feature of non-rebreathing circuits is that elimination of carbon
dioxide is accomplished by removing all expired gases from the system
and venting them to atmosphere. This is normally achieved by using
the fresh gas flow from the anesthetic machine to direct the expired
gases out of the circuit via a valve or other arrangement.
non-rebreathing systems provide good control of the inspired
gas concentrations, since fresh gas delivered from the anesthetic
machine is inspired in each breath. They are, however, are less
economical in use than rebreathing systems because the minute
volume of ventilation (or more) must be supplied to the patient
to prevent rebreathing, and they contribute more to the problem
of atmospheric pollution with anesthetic agents. They are also
less forgiving of operator error since an inadequate fresh gas
supply will result in rebreathing
Classification of Non-rebreathing Circuits
classification divides non-rebreathing circuits into functionally
similar groups, on the basis of the fresh gas flow required
to prevent rebreathing and the ease with which intermittent
positive pressure ventilation may be performed.
A - the Magill and Lack
Mapleson B and C - Rebreathing of exhaled gases occurs even
when very high fresh gas flow rates are used, since inspiration
is taken from the same space into which the previous breath was
expired. These are unsatisfactory for anesthesia, but may be used
in emergency for resuscitation.
Mapleson D - the modified Bain
Mapleson E - Ayre's T piece and the
"Mapleson F" - not originally classified by Mapleson,
but is used to refer to Jackson-Rees'
modification of Ayre's T-piece.
ADE is a new circuit that provides the ability to switch between
the Mapleson A, D and E arrangements.
There is a vast number of ways in which tubes, bags and valves may
be inter-connected to fabricate an anesthetic breathing circuit.
Caution should be exercised when using any "new" circuit,
since it may not work in the way its designer intended.