2. Introduction
Breathing system is defined as an assembly of components,
which connect the patient’s airway to the anesthetic machine
creating an artificial atmosphere, from and into which the
patient breathes.
Also known as breathing circuit, respiratory system/circuit,
patient circuit
It primarily consists of
- A fresh gas entry port or delivery tube through which the gases
are delivered from the machine to the system
- a port to connect it to the patient’s airway
- a reservoir for gas , in the form of a bag or a corrugated tube to
meet the peak inspiratory flow requirements
3. Cont.
- An expiratory port or valve through which the
expired gas is vented to the atmosphere
- Flow directing valves and CO2 absorber if total
rebreathing is to be allowed
- Corrugated tubes for connecting these components
4. Requirements of a breathing
system
Essential-
the breathing system must
1. Deliver the gases from the machine to the alveoli in the
same concentration as set and in the shortest possible
time
2. Effectively eliminate carbon dioxide
3. Have minimal apparatus dead space
4. Have low resistance
5. Desirable-
1. Economy of the fresh gas
2. Conservation of heat
3. Adequate humidification of inspired gas
4. Light weight
5. Convenience during use
6. Efficiency during spontaneous as well as controlled
ventilation
7. Adaptability for adults, children, and mechanical
ventilators
8. Provision to reduce theatre pollution.
6. General principles
Resistance-when gas passes through a tube the pressure at the outlet will be
lower than that at inlet. The drop in pressure is a measure of resistance.
Laminar flow- flow is smooth and orderly, and particles move parallel to the
walls of the tube. Flow is fastest in the centre of the tube.
For laminar flow the HAGEN POISEUILLE Law applies.
Hagen–Poiseuille equation
Flow = πPr4/8ἠl
where P = pressure drop along the tube (p1-p2),
r = radius of tube,
l = length of tube
ἠ = viscosity of fluid.
The most important aspect of the equation is that flow is proportional to the
4th power of the radius. If the radius doubles, the flow through the tube will
increase by 16 times
Here resistance is directly proportional to the flow rate.
7. Turbulent flow-the flow lines are no longer parallel. Eddies
composed of particles moving across or opposite the general
direction of flow. For turbulent flows ,
∆ P = (l× V2×K)/r5
where K= constant which includes factors like gravity, friction, gas
density, viscosity
here Resistance is proportional to the square of the flow rate.
8. Reynold’s number
Re = ῤvd/ἠ
where Re = Reynold’s number,
ῤ = density of fluid,
v =velocity of fluid,
d =diameter of tube
ἠ =viscosity of fluid.
Reynold’s number is dimensionless (it has no units) and it is
simply taken that when Re<2000 flow is likely to be laminar
and when Re>2000 flow is likely to be turbulent.
In actuality values between 2000 and 4000 provide a mixed
or transitional pattern(laminae and turbulent) but most
respiratory care references refer to values within this range as
turbulent flow.
9. Significance of resistance
Resistance imposes a strain, especially with
ventilatory modes, where the patient must
do part or all of the respiratory work.
Changes in resistance tend to parallel
changes in the work of breathing.
Tracheal tube is usually the source of most
resistance and more important factor when
determining the work of breathing than the
breathing system.
Anaesthesia provider should be aware of
how much resistance, components of
breathing system offers.
Flow-volume loops can show changes in
resistance to flow in a breathing system.
10. Compliance
It is the ratio of a change in volume to a change in pressure.
It is a measure of distensibility
Usually expressed in ml/cm of H2O
Most distensible components in breathing systems are the
reservoir bag and the breathing tubes.
Compliance will help to determine the tidal volume.
Compliance can be illustrated graphically by pressure-volume
loop.
11. Rebreathing
Means to inhale previously respired gases from which CO2 may
or may not have been removed.
There may be or may not be increase in the CO2 level.
Factors influencing rebreathing:
1. Fresh gas flow(FGF) – amount of rebreathing inversely related
to FGF. If the volume of fresh gas supplied per minute is equal
to or greater than the patient’s minute volume, there will be no
rebreathing. If the total volume of gas supplied per minute is
less than the MV some exhaled gases must be rebreathed to
make up the required volume.
