Add to bookmarks

Automated End Tidal Control Device Achieves and Maintains Concentration of Exhaled Agent and Oxygen Effectively

Automated gas control is a novel method that alters Fresh Gas Flow (FGF) and controls end tidal agent and oxygen using an End Tidal Control (EtC) device

The poster can be downloaded at the end of the page


  • Automated gas control is a novel method that alters Fresh Gas Flow (FGF) and controls end tidal agent and oxygen using an End Tidal Control (EtC) device, see Screenshot
EtC GE Aisys Screenshot
EtC GE Aisys Screenshot
  • EtC is proprietary software installed on the GE Aisys CS2 anesthesia machine (GE Healthcare, Madison WI).
  • The user selects desired end tidal anesthesia agent (EtAA) and end tidal oxygen (EtO2) contentrations. EtAA/EtO2 measured every breath.
  • The EtC software algorithm adjusts mixer (FGF) and vaporizer output to achieve and maintain target values, then FGF is automatically reduced to minimal flow when using EtC, to 0.5 L/min


  • A prospective RCT of 220 patients ≥ 18 y, ASA PS 1-3, assigned to Manual Control (MC) or to use EtC to alter FGF and agent/oxygen concentrations automatically. Non-cardiac cases were studied.
  • MC arm used standard manual control of FGF or agent/ oxygen, and providers recorded their intended set points.
  • EtC arm set the desired EtAA and minimal flow on the Aisys and the EtC software then altered FGF and concentrations.
  • Gas data extracted from the Aisys internal log.
  • Primary objective; EtC achieves and maintains EtAA and EtO2 in a manner that is non-inferior to MC by a margin of 5%.
  • Secondary objectives; safety data for EtC arm, amount of agent used in each arm, number of user interactions.
  • Performance of EtC examined percentage of time with agent of oxygen within acceptable concentrations (the greater of ± 5% from steady state mean concentration (SSMC) set), efficacy, response time to reach 90% of the desired SSMC; settling time, time to achieve the desired EtAA and EtO2 SSMC; overshoot, amount the EtAA and EtO2 deviated temporality from final SSMC.
Example of close matching of EtC to desired concentrations
Fig. 1
% duration within acceptable limit at steady state
Fig. 2
Response and Settling Times in seconds
Fig. 3
Overshoot %
Fig. 4
Agent usage from induction to patient disconnect
Fig. 5


  • Fig. 1 shows a case example of close matching of EtC to desired concentrations. Subsequent figures show means values.
  • No significant difference was found in study population ages, adverse events, user interactions or vasoactive drug use.
  • Accuracy was high for EtC which maintained concentrations within 0.1% DES, 0.03% ISO, 0.04% SEV. EtAA was within acceptable limits for 98% using EtC and EtO2 98.8% of the time, but MC only 45.9% and 41% respectivesly, see Fig. 2.
  • Fig. 3 shows response time and settling time in seconds.
  • Fig. 4 shows the limited overshoot using EtC.
  • EtC superiority was highly significant at p<0.001 (except for agent usage) in all domains.
  • Mean inhaled agent usage was reduced by 26% for DES, 30% ISO, 5% SEVO; Sevo savings were small as minimal flow was set at 2L/min to avoid Compound A issues, others used 0.5L/min. See Fig. 5
  • 99% of staff rated ease of use of EtC same or easier than MC, most rated EtC Purge during emergence as same (30.1%) or easier (64.1%) than MC.


  • EtC is safe and effective in achieving the desired EtAA and EtO2 concentrations
  • EtC rapidly attains set levels.
  • EtC maintained the end tidal level within a closer tolerance with minimal overshoot than standard anesthesia practice.
  • A large majority of staff found EtC easy to use


In the USA, Et Control is indicated for patients 18 years of age and older


  • Oxygenation
  • Respiratory
  • Intensive care
  • Clinical