This document discusses breathing circuits used in anesthesia. It begins by classifying breathing systems as open, semi-open, semi-closed, closed, or insufflation based on gas flow and carbon dioxide absorption. Characteristics of an ideal breathing system are described. The Mapleson breathing systems are then introduced, which lack unidirectional valves and rely on fresh gas flow to wash out carbon dioxide. Specific Mapleson systems - A, B, C, D, E, and F - are explained in detail regarding their components and functional analysis during spontaneous and controlled ventilation. Advantages of the Bain modification of the Mapleson D system are provided.

1. BREATHING CIRCUITS
PRESENTER: DR HARSHNI KANNAN
MODERATOR: DR OSMANI

2. CLASSIFICATION OF BREATHING SYSTEMS
Open semiopen semiclosed closed insufflation
Pt inhales
only gas
delivered
from
machine ±
bag. No
CO2
absorption
Exhaled gas to
be
rebreathed. No
CO2
absorption. Bag
and directional
valve optional
Some exhaled
gases go
to scavenging
system
and part +fresh
gas
are rebreathed.
CO2
absorption,
directional
valves, and bag
present
Complete
rebreathing
expired gas
No valves,
reservoir
bag, or CO2
absorption

3. CLASSIFICATION OF BREATHING SYSTEMS

4. CHARACTERISTICS OF AN IDEAL BREATHING SYSTEM
• Should be safe, simple and inexpensive
• Able to deliver intended inspired gas mixture
• Permit spontaneous, controlled or assisted ventilation in all age groups
• Efficient and allow low fresh gas flow
• Able to protect patients from barotrauma
• Sturdy, compact, light weight
• Easily remove waste gases
• Warming and humidification of inspired gases

5. • Effectively eliminate CO2
• Have low resistance- minimal length, maximal diameter, without sharp curves
or sudden changes in diameter
• Dead space should be minimal

6. MAPLESON BREATHING SYSTEMS

7. MAPLESON BREATHING SYSTEMS
• The Mapleson systems are characterized by the absence of unidirectional
valves to direct gases to or from the patient.
• Because there is no means for absorbing CO2, the fresh gas flow must wash
CO2 out of the circuit.
• For this reason, these systems are sometimes called carbon dioxide washout
circuits or flow-controlled breathing systems.

8. • Semi closed anaesthetic system
• Classified from A to E in 1954 by William W Mapleson
• The Mapleson F was added later in 1975

9. COMPONENTS OF A BREATHING SYSTEM
• Breathing tubes
Large bore, usually corrugated tubes, made of rubber or plastic
Corrugations increase flexibility and resistance to kinking
Clear plastic tubes are lightweight and low resistance
Act as a reservoir in certain systems
Have some distensibility but not enough to prevent excessive pressures
from developing in the circuit

10. ADJUSTABLE PRESSURE LIMITING VALVE
• Also called pop off valve, exhaust valve, scavenger valve, relief valve,
expiratory valve, over spill valve, Heidbrink valve
• This valve allows exhaled waste gases and fresh gas flows to leave the
breathing system if it 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

11. RESERVOIR BAG
• Made of anti static rubber or plastic
• Black bags are anti static, green bags are made of low charging material that
protects the bag from electric fields
• Accommodates fresh gas flow during expiration, acting as a reservoir available
for use in the next inspiration
• Acts as monitor of patient’s ventilator pattern
• Can be used to assist or control ventilation
• Most distensible part of the breathing system, protects the patient from
excessive pressure in the system

12. CONNECTORS AND ADAPTORS
• Extends the distance between patient and breathing system
• Allows more flexibility for maneuvering
• Increases dead space and resistance

13. MAPLESON A (MAGILL SYSTEM)
• Expiratory valve close to the face
mask, separated by corrugated tube
from reservoir bag and supply of
fresh gases

14. MAPLESON A (MAGILL SYSTEM)
• At one end, an inlet for fresh gas
linked to a 2 litre distensible rubber
reservoir bag
• This is attached to a length of
corrugated breathing hose
(minimum length 110cm with an
internal volume of 550ml)
• This volume minimizes the
backtracking of exhaled alveolar gas
back to the reservoir bag

15. MAPLESON A (MAGILL SYSTEM)
• This is in turn connected a variable
tension, spring-loaded flap valve for
venting of exhaled gases
• This valve should be attached at the
opposite end of the system from the
reservoir bag and as close to the
patient as possible (APL valve)

16. TECHNIQUE OF USE
• Spontaneous ventilation: APL valve is kept fully open. Excess gas exits through
it during latter part of exhalation
• Controlled or assisted ventilation: intermittent positive pressure is applied to
the bag. APL valve is kept partially closed, for pressure to inflate lungs. Valve is
opened during inspiration

17. ASSUMPTIONS MADE FOR FUNCTIONAL ANALYSIS
• Gases move en bloc. They maintain
their identity as fresh gas, dead
space gas and alveolar gas. There is
no mixing of these gases
• The reservoir bag continues to fill
up, without offering any resistance
till it is full

