Technology overview

This briefing describes the regulated use of the technology for the indication specified, in the setting described, and with any other specific equipment referred to. It is the responsibility of healthcare professionals to check the regulatory status of any intended use of the technology in other indications and settings.

About the technology

End-tidal Control is a gas delivery software option for the GE Healthcare Aisys Carestation and Aisys CS2 anaesthesia delivery systems. It monitors and automatically adjusts the levels of anaesthetic concentration in a closed circuit system across a specified flow range of 0.5–10 litres per minute. The closed circuit is currently the most widely used form of breathing system in anaesthetic machines, and usually contains integrated gas, pressure and volume-monitoring sensors.

When using End-tidal Control, the anaesthetist sets target end-tidal oxygen concentration, minimum flow rate and target end-tidal anaesthetic concentration. The system monitors these concentrations by sampling gas in the breathing circuit on a breath-by-breath basis. It applies a proprietary algorithm to automatically adjust fresh gas flow and anaesthetic concentrations to ensure that the patient's uptake of oxygen and anaesthetic are maintained at the correct level. The system contains a carbon dioxide absorber to allow the rebreathing of any anaesthetic gases in the exhaled air.

During manual gas control, the anaesthetist controls the concentration of anaesthetic by monitoring the concentration of gases in the exhaled (end‑tidal) air and manually adjusting fresh gas rates (Singaravelu and Barclay 2013).

CE marking

End-tidal Control is part of current system software versions 10 x on the Aisys CS2 and 8 x on the Aisys Carestation, and is compatible only with the Carestation and CS2 systems. It is available as a separate standalone software option. These software versions and compatible airway modules were CE marked to GE Healthcare in July 2013 and April 2011 respectively, as class IIb devices.


End-tidal Control is a software option requiring 1 of 3 compatible GE Healthcare airway modules:

  • E‑series modules (E‑CAiO, E‑CAiOV, E‑CAiOVX) for the Aisys Carestation

  • M‑series modules (M‑CAiO, M‑CAiOV, M‑CAiOVX) for the Aisys Carestation

  • CARESCAPE Respiratory Modules (E‑sCAiOE or E‑sCAiOVE) for the Aisys CS2.

The airway module is an optional piece of hardware that slots into the main anaesthesia system and forms part of a closed-loop circuit with gas sampling of the patient's airway, circle and fresh gas concentrations, supplies (including sodalime CO2 absorber and antibacterial filter) and water trap components. The airway modules are not required for the basic operation of the Aisys systems, but provide additional measurement and monitoring functionality, and their presence is essential for the End-tidal Control option. Module verification tests must be run to confirm correct installation. End-tidal Control is designed for use with the anaesthetics desflurane, isoflurane and sevoflurane, housed in colour-coded vaporiser cassettes. Only 1 anaesthetic cassette can be installed and active at any given time. When all hardware components are correctly installed, calibrated and warmed up, with the system measuring a patient carbon dioxide respiratory rate of 35 breaths per minute or less and registering a minute volume, End-tidal Control is ready for use. The airway module warm-up takes approximately 2 minutes.

The minimum flow rate setting for End-tidal Control provides a patient safeguard by ensuring the gas flow does not fall below the set rate. Increasing the minimum flow does not affect the speed of change to achieve target concentrations.

When active, End-tidal Control includes a number of additional safety mechanisms to protect the patient. These include system checks, fresh gas sampling checks every 3 minutes, leak checks both before starting and during End-tidal Control, and the delivery of increased fresh gas flow, for example, when a leak is detected. Automatic return to active End-tidal Control resumes when the leak is resolved.

End-tidal Control supervisor is an additional safeguard included in End‑tidal Control, which monitors set concentration and flow rates against actual measured values to prevent incorrect delivery of oxygen and anaesthetic. If the End-tidal Control supervisor detects any system failures, this results in automatic exit from End-tidal Control mode. Some issues, for example calibration of the airway module, need anaesthetist input. Manual re-entry into End-tidal Control mode is then needed when these issues are resolved. The system creates an End-tidal Control log that records actions, settings and measurements for later review.

