Correspondence  |   February 2007
Malfunction of the New Aisys® Anesthesia Machine
Author Notes
  • GE Healthcare, Life Support Solutions, Madison, Wisconsin.
Article Information
Correspondence   |   February 2007
Malfunction of the New Aisys® Anesthesia Machine
Anesthesiology 2 2007, Vol.106, 405. doi:
Anesthesiology 2 2007, Vol.106, 405. doi:
In Reply:—
GE Healthcare would like to thank Anesthesiology for the opportunity to respond to the Letter to the Editor by Drs. Wax and Neustein.
In their letter, the authors discuss two issues pertaining to the Aisys® machine. The first concerns the function of the EZchange absorber manifold, the second concerns the effect of water on the inspiratory and expiratory flow sensors.
We have been able to reproduce the leak described by the authors. The breathing circuit leaks experienced at Mt. Sinai (New York, NY) were the result of an inadequate seal between the manifold and the absorber canister; small frays on the drain port of the disposable absorber canister produced the inadequate seal. This issue may be identified during the Aisys® automatic system checkout procedure; we have verified this with affected canisters. Of course, if the canister is changed in the middle of a case, there would be no additional system checkout and a leak may result.
We have not been able to reproduce a system leak when the EZchange manifold is in place without a disposable canister because the leak exists where the manifold and the disposable absorber canister connect, as suggested by the authors.
We have taken a two-pronged approach to resolving this issue. First, we are addressing the root cause, the disposable absorber canister, by working with the third-party supplier to remedy the issue with the drain port flashing. Second, we are currently revising the drain seal on the EZchange module so this flashing, even if unchanged, will not affect the seal between the canister and the manifold.
With respect to the moisture and flow sensor issue, the root cause was most likely the impact that moisture or water may have on the function of the flow sensor. Our flow sensors are a vital component of the Aisys® ventilator. Like anesthesia practice, these sensors have undergone extensive evolution since they were first introduced. As clinical anesthesia has moved toward lower and lower fresh gas flows, the impact of the increased humidity has necessitated a redesign of the basic flow sensor. At the time of the events, Mt. Sinai was using an earlier version of the flow sensor. The current flow sensor incorporates an offset in the area of the flow sensor flap that helps to overcome the issue associated with high moisture or water. This version can be readily recognized by the presence of grooves on the bezel of the flow sensor closest to the patient.
The final issue the authors describe is the use of the D-Lite sensor to obtain spirometry instead of using the flow sensors. The D-Lite sensor and the direct patient monitoring of respiratory mechanics the use of the D-Lite may provide are a design feature of the Aisys®. Using the D-Lite will not resolve alarm issues produced by the inspiratory and expiratory flow sensor. The authors’ description of the ventilator alarms suggests that the old-style flow sensors they were using at the time may have either had some moisture on the inspiratory sensor or may not have been calibrated.
The flow sensors should be calibrated daily simply by removing the flow sensor module, waiting for the “no insp flow sensor” and “no expiratory flow sensor” messages to appear, and then reattaching the flow sensor module. The alarm messages reported by Mt. Sinai would not have occurred with calibrated offset flow sensors.
GE Healthcare commends the authors for their insightful and accurate Letter to the Editor.
GE Healthcare, Life Support Solutions, Madison, Wisconsin.