Circulation 122,210 • Volume 33, No. 2 • October 2018   Issue PDF

Volatile Anesthetic Unintentionally Not Delivered

My hospital had three incidents in the last four years that may be related to volatile anesthetics unintentionally not being delivered to the patient. After each of these incidents we reported to GE (we use GE Healthcare Aisys™ anesthesia machines) that we felt there should be an alarm on the machine to alert providers if the following circumstances occur:

  1. if the ventilator is in operation, but no volatile anesthetic (VA) or nitrous oxide was turned on
  2. if the ventilator is in operation, and the VA was turned off due to cassette change, but not turned back on.

We welcome a reply from representatives from GE.


Dr. Joshua Berris
Chairman, Department of Anesthesiology
Beaumont Hospital, Farmington Hills, MI



Dear Dr. Berris,

Thank you for writing about this important issue, which is critical to patient safety during the perioperative period. When using the GE Healthcare Aisys or Aisys CS2 anesthesia systems and “start case” is selected, the system allows the clinician to begin the case with either:

  1. manual ventilation by moving the bag/vent switch to “bag” or
  2. mechanical ventilation by toggling the bag/vent switch from “bag” to “vent.”

The system allows this flexibility so the clinician can decide which mode of ventilation is appropriate for that phase of the case. Similarly, the system allows the clinician to decide when to turn ON inhalation anesthetic agent during the case. This is not done automatically since total intravenous anesthesia (TIVA) may be the selected method of anesthesia delivery, and automatically enabling inhalation anesthetic may result in an unsafe level of total anesthetic delivered. In addition, an alarm that inhalation anesthetic is OFF is not provided since it would result in a nuisance alarm for the TIVA cases. However, the vaporizer setting does clearly display “Off” and the monitored inhalation anesthetic concentrations display “—.” If the user does turn ON inhalation anesthetic and if the agent cassette was removed while the agent concentration setting was non-zero, the anesthesia machine will annunciate a low priority “insert cassette” alarm. If the clinician may want to refill an agent cassette during a patient case, to avoid the alarm, the clinician can set the agent concentration to “Off” before removing the cassette. This mirrors the workflow with a mechanical vaporizer, where the clinician would normally turn it off before removing it from the anesthesia machine or filling it with agent. The Aisys and Aisys CS2 remember the last non-zero agent concentration setting when an agent cassette is removed during that patient case. When an agent cassette of the same agent type is re-inserted, the system displays the last non-zero agent concentration setting, sounds a single low priority alarm tone, flashes the setting at a 1 Hz rate, and displays the message “Confirm?” under the setting. This behavior is a prompt to the clinician to confirm the previous agent concentration setting or to enter and confirm a new agent setting. If the clinician does not confirm an agent concentration setting in 30 seconds, the agent concentration will revert to the current agent delivery, which is Off (zero), and sounds a single reject tone. The prompt to confirm the previous agent concentration setting (or enter and confirm a new agent setting) may not occur if certain other higher priority menus are open. If the agent is changed, the clinician needs to start from “Off” as we do not know what setting would be appropriate. Since some clinicians stop agent delivery by simply removing the cassette rather than setting agent delivery to “Off,” it would not be appropriate to automatically resume agent delivery when the cassette is reinserted since the user intent is unknown. However, if the clinician wanted to restart agent delivery during the maintenance phase and missed the audible and visual clues to reinitiate the vaporizer, then the anesthetic agent monitoring alarms should catch the event if the alarm limits are set appropriately. I hope this clarifies the Aisys and Aisys CS2 functionality and the rationale behind it.


Tim McCormick
Principal Engineer
Anesthesia & Respiratory Care
GE Healthcare

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