18. ASSUMPTIONS MADE FOR FUNCTIONAL ANALYSIS
• The expiratory valve opens as soon
as the reservoir bag is full and the
pressure inside the system goes
above the atmospheric pressure
• The valve remains open throughout
the expiratory phase, without
offering resistance to gas flow and
closes at the start of next inspiration

19. FUNCTIONAL ANALYSIS – SPONTANEOUS RESPIRATION
• Initially when the patient inspires,
the fresh gas from the machine and
the reservoir bag flows to the
patient

20. FUNCTIONAL ANALYSIS – SPONTANEOUS RESPIRATION
• During expiration the fresh gas
continues to flow into the system
and fill the reservoir bag. The
expired gas consisting of dead space
gas and alveolar gas pushes the
fresh gas from the corrugated tube
into the reservoir bag and collects
inside the corrugated tube

21. FUNCTIONAL ANALYSIS – SPONTANEOUS RESPIRATION
• As soon as the reservoir bag is full,
the expiratory valve opens and the
alveolar gas is vented into the
atmosphere.

22. FUNCTIONAL ANALYSIS – SPONTANEOUS RESPIRATION
• During expiratory pause the alveolar
gas that had come into the
corrugated tube is also pushed out
through the valve, depending on the
FGF

23. FUNCTIONAL ANALYSIS – SPONTANEOUS RESPIRATION
• If fresh gas flow is equal to or more
than MV (70-100 ml/kg/min) it will
force the expired alveolar gas out
• If flow is less than MV, some
alveolar gas is retained in the
system and rebreathing occurs
• If FGF is very low, more alveolar gas
will be retained

24. FUNCTIONAL ANALYSIS – SPONTANEOUS RESPIRATION
• During the next inspiration the
system is filled with only fresh gas
and dead space gas when FGF = MV

25. FUNCTIONAL ANALYSIS – SPONTANEOUS RESPIRATION
• Maximum efficiency when the FGF=MV and the dead space gas is allowed to
be rebreathed and utilized for MV
• Mapleson A is the circuit of choice for spontaneous respiration, because there
is negligible rebreathing
• Rebreathing begins when the fresh gas flow is reduced to 56 to 82 mL/kg/
minute, or 58% to 83% of minute volume. Fresh gas flows of 51 to 85
mL/kg/minute and 42% to 88% of minute volume have been recommended to
avoid rebreathing.

26. FUNCTIONAL ANALYSIS – CONTROLLED VENTILATION
• For 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

27. FUNCTIONAL ANALYSIS – CONTROLLED VENTILATION
• During expiration, the fresh gas
from the machine flows into the
reservoir bag and all the expired gas
(dead space gas + alveolar gas) flows
back into the corrugated tube till
the system is full -

28. FUNCTIONAL ANALYSIS – CONTROLLED VENTILATION
• 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 fresh gas escape through the
valve.

29. FUNCTIONAL ANALYSIS – CONTROLLED VENTILATION
• This leads to considerable rebreathing,
as well as excessive waste of fresh gas.
- The composition of 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

30. MODIFICATION OF MAPLESON A
• Lack’s Modification
Separate expiratory limb which starts from patient connection to the
APL valve at the machine end of the system
It facilitates the scavenging of gas to prevent theatre pollution
The disadvantage is that it increases the work of breathing

31. • The Lack system is available in two arrangements:
Parallel tube
Co axial configuration in which expiratory limb runs concentrically
inside the outer inspiratory limb

32. MAGILL SYSTEM VS. LACK SYSTEM
• DISADVANTAGES OF THE TRADITIONAL MAGILL SYSTEM (with the APL
valve as close to the patient as possible):
reduces the access to the valve in head and neck surgery
increases the drag on the mask or endotracheal tube when the valve is
shrouded and connected to scavenging tubing
The Lack system overcomes these two problems

33. MAPLESON B AND C SYSTEM
• Expiratory valve, supply of fresh
gases and reservoir bag, all close to
face mask. (No corrugated tube.)
• Expiratory valve and supply of fresh
gases close to face mask, separated
by corrugated tube from reservoir
bag

34. • They are not commonly used in anaesthetic practice
• C system may be used for emergency resuscitation. High flow of gases is
needed to prevent rebreathing of CO2 and theatre pollution is maximum.
• Fresh gas flow required is equal to 2 to 3 times the MV to prevent
rebreathing. So lot of wastage of fresh gases

35. MAPLESON D
• Supply of fresh gases close to face mask, separated by corrugated tube from
reservoir bag and expiratory valve.
• Classic form of Mapleson D has a 6 mm tube that supplies the fresh gas from
the machine. It connects to the 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 and the expiratory valve is positioned near the bag.

36. BAIN’S MODIFICATION
• 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 22 mm
and inner tube is 7 mm
• Length of the circuit is 1.8 metre

37. BAIN’S MODIFICATION
• Outer tube is transparent so that inner tube
can be inspected for any disconnection or
kinking
• Length of the circuit can be increased to
modify it for use at remote locations. As the
length increases, the resistance increases
during spontaneous breathing.

