• Co-ordinator : Prof. Dr.Pradeep sahi(DA,MD)
• Presented By : Dr. Fahad Suhail
• Earlier circuits were simple, differing in the
type of anesthetic agent administered.
• The purpose of breathing systems that have
evolved in anesthetic practice is to deliver Gas
& Vapor to the patient in an
appropriate, controlled & efficient manner.
• A breathing system is defined as an assembly
of components, which connects the patient’s
airway to the anesthetic machine creating an
artificial atmosphere form and into which the
• The breathing system converts a continuous
flow from the anaesthesia machine to an
• In practice the breathing system is usually
regarded as extending from the point of fresh
gas inlet to the point at which gas escapes to
the atmosphere or a scavenging system.
• Rebreathing: in anesthetic systems, it is now
conventionally refers to the breathing again of
some or all of the previously exhaled gases
including CO2 & water vapor.
Components of breathing system:
• Formally these were called breathing apparatus or
breathing circuits. These names have been
It primarily consists of
a) A fresh gas entry port/delivery tube through
which gases are delivered from the machine to the
b) A port to connect it to the patients airway.
c) A reservoir for a gas in the form of a bag or a tube
to meet the peak inspiratory flow requirements
d) An expiratory port/valve through which the expired gas
is vented to the atmosphere.
e) Tubes for connecting these components.
f) Flow directing valves may or may not be used.
g) A CO2 absorber if total rebreathing is to be allowed.
h) Connectors & adaptors
• A connector is a fitting that joins
together 2 or more similar
• An adaptor is a specialized connector
that establishes functional continuity
between otherwise disparate or
• There sizes are universal & either
male/female, 15/22mm connections.
Some incorporate gas sampling ports.
i) Bacterial filters• they prevent
transmission of infection
to the patients or
Generally a new filter
should be used for every
patient or in the absence
of filter, a disposable
system should be used
on every patient.
j) Heat & Moisture
Filters)• These humidify &
warm the Anesthetic
gases being delivered
to the patients.
• These devices also
help to dehumidify
the gases that are
been sampled for
analysis by the side
• Composition Rubber, synthetic
• Ellipsoidal in shape.
• Available in size ranging from 0.25L
• A normal size adult bag holds a volume
exceeding the patients inspiratory capacity.
iii. It provides a means whereby ventilation
may be assisted or controlled.
iv. It protects the patient from excessive
pressure in the breathing system.
It can serve through visual & tactile
observation as a monitor of patients
• ASTM Standards
a. For bags < 1.5L, min
pressure 30cms. & max
pressure 50cms of
b. For bags > 1.5L, min
pressure more than
35cms & max pressure
not exceeding 60cms
1. Made of rubber or plastic or
2. Can be impregnated with silver to
add antimicrobial effect.
3. Length is variable.
4. Internal diameter
Adults – 22mm.
Pediatric – 15mm.
5. Internal volume 400-500ml/m.
6. Distensibility 0-5ml/m/mmHg.
7. Resistance to gas flow <1mm of H₂O/litre/min
8. Corrugations prevent kinking & increased
9. Backlash seen during spontaneous breathing.
10.Wasted ventilation seen during controlled
1. Act as reservoir in certain systems.
2. They provide connection from 1part of system to
Adjustable Pressure Limiting Valve
Also called as expiratory valve, pressure
relief valve, pop off valve, Heidbrink
valve, Dump valve, Exhaust valve, Spill valve
TYPES OF APL VALVES
• Spring Loaded Disc
Has 3 ports –
– The Patient &
– Exhaust Port.
Exhaust port may
be open to
• Stem & Seat type
• Control Knob type
• Collection Device &
• Humphrey Type valve.
APL Valves with Inbuilt
Overpressure Safety devices
Uses of APL valves in spontaneous &
Valve is kept fully opened.
Partial closing will result in PEEP.
Pressure <1cm H₂O needed to open valve.
Should have pressure drop 1-3cm of H₂O for airflow
of 3L/min & 1-5cms of water at 30L/min.
Valve is partially left open.
Essential/ Principle Criteria
The breathing system must
a) Deliver the gases from the machine to the alveoli
in the same concentration as set and in the
shortest possible time.
b) Effectively eliminate carbon-dioxide.
c) Have minimal apparatus dead space.
d) Have low resistance.
The desirable requirements are
a) economy of fresh gas.
b) conservation of heat.
c) adequate humidification of inspired gas.
d) light weight
e) Convenience during use.
f) Efficiency during spontaneous as well as
controlled ventilation (efficiency is
determined in terms of CO2 elimination and
fresh gas utilization)
g) Adaptability for adults, children and
h) Provision to reduce theatre pollution
Breathing System Classification
• Classification by Function System
• Classification by Equipment
• It is based on rebreathing, presence or absence of
reservoir, CO2 absorption & directional valves.
