The Anesthesia Gas Machine

Michael P. Dosch CRNA PhD
University of Detroit Mercy - Nurse Anesthesia
This site is https://healthprofessions.udmercy.edu/academics/na/agm/index.htm.

Revised May 2025

Purchasing new gas machines

• Purchasing new gas machines
  • Education and training (Advanced ventilation, Computer and monitor integration, Low flows, Laryngeal mask airway and mechanical ventilation, Electronic Checkout)
  • Operating costs
  • Installation of new machines

What to consider when buying a new gas machine

How is anesthesia going to change in the next 15 years?

• No one knows - but there are some indications already from patient population and demographics. The patient population will be both younger and older, sicker and bigger than today. This puts stress on the ventilation ability. Buy the best ventilator you can.
• More spontaneous breathing. The LMA and the shift of all procedures to ambulatory are revolutionizing anesthesia practice. Buy a ventilator that allows pressure limited volume-guarantee ventilation, modes that support spontaneous ventilation (PSV, CPAP, APRV) and lung-protective ventilation.
• Make sure that the system doesn't restrict your future options. Make sure the machine you purchase will allow the exporting of fresh gas values and all monitor data to any information system or automated record-keeper. Make sure that whatever you buy can support an electronic anesthesia record.
• Make sure that you are comfortable with the integrated monitoring.

Education and training

An anesthetist who knew how to use an Excel could easily walk up to a Modulus or any of the Narkomeds and use them with very few problems, and essentially no training time or reading. However, the new machine features such as advanced ventilation modes, computer and monitor integration, and the electronic checklist are very different than anything that has gone before. New models are substantially different- look at the three different approaches to flowmeters in the Aestiva or Aespire (mechanical needle valves and glass flowtubes), Fabius/Apollo (mechanical needle valves, electronic display of flows backed up by common gas outlet flowmeter), and Aisys and Perseus (all electronic gas mixer, digital display in which the inspired oxygen, carrier gas flow, and total fresh gas flow are set). And Et control really shuffles the deck- instead of setting process variables (what flow and concentration do I want to give?), we now set the desired outcomes (patient's end tidal oxygen and anesthetic agent), and allow the machine to choose the best gas flows and concentrations to achieve the end result quickly and safely. The bottom line? Comfort with one make and model translates much less to other models than it used to.

Furthermore, anesthesia practice is changing. Spontaneous ventilation for longer than a few moments during general anesthesia was rare. Now because of the laryngeal mask airway it is much more common. Substantial cost and environmental impact of the volatile agents are driving the use of low flows (and total IV anesthesia [TIVA]). When users at a total fresh gas flow of 1 L/min find inspired oxygen dropping slowly, or a 2-3% difference between dialed and end-tidal sevoflurane in the middle of a case, they may have trouble remembering that these are expected findings at low fresh gas flow.

Comfort with the monitoring technology can be an issue. I know that a little ball in a glass tube would drop unless oxygen is flowing- a physical fact that I can sense. You mean my trust must now repose in a green bar graph??

The new machines simply cannot be used safely without a personal and institutional commitment to time spent in training and reading.

Operating costs

With the new machines, operating costs may be higher. Carefully compare the cost of disposables per case (e.g. spirometry tubing, carbon dioxide granule canisters, breathing circuits). This can be mitigated by several tactics:

• Emphasis on low flows to decrease usage of volatile agent
• Some machines permit use of loose carbon dioxide granules rather than single-use canisters

Installation of new machines

A few pearls from folks who have "been there":

• Budget weekend training time. Don't skimp here- and make it mandatory for all attendings, CRNA's, students, and residents. Buy them lunch and arrange to get CEs or CMEs.
• Work closely with the manufacturer's installation team. Invest some time in trying to foresee problems.
• Don't assume in a multi-building installation, that everything that worked well in your new ambulatory center will function identically in your aging main OR.
• Check for suction adequacy. Open scavenger interfaces demand a lot of suction.
• Make a plan for disposables early. Four days before "go-live", we found that our former breathing circuits, which we had "assumed" would fit, wouldn't.
• Involve in the planning those anesthetists who are most familiar with obstetrics, pediatrics, ambulatory, and cardiovascular. All these areas have special needs for equipment.
• Consider the pluses and minuses of integrated monitoring. The gas machine will last 10-15 years. Will you get tired of an integrated monitor before then, or wish you weren't locked into one company's monitoring solution? On the other hand, integrated monitors are compact, and there's a logic to the whole system that is very comfortable, once the initial learning curve is climbed.
• Your temperature probe and transducer sales representatives will be happy to get cabling for you that lets their disposable sensors talk to anyone's monitor.