38. BAIN’S MODIFICATION
• A long version of the Bain system may be used for remote anaesthesia in
locations such as the magnetic resonance imaging (MRI) unit
• Compared with the usual Bain system, static compliance is increased with a
reduction in peak inspiratory pressure and tidal volume with the same
ventilator settings. Also, PEEP is increased
• A longer Bain system also presents increased resistance to spontaneous
breathing.

39. FUNCTIONAL ANALYSIS – SPONTANEOUS VENTILATION
• When the patient inspires, the fresh
gas is delivered to the patient.

40. • During expiration, the expired gas gets
continuously mixed with the fresh gas and
flows back into the corrugated tube and
the reservoir bag.
• When the bag is full, APL valve opens and
excess gas is vented to the atmosphere
through the valve

41. • During the expiratory pause the fresh gas
continues to flow and fills the proximal
portion of the corrugated tube

42. • During the next inspiration, the patient
breathes fresh gas as well as the mixed gas
from the corrugated tube

43. FACTORS INFLUENCING THE COMPOSITION OF INSPIRED
MIXTURE IN SPONTANEOUS VENTILATION
• FGF : Recommendations for fresh gas flows based on body weight vary from
100 to 300 mL/kg/minute. Most studies have recommended that the fresh gas
flow be 1.5 to 3.0 times the minute volume, whereas others have held that a
fresh gas flow approximately equal to minute ventilation is adequate.
• RR
• expiratory pause
• TV

44. FUNCTIONAL ANALYSIS – CONTROLLED VENTILATION
• To facilitate IPPV, 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.

45. • During expiration, the expired gas flows
down the corrugated tubing. It gets mixed
with the fresh gas that is continuously
flowing into the tubing

46. • During the expiratory pause the fresh gas
continues to enter the tubing and pushes the
mixed gas toward the reservoir bag.
• 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.

47. • 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 depending upon the FGF

48. • If the FGF is low, patient will inhale some exhaled gas also. Rebreathing can be
avoided by keeping the FGF high
• 1.5 to 2 times MV 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
• Factors influencing the composition of gas mixture with which the patient
gets ventilated are the same as for spontaneous respiration (FGF, RR, TV and
pattern of ventilation)

49. ISOPLETH OF MAPLESON D
• Combining fresh gas flow, minute volume, and arterial CO2 levels, a series of
curves can be constructed .
• An infinite number of combinations of fresh gas flow and minute volume can
be used to produce a given PetCO2.
• High fresh gas flows and low minute volumes or high minute volumes and
low fresh gas flows or combinations in between can be used.

50. • At the left, with a high fresh gas flow, the
circuit is nonrebreathing and end-tidal CO2
depends only on ventilation.
• Such high flows are uneconomical and
associated with lost heat and humidity.
• End-tidal CO2 depends on minute volume,
which is difficult to accurately adjust,
especially in small patients.
• On the right is the region of hyperventilation
and partial rebreathing.

51. • End-tidal CO2 is regulated by adjusting the
fresh gas flow.
• Lower fresh gas flows (and increased
rebreathing) are associated with higher
humidity, less heat loss, and greater fresh
gas economy.
• Hyperventilation can be used without
inducing hypocarbia.
• Individual differences in the ratio of dead
space to tidal volume are minimized at high
minute volumes.

52. MAPLESON D SYSTEM
• To prevent rebreathing in the Mapleson D system during both
spontaneous and controlled ventilation, the fresh gas flow must be
sufficiently high enough to :
 purge the breathing hose of exhaled gasses
 supplement the stored fresh gas in this breathing hose so that any mixed
gas in the reservoir bag is prevented from reaching the patient.
 The amount of fresh gas required will always be greater than the patient’s
minute volume and will depend largely on the expiratory pause.
 The longer the pause, the more effective will be the ability of the fresh
gas to purge the breathing hose of expired gas

53. ADVANTAGES
• Light weight.
• Minimal drag on ETT as compared to Magill's circuit.
• Low resistance.
• As the outer tube is transparent, it is easy to detect any kinking or
disconnection of the inner fresh gas flow tube.
• It can be used both during spontaneous and controlled ventilation and change
over is easier.

54. ADVANTAGES
• It is useful where patient is not accessible as in MRI suites.
• Exhaled gases do not accumulate near surgical field, so risk of flash fires is
abolished.
• Easy for scavenging of gases as scavenging valve is at machine end of the
circuit.
• Easy to connect to ventilator.
• There is some warming of the inspired fresh gas by the exhaled gas present in
outer tubing

55. DISADVANTAGES
• Due to multiple connections in the circuit there is a risk of disconnections.
• Wrong assembling of the parts can lead to malfunction of the circuit.
• Theatre pollution occurs due to high fresh gas flow. However, it can be
prevented by using scavenging system.
• Increases the cost due to high fresh gas flows.
• There can be kinking of the fresh gas supply inner tube blocking the fresh gas
supply leading to hypoxia - There can be crack in the inner tube causing
leakage - It cannot be used in paediatric patients

56. CHECKING OUTER TUBE INTEGRITY
• Wet the hands with spirit
• Blow air through the tube
• Wipe the tube with wet hands
• Leak will produce chillness in the hands

57. CHECKING INNER TUBE INTEGRITY
• Set low flow on the oxygen flowmeter
• Occlude the inner tube with a finger or barrel of a small syringe at the patient
end while observing the flow meter indicator APL valve is subsequently
opened
• If the inner tube is intact and correctly connected, the indicator will fall.