2. Mechanical dead space/ apparatus dead space
3. Breathing system design
12. Mechanical dead space or apparatus
dead space-
It is the volume of the breathing system from the patient-end to
the point up to which to and fro movement of expired gas takes
place.
In an afferent reservoir system with adequate FGF, the apparatus
dead space extends up to the expiratory valve positioned near the
patient (Figs 3A to C).
If the FG enters the system near the patient-end as in an efferent
reservoir system, the dead space extends up to the point of FG
entry.
In systems where inspiratory and expiratory limbs are separate, it
extends up to the point of bifurcation.
13. The dynamic dead space will depend on the FGF and
the alveolar ventilation. The dead space is minimal with
optimal FGF.
If the FGF is reduced below the optimal level, the dead
space increases and the whole system will act as dead
space if there is no FGF.
Increasing the FGF above the optimum level will only
lead to wastage of FG.
14. Effects of Rebreathing
With no rebreathing composition of inspired gas is identical to
that of the fresh gas delivered by the anaesthesia machine.
With rebreathing the inspired gas is composed partly of fresh
gas and partly of rebreathed gas.
Heat and moisture retention- rebreathing reduces heat and
moisture loss from the patient.
Altered inspired gas tension- the effects of rebreathing on
inspired gas tensions will depend on what parts of the exhaled
gases are rebreathed and whether these pass to alveoli or only
to the anatomical dead space.
15. Oxygen- rebreathing alveolar gas will cause a reduction in the
inspired oxygen tension.
Inhaled anaesthetic agents- rebreathing alveolar gas exerts a
cushioning effect on changes in the inspired gas composition
with alteration in the fresh gas composition.
During induction, when alveolar tension are lower than those in
the fresh gas flow, rebreathed alveolar gas will reduce the
inspired tension and prolong induction.
During recovery , the alveolar tension exceeds that of the inspired
gases, and rebreathing slows agent elimination.
Carbon dioxide- rebreathing alveolar gas will cause an increased
inspired CO2 tension unless the gas passes through an absorbent
before being rebreathed.
16. Discrepancy between Inspired and
delivered volumes
the volume of gas discharged by a ventilator or
reservoir bag usually differs from what enters the
patient.
Causes of increased inspired volume- when the
ventilator is in use and the FGF is higher than that is
absorbed by the patient or lost through leaks,the FGF
delivered during inspiration may be added to the tidal
volume delivered by the ventilator.
17. Causes of decreased volume-
Wasted ventilation -
Due to Gas compression and Distension of breathing
system components during inspiration, there is
reduction in tidal volume delivered to the patient.
Increases with increase in airway pressure, tidal
volume, increased breathing system volume and
component distensibility
Leaks in the breathing system
18. Discrepancy between inspired and delivered oxygen and
anaesthetic gas concentration
The mixture the patient inspires differs considerably from
that delivered to the system.
The contributing factors-
1. Rebreathing
2. Air dilution
3. Leaks
4. Anaesthetic agent uptake by the breathing system
components i.e. the agents may adhere to rubbers,
plastics, metal and carbon dioxide absorbent.
5. Anaesthetic agent released from the system
19. Common components
BUSHINGS/MOUNTS – modify the internal diameter of
a component
SLEEVES – alters the external diameter of a component
CONNECTORS AND ADAPTORS –
Connector- fitting intended to join two or more similar
components together
Adaptors- specialised connector that establishes
functional continuity between otherwise incompatible
components.
20. An adaptor or connecter may be distinguished by
1. Shape (like straight, right angle or elbow, T or Y)
2. Components to which it is attached
3. Added features
4. Size and type of fitting at either end( 15 mm male or
22 mm female)
21. Connectors and adaptors can be used to
1. Extend the distance between the patient and the
breathing system- important in HEAD and NECK surgery.
2. Change the angle of connection between the patient and
breathing system
3. Allow a more flexible and/or less kink able connection
between the patient and breathing system
4. Increase the dead space.
22. Factors to keep in mind while selecting a
connector-
1. Resistance increases with sharp curves and rough
sidewalls
2. Connectors add dead space if positioned between the
breathing system and the patient- in infants this
increase in dead space may be excessive
3. Connectors increase the number of locations at which
disconnection can occur.
