are used with anesthesia machines that have a CO2
absorber head and/or a ventilator. These circuits consist of a tube
from the machine to the patient, which is connected to a Y-piece at
the patient, and then another tube extending back to the machine.
One-way valves within the machine assure that the gas moves through
the tubes in a circular path to the patient and then back to the machine.
This type of circuit recycles the unused gas to the anesthesia machine
for reuse. The tubes range from less than 2mm ID and only an inch
or two in length, to over 2" ID and 60" in length.
circuits also consist of two tubes. One delivers gas from the anesthesia
machine to the patient connection, then a second, usually larger tube,
channels the waste gases to evacuation. In this type of circuit any
gas not utilized is immediately directed toward the evacuation circuit.
The waste gas tube should be easily connectable to either a disposable
charcoal canister or to an in-house evacuation system. This type of
circuit is usually configured with an elbow, a tee or a straight connection
to the nosecone/ET tube at the patient end. The fresh gas tube can
be located inside or outside the waste gas tube. The internal diameters
and overall lengths of the fresh gas and waste gas tubes can vary
Selecting Breathing Circuits
Key factors to
consider when selecting a breathing circuit for your procedure:
- Is the internal
diameter of the fresh gas tube sufficient to deliver an adequate
volume of fresh gas to the patient?
- Is the internal
diameter of the waste gas tube sufficient to not create resistance
in the flow of the departing gas? This is a very important factor
to consider because gases will follow the path of least resistance.
If there is resistance in the evacuation tube, the gases will
try to escape elsewhere, such as from around the facemask or other
- Does the
nosecone/endotracheal tube connection fit within my procedure
boundaries? For example, an elbow may force the patient's head
into an unacceptable position for the procedure you are doing,
or a tee connection may not fit in your MRI tube.
- Custom breathing
circuits can be constructed.