58. CHECKING INNER TUBE INTEGRITY
PETHICKS TEST
• Activate the oxygen flush and observe the bag
• Due to venturi effect the high flow from the inner tube at the patient end will
create a negative pressure in the outer exhalation tubing and this will suck gas
from the bag and bag will deflate
• If the inner tube is not intact, this maneuver will cause the bag to inflate
slightly

59. MAPLESON E SYSTEM –T-PIECE SYSTEM
• Ayre's T-piece was invented by Phillip Ayer in
1937.
• This consists of a 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.
• Fresh gas enters the system through the side
arm and the expired gas is vented into the
atmosphere and there is no rebreathing

60. MAPLESON E SYSTEM –T-PIECE SYSTEM
• Use of this system has decreased in
anaesthesia because it is difficult to scavenge
excess gases and high fresh gas flows, i.e.,
peak expiratory flow rate are required.
• Mapleson E system is derived from Ayre's T
piece configuration by adding tubing to the
expiratory part of the circuit.

61. MAPLESON E SYSTEM –T-PIECE SYSTEM
• It acts as a fresh gas reservoir during inspiration. Its capacity should be more than the
expected tidal volume.
• It is mainly used in neonates, infants and paediatric patients which are less than 20 kg
in weight or less than 5 years of age
• For spontaneous ventilation, the expiratory limb is open to atmosphere.
• Controlled ventilation can be performed by intermittently occluding the expiratory
limb and allowing the fresh gas to inflate the lungs.
• Mapleson E functions on the same principles as Mapleson D

62. MAPLESON E SYSTEM –T-PIECE SYSTEM
During inspiration:
• The patient inspires fresh gas from the fresh gas
inlet as well as reservoir tube.
During expiration:
• The patient expires into the reservoir tube and
expired to the atmosphere along with some fresh
gas which is continuously flowing into the reservoir
tube.

63. MAPLESON E SYSTEM –T-PIECE SYSTEM
During expiratory pause:
• The expired gas is vented out and the fresh gas
is filled in expiratory tube for next respiration
• Rebreathing and air dilution can occur with this
system, depending on the fresh gas flow, the
patient's minute volume, the volume of the
expiratory limb, and type of ventilation whether
spontaneous or controlled

64. MAPLESON E SYSTEM –T-PIECE SYSTEM
• Fresh gas flow required is 2.5 to 3 times the minute volume during
spontaneous ventilation and 1.5 to 2 times the minute volume during
controlled ventilation.
• Air dilution can be prevented by keeping the volume of the expiratory limb
greater than patient's tidal volume.

65. HAZARD ASSOCIATED WITH MAPLESON E SYSTEM
• Controlling ventilation by intermittently occluding the expiratory limb may lead to
over inflation and barotrauma
• This is because the anaesthesia provider does not have the “feel” of the bag
during inflation
• The pressure-buffering effect of the bag is absent, and there is no APL valve to
moderate the pressure in the lungs.

66. MAPLESON F SYSTEM
• It is a modification of Mapleson E by Jackson
Rees and is known as 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.

67. MAPLESON F SYSTEM
• The bag has a hole in the tail of the bag that
is occluded by using a finger to provide
pressure.
• The bags with valve are also available.
• It is used in neonates, infants, and pediatric
patients less than 20 kg in weight or less than
5 years of age.

68. TECHNIQUE OF USE
• For spontaneous respiration : The relief mechanism of the bag is left fully
open.
• For controlled respiration : The hole in the bag can be occluded by the user
during inspiration and ventilation is done by squeezing the bag.

69. • It also functions like Mapleson D system.
• The flows required to prevent rebreathing are 2.5-3.0 times minute volume
during spontaneous ventilation and 1.5 to 2 times the minute volume during
controlled ventilation.
• During expiration fresh gas and exhaled gas will collect and mix in the bag

70. • The next inspiration results in patient inhaling fresh gas both direct from inlet
and from expiratory part of the circuit as in Mapleson E.
• During expiratory pause the expired gases are replaced by fresh gas in the
expiratory limb.
• Observation of bag movements helps in assessing respiration during
spontaneous breathing.
• It also allows controlled ventilation by squeezing the bag.