23. Breathing tubes
Large bore, usually
corrugated tube, made of
rubber or plastic
Corrugations increases
flexibility and help to prevent
kinking
Acts as a reservoir in certain
systems
Have some distensibility but
not enough to prevent
excessive pressures from
developing in the circuit.
24. Reservoir bag
Important component
Made up of antistatic rubber or plastic.
Black bags are antistatic where as green
bags are made up of low charging material
which will not create harmful charges
Accommodates fresh gas flow during
expiration acting as reservoir available for
use in next inspiration
Acts as a monitor of the patient’s
ventilatory pattern
Can be used to assist or control the
ventilation
Bag being the most distensible part of the
breathing system, protects the patient from
excessive pressure in the system
25. The American society for testing and materials(ASTM)
standard for reservoir bags of 1.5L or smaller, the
pressure shall be not less than 30cm H2O or over 50
cm H2O when the bag is expanded to four times its
capacity .
For bags larger than 1.5 L, the pressure shall be not
less than 35cm H2O or over 60 cm H2O when the bag
is expanded to four times its size.
26. Adjustable pressure limiting
valve
Also called as pop off valve, exhaust
valve, scavenger valve, Heidbrink valve,
relief valve, expiratory valve, over spill
valve etc.
This valve allows exhaled waste gases
and fresh gas flows to leave the
breathing system when the pressure
within the breathing system exceeds the
valve’s opening pressure
It is a one way , adjustable, spring loaded
valve
The spring adjusts the pressure required
to open the valve.
27. Construction
Control part- serves to control the pressure at which valve
opens.
Spring loaded disc
Stem and seat
Control knob –
Most APL valves have a rotatory control knob.
The ASTM standard requires that valves with rotating
controls be designed so that a clockwise motion increases
the limiting pressure and ultimately closes the valve.
It also requires an arrow or other marking to indicate the
direction of movement required to close the valve.
Standard recommends that the full range of relief pressure
be adjusted by less than one full turn of the control.
28. Collection device and Exhaust port-
Collection device – to remove the excess gases from the
breathing system and to directs them towards scavenging
system through transfer tubing.
Exhaust port- aperture through which excess gases are
discharged to the scavenging system through a 19 mm or
30 mm male connector
Use:
1. Spontaneous respiration: APL valve is closed during
inspiration and open during expiration. Normally the
valve is fully open during spontaneous ventilation.
Partially closing the valve results in Continuous Positive
Airway Pressure (CPAP).
2. Manually controlled and assisted ventilation: Valve is
usually left partially open
29. They are of two basic types-
1. Variable resistor or variable orifice
type
2. Pressure regulating type
Variable type – functions as a
needle valve much like a flow
control valve. The operator adjusts
the outlet orifice size so the
resultant breathing system pressure
at a given adjustment is directly
related to FGF rate.
30. Pressure regulating type - it has
an adjustable internal tension
spring and an external scale
indicating approximate or relative
opening pressure. When the
pressure in the system exceeds
spring tension a disc opened and
the gas is vented.
31. Positive end expiratory pressure valves
Positive end expiratory pressure (PEEP) and continuous positive
airway pressure (CPAP) are used to improve oxygenation.
PEEP may be used with spontaneous or controlled ventilation.
CPAP is used during spontaneous and during one lung ventilation.
PEEP valve can be UNIDIRECTIONAL or BIDIRECTIONAL.
It has been recommended that only bidirectional PEEP valves be
used.
The ASTM standard requires that a PEEP valve be marked with an
arrow indicating the proper direction of the gas flow or the words
INLET or OUTLET or BOTH.
32. Filters
Filters are used to protect the patient from microorganisms and
airborne particulate matter and protect anaesthesia equipment
and the environment from exhaled contaminants.
It may help to increase the inspired humidity.
