Unusual Cause for a Circle System Leak

To the Editor: A rare but major technical disorder occurred in a Drager Sulla 808 V anesthesia machine (Dragerwerk AG, Lubeck, Germany) and led to a massive leak in the circle system without any visually apparent disconnection. Before the first operation of the day, the apparatus was tested for about 30 minutes by mechanical ventilation of an artificial lung. During this procedure, no significant leak was detectable. After that, the anesthesia machine was switched to manual ventilation, which could not be performed due to massive gas loss. In spite of extensive releasing of the flush valve, the hand bag could not even be partially inflated. There was no obvious disconnection, such as hose displacement, or valve malfunction in the circle system. Only after an intensive search was the cause of the leak identified inside the switch for changing over from mechanical to manual ventilation, which is controlled by compressed air. The main component of this device, a rubber diaphragm Figure 1, was broken and led to this unusual kind of failure, which was characterized by airtightness ensured only during automatic ventilation. It is remarkable that such a malfunction is unlike the much more common ventilator failures, when manual ventilation still remains possible. This defect occurred in spite of regular inspections and changing of spare parts by the authorized technical service and is the only serious incident that happened in our department since this type of anesthesia machine was introduced in the early 1980s. Presumably, it was only by chance that the diaphragm rupture did not happen during performance of regular anesthesia. However, the necessity of carefully testing both modes of function, manual and automatic, before the anesthesia machine is connected to a patient is emphasized.Figure 1: Left side: This uncommon defect was located within the switch that controls the ventilation mode (arrow). Right side: The pen penetrating through the rupture indicates its huge dimension, which extends over 3/4 of the diaphragm's circumference.