Anesthesia Breathing Systems

1. Dr.Mohammad Abdeljawad
Anesthesia Specialist
AL-Bashir Hospital
8/20/2020 1

2. ANESTHESTIC BREATHING SYSTEMS
(CIRCUITS)
8/20/2020 2

3. 8/20/2020 3
Properties of the ideal breathing system
1. Simple and safe to use.
2. Delivers the intended inspired gas mixture.
3. Permits spontaneous, manual and controlled ventilation
in all age groups
4. Efficient, requiring low FGF rates.
5. Protects the patient from barotrauma.
6. Sturdy, compact, portable and lightweight in design.
7. Permits the easy removal of waste exhaled gases.
8. Ability to conserve heat and moisture.
9. Easy to maintain with minimal running costs.

4. 8/20/2020 4

5. 8/20/2020 5

6. 8/20/2020 6
Note :
This classification is not preferred because there is confusion
especially in the terms "semi-open" an "semi-closed" where in
the UK, systems such as the Magill, which are neither closed
nor open, are oftern referred to as "semi-closed"; however, in
the USA, the term "semi-open" is used instead, and the term
"semi-closed" is used for the closed system with leak .

7. 8/20/2020 7
A- Rebreathing Systems with CO2 Absorption.
B- Non –Rebreathing Systems.
C- Systems without Gas Resevoir.

8. 8/20/2020 8
A- Rebreathing Systems with CO2 Absorption:
There is mixing of expired gas with fresh gas. This mixture is rebreathed
(recycling) by the patient after chemical absorption of C02 by soda lime
or baralyme.
They include:
1-To and Fro or Single-Phase Systems:
In which gases pass through the C02 absorber during both inspiration
and expiration.

9. 8/20/2020 9
2- Circle or Two-Phase Systems:
In which gases pass through the C02 absorber through two separate
inspiratory and expiratory tubes with unidirectional valves to ensure
one-way flow of gases.

10. 8/20/2020 10
B- Non –Rebreathing Systems
The expired gas containing C02 is removed and replaced by fresh gas.
They include:
1- Valve-Controlled Systems (Draw-Over Systems):
Idea:
In which the expired gas is discharged from the system through a non-
rebreathing one-way valve.These systems use draw-over vaporizers .

11. 8/20/2020 11
The valve (e.g., Ambu E valve) contains moulded silicone rubber one-
way inspiratory and expiratory valves (figure 6-39).They allow
patient's inspiration through one connection and expiration through
the other connection. During inspiration, the inspiratory valve opens
while the expiratory valve closes (the reverse occurs during
expiration). This prevents rebreathing. It can be used during
spontaneous and controlled ventilation.

12. 8/20/2020 12
Advantages:
• Simple • Usable with any agent
• Portable. • Low resistance to gas flow.
Disadvantages:
1-Poor control of inspired gas concentration and depth of
anesthesia.
2-Because of absence of the reservoir bag in some types, the
depth of tidal volume is not well appreciated during spontaneous
ventilation.
3-There is no conservation of exhaled heat or humidity.
4-There is pollution of the operating room with a large volume of
waste gas.

13. 8/20/2020 13
2-Flow Controlled Systems
Idea:
In which the expired gas is displaced from the system by an
adequate fresh gas flow, and then discharged through the expiratory
valve.

14. 8/20/2020 14
C- Systems without Gas Resevoir
They are open systems. The absence of a fresh gas reservoir allows
uncontrolled entry of atmospheric air resulting in marked changes in
the concentration of inhaled anesthetics.
They include:
1-Insufflation Method:
The anesthetic gases blow over the patient's face by one of the
following means:
With out direct connection between a breathing circuit and a
patient's airway, or through a cupped hand containing the end of
the gas delivery tube.