It prevents exposure to latex allergens
The Centres for disease control and prevention and the American
society of Anaesthesiologists ( ASA) make no recommendation
for placing a filter in the breathing system unless there is
suspicion that the patient has an infectious pulmonary disease.
Filtration efficiency- it varies. High efficiency particulate aerosol
grade device is defined as one capable of trapping at least
99.97%of particles having a diameter of 0.3 μm
33. Classification
There are numerus classifications of breathing systems,
many of them are irrelevant . Different researchers
classified the same system under different headings,
adding to confusion.
McMohan in 1951 classified them taking the level of
rebreathing into account as follows-
Open- no rebreathing
Semiclosed- partial rebreathing
Closed- total rebreathing
34. Dripps et al. have classified them taking into account the
presence or absence of reservoir, rebreathing, CO2
absorption and directional valve as –
1. Insufflation
2. Open
3. Semiopen
4. Semiclosed
5. Closed
To overcome this problem Conway suggested a functional
classification according to the method used for the CO2
elimination as
1. Breathing systems with CO2 absorber
2. Breathing system without CO2 absorber
35. DM miller in 1988 widened the scope of this classification
so as to include the enclosed afferent reservoir system
A new breathing system called the MAXIMA has been
designed by Miller in 1995 and to include it the
classification the enclosed afferent reservoir systems have
been grouped under ‘displacement afferent reservoir’
systems.
37. Mapleson Breathing systems
History-
in 1954 Mapleson 1st described 5 systems naming A,B,C,D and E.
Later in 1975 Willis et al added another system named as
Mapleson F
Characteristics-
1. absence of unidirectional valve
2. No device for absorbing CO2
3. fresh gas flow must washout CO2 of the circuit. For this
reason they are also known as co2 washout circuits or flow
control breathing systems.
38.
39. Mapleson made a few basic assumptions while
analysing breathing systems. These are-
1. Gases move enbloc. They maintain their identity as
fresh gas, dead space gas and alveolar gas. There is
no mixing of these gases.
2. The RB continues to fill up without offering any
resistance till it is full
3. The expiratory valve opens as soon as the RB is full
and the pressure inside the system goes above
atmospheric pressure
4. The valve remains open throughout the expiratory
phase without offering any resistance to gas flow and
closes at the start of the next inspiration.
40. Mapleson A
Aka Magill attachment or system
It differs from other system that the fresh gas flow
enters opposite to the patient end i.e near the
reservior bag
A corrugated tubing connects the bag to an APL valve
located near the patient end.
41. Techniques of use -
SPONTANEOUS VENTILATION –
the APL valve is kept in fully open position.
Excess gas exit through it in the later part of exhalation.
CONTROLLED VENTILATION/ ASSISTED VENTILATION
intermittent positive pressure is applied
APL valve is partially closed, so that when the bag is squeezed
42. Functional analysis – SPONTANEOUS RESPIRATION
During expiration,
o 1st the dead space gas and then
alveolar gases flow into the
corrugated tubing toward the bag
o At the same time fresh gas flows into
the bag
o When the bag is full, pressure in the
bag rises and APL valve opens.
o 1st gas to be vented out will be the
alveolar gas.
o The continuing inflow fresh gas,
reverse the flow of exhaled gases into
the tubing
43. Cont.
If the FGF is
I. High - it will force the dead space gas out.
II. Intermediate - some dead space gas will be
retained in the system.
III. Low - more alveolar gas will be retained.
During inspiration –
at the start the 1st gas to be inhaled will be from
dead space between patient and APL valve.
The next gas will be either alveolar gas, dead space
gas or fresh gas depending upon the FGF rate.
44. Functional analysis- CONTROLLED RESPIRATION
To facilitate controlled ventilation the
expiratory valve has to be partly closed
During inspiration the patient gets ventilated
with fresh gas and part of the fresh gas is
vented out through the valve after sufficient
pressure has developed to open the valve.
During expiration, the fresh gas from the
machine flows into the reservoir bag and all
the expired gas i.e. dead space gas and
alveolar gas flows back into the corrugated
tube till the system is full.
During the next inspiration the alveolar gas in
the tubing flows to the patient followed by
the fresh gas.