71. ADVANTAGES
• Easy assembly
• Inexpensive
• Low resistance system due to the absence of valves
• Barotrauma can occur during controlled ventilation in Mapleson E, due to
over inflation.
• This is not seen with Mapleson F as there is a bag in the system

72. DISADVANTAGES
• High FGF are required
• Humidification of gases does not occur as in coaxial circuits
• Atmospheric pollution

73. WHICH SYSTEM IS EFFICIENT FOR SPONTANEOUS
RESPIRATION AND CONTROLLED VENTILATION?
• Mapleson A for spontaneous respiration has the best efficiency since FGF
required to prevent rebreathing is equal to minute ventilation
• Mapleson D or Bain’s circuit is best for controlled ventilation
• Mapleson D, E, F require higher FGF to prevent rebreathing. They are next in
order of preference list for spontaneous respiration. But they are better than
Mapleson A for controlled ventilation.

74. ADVANTAGE OF MAPLESON’S
• Simple and low cost
• Components are easy to disassemble and can be disinfected or sterilized
• Light weight (Do not cause drag on tracheal tube)
• The length of the Mapleson D can be increased. So, they are suitable for use
in remote locations like MRI suit
• Humidification of the gases occurs in coaxial systems (Lack and Bain)

75. ADVANTAGE OF MAPLESON’S
• Resistance of these systems is low.
• So they are good for spontaneous respiration.
• But if the APL valve is not opened properly, it can add to resistance
• There is no risk of toxic products production such as compound A as with
circle system due to CO2 absorbent

76. DISADVANTAGE OF MAPLESON’S
• FGF required for these circuits is high which increases the cost
• More theatre pollution due to high gas flows required
• Due to high FGF, inspired heat and humidity tend to be less. So, humidification
of the gases is required separately
• The optimum FGF is difficult to ascertain. If it is lowered by any cause it can
result in rebreathing

77. DISADVANTAGE OF MAPLESON’S
• In Mapleson A, B and C systems, APL valve is close to the patient. So,
scavenging is difficult
• In Mapleson E, air dilution can occur
• They are not suitable for patients with malignant hyperthermia because very
high FGF is required to washout excess CO2 load

78. DISINFECTION AND STERILISATION
• Mapleson systems are disassembled and cleaned
• Metal components are autoclaved
• Rubber and plastic parts are sterilised by gas or plasma sterilisation or a liquid
chemical agent (glutaraldehyde) is used

80. CIRCLE SYSTEM

81. INTRODUCTION
 Circle system is a closed circuit
 Designed with a CO2 absorber as an essential component of the system
 It is so named because gases flow in a circular pathway through separate
inspiratory and expiratory channels
 Carbondioxide exhaled by the patient is removed by an absorbent

82. COMPONENTS OF CIRCLE SYSTEM
• The essential components of the circle system are:
Carbon dioxide absorber / absorbents
Unidirectional valves
 Inspiratory and expiratory ports
 Y-piece to connect to the patient
 Fresh gas inlet
 Adjustable pressure limiting valve
 Pressure gauge

83.  Breathing tubes
 Reservoir bag (RB)
 Ventilator
 Bag / ventilator selector switch
 Respiratory gas monitor sensor
 Airway pressure monitor sensor
 Respirator
 Optional
 PEEP valve
 Filters
 Heated Humidifier

84. ABSORBER
 An absorber assembly consists of
an absorber
two ports for connection to breathing tubes
a fresh gas inlet.
Other components that may be mounted
an inspiratory and expiratory unidirectional valves,
an APL valve and
a bag mount.

85. CANISTER
• Absorbent is held in canister
• Canister side walls are transparent
• A screen at the bottom of each canister hold the absorbent in place
• Types :
Small single canister
Two canister in series
Single small disposable canister
Prepacked absorbant containers

87. • Absorber with two canisters in
series,
 a dust/moisture trap at the
bottom and
 a drain at the side.
• The lever at the right is used to
tighten and loosen the
canisters.

88. • Absorption pattern:
 Absorption first occurs at the inlet and along the sides of the canister
 As this absorbent becomes exhausted, Co2 will be absorbed farther downstream
in the canister

89. SIDE OR CENTRE TUBE

90. ABSORBENTS
• Co2 absorption employs the general principle of a base neutralizing an acid
• The absorption of carbon dioxide is an exothermic reaction .
• Co2 + H2o H2co3
• H2co3 + 2NaOH Na2co3 + 2H2o
• H2co3 + 2KOH K2co3 + 2H2o
• Na2co3 + Ca(OH)2 2NaOH (2KOH) + Caco3

91. CHEMISTRY OF ABSORBENTS
• Two formulations of carbon dioxide absorbents are commonly available
today:
 Soda lime – High alkali absorbents and
 Calcium hydroxide lime (Amsorb) – Alkali free absorbents.
• Of these agents, the most commonly used is soda lime.
• Sodium hydroxide is the catalyst for the carbon dioxide absorptive properties
of soda lime

92. • By weight, the approximate composition of “high-moisture” soda lime is
 80% calcium hydroxide,
 15% water,
 4% sodium hydroxide, and
 1% potassium hydroxide (an activator).
• Small amounts of silica are added to produce calcium and sodium silicate. This
addition produces a harder, more stable pellet and thereby reduces dust
formation.