15. 8/20/2020 15

16. 8/20/2020 16
Edinburgh mask (obsolete) where the anesthetic gases reach the
mask by a side opening and the patients expiration occurs through
a wide opening to room air. It produces a negligible increase in the
respiratory dead space.
 A mouth cannula that carries the anesthetic gases to the side of
the patient's mouth using a special ga2 device
 A nasal cannula through the patient's nostrils.
Simple O2 mask.
Venturi 02 mask

17. 8/20/2020 17
Advantages:
There is usually no rebreathing of exhaled gases especially if the
flow is high enough because there is resistance to the patient's
breathing, as there is no or minimal contact with the patient.
Disadvantages:
• There is poor control of the patient's ventilation and concentrations
of 02 and other gases received by the patient because there is always
air dilution.
• There no conservation of exhaled heat or humidity.
• There is pollution of the operating room with a large volume of
waste gas.

18. 8/20/2020 18
Uses:
• During induction in pediatric anesthesia with inhalation anesthetics
especially by cupped hand methoc because children often resist the
placement of a face mask or an intravenous line.
• During 02 supply in the operating room, post-anesthetic care units,
and intensive care units to maintair arterial oxygenation.

19. 8/20/2020 19
2- Open Drop Method:
Idea: (it is of historical importance and not used now).
A highly volatile anesthetic, most commonly ether or halothane, is
dripped onto a gauze-covered mas (Schimmelbusch mask) applied to
the patient's face. As the patient inhales, air passes through the gauze
vaporizes the liquid agent, and carries high concentrations of
anesthetic to the patient. It is a type of drawover vaporization as it
depends on the patient's inspiratory efforts to draw ambient air (no
need for a source of 02 supply).

20. 8/20/2020 20
As the patient inhales, air passes through the gauze,
vaporizing the liquid agent, and carrying high concentrations
of anesthetic to the patient. The vaporization lowers mask
temperature, resulting in moisture condensation and a drop in
anesthetic vapor pressure (vapor pressure is proportional to
temperature).

21. 8/20/2020 21

22. 8/20/2020 22
Leaks and obstruction represent the two most important
hazards associated with the breathing circuit.
Most of the time, these problems can be detected during the
pre-use checkout of the workstation

23. 8/20/2020 23
Mapleson systems are used
 in anesthesia workstations, particularly in pediatrics,
 and they are often used by anesthesia providers during transport of
patients,
procedural sedation,
liberation from tracheal intubation (the T-piece),
and preoxygenation during out-of-the-operating- room airway
management.

24. 8/20/2020 24

25. 8/20/2020 25

26. 8/20/2020 26
Components of Mapleson Systems:
A-Breathing tubes:
It is made of: rubber (reusable, but not autoclavable). It is black in
color due to its high carbon content to allow escape of
static electricity i.e., antistatic.
silicon (reusable, and autoclavable). It is expensive.
plastic (disposable).
 Shape :is corrugated to avoid its closure during kinking.
Diameter :is wide (usually 22mm) to create a low-resistance
pathway . However, paediatric tubing is 15-mm wide, to reduce
bulk.
Volume :should be a large volume, at least equal the patient's tidal
volume, to act as a reservoir for anesthetic gases. Very large volumes
are avoided to decrease the fresh gas flow requirements .

27. 8/20/2020 27
Compliance ( volume change/ pressure change):
It is very important during positive mechanical ventilation. ~-
High compliance tubes make an increased difference between the
volume of gas delivered to a circuit by a resevoir bag or ventilator and
the volume actually delivered to the patient.
The compliance of the standard adult breathing circuit is 5 mL
gas/ cm H20.
The compliance of the standard pediatric breathing circuit is 1.5-
2.5 mL gas/ cm H20.
example, if a breathing circuit with a compliance of 7 mL/ cm H20
is pressurized, during delivery of a tidal volume, to 20 cm H20,
140 mL (7 x 20) of the tidal volume will be lost to the circuit due
to tube expantion .

