Circulation 84,122 • Volume 25, No. 1 • Spring 2010   Issue PDF

Why Do New Defaults Turn Off CO2 and Apnea Alarms?

Patricia Roth, MD; Kevin Tissot

GE has proposed “approved” changes to their default ventilator settings on our Aisys anesthesia machines which set the CO2 and/or Apnea default alarms to OFF when in the manual ventilation mode. I am concerned about the safety of these default settings.

Patricia Roth, MD
San Francisco, CA

Dear Dr. Roth,
Thank you for your concern. We have applied decades of clinical experience and customer feedback to ensure that our anesthesia machines are safe and effective for clinical practice around the world, and additional feedback such as yours is always welcome. I’d like to start by reassuring you that every Aisys machine leaves the factory with Apnea and CO2 alarms active during manual ventilation. Deliberate action is required by the clinician and/or institution to allow these alarms to be turned off, and even in that case the circumstances are limited as described below.

As I am not sure which version of software is currently installed on your Aisys machines, I will use Aisys Version 6.0 software for illustration purposes. We continue to improve the features and functionality with each software release, so I encourage you to consult the User’s Reference Manual provided with your machine or with your latest software upgrade for exact details.

In the Aisys machine the Apnea alarm can come from 2 sources, the end-tidal CO2 measurement from the gas monitor, and the measurement of exhaled volume from the patient. I’ll describe each one individually.

In order to turn off CO2 alarms, including Apnea, during manual ventilation the user must choose to turn them off. The user can do so either in the Start Case menu (where they always default to “On”) or in the Alarm Setup menu once the case has started. Switching from manual to mechanical ventilation automatically turns the CO2 alarms to “On.” The CO2 alarms will stay in the “On” state unless or until the user returns to manual ventilation and again chooses to turn them off using the Alarm Setup menu. Simply switching from mechanical to manual ventilation leaves the CO2 alarms in the “On” state. The CO2 alarms cannot be turned off during mechanical ventilation.


The situation with the Volume Apnea alarm depends on how the machine is configured. By putting the machine into “Super User” mode there are many configuration selections available that allow tailoring of the machine to better meet the needs of your particular practice and institutional policies. There are of course factory defaults for all of the configuration selections, but it is always a good idea to review the selections available and decide what is best for your institution. The configuration selections available in “Super User” mode are described in your User’s Reference Manual. There are additional configurations that are only available to a trained service person—this could be a GE service engineer or someone in your local biomedical department. One handy feature available to service personnel is the ability to copy a configuration from one machine to another, allowing you to configure your machines identically based on the selections made for your institution.

One of the menus available in “Super User” mode is shown in Figure 1. As you can see, this menu allows configuration of the Volume Apnea selections and default values for each of the 4 selectable case types. If the Volume Apnea Selection is set to disable at the top of the menu—which is the factory default—the menu selections that allow the Volume Apnea alarm to be turned off during manual ventilation will not appear on the menus during clinical use.

Note that even if the Volume Apnea selection is enabled and the default is configured to “Off,” when the user switches from mechanical ventilation to manual ventilation a message will appear on the screen saying “Select Yes to turn off the volume apnea alarms during manual ventilation.” There are 2 selections available: “Yes” and “No” and the user must select “Yes” to turn the alarm off.

I hope this explanation addresses your concerns, and thank you for the opportunity to remind everyone of the importance of properly configuring the equipment for their needs.

Kevin Tissot
Engineering Shared Services Manager, Anesthesia
Life Support Solutions – GE Healthcare

Note: Dr. Roth has informed us recently that a new version of software from GE Healthcare was installed and solved her concerns.

The information in this column is provided for safety-related educational purposes only, and does not constitute medical or legal advice. Individual or group responses are only commentary, provided for purposes of education or discussion, and are neither statements of advice nor the opinions of APSF. It is not the intention of APSF to provide specific medical or legal advice or to endorse any specific views or recommendations in response to the inquiries posted. In no event shall APSF be responsible or liable, directly or indirectly, for any damage or loss caused or alleged to be caused by or in connection with the reliance on any such information.