93. • The most significant advantage of calcium hydroxide lime (Amsorb) over other
agents is its lack of the strong bases like sodium and potassium hydroxide.
• Absence of these chemicals eliminates the undesirable production of CO and
the nephrotoxic substance known as compound A, and it may reduce or
eliminate the possibility of a fire in the breathing circuit.
• Baralyme is a mixture of approximately 20% barium hydroxide and 80%
calcium hydroxide. It may also contain some potassium hydroxide
• Baralyme is the primary carbon dioxide absorbent implicated as an agent that
may produce fires in the breathing system when used with sevoflurane.

95. INDICATOR
• An indicator is an acid or base whose colour depends on pH.
• It is added to the absorbent to signify when the absorbent’s ability to absorb
carbon dioxide is exhausted.

96. • Ethyl violet is most commonly employed, because the color change is vivid
with a high contrast.
• This compound is a substituted triphenylmethane dye with a critical pH of
10.3.
• Ethyl violet changes from colorless to violet when the pH of the absorbent
decreases as a result of carbon dioxide absorption.
• This change in color indicates that the absorptive capacity of the material has
been consumed.

97. SHAPE AND SIZE
• Absorbents are supplied in pellets or granules
• The smaller the granule size, the greater the surface area that is available for
absorption.
• However, as particle size decreases, airflow resistance increases and causes
caking.
• Granule size is measured by mesh number.
• Most absorbents used in anesthesia today consist of granules in the range of 4
to 8 mesh.

98. THE ABSORPTIVE CAPACITY
• The maximum amount of carbon dioxide that can be absorbed by soda lime is
26 L of CO2 per 100 g of absorbent.
• The absorptive capacity of calcium hydroxide lime is significantly less and has
been reported to be 10.2 L per 100 g of absorbent.
• In practice, the efficiency of soda lime may be reduced such that only 10 to 20
L or less of carbon dioxide can actually be absorbed per 100 g of absorbent.

99. INTERACTION OF INHALED ANESTHETIC WITH
ABSORBENT
• Trichloroethylene, reacts with soda lime to produce toxic compounds. In the
presence of alkali and heat, trichloroethylene degrades into the cerebral
neurotoxin dichloroacetylene, which can cause cranial nerve lesions and
encephalitis.
• Further degraded to Phosgene, a potent pulmonary irritant, and can cause
adult respiratory distress syndrome.

100. • Sevoflurane has been shown to produce degradation products upon
interaction with carbon dioxide absorbents.
• The major degradation product produced is an olefin compound known as
fluoromethyl-2,2-difluoro-1-(trifluoromethyl)vinyl ether, or compound A.
• Desiccated strong-base absorbents (particularly Baralyme) can react with
sevoflurane and produce extremely high absorber temperatures and
combustible decomposition products

101. • During sevoflurane anesthesia, factors apparently leading to an increase in
the concentration of compound A include
 low-flow or closed circuit anesthetic techniques,
 Absorbents containg strong alkali
 higher concentrations of sevoflurane in the anesthetic circuit
 higher absorbent temperatures, and
 Dehydrated absorbents
 Longer anesthetic

102. • During desflurane anesthesia, carbon monoxide can be produced, particularly
with desiccated absorbents.
• Desiccated strong-base absorbents can also degrade contemporary inhaled
anesthetics to clinically significant concentrations of CO, which can interfere
with monitoring of anesthetic gases

103. • Fresh gas flow rates of 5 L/min or greater through the breathing system and
absorbent (without a patient connected) are sufficient to cause critical drying
of the absorbent material.
• This results in Higher levels of CO production.
• CO poisoning have been most common in patients anesthetized on Monday
morning, because of continuous flow from the anesthesia machine has
dehydrated the absorbents over the weekend.

104. • Several factors appear to increase the production of CO and resultant
elevated carboxyhemoglobin levels, including :
 The magnitude of CO production from greatest to least is desflurane = enflurane
> isoflurane » halothane = sevoflurane
 dryness of the absorbent

105.  the type of absorbent (at a given water content, Baralyme produces more CO
than soda lime does)
 the increased temperature
 the higher anesthetic concentration
 low fresh gas flow rates

106. WHEN AND HOW TO CHANGE THE ABSORBENT
• Inspired Carbon Dioxide- Most reliable method
• Indicator Color Change
• Heat in the Canister
• If excessive dust is present

107. UNIDIRECTIONAL VALVES
• The circle system has two unidirectional valves
• These ensure flow only in one direction
• They are usually part of the absorber assembly

108. A unidirectional valve leak produces characteristic waveform on
the capnography

109. INCOMPETENT UNIDIRECTIONAL VALVES
• Incompetent inspiratory valve

110. • Incompetent expiratory valve

111. INSPIRATORY AND EXPIRATORY PORTS
• The inspiratory port has a 22mm male connector
downstream of the inspiratory unidirectional valve
• The expiratory port has a 22mm male connector
upstream of unidirectional valve
• Usually these are mounted on the absorber

112. Y-PIECE
• Y-piece is a three way tubular connector with
• two 22mm male ports connection to the breathing
tubes and
• one15mm female connector for a tracheal tube or
supraglottic airway device
• A septum may be placed in the Y-piece to decrease
the dead space.