28. 8/20/2020 28
B- Fresh Gas Inlet :
It is the site where continuous entering of anesthetics and 02 from
the anesthetic machine to the breathing system occurs.
The position of fresh gas inlet in the breathing circuits is an
important factor in differentiating Mapleson circuit from other
types.
C- Adjustable Pressure –Limiting Valve ( APL Valve ) :
(Pressure-Relief Valve, Pop-off Valve, Spill Valve, Heidbrink
Valve, and Expiratory valve)
Function:
It allows gases to exit the circuit when there is a positive pressure within
the system to control the pressure inside the circuit. Exiting waste gases
are then delivered to the operating room atmosphere or scavenging
system. It prevents damage of the patient's lung.

29. 8/20/2020 29
Comprises the following parts:
• A light-weight disc which rests on a knife edge seat to minimize the
area of contact and reduce the n.sk of adhesion resulting from surface
tension of condensed water.
• A stem which is connected to the disc to act as a guide to position
the disc correctly.
• A light spring is incorporated in the valve so that the pressure
required to open the valve may be adjusted.

30. 8/20/2020 30
Mechanism of action
1. This is a one-way, adjustable, spring-loaded valve. The spring is
used to adjust the pressure required to open the valve. The disc
rests on a knife-edge seating in order to minimize its area of
contact.
2. The valve allows gases to escape when the pressure in the
breathing system exceeds the valve’s opening pressure
3. During spontaneous ventilation, the patient generates
a positive pressure in the system during expiration, causing the valve
to open. A pressure of less than 1 cm H2O (0.1 kPa) is needed to
actuate the valve when it is in the open position.
4. During positive pressure ventilation, a controlled leak is produced by
adjusting the valve dial during inspiration. This allows control of the
patient’s airway pressure.

31. 8/20/2020 31
State of the Valve:
 should be fully open i.e., low tension of the spring and low resistance
occur during spontaneous ventilation as expiration will generate positive
pressure which in turn pushes the disc up and opens the valve The
resistance to expiration should be very minimal .
 It should be partially closed i.e., screwed down to increase the
tension in the spring during assiste manual ventilation by reservoir
bag compression to produce controlled escape of the gas during
inspiratory phase
It should be closed i.e., high tension of the spring and high resistance
are present during controlled mechanical ventilation by a ventilator to
avoid any leak in the circuit (the ventilator exhaust valve is tl one that
allows gases to exit to outside the circuit).

32. 8/20/2020 32
When the valve is left unintentionally closed, fresh gas flow
continues to enter into the circuit; the valve should open at a peak
pressure, usually 40-60cm H20, to avoid barotrauma to the
patient's lungs.
 When fully open, a pressure of less than 1 cm H2O is needed to
actuate it.( During spontaneous ) .

33. 8/20/2020 33
D- Reservoir Bag (Breathing Bag) :
Function: It acts as:
• a reservoir of anesthetic gases and
• a method of generating positive pressure ventilation.
Compliance:
It is designed to increase in compliance when its volume increases.
The reservoir bag is highly distensible and rarely reaches pressures
above 60cm H20.
The volume of the reservoir bag is determined by the fresh gas flow
(FGF)and the adjustment of the APL valve.
:
The standard adult size is 2 L . The smallest size for paediatric use is
0.5 L.

34. 8/20/2020 34
Three phases are present during its filling:
Phase I: At the start of bag filling the pressure is minimal until the
bag is filled up to its capacity e.g., 0.25 0.5, 1, 2, or 3 liters.
Phase II: The pressure increases rapidly to a peak.
Phase III: The pressure reaches a plateau or even a slight decrease
occurs, due to opening of the pressure-relief valve to avoid
barotrauma of the patient's lungs, if the valve is unintentionally left
in the closed position as above.

35. 8/20/2020 35
Problems in practice and safety features
1 -Because of its compliance, the reservoir bag can accommodate
rises in pressure in the breathing system better than other parts.
When grossly overinflated, the rubber reservoir bag can limit the
pressure in the breathing system to about 40 cm H2O. This is due to
Laplace’s law dictating that the pressure (P) will fall as the bag’s
radius (r) increases: P = 2(tension)/r.
2. The size of the bag depends on the breathing system and the
patient. A small bag may not be large enough to provide a sufficient
reservoir for a large tidal volume.
3. Too large a reservoir bag makes it difficult for it to act
as a respiratory monitor.

