2. What is a breathing system?
An assembly of
components that
Connects the patient’s
airway to the anesthesia
machine
Creating an artificial
atmosphere from and
into which the patient
breathes.
3. Components
A fresh gas entry port
/ delivery tube
A reservoir for gas, in
the form of a bag
A port to connect it to
the patient's airway;
An expiratory port /
valve
Corrugated tubes for
connecting these
components.
4. Components
A CO2 absorber if total rebreathing is to be allowed
Flow directing valves may or may not be present
Connectors and adapters
Filters
5. Requirements
Essential Desirable
Deliver gases from machine
to alveoli
Eliminate CO2
Have minimal apparatus
dead space
Have low resistance
Economy of fresh gas
Conservation of heat
Adequate humidification of
inspired gas
Light weight
Convenient
Efficient for both spontaneous
and controlled ventilation
Adapatable
7. Classification
Without CO2 absorption With CO2 absorption
Unidirectional flow
Non rebreathing systems
Circle systems
Bidirectional flow
Afferent reservoir systems
Efferent reservoir systems
Enclosed afferent reservoir
Combined system
Unidirectional flow
Circle system with absorber
Bidirectional flow
To and fro system
11. Non rebreathing systems
No rebreathing
Unidirectional flow
The FGF should be equal to the minute
ventilation of the patient.
Disadvantages
FGF has to be constantly adjusted and is not
economical
No humidification or heat conservation
Bulk of valve near patient – inconvenient
Valves malfunction due to moisture condensation
12. Classification
Without CO2 absorption With CO2 absorption
Unidirectional flow
Non rebreathing systems
Circle systems
Bidirectional flow
Afferent reservoir systems
Efferent reservoir systems
Enclosed afferent reservoir
Combined system
Unidirectional flow
Circle system with absorber
Bidirectional flow
To and fro system
14. Afferent Reservoir Systems
The afferent limb is that part of the breathing
system which delivers the FG from the machine to
the pt. If the reservoir is placed in this limb, they are
called afferent reservoir systems.
Mapleson A, B, C
15. Efferent reservoir systems
The efferent limb is that part of the breathing
system which carries expired gas from the patient
and vents it to the atmosphere through the
expiratory valve/port. If the reservoir is placed in
this limb, they are called efferent reservoir systems
Mapleson D, E, F
19. Bidirectional flow
Depend on FGF for effective elimination of CO2
Can be manipulated by changing parameters
Fresh gas flow
Alveolar ventilation
Apparatus dead space
20. Fresh gas flow
It is imperative to specify optimum FGF for a
breathing system for efficient functioning.
FGF should be delivered as near the patient’s
airway as possible.
21. Fresh gas flow
Essential requisite of a breathing system
High
Optimal
Low
CO2 not
eliminated
Wastage
of gases
22. Apparatus dead space
Part of the breathing system from which exhaled
alveolar gases are rebreathed without any
significant change in their CO2 concentration
Volume of the breathing system from the patient
end to the point upto which to and fro
movement of expired gas takes place.
24. Apparatus dead space
Should be minimal - rebreathing of CO2 could result
in hypercapnia
The dynamic dead space depends on FGF and
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
25. Afferent reservoir systems
Efficient during spontaneous breathing
provided the expiratory valve is separated
from the reservoir bag and FGF by at least
one tidal volume of the patient and
apparatus dead space is minimal
one tidal volume
30. Lack circuit
Lack system has an
afferent limb reservoir
and an efferent limb
through which the
expired gas traverses
before being vented
into the atmosphere.
This limb is coaxially
placed inside the
afferent limb.
Efferent limb
Afferent limb
31. Mapleson’s analysis
1. Gases move enbloc. They maintain their identity as
fresh gas, dead space gas and alveolar gas- No mixing
of gases.
2. The reservoir bag continues to fill up, without offering
any resistance till it is full
3. The expiratory valve opens as soon as the reservoir
bag 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.
32. Functional analysis
Mapleson ‘A’/Magill’s system:
Spontaneous breathing: system is filled with FG before connecting to
the pt.When the pt inspires, FG from the machine and the reservoir
bag flows to the pt- bag collapses . During exprn, the FG continues
to flow into the system and fill the reservoir bag.The expired gas,
initial part - dead space gas, pushes the FG from the corrugated
tube into the reservoir bag and collects inside the corrugated tube.
As soon as the reservoir bag is full, the expiratory valve opens and
the alveolar gas is vented into the atmosphere . During the
expiratory pause, alveolar gas that had come into the corrugated
tube is also pushed out through the valve, depending on the FGF.
The system is filled with only FG and dead space gas at the start of
the next insprn when FGF = alveolar ventilation .The entire alveolar
gas and dead space gas is vented through the valve and some FG
also escapes, if the FGF > MV. Some amt of alveolar gas will remain
in the system and lead to rebreathing with a FGF< MV. Max
efficiency, when the FGF = alveolar ventilation and the dead space
gas has is allowed to be rebreathed and utilized for alveolar
ventilation.