113. FRESH GAS INLET
• The fresh gas inlet may be connected to the common gas outlet on the
anesthesia machine by flexible tubing
• Fresh gas inlet port has an inside diameter of atleast 4mm
• Fresh gas delivery tube has an inside diameter of atleast 6.4mm
• It should be placed in the inspiratory limb

114. APL VALVE
• Is a user-adjustable valve that releases gases to a
scavenging system or atmosphere
• It is intended to provide control of the pressure in the
breathing system

115. PRESSURE GAUGE
• The gauge is usually diaphragm type
• Changes in the pressure in breathing
system are transmitted to the space in
between two diaphragms causing them
to move inward or outward

116. • Movements of one diaphragm are
transmitted to the pointer ,which
moves over a calibrated scale
• The gauge is marked in units of kPa
and/or cm H2o

117. BREATHING TUBES
• Two breathing tubes, an inspiratory limb and an expiratory limb together with
y-piece complete the circle system
• Large bore, non rigid corrugated rubber tubes
• Corrugation increase flexibility and help to prevent kinking
• Usually one meter in length, has a diameter 22mm
• Internal volume is 400 to 500 ml/metre of length
• The pattern of gas flow is almost always turbulent because of corrugations

118. RESERVOIR BAG
• This is usually connected to the circle
absorber system via a long corrugated or
a metal tube with a 22mm male bag port
• A metal or plastic cage is often attached
to the part of connector that fits inside
the bag
• This prevents the inlet being occluded if
the bag were folded
• Commonly used size is 2L

119. BAG/VENTILATOR SELECTOR SWITCH
• It provides a convenient method to shift rapidly between manual or
spontaneous respiration and automatic ventilation without removing the bag
or ventilator hose from its mount

120. OTHER COMPONENTS
• A gas monitoring line is best placed along with a HME
• A respirometer usually placed in expiratory side upstream of unidirectional
valve to measure ventilatory volumes
• Airway pressure monitor placed on the expiratory as well as inspiratory side
• PEEP valve placed in the expiratory limb
• Anesthetic ventilator placed upstream of absorber near APL valve

121. ARRANGEMENT

122. GAS FLOW DURING SPONTANEOUS INSPIRATION

123. GAS FLOW DURING SPONTANEOUS EARLY
EXHALATION

124. GAS FLOW DURING SPONTANEOUS LATE
EXHALATION

125. GAS FLOW DURING INSPIRATION WITH MANUAL
VENTILATION

126. GAS FLOW DURING EXPIRATION WITH MANUAL
VENTILATION

127. GAS FLOW DURING INSPIRATION WITH MECHANICAL
VENTILATION

128. GAS FLOW DURING EXPIRATION WITH MECHANICAL
VENTILATION

129. CERTAIN CHARACTERISTICS OF CIRCLE SYSTEM
• Resistance and work of breathing
• the resistance or work of breathing with the circle system is not significantly
greater than any other breathing systems and may be less
• coaxial tubings increase resistance

130. DEAD SPACE OF THE CIRCLE SYSTEM
• The dead space extends from the patient port of the Y-piece to the partition
between the inspiratory and expiratory tubings
• When inhalation or exhalation starts, the gases in the breathing tubes move
in opposite direction from their usual flow until stopped by unidirectional
valves. This is referred to as Backlash.

131. HEAT AND HUMIDITY
• Moisture from exhaled gases, the absorbent, and water liberated from the
neutralisation of Co2 - all these contribute to total humidity
• Humidity will be higher with lower fresh gas flows, smaller canisters and
coaxial breathing system
• Using an HME will result in decreased humidity in the circle system but
increased humidity in the inspired gases.

132. RELATIONSHIP BETWEEN INSPIRED AND DELIVERED
CONCENTRATIONS
• In a system with no rebreathing, the concentrations of gases and vapours in
the inspired mixture will be close to those in fresh gas.
• With rebreathing, however, the concentrations in the inspired mixture may
differ considerably from those in the fresh gas
• Canister size is most important determinant of internal volume

133. NITROGEN
• Nitrogen is important, because it hinders establishing high concentrations of
nitrous oxide and may cause low inspired oxygen concentrations
• Before any fresh gas delivered ,the concentration of nitrogen in the breathing
system is approximately 80%
• Using high fresh gas flows for few minutes to eliminate most nitrogen from
the system and much of that in patient is called denitrogenation

134. • A tight mask fit is necessary for proper denitrogenation because air will be
inspired around a loose-fitting mask.
• Even if all the body’s nitrogen is exhaled ,the concentration in the breathing
system should not increase to more than 18%
• In certain anesthesia machines has fresh gas decoupling, this introduces the
possibility of entraining room air into the gas circuit through a negative
pressure relief valve.