36. 8/20/2020 36
Types of Mapleson Systems
Mapleson A (and Lack system), B,C, D (and Bain system), E and F .

37. 8/20/2020 37

38. 8/20/2020 38

39. 8/20/2020 39

40. 8/20/2020 40
F (Jackson Rees) : Fresh gas flows required to prevent rebreathing
are approximately 2.5 to 3 times minute volume for spontaneous
breathing, and 1.5 to 2 times minute volume for controlled
ventilation

41. 8/20/2020 41

42. 8/20/2020 42
Efficiency of Maplseon Systems :
The efficiency is measured by the amount of fresh gas flow
required to eliminate, as much as possible C02 rebreathing.
 As these circuits do not contain any unidirectional valves or
C02 absorber, there is usually some rebreathing in any
Mapleson circuit.
To attenuate this rebreathing, high fresh gas flow is
required, the higher the flow required, the less the efficiency.
The relative efficiency of different Mapleson systems with respect to
prevention of rebreathing are:
 A > DFE > CB during spontaneous ventilation,
 DFE > BC > A during controlled ventilation

43. 8/20/2020 43
The amount of CO2 rebreathing with each system is multifactorial
and affected by:
(1) . the fresh gas inflow rate,
(2) . minute ventilation,
(3). Ventilation mode (spontaneous or controlled),
(4) . tidal volume,
(5) . respiratory rate,
(6) . the inspiratory-to-expiratory ratio,
(7) . the duration of the expiratory pause,
(8) . peak inspiratory flow rate,
(9) . the volume of reservoir tubing,
(10) . the volume of the breathing bag,
(11). the airway device being used (mask or endotracheal tube),
(12) . the CO2 sampling site.

44. 8/20/2020 44
Mechanism of Action of Mapleson Systems
Mapleson A (Magill Systems )
Corrugated rubber or plastic tubing (usually 110– 180 cm in length)
and an internal volume of at least 550 mL.

45. 8/20/2020 45
Mechanism of Action of Mapleson Systems
Mapleson A (Magill Systems )
A- During spontaneous ventilation :
During inspiration:
- Gas is inhaled from the corrugated tube and the bag as they
contain FG and expired dead space gas (contains no CO2), so this
system can be used at a FGF of even 70% of the patient's minute
ventilation

46. 8/20/2020 46
During expiration:
- During the initial part of the expiration, the reservoir bag is not full
and thus the pressure in the system does not increase, so that the first
part of the exhaled gas (which is the dead space gas containing no C02)
will pass along the corrugated tube towards the bag and will not exit
through the spill valve. Therefore, the bag is filled by the dead space
gas and the FG from the anesthetic machine.
- During the late part of expiration, the bag becomes full, the
pressure in the system increases and so, the spill valve opens (usually
at 0.5 cmH20 pressure), venting all subsequent exhaled alveolar gas
to the atmosphere .

47. 8/20/2020 47
During the expiratory pause:
When FGF is sufficiently high and continues to flow from the
anesthetic machine to the svstem, it pushes all the remaining exhaled
alveolar gas (with C02) distally along the corrugated tube to be vented
through the spill valve before the next inspiration. Therefore, no
rebreathing occurs .

48. 8/20/2020 48
B) During controlled manual ventilation:
During controlled inspiration:
It is produced by the anesthesiologist squeezing the reservoir bag while
the spill valve is partially closed. Pure alveolar gas contains C02)
reenters the patient's lung and is followed by a mixture of FG, dead
space gas, and alveolar gas which in tum re-enters the patient's lung
too. When the pressure in the system increases, it will open the spill
valve venting this mixture also to the outside.
Therefore, rebreathing occurs. To avoid this, FGF must be sufficient
and high enough to vent gas from the system and to ..:~atethe
patient's lung (2-3 x MV) (figure 6-57, a and b).