Intended use

End-tidal Control is intended for use during inhalational anaesthesia and needs a controlled patient airway to be in place, for example an endotracheal tube or laryngeal mask airway.

End-tidal Control cannot be used with a face-mask airway, or with halothane as the anaesthetic agent, or while the module is in non‑circle circuit, cardiac bypass, alternate oxygen, and air‑only modes. It is recommended that End‑tidal Control is not used during surgical procedures that cause disturbance to the lungs, such as chest surgery. The system may deliver 100% oxygen in End-tidal Control mode, therefore End-tidal Control mode should not be used when delivery of 100% oxygen may injure the patient (for example, in premature neonates in whom excessive inspired oxygen concentrations can cause retinopathy, or in patients with some forms of congenital heart disease). End-tidal Control mode stops if the anaesthetic is changed while the module is active. The manufacturer recommends exiting End-tidal Control mode before changing the anaesthetic. However, it is not routine practice to change anaesthetic agent between the anaesthetic room and the operating theatre.

The manufacturer does not specify a lower age limit for End-tidal Control, however specified respiratory rates (35 breaths per minute or less) must be met, and the system must be registering a minute volume.

Setting and intended user

End-tidal Control is intended for use by an anaesthetist in the anaesthetic room and operating theatre, depending on local facilities.

Current NHS options

General inhalational anaesthesia is delivered and monitored by an anaesthetist. This is currently performed manually by continually altering the fraction of inspired gases, fresh gas flow and vaporiser settings to ensure optimal anaesthesia delivery (Tay et al. 2013) while minimising anaesthetic waste. This approach can be automated using the GE Healthcare Aisys Carestation or Aisys CS2.

NICE is aware of the following devices that appear to fulfil a similar function to the GE Healthcare End-tidal Control automated gas control option on Aisys anaesthesia delivery systems:

  • Zeus IE anaesthesia system (Draeger Medical)

  • FLOW‑i Anaesthesia Delivery System (Maquet)

  • FELIX AInOC anaesthetic station (Air Liquide Medical Systems).

NICE has not investigated the regulatory status of these devices; it is the responsibility of healthcare professionals to check this status for any intended use.

Costs and use of the technology

The list prices for the End-tidal Control components for use with the Aisys Carestation (excluding VAT) are:

Anaesthetic system

System cost

Cost of purchasing End‑tidal Control when ordering system

Cost of adding End‑tidal Control to existing system

Cost of additional module (required for End‑tidal Control)

Aisys Carestation

Supported by the manufacturer but no longer available for purchase

Not applicable


Supported by the manufacturer but no longer available for purchase

(E‑series module, E‑CAiOVX)

Aisys CS2





(CARESCAPE Respiratory Module series, E‑sCAiOVE)

The M‑series airway module is no longer commercially available, but users can still add the End-tidal Control software to existing Aisys Carestation systems fitted with an M‑series airway module.

The manufacturer states there are no additional consumables, or specific checks or calibrations needed, to use End-tidal Control.

The manufacturer recommends annual maintenance checks for Aisys systems, including airway module service and calibration. Replacement parts for each annual Aisys service cost less than £10, internal battery replacement costs £180 every 4 years, and the annual airway module service kit costs £135. A fully comprehensive contract for the Aisys CS2 and End-tidal Control fitted with an airway module is £1562 per year. This cost can be reduced for customised contracts, tailored to individual customer requirements. The anticipated lifespan of the Aisys Carestation and Aisys CS2 is 8–10 years.

The manufacturer provides training to new users as part of the initial anaesthesia system purchase, including all aspects of the Aisys systems and End-tidal Control. Training records are kept for all attendees and submitted to the hospital on completion of training. Further support is provided in theatre during the first weeks after installation. This includes providing support during the use of End-tidal Control mode in patients having anaesthesia. After initial system training, there is no cost for additional training of new users if requested.

