4 4 S U P P L E M E N T T O O U T P A T I E N T S U R G E R Y M A G A Z I N E J U LY 2 0 1 5
1. Flow meters
Flow meters set the levels of nitrous oxide, oxygen and air, as well as the per-
centage of inspired oxygen and total gas flow for the patient. In older models,
this was regulated with manual flow control valves that set gas distribution
based on a provider's manual calculations. New machines, though, do all of this
electronically.
The latest models include a system that acts like a computer to automatically
determine relative gas flows. You use a digital screen to select the amount and
mixture of gas you want and let the machine do the heavy lifting. For example,
if you want to achieve 50% inspired oxygen in the fresh gas mixture, you input
that into the system. The machine then determines how much of the second gas
(either air or nitrous oxide) must be mixed in to reach that 50% concentration.
There are other benefits to electronic flow meters. Compared to mechanical
valves, new electronic machines require less maintenance or calibration, and
can be integrated into your EHR system. Importantly, new machines have
mechanical backup valves that can continue the delivery of oxygen to patients if
power is lost.
2. Vaporizer
The machine's vaporizer adds exact amounts of volatile anesthetic to the fresh
gas flow. Fresh gas is divided as it enters the machine. Part of it enters the
vaporizer, which mixes the gas with the anesthetic vapor. This mixture then
joins back with the other part of the fresh gas flow before entering the patient's
breathing circuit. Previously, anesthesia providers manually controlled this split-
ting ratio using a dial to adjust the amount of anesthetic a patient would get.
Now, sensors inside the electronic vaporizer determine the splitting ratio auto-
matically based on the provider's desired amount and report that electronically.
Some of the latest vaporizers can even precisely inject liquid volatile anesthetic
into the fresh gas flow, much like the fuel injection system in your car.
Compared to older models, these electronic vaporizers are extremely accurate