49. 8/20/2020 49

50. 8/20/2020 50
During expiration:
 Exhaled dead space gas (without C02) and alveolar gas (with -02,)
pass along the corrugated tube and are likely to reach the partially
full bag (from the previous squeezing by the thesiologist during
previous inspiration) .
 the bag is now filled with a mixture of FG, dead space gas, and
alveolar gas.
 The exhaled alveolar gas does not exit through the spill valve
because it is partially closed to allow the gases to reach the
patient' s lung during the next controlled inspiration .

51. 8/20/2020 51
During the expiratory pause: (if it is incorporated into the ventilatory
cycle )
FG fills the corrugated tube and the bag where it may dilute the
exhaled gas present
Disadvantages of Mapleson"A":
1-The system increases the apparatus dead space which extends from
the anesthetic facemask to the spill valve (it is about 100mL).This
apparatus dead space is added to the patient's dead space. Therefore
, Mapleson"A" system is not used in pediatrics< 4 years of age.
2-It is heavy and unsuitable during head and neck surgery
especially when a scavenging system is used because the spill valve
is attached close to the patient. Lack coaxial modification Permits
the spill valve to be away from the patient.
of less than 25–30 kg body weight

52. 8/20/2020 52

53. 8/20/2020 53
Mapleson "D" System
A) During spontaneous ventilation:
During inspiration:
- The patient inhales FG and some of the expired dead space gas
and expired alveolar gas (with C02) according to the FGF

54. 8/20/2020 54
During expiration;
- Exhaled dead space gas, exhaled alveolar gas, and FG, mix in the
corrugated tube and travel towards the bag where the bag starts to
fill (the exhaled dead space gas starts to fill the bag at first).
- When the bag is full, the pressure in the system increases, the
spill valve opens and the mixture of gases (dead space, alveolar and
FG) is vented to the outside .

55. 8/20/2020 55
During the expiratory pause:
- When FGF continues to flow from the anesthetic machine to the
system, it pushes the exhaled alveolar gas (with C02) along the
corrugated tube to be vented through the spill valve before the next
inspiration, but some of the alveolar gas is still in the corrugated tube
and is inhaled in the next inspiration so rebreathing occurs. To avoid
this, the FGF must be 2-3 x MV (at least 12 L/min in an adult) .

56. 8/20/2020 56
B) During controlled manual ventilation:
During controlled inspiration:
It is produced by the anesthesiologist squeezing the reservoir bag
while the spill valve is partially closed. The FG and minimal
exhaled gas enter the patient's lung. When the pressure inside
the system increases, the spill valve opens and a mixture of the FG
and the alveolar gas is vented. Therefore, no rebreathing occurs
and so the FGF can be 1 x Mv

57. 8/20/2020 57
During expiration:
Exhaled dead space gas (without C02), alveolar gas (with C02) and FG
pass along the corrugated tube and are likely to reach the partially full
bag (from the previous squeezing by the anesthesiologist during
previous inspiration) i.e., the bag is now filled with a mixture of FG,
minimal dead space gas, and minimal alveolar gas where the exhaled
alveolar gas exits through the spill valve .

58. 8/20/2020 58
During the expiratory pause: (if it is incorporated into the
ventilatory cycle)
FG fills the corrugated tube and the bag where it may dilute the
exhaled gas present. Presence of the expiratory pause increases
the efficiency of the Mapleson "D'' system.

59. 8/20/2020 59
with gas distribution at end-expiration

60. 8/20/2020 60

61. 8/20/2020 61
Components
1. 1.8-m length coaxial tubing (tube inside a tube). The
FGF is through the outside tube, and the exhaled gases
flow through the inside tube (Fig. 4.7A).
2. The inside tube is wide in diameter (14 mm) ( 7 mm ‫الكتب‬ ‫بعض‬
‫تذكر‬ (to reduce resistance to expiration. The outer tube’s diameter
is 30 mm.( 22mm ‫تذكر‬ ‫الكتب‬ ‫)بعض‬
3. The reservoir bag is mounted at the machine end.
4. The APL valve is mounted at the machine end
eliminating the drag on the connections at the patient
end, which is a problem with the Magill system.

