of the breathing circuit were contaminated with unexpected deposits. The build-up of deposits occurred within a year after the previous regular inspection. Our troubleshooting process determined the issue with the PEEP/Pmax valve, which could go unnoticed because the valve is encased inside the breathing circuit, and requires disassembly for close inspection. Our findings should raise awareness regarding the importance of the preventive maintenance cycle as a safety precaution to keep the anesthetic circuit free of unexpected contamination.