• Insufflation system – gases are delivered directly
into the patient’s airways, no reservoir bag, no
valves, no CO2 absorber – open drop method
• Open type – gases are directed to the patient
from anesthesia machine, and valves direct
exhaled gases to the atmosphere – intermittent
flow machines, systems with non rebreathing
• Semiopen type – mixing of inspired and expired
gases occur and rebreathing depends on fresh
• No CO2 absorber – Mapleson system
• Semiclosed system – part of the exhaled gases go
out to the atmosphere, part of it gets mixed with
inspired gases and is rebreathed. CO2 absorber is
• Closed system – complete rebreathing of expired
gas. CO2 absorber is present.
Breathing system without CO₂ absorption Breathing system with CO₂ absorption
1. Non-rebreathing Valve.
2. Circle Systems.
• Circle system with Absorber
Bi Directional Flow
a) Afferent Reservoir Systems
• Mapleson A
• Mapleson B
• Mapleson C
• Lack`s system
b) Enclosed Afferent Reservoir Systems
• Millers (1988)
c) Efferent Reservoir Systems
• Mapleson D
• Mapleson E
• Mapleson F &
• Bain`s system.
d) Combined Systems
• Humphrey ADE
Bi directional flow
•To & Fro System
Breathing systems without CO2
1) Unidirectional flow
• non rebreathing system
– They make use of non-rebreathing valves.
– To prevent rebreathing FGF =MV.
Though it satisfies all the 4 essential
requirements, still not very popular because
1) Fresh gas flow has to be constantly adjusted
and is not economical.
2) There is no humidification of inspired gases.
3) There is no conservation of heat
4) The valve is bulky and has to be placed close
to the patient.
5) Malfunctioning of the valve can occur due to
condensation of moisture.
6) Can be noisy at times.
7) Cleaning and sterilization is somewhat
2. Bidirectional flow
• E.g. Water`s canister
• These are obsolete
in current anesthetic
• In 1954 – on
advice of William
For better understanding of functional analysis they have
been classified as
1) Afferent Reservoir System (ARS)
2) Enclosed Afferent Reservoir System
3) Efferent Reservoir System
4) Combined System
The efficiency of a system is determined in terms of CO₂
elimination & FGF utilization.
• Afferent limb is that part of the breathing system
which delivers the fresh gas from the machine to
• If the reservoir is placed in this limb as in Mapleson
A, B, C and Lack’s systems they are called as
afferent reservoir system.
• Efferent limb is that part of the breathing system
which carries the expired gas from the patient and
vents it to the atmosphere through the expiratory
• If the reservoir is placed in this limb as in Mapleson
D, E, F and Bain systems they are called efferent
• For spontaneous ventilation in the order of
efficiency – ADCB (All Dogs Can Bite).
• For controlled ventilation – DBCA (Dead Bodies
• Here D includes E, F and Bain`s system
Mapleson postulates (1954)
• Mapleson has analyzed these bi-directional
flow systems & few basic assumptions have
been made which are of historical interest.
• Gases move En-bloc i.e they maintain their
identity as fresh gas, dead space gas &
alveolar gas. There is no mixing of these gases.
• Reservoir bags continues to fill up, without
offering any resistance till it is full.
• The expiratory valve opens as soon as the
reservoir bag is full & pressure inside the
system goes above the atmospheric pressure.
• The valve remains open throughout the
expiratory phase without offering any
resistance to gas flow & closes at the start of
• Originally described by
• Length of breathing
tube 110-180 cms.
• FGF from machine
• APL close to patient.
• Sampling ports to be
placed between APL
valve & the tube.
• To prevent
• FGF = 70 ml/kg/min
• Extremely efficient
• These systems are
• FGF >20L/min required
for CO₂ elimination.
• This system cannot be
used in patients less
• Co-axial Mapleson A.
• Outer tube 30mm in
• Inner tube 14mm in
• APL valve placed near
Testing for Leaks in Magills & Lacks
Magill – tested for leaks by occluding the patient
end & closing valve & pressurizing the system.
• Opening the APL valve will conform proper
functioning of the component.
• In addition the user or patient should breathe
through the system to rule out block.
Lack – tested same as for Mapleson A with
testing integrity of inner tube.
• ET tube is attached to inner tube & valve is
closed. Air is blown. If leak is
present, excursions will be seen in the
• Occlude both the limbsat the patient
connection with APL valve open, squeeze the
bag. Any leak is confirmed by release of gas
from APL valve.
Mapleson B system
• This circuit functions
similarly during both
• FGF > 2x Min Volume
used for both
Mapleson C system
• Also called as
Westminster face piece
• FGF > 2 x Min Volume for
both Spontaneous &
• Used for short periods
during transportation of
Enclosed Afferent Reservoir System
• Described by Miller & Miller.