33.
34. Controlled ventilation: For IPPV the expiratory
valve - partly closed. During insprn, the pt gets
ventilated with FG and part of the FG is vented
through the valve after sufficient pressure has
developed to open the valve. During exprn, the FG
from the machine flows into the reservoir bag and
all the expired gas flows back into the corrugated
tube till the system is full . During next insprn the
alveolar gas is pushed back into the alveoli followed
by the FG.When sufficient pressure is developed,
part of the expired gas and part of the FG escape
through the valve. Considerable rebreathing,
excessive waste of FG.
35.
36. To summarize afferent
reservoir systems.....
Mapleson A is efficient only for spontaneous
respiration and is inefficient for controlled
ventilation
Mapleson B and C are inefficient for both
spontaneous respiration and controlled
ventilation
37. Efferent reservoir systems
Works efficiently and economically for
controlled ventilation as long as the FG entry
and the expiratory valve are separated by a
volume equivalent to atleast oneTV of the
patient
Not economical during spontaneous
breathing
40. Ayre's T-piece (1937)
Light metal tube 1 cm
in diameter, 5 cm in
length with a side arm
Used as such, it
functions as a non-
rebreathing system
FGF equal to peak
inspiratory flow rate of
the patient
RESERVOIR
TUBE
TO PATIENT
FRESH GAS
FLOW
44. Bains circuit- spontaneous
When pt inspires, the FG from the machine, the reservoir
bag and the corrugated tube flow to the pt . During exprn,
there is a continuous FGF into the system at the pt end.The
expired gas gets continuously mixed with the FG as it flows
back into the corrugated tube and the reservoir bag . Once
the system is full the excess gas is vented to the atmosphere
through the valve situated at the end of the corrugated tube
near the reservoir bag. During the expiratory pause the FG
continues to flow and fill the proximal portion of the
corrugated tube while the mixed gas is vented through the
valve . During the next inspiration, the patient breaths FG as
well as the mixed gas from the corrugated tube . Many
factors influence the composition of the inspired mixture.
They are FGF, respiratory rate, expiratory pause, tidal
volume and co2 production in the body. Factors other than
FGF cannot be manipulated in a spontaneously breathing
patient. FGF should be atleast 1.5 to 2 times the patient’s
minute ventilation to minimise rebreathing.
45.
46. Bains -controlled
To facilitate IPPV, the expiratory valve has to be partly closed so that it
opens only after sufficient pressure has developed in the system.
When the system is filled with fresh gas, the patient gets ventilated
with the FGF from the machine, the corrugated tube and the
reservoir bag. During expiration, the expired gas continuously gets
mixed with the fresh gas that is flowing into the system at the
patient end. During the expiratory pause the FG continues to enter
the system and pushes the mixed gas towards the reservoir .When
the next inspiration is initiated, the patient gets ventilated with the
gas in the corrugated tube i.e., a mixture of FG, alveolar gas and
dead space gas . As the pressure in the system increases, the
expiratory valve opens and the contents of the reservoir bag are
discharged into the atmosphere. Factors that influence the
composition of gas mixture in the corrugated tube are FGF, RR,TV
and pattern of ventilation.These parameters can be totally
controlled by the anaesthesiologist and do not depend on the
patient. Using a low respiratory rate with a long expiratory pause
and a high tidal volume, most of the FG could be utilized for
alveolar ventilation without wastage.
47.
48. Advantages of Bain’s
Light weight
Convenient
Easily sterilized
Scavenging facilitated as the expiratory valve being
located away from the patient
Exhaled gases in the outer reservoir tubing add
warmth to the inspired fresh gases
49. Disadvantages
Kinking, leakage and disconnections of inner
tube which can cause severe hypercapnia
Outer tube should be transparent to allow
inspection of the inner tube
Special tests
50. Test for Bain’s circuit
Set a low flow of oxygen on the flowmeter
and occlude the inner tube .The indicator in
the flowmeter will fall slightly if the inner
tube is intact
Pethick test
55. Circuit FGF for spontaneous
respiration
FGF for controlled
ventilation
Mapleson A 70 – 80 ml/kg/min 2 ½ x MV =
12 – 15 L/min
Mapleson B > 2 x MV
20 – 25 L/min
2 – 2.5 x MV
Mapleson C 2 – 2.5 x MV 2 – 2.5 x MV
Mapleson D 2 x MV or 8 – 10 L/min
or 150ml/kg/min
70 ml/kg/min
Mapleson E 2 - 3 x MV 2 x MV
Mapleson F 2 x MV 1000ml + 100ml/kg
56. Efficiency of Mapleson systems
Spontaneous
Controlled
A > DFE > CB
DFE > BC > A
All Dogs Can Bite
Dead Bodies Can’t Argue
57. Conclusion
What is a breathing system?
What are the components?
What are the requisites?
What is the classification?
Can we identify the different circuits?
Functional analysis of each
Advantages and disadvantages of each.