In general anaesthesia, recovery and emergency resuscitation
procedures involve the use of a breathing system. The principle of
anaesthetic systems is to efficiently eliminate exhaled carbon
dioxide, without greatly increasing dead space or resistance. In
1954 Mapleson classified breathing systems based on their
efficiency in eliminating carbon dioxide during spontaneous
respiration. The breathing systems are classified in order of fresh
gas flow (FGF) to prevent rebreathing during spontaneous
respiration. Further information on the Mapleson classification can
be found in our educational section.
Mapleson A - (Magill, Parallel
Lack and Coaxial Lack)
This system consists of a reservoir bag close to the fresh gas
outlet with the APL valve placed at the patient end (Magill A, or
expiratory limb-Parallel Lack). During inspiration, as the
patient's inspiratory flow is greater than the Fresh Gas Flow,
additional gasses will be drawn out from the reservoir bag. During
the expiratory phase, exhaled gases will force the fresh gas back
into the circuit and reservoir bag. In the expiratory phase,
exhaled gases will force the fresh breathing system and thus
forcing the exhaled gasses to escape through the APL valve
(scavenging port). The system requires a low flow (0.8-1 times of
Minute Volume, approximately 6-8 litres/ minute) during spontaneous
respiration to prevent Rebreathing. This system is not recommended
for intermittent positive pressure ventilation. (IPPV)
Mapleson C - (Waters Bag,
Bagging System - Adult, Direct and Paediatric and Resuscitation
Bag).
This system is similar to Mapleson B, however, the bag is
positioned very close to the patient. This system is used for
manual ventilation during resuscitation. A flow rate of 1.5-2 times
of the minute volume is required to avoid Rebreathing.
Mapleson D - Coaxial
Bain
This system is mainly used with ventilated patients. The Fresh Gas
Flow is close to the patient and the APL valve is placed away from
the patient. The risk of Rebreathing in this circuit is high
especially in patients who have a short expiratory pause or do not
have an expiratory pause (infants). To overcome this problem a high
FGF of 2 - 4 times of the patient's Minute Volume is required to
prevent all Rebreathing. In practice some rebreathing is tolerated
and in an adult FGF of 6 - 7 litres/minute will maintain a normal
arterial CO2 tension.
Argentic Systems
Argentic is a range of anti-microbial breathing systems to combat
microbial contamination within the clinical setting and reducing
the risk of Hospital Acquired Infections (HAI). Argentic breathing
systems are impregnated with a silver ion additive which rapidly
reduces the number of bacterium. When oxygen in the ambient air
comes into contact with silver particles it creates a catalytic
reaction which helps to inactivate the microbes.