135. CARBON DI OXIDE
• The inspired carbon dioxide concentration should be nearly zero
• Unless there is failure of one or both unidirectional valves, exhausted
absorbent or a bypassed absorber
• If one of these conditions exists, a high fresh gas flow will limit the increase in
inspired carbon dioxide concentration

136. OXYGEN
• The concentration of oxygen in the inspired mixture is affected by
 Rate of oxygen uptake by the patient
 Uptake and elimination of other gases by the patient
 Arrangement of components
 the ventilation
 Fresh gas flow, the volume of the system
 The concentration of oxygen in FGF

137. ANESTHETIC AGENTS
• The uptake of anesthetic agents is influenced by many factors
• The greatest variation occurs during induction ,when anesthetic uptake is high
and nitrogen washout from the patient dilutes the gases in the circuit
• So its recommend that anesthesia administration be started with high fresh
gas flows
• The time interval for equilibration between inspired and end expired
concentrations varies with the agent

138. • High flows are also commonly used at the end of a case to increase anesthetic
agent elimination. The elimination rate may be increased by bypassing the
absorber.
• When malignant hypothermia is suspected ,increasing the fresh gas flow is
the most important measure that will aid in washing out anesthetic agents

139. GAS AND VAPOUR CONCENTRATION
• The fate of the various gases within the system needs to be understood in order that it may
be used safely and effectively
• The internal volume of apparatus with 2 kg absorbent
 Inter granular space 1 litre
 Breathing hoses 1 litre
 Pathways with in the absorber 1 litre
 Patient FRC 1.25 litres
 Total 4.25 litres
• Provides a large reservoir into which anesthetic gas get diluted at beginning of anesthesia

140. • Lung ‘wash out’ will of course depend on the patient’s minute ventilation. The
greater this is, the less time the process takes.
• The alveolar uptake of anesthetic agent is greatest at the beginning of
anesthesia
• When a near equilibrium of anesthetic agents in the alveoli and blood has been
reached.
• Fresh gas flow is usually reduced in stages
• First stage
• Second stage
• Third stage

141. • First stage
 usually takes approximately 5-10 minutes
 flow rate is at or greater than the patient’s minute ventilation
 When used in this mode it is often referred to as high flow system
• Second stage
 An intermediate flow rate
 70% of the minute ventilation for a further 5 minutes
• Third stage
 Flows of the order 0.5-2 L/min are commonly used
 In this mode it is often referred to as Low flow system

142. TECHNIQUES
• Induction
 Most commonly, induction is accomplished by using high flows to allow
denitrogenation, to establish anesthetic agent concentrations and provide oxygen
well in excess of consumption
 During intubation, the vaporizer should be left ON and the fresh gas flow turned to
minimum or OFF
 After gas exchange has stabilized, lower fresh gas flows are used

143. • Maintenance
 During maintenance, gas flows and vaporizer settings should be adjusted to
maintain a satisfactory oxygen concentration and desired level of anesthesia
 If a rapid change in any component of the inspired mixture is desired, the fresh
gas flow should be increased
 If, for any reason, the circle system integrity is broken ,high flows with desired
inspired concentrations should be used for several minutes before returning to
low flows

144. • Emergence
 Recovery from anesthesia will be slower if low flows are used
 High flows are usually needed at least briefly to eliminate nitrous oxide
 Coasting ,in which anesthetic administration is stopped toward the end of
operation and the circuit is maintained closed with enough oxygen flow to
maintain a constant end tidal volume of the ventilator or reservoir can be used

145. • Advantages
 Economy
 Reduced operating room pollution
 Reduced environmental pollution
 Estimating anesthetic agent uptake and oxygen consumption
 Buffered changes in inspired concentrations
 Heat and humidity conservation
 Less danger of barotrauma

146. • Disadvantages
 More attention required
 Inability to quickly alter inspired concentrations
 Danger of hypercarbia
 Accumulation of undesirable gases in the system
 Uncertainty about inspired concentrations
 Faster absorbent exhaustion

147. CIRCLE SYSTEM FOR PEDIATRIC ANESTHESIA
• Adult circle systems can be used even in small infants and with low fresh gas
flows
• It is important not to add devices with large dead space or resistance between
the y-piece and the patient
• Nowadays Pediatric circle system is usually a standard absorber assembly with
short ,small-diameter breathing tubes and a small bag.

148. REFERENCES
• Andrew J Davey, Breathing systems and their components, Ali Diba, Ward’s
Anaesthetic Equipment, edition 6: 107-136
• Tej K Kaul and Geeta Mittal, Indian Journal of Anesthesia, 2013 Sep-Oct; 57(5):
507-515
• Mapleson W W. The elimination of re breathing in various semi closed
anaesthetic systems. Br J Anaesth 1954;26:323-332
• Jerry A. Dorsch, Susan E. Dorsch, A Practical Approach to Anesthesia
Equipment, edition 5: 108-162

149. THANK YOU!