When sufficient pressure is developed by
squeezing the bag, part of the expired gas
and part of the fersh gas escape through the
valve.
45. Cont.
This leads to considerable rebreathing
as well as excessive waste of fresh gas.
The composition of the inspired gas
mixture depends on the respiratory
pattern.
The system becomes more efficient as
the expiratory phase is prolonged.
However it should not be used for
controlled ventilation unless EtCO2 is
monitored.
46. Lack modification of
mapelson A
It has an added expiratory
limb
This limb runs from the
patient connection to APL
valve
This makes it easier to
adjust the valve and
facilitates scavenging
excess gases
Increase in work of
breathing slightly
Available in in both dual
and tube within a tube
configuration.
47. Advantage of Mapleson A circuit
1. Best circuit for spontaneous respiration as no
rebreathing occurs with adequate flows
2. Less fresh gas flow is require during spontaneous
respiration
3. Easy scavenging of gases in Lack’s system to prevent
theatre pollution.
48. Disadvantages of Mapleson A
1. Wastage of gases
2. Theatre pollution by Magill’s circuit
3. Mechanical ventilator should not be used with this
circuit because the entire system becomes dead space
4. Incorrect manufacturing or assembling of Lack’s circuit.
49. Checking of circuit before use
Mapleson A is tested for leaks by occluding the patient
end, closing the APL valve and pressuring the system.
APL valve functioning should be checked by opening and
closing it.
In addition checking is done by breathing through it.
50. Lack system requires additional testing to confirm the
integrity of inner tube
Attach a tracheal tube to the inner tubing at patient
end→ blow down the tube with APL valve closed→ there
will be movement of the bag if there is leak between the
two tubes.
Occlude both the limbs at patient connection with the
valve open and then squeeze the bag. If there is leak in
the inner limb, gas will escape through the valve and bag
will collapse.
51. Enclosed Afferent Reservoir Systems
This has been described by Miller
The system consisted of a Mapleson A
system enclosed within a nondistensible
structure (Fig. 8A).
It may also be constructed by enclosing
the RB alone in a bottle and connecting
the expiratory port to the bottle with a
corrugated tube and a one way valve
(Fig. 8B).
To the bottle is also attached a reservoir
bag and a “variable orifice” for providing
positive pressure ventilation.
52. Functional Analysis-
During spontaneous ventilation, the gas is
vented from the system in a manner which is
identical to the Mapleson A system. In this
mode, the variable orifice is kept widely open
to allow free communication to the
atmosphere.
In controlled ventilation, the reservoir bag “B”
is squeezed intermittently and the variable
orifice is partly closed to allow building-up of
pressure in the bottle. The pressure thus
developed closes the expiratory valve, and
squeezes the enclosed afferent reservoir and
the patient gets ventilated. The expiration
takes place in a manner similar to that
described during spontaneous ventilation
when the pressure is released in reservoir “B”.
Hence, this system should function efficiently
during spontaneous and controlled ventilation
with a FGF equivalent to alveolar ventilation.
53. Mapleson B and C
Similar in construction
FGF entry and expiratory
valves located at the
patient end and reservoir
bag is at the machine end
the of the circuit
Corrugator tubing is
omitted in the Mapleson C
Not commonly used in
anesthesia practice
54. C system may be used for emergency resuscitation
High FGF is needed to prevent rebreathing
Theatre pollution is maximum
FGF required is equal to peak inspiratory flow rate (20-
25 lit/min) to prevent rebreathing
i.e. lot of wastage of fresh gases
55. Mapleson D
The Mapleson D, E,F systems have t piece near the
patient. Mapleson D is the most efficient system during
controlled ventilation.
Configuration-
Classic form of Mapleson D has a 6 mm tube that supplies
the fresh gas from the machine.
It connects to T piece at the patient end and other limb
of the T is attached to a wide bore corrugated tube to
which the reservoir bag is attached
The expiratory valve positioned the near the bag.
56. Bain modification
In principal it is modification of system
used by Macintosh and Park during
second world war to administer
anaesthesia.
Introduced by Bain and Spoerel in
1972.