It is anticipated that the End-tidal Control software and necessary hardware (airway module and Aisys anaesthesia delivery system) could be used for inhalational general anaesthesia for many different types of procedure. Therefore it is difficult to precisely quantify the number of patients for whom End-tidal Control could be used. The cost per patient using End-tidal Control would depend on the duration of general anaesthesia, the price of the chosen anaesthetic and the concentration of anaesthetic given.

Likely place in therapy

End-tidal Control is intended to be used in patients having general anaesthesia that is induced and/or maintained by the volatile inhalational agents isoflurane, desflurane or sevoflurane. Because the technology is embedded in existing anaesthesia delivery systems, it will be used in anaesthesia rooms or operating theatres during a surgical procedure, unless contraindicated. Some hospitals may induce anaesthesia in the operating theatre and will therefore need 1 anaesthesia machine with End-tidal Control per patient. However, other hospitals may induce anaesthesia in an anaesthesia room and then use another anaesthesia machine to maintain anaesthesia in the operating theatre, needing 2 anaesthesia machines with End-tidal Control per patient.

Specialist commentator comments

Although there are no data available to describe how many patients have inhalational agents during general anaesthesia, 2 specialist commentators estimated that less than 10% of general anaesthesia patients will have total intravenous anaesthesia, and therefore 90% have some form of inhalational anaesthesia.

Two specialist commentators considered that any clinical and resource benefits of End-tidal Control were unlikely to be realised in brief procedures, in which duration of general anaesthesia was short.

One specialist commentator felt that End-tidal Control would be of little economic benefit to hospitals already practising low-flow anaesthesia, and that it would be difficult to measure whether End-tidal Control would reduce the anaesthetist's workload sufficiently to allow the anaesthetist to focus on other areas of patient care during the course of the anaesthesia. This specialist commentator also felt that quality or depth of anaesthesia should be considered a primary outcome measure, as the ability to automate anaesthesia parameters and achieve these quickly may minimise awareness during anaesthesia, therefore making anaesthesia safer.

One specialist commentator observed that the randomised trial was conducted in India, where anaesthetic agent costs are much lower than in developed countries. This may account for the difference in costs between this trial and that specified in other publications. A second specialist commentator, with practical experience of End-tidal Control, stated that the main economic burden comes during the wash-in phase of the anaesthetic, when high gas flows are traditionally employed. This is often a busy time clinically, with many distractions, and the anaesthetist often forgets to reduce initial high flows. Therefore the automation of End-tidal Control may be most beneficial here. A third specialist commentator felt that reducing anaesthetic agent and greenhouse gas emissions would have to result in a clear cost benefit in order for End-tidal Control to become widely used.

The use of anaesthetic rooms in UK clinical practice was referenced by 2 specialist commentators as limiting the economic benefits of End-tidal Control. Patient anaesthesia can be induced in the anaesthetic room using 1 anaesthetic (typically isoflurane, which is less costly), before being transferred to the theatre where a more expensive anaesthetic agent (typically desflurane) is used. When a single anaesthesia machine is used per patient, End‑tidal Control will not work until the first agent has been washed out of the circuit (using oxygen). This operational delay reduces the economic benefit of the system.

One specialist commentator thought that there is no reason why End‑tidal Control cannot be used during cardiac surgery; the user would revert to manual mode during cardiopulmonary bypass and restart End-tidal Control again when the patient was off bypass.

Equality considerations

NICE is committed to promoting equality and eliminating unlawful discrimination. We aim to comply fully with all legal obligations to:

  • promote race and disability equality and equality of opportunity between men and women, and

  • eliminate unlawful discrimination on grounds of race, disability, age, sex, gender reassignment, pregnancy and maternity (including women post-delivery), sexual orientation, and religion or belief, in the way we produce our guidance. (NB these are protected characteristics under the Equality Act [2010]).

No equalities considerations were identified for the GE Healthcare End‑tidal Control software.