- Because insufflation avoids any direct patient
contact, there is no rebreathing of exhaled gases if the flow is
high enough. Ventilation cannot be controlled with this technique,
however, and the inspired gas contains unpredictable amounts of entrained
- Long breathing tubes with high compliance increase
the difference between the volume of gas delivered to a circuit
by a reservoir bag or ventilator and the volume actually delivered
to the patient.
- The adjustable pressure-limiting (APL) valve should
be fully open during spontaneous ventilation so that circuit pressure
remains negligible throughout inspiration and expiration.
- Because a fresh gas flow equal to minute ventilation
is sufficient to prevent rebreathing, the Mapleson A design is the
most efficient Mapleson circuit for spontaneous ventilation.
- The Mapleson D circuit is efficient during controlled
ventilation, because fresh gas flow forces alveolar air away from
the patient and toward the APL valve.
- The drier the soda lime, the more likely it will absorb
and degrade volatile anesthetics. Desflurane can be broken down
to carbon monoxide by dry barium hydroxide lime to such a degree
that it is capable of causing clinically significant carbon monoxide
- Malfunction of either unidirectional valve in
a circle system may allow rebreathing of carbon dioxide, resulting
- With an absorber, the circle system prevents rebreathing
of carbon dioxide at fresh gas flows that are considered low (fresh
gas flow ≤ 1 L) or even fresh gas flows equal to the uptake of anesthetic
gases and oxygen by the patient and the circuit itself (closed-system
- Because of the unidirectional valves, apparatus dead
space in a circle system is limited to the area distal to the point
of inspiratory and expiratory gas mixing at the Y-piece. Unlike
some Mapleson circuits, the breathing-tube length of a circle system does
not directly affect dead space.
- The fraction of inspired oxygen (Fio2) delivered by a resuscitator
breathing system to the patient is directly proportional to the
oxygen concentration and flow rate of the gas mixture supplied to
the resuscitator (usually 100% oxygen) and inversely proportional
to the minute ventilation delivered to the patient.
Breathing systems provide the final conduit for the delivery
of anesthetic gases to the patient. Breathing circuits link a patient
to an anesthesia machine (Figure 3–1).
Many modifications in circuit design have been developed, each with
varying degrees of efficiency, convenience, and complexity. This
chapter reviews the most important breathing systems: insufflation,
draw-over, Mapleson circuits, the circle system, and resuscitation
The relationship between the patient, the breathing system,
and the anesthesia machine.
Most traditional attempts to classify breathing systems artificially
consolidate functional aspects (eg, the extent of rebreathing) with
physical characteristics (eg, the presence of unidirectional
valves). Because these often contradictory classifications (eg, open,
closed, semiopen, semiclosed) tend to result in confusion rather
than understanding, they are avoided in ...