In this circuit the fresh gas supply tube
runs coaxially inside the corrugated
tubing.
The diameter of the outer tubing is
22mm and inner tube is 7mm.
Length of the circuit is 1.8 m
57. Outer tube is transparent so that inner tube can be
seen for any disconnection or kinking.
Length of the circuit can be increased to modify to use
at remote location.
But increase in length increases resistance during
spontaneous breathing.
Also ventilator setting should be adjusted to deliver set
tidal volume with long Bains circuits.
58. Technique of use
SPONTANEOUS RESPIRATION- APL valve is fully opened.
Patient inspires fresh gas from the circuit and excess gases
are vented out through the APL valve during expiration.
CONTROLLED VENTILATION- the APL valve is kept partially
closed and patient is ventilated by squeezing the reservoir
bag. Here excess gases are vented out during inspiration.
Ventilation can also be instituted by connecting hose of
mechanical ventilator to the circuit in place of reservoir bag
and valve.
The length corrugated tubing between ventilator and the
Bains circuit should be 1 m to to prevent air dilution.
Tidal volume should be set and fresh gas flow should be
kept at 1.5 to 2 times the minute ventilation.
59. Functional analysis Spontaneous respiration
When the patient inspires, the fresh gas goes
to the patient [Figure a].
During expiration, the expired gas gets
continuously mixed with the fresh gas and
flows back into the corrugated tube and the
reservoir bag [Figure b].
When the bag is full, APL valve opens and
excess gas is vented to the atmosphere
through this valve.
During the expiratory pause the fresh gas
continues to flow and fills the proximal
portion of the corrugated tube [Figure c].
During the next inspiration, the patient
breathes fresh gas as well as the mixed gas
from the corrugated tube [Figure d].
60. Cont.
Many factors influence the composition of the
inspired mixture like fresh gas flow, respiratory
rate, expiratory pause, and tidal volume.
If the fresh gas flow is high (1.5-2 times minute
volume), patient will inhale only fresh gas from
the corrugated tubing and if the fresh gas flow is
low (less than 1.5 times minute volume), some
expired gas containing CO2 will be inhaled along
with the fresh gas causing rise in end tidal CO2.
Fresh gas flow should be at least 1.5 to 2 times
the patient’s minute ventilation in order to
minimize rebreathing to acceptable levels.
Based on body weight, recommendations for
fresh gas flow are 150-200 ml/ kg/min to prevent
rebreathing during spontaneous respiration
61. Functional analysis- Controlled ventilation
To facilitate intermittent positive pressure
ventilation, the expiratory valve has to be
partly closed.
When the system is filled with fresh gas,
the patient gets ventilated with the fresh
gas from the corrugated tube [Figure a].
During expiration, the expired gas flows
down the corrugated tubing. It gets mixed
with the fresh gas that is continuously
flowing into the tubing.
During the expiratory pause the fresh gas
continues to enter the tubing and pushes
the mixed gas toward the reservoir bag
[Figure b].
62. Cont.
As the bag is squeezed to ventilate,
pressure in the system increases, the
expiratory valve opens and the contents of
the reservoir bag are discharged into the
atmosphere.
It contains dead space gas, some of the
alveolar gas, and fresh gas.
During the next inspiration, the patient gets
ventilated with the fresh gas and gas in the
corrugated tube i.e., a mixture of fresh gas,
alveolar gas [Figure c] depending upon the
fresh gas flow.
If the fresh gas flow is low, patient will
inhale some exhaled gas also.
63. Cont.
Rebreathing can be avoided by keeping the
fresh gas flow high, i.e., 1.5-2 times minute
ventilation or by increasing the expiratory pause
so that fresh gas can push exhaled gases down
the tubing toward the reservoir bag to be vented
out.
Other factors that influence the composition of
gas mixture with which the patient gets
ventilated are the same as for spontaneous
respiration namely fresh gas flow, respiratory
rate, tidal volume and pattern of ventilation. But
these parameters can be controlled by the
anesthesiologist to maintain normocarbia.