• Consists of Mapleson A system
enclosed within a non-distensible
• Spontaneous ventilation variable
orifice kept open, behaves like
• Controlled ventilation variable
orifice partially closed.
• It is more efficient than Bain`s
system when FG is > than Alveolar
Efferent Reservoir System
• Mapleson D,E,& F systems, all
have a T piece in common.
• T piece is 3 way tubular
connector, 1cm in diameter & 5cm
• It has 3 ports
1. To Patient
2. The expiratory Port.
3. Fresh Gas Port.
• FGF = PIFR has been used to
prevent air dilution.
Bain modification of Mapleson D
• Originally modified by
Bain & Sporel in 1972.
• Is co-axial system.
• Usual length is 180cm.
• Outer tube
– Diameter -22mm.
– Carries exhaled gas.
• Inner tube
– Carries fresh gas.
• FGF of atleast 1.5-3
times MV is advised
• Based on body wt.
200 ml/kg/min flow
• FGF to maintain
normocarbia is advised
to be around
• Most efficient among
the Mapleson Systems.
Recommendations by Bain & Sporel
• 2L/min FGF in patients <10kg.
• 3.5L/min FGF in patients between 10-50 kg.
• 70ml/kg/min FGF in patients more than 60kg.
• Tidal volume to be set at 10ml/kg.
• Respiratory rate at 12-16 breaths/min.
Advantages of Bains circuit
1) light weight
2) convenient to use
3) scavenging of exhaled gases is facilitated
4) exhaled gases in the outer tubing add warmth to
the inspired gases
5) a long corrugated tubing with an aluminium APL
valve may be used to ventilate a patient
For the integrity of the inner tube
1) Set a low flow of O2 on the flow meter and
occluding the inner tube (with a finger or the
barren of a small syringe) at the patient end
while observing the flowmeter indicator.
• If the inner tube is intact and correctly
connected, the indicator will fall.
2) Pethick’s test –
• High flow O2 is fed into the circuit while the
patient end is occluded until the bag is filled.
• The patient end is opened and simultaneously
‘O2 flush’ is activated.
• If the inner tube is intact, the Venturi effect
occurring at the patient end, causes a decrease
in pressure within the circuit and the reservoir
• Conversely if there is a leak in the inner
tube, gas escapes into the outer tube and the
reservoir bag remains inflated
Mapleson E system
• Modification of Ayre`s T Piece.
• Used initially for pediatric patients
undergoing palate repair &
• Minimal dead space, no
valves, v.little resistance.
• Volume of expiratory limb > Pts
tidal volume to prevent air dilution.
• Used in neonate &
• Sampling port is
port & tubing.
• FGF > 3 times min.
Problems with this system are
1) Air dilution of the expiratory
limb is short.
2) High fresh gas flow is required to
prevent rebreathing and air
3) During controlled ventilation feel
of the bag is not there and hence
hazard of ‘barotrauma’ is a
• Used to administer O₂ for
spontaneously breathing patients
Mapleson F system
• T piece arrangement with a reservoir bag.
• Relief mechanism is either an adjustable valve
at end of bag or a hole on side of Bag.
• Newer modification incorporates APL valve
before the reservoir bag.
• Pressure relief is actuated at 30cms of water.
• FGF = 2-3 x MV for spontaneous respiration.
• FGF = Bain`s for controlled respiration.
1) light weight
2) simple construction
4) minimal resistance
5) minimal dead space
6) controlled ventilation is
7) scavenging is easily
1) lack of humidification
2) need for high fresh gas flows
3) occlusion of relief valve can increase the
airway pressure, producing barotraumas
Advantages of Mapleson systems
1) the equipment is simple, inexpensive and rugged.
2) components can be easily disassembled and can be
3) the systems provide buffering effect so that variations in
minute volume affect end tidal CO2 less than in a circle
4) rebreathing will result in retention of heat and moisture
5) resistance is within the recommended ranges
6) light weight and not bulky
7) do not cause excessive drag on ET tube
8) easy to position conveniently.
9) compression & compliance losses are less with
these systems than with circle systems.
10) Changes in fresh gas concentration result in
rapid changes in inspiratory gas composition
1) require high gas flows, higher costs, increased
2) optimal fresh gas flow may be difficult to
determine. Necessary to change fresh gas flows
when changing from spontaneous to controlled
3) anything that causes decreased fresh gas flow
can produce dangerous rebreathing
4) in Mapleson A, B and C system the APL valve is
close to the patient end and may be
5) Mapleson E and F are difficult to scavenge.
6) These are not suitable for patients with
Malignant Hyperthermia because it may not
be possible to increase the fresh gas flow
enough to remove the increased CO2 load.
• Designed by Humphrey
D, Brock & Downing.
• Has 2 reservoirs,
• While in use, only 1 reservoir
• Lever helps in switch over
• Can be used in adults as well as
• Not yet widely used.