Fresh gas flow recommended is 1.5-2.0 times
minute ventilation. Bain, Spoerel and Aitken
recommended fresh gas flow 70-100 ml/kg/min
with guidelines of ventilating with tidal volume
of 10 ml/kg and frequency between 12 and
14/min
64. Advantages of Bain system
1. Light weight
2. Minimal drag on ETT as compared to Magill’s circuit
3. Low resistance
4. As the outer tube is transparent, it is easy to detect any
kinking or disconnection of the inner fresh gas flow tube
5. It can be used both during spontaneous and controlled
ventilation and change over is easier
65. Cont.
6. Useful where patient is not accessible as in MRI suits
7. Exhaled gases do not accumulate near surgical field,
so risk of flash fires is abolished
8. Easy for scavenging of gases as scavenging valve is
at the machine end of the circuit
9. Easy to connect to ventilator
10. Some warming of inspired fresh gas by the exhaled
gas present in the outer tubing
66. disadvantages
1. Due to multiple connections in the circuit there is a risk of
disconnection
2. Wrong assembling of parts can lead to malfunction of the
circuit
3. Theatre pollution can occur due to high fresh gas flow, can be
prevented by using scavenging system
4. Increases the cost due to high fresh gas flows
5. There can be kinking of the fresh gas supply inner tube,
blocking the fresh gas supply leading to hypoxia
6. There can be crack in the inner tube causing leakage
7. Can not be used in paediatric patients with weight less than 20
kg.
67. Checking of the circuit
Mapleson D system is checked for leaks by occluding the
patient end, closing the APL valve and pressuring the
system.
The APL valve is then opened.
The bag should deflate easily if the valve is working
properly
Outer tube integrity should also be checked by following
simple method- wet the hand with spirit → blow air
through the tube → wipe the tube with wet hands → leak
will produce chillness in the hand
68. For checking the integrity of the inner tube a test is
performed –
setting the a low flow on the oxygen flowmeter
occluding the inner tube with a finger or barrel of a small
syringe at the patient end
Flowmeter indicator is observed
If the inner tube is intact and correctly connected, the
indicator will fall.
69. PETHICKS test-
To check the integrity of the inner tube
Here, oxygen flush is activated and the bag is observed
Due to Venturi effect high flow from the inner tube at the
patient end will create a negative pressure in the outer
exhalation tube
This will suck the gas from the bag and bag will deflate.
If inner tube is not intact, this manoeuvre will cause the
bag to inflate slightly.
70. Mapleson E
Mapleson E system is derived from Ayre’s T
piece configuration by adding tubing to the
expiratory part of the circuit
Does not have a bag
A length of tubing may be attached to the T
piece to form a reservoir
The expiratory port may be enclosed in a
chamber from which excess gases are
evacuated.
A sensor or sampling site for the respiratory
gas monitor may be placed between the
expiratory port and the expiratory tubing.
Volume of the corrugated tubing should be
equal to the tidal volume of the patient.
71. Cont.
It is commonly used to administer oxygen and humidified
gases to patient with spontaneous breathing.
Use has decreased as difficulty in scavenging excess gases.
Techniques of use-
Spontaneous ventilation- the expiratory limb is open to
atmosphere
Controlled ventilation- by intermittently occluding the
expiratory limb and allowing FGF to inflate the lung.
Assisted ventilation- difficult to perform
72. Functional analysis
The sequence of events during the respiratory cycle is similar to that
of Mapleson D system.
The presence or absence and amount of rebreathing or air dilution
will depend on
• the fresh gas flow,
• the patient’s minute volume,
• the volume of the exhalation limb,
• the type of ventilation(spontaneous or controlled)
• the respiratory pattern.
Hazards- controlling ventilation by intermittently occluding the
expiratory limb may lead to over inflation and barotrauma (‘feel’ of
the Bag is absent)
73. Mapleson F
Modification of E system by Jackson Rees (aka Jackson
Rees modification.
It has a 500 ml bag attached to the expiratory limb.
This bag helps in respiratory monitoring or assisting the
respiration.
It also helps in venting out excess gases.
The bag has a hole in the tail of the bag that is occluded
by using a finger to provide pressure
The bag with valves are also available
It is used in neonates, infants and paediatric patients less
than 20 kg in weight or less than 5 yrs.
74. Technique of use
Spontaneous respiration – the relief mechanism of tr bag
is fully pen.
Controlled respiration- the hole in the bag can be
occluded by the user during inspiration and ventilation is
done by squeezing the bag.
Functional analysis- functions like mapleson D system.
The flows required to prevent rebreathing :
2.5 to 3 times the minute ventilation during spontaneous
ventilation
1.5 to 2 times the MV during controlled ventilation
75. In this system during expiration fresh gas and exhaled gas will
collect and mix in the bag.
The next inspiration results in patient inhaling fresh gas both
direct from inlet and from expiratory part of the circuit.
During expiratory pause the expired gases are replaced by fresh
gas in expiratory limb.
Observation of bag movements helps in assessing respiration
during spontaneous breathing.
It also allows controlled ventilation by squeezing the bag.
Heat and moisture exchanger should not be used with Mapleson
E and F during spontaneous respiration as it increases resistance.
So most of the fresh gas will enter expiratory limb leading to
wastage of fresh gases and delaying induction by inhalation
agents.
76. Advantages of MAPLESON E
AND F
Easy assembly.
Inexpensive.
Low resistance system due to the absence of valves.
77. Disadvantages of Mapleson
E and F
Barotrauma can occur during controlled ventilation in
Mapleson E, due to over inflation. This is because
anesthetist does not have the feel of the bag during
inflation. Pressure buffering effect of the bag is absent.
This problem is not seen with Mapleson F as there is a
bag in the system.
High fresh gas flows are required.
Humidification of gases does not occur as in coaxial
circuits.
Atmospheric pollution
78. Advantages-
1. Simple, inexpensive, and rugged, light weight and not bulky.
2. Variation in minute ventilation affects end tidal CO2 less than
that of circle system.
3. The coaxial systems (Lack, Bain), the inspiratory limb is heated
by the warm exhaled gas in the coaxial expiratory limb
4. Resistance is usually low at flows likely to be experienced in
Practice.
5. They are easy to position conveniently
6. Compression and compliance volume losses are less with
Mapleson systems than with the circle system
7. Changes in fresh gas concentrations results in rapid changes in
inspiratory gas composition.
8. No toxic products like CO or COMPOUND A as no CO2
absorber.
79. Disadvantages-
1. These systems require high flows – thus results in higher costs,
increased atmospheric pollution, difficulty in assessing
spontaneous ventilation.
2. As high FGF is required, inspired heat and humidity tend to be
low
3. The optimum fresh gas flow may be difficult to determine.
4. In the Mapleson A,B,C systems the APL valve is near the
patient-may be inaccessible to the user.
5. Mapleson E & F are difficult to scavenge. air dilution can occur
with Mapleson F.
6. Mapleson systems are not suitable for patients with Malignant
hyperthermia.(as it may not be possible to increase FGF
enough to remove the increased CO2 load.
80. Gas flows in anaesthetic
breathing systems
system Spontaneous
ventilation
Intermittent positive
pressure ventilation
Mapleson A
(lack or magill)
Minute
ventilation(MV)
2.5×MV
80 ml/kg/min 200ml/kg/min
Mapleson D
(bain or coaxial
mapleson D)
2-3× MV 70 ml/kg/min for
PaCO2 of 5.3 kPA
150-250ml/kg/min 100ml/kg/min for
PaCO2 of 4.3 kPA
Mapleson E
(Ayre’s T piece)
2× MV As mapleson D,
minimum fgf required
3 L/min
Mapleson F As Mapleson E As mapleson E
81. Combined system
To overcome the difficulties of changing
the breathing systems for different modes
of ventilation, Humphrey designed a
system called Humphrey ADE with two
reservoirs, one in the afferent limb and the
other in the efferent limb.
While in use, only one reservoir will be in
operation and changing the position of a
lever can change the system from ARS to
ERS.
It can be used for adults as well as children.
The functional analysis is the same as
Mapleson A in ARS mode and as Bain in
ERS mode.
It is not yet widely used