62. 8/20/2020 62
 Instead of the coaxial design, a parallel tubing
version of the system exists (Fig. 4.7B). This has separate
inspiratory and expiratory tubing, and retains the same
flow characteristics as the coaxial version.

63. 8/20/2020 63

64. 8/20/2020 64
Bain System :
It is a modified Mapleson "D" system. It is the most commonly used
coaxial system.
Description:

65. 8/20/2020 65
Components
1. A length of coaxial tubing (tube inside a tube). The usual length is 180
cm, but it can be supplied at 270 cm (for dental or ophthalmic surgery)
and 540 cm (for magnetic resonance imaging [MRI] scans where the
anaesthetic machine needs to be kept outside the scanner’s magnetic
field). Increasing the length of the tubing does not affect the physical
properties of the breathing system.
2. The fresh gas flows through the narrow inner tube
(6 mm) while the exhaled gases flow through the
outside tube (22 mm) The internal lumen has a swivel mount at the
patient end. This ensures that the internal tube cannot kink, thereby
ensuring delivery of fresh gas to the patient
3. The reservoir bag is mounted at the machine end.
4. The APL valve is mounted at the machine end.

66. 8/20/2020 66

67. 8/20/2020 67
Advantages :
1- Warming of the inspired gases in the inner tube by the surrounding
warm expired gases in the oute tube.
2- Improved humidification of inspired gases due to partial
rebreathing.
3- Easy scavenging of the waste gases because the expiratory valve
is away from the patient.
4- The length and light weight allow the anesthesia machine to be
removed away from the patient during head and neck surgery.
5- Some types of automatic ventilators e.g., Penlon Nuffield 200
can be connected to the Bain system by one-meter length of
corrugated tubing. The tube is placed instead of the bag and the
spill valve is kept closed completely.

68. 8/20/2020 68
During inspiration, the gas from the ventilator pushes a mixture
of ventilator fresh gas and alveolar gas from the corrugated outer
tube of the Bain system into the patient's lung.
During expiration, the ventilator fresh gas and some of the
alveolar gas are vented through the exhaust valve of the ventilator.
To prevent rebreathing, FGF should be 70-80 ml/kg/min (to
maintain normocapnia) or 100 mL/kg/min: (to cause moderate
hypocapnia).

69. 8/20/2020 69
Disadvantages :
1- A large waste of gases is produced due to high FGF (200-300
mL/kg/min) during spontaneous ventilation.
2- Kinking of the inner tube prevents inhalation of FGF.
3-Movement of the reservoir bag during anesthesia does not
indicate that FG is delivered to the patient :Becausethe bag is
connected to the outer expiratory tube.

70. 8/20/2020 70
3- Unrecognized disconnection or cutting of the inner tube causes a
large apparatus dead space an - marked rebreathing of the exhaled
gases.
Therefore,
• The outer tube should be transparent to
allow insapection of the inner tube.
• Occlusion test should be performed before use; the system
should be tested by occluding the distal end of the inner tube
transiently with a finger or with the plunger of a 2-mL syringe
while the FG flows to the system. There should be a reduction in
the flowmeter bobbin reading during occlusion and an audible
release of pressure when occlusion is disconnected .

71. 8/20/2020 71
Mapleson "E" System (Ayre's T-piece)
- It acts in a similar manner to the Mapleson "D" system
During Expiration :
The corrugated tube fills with a mixture of exhaled and fresh gas
where the dead space is present at the destael end (area A), the
exhaled alveolar gas at (area B), and then the FG at (area C).
During the Expiratory Pause :
Only the FG will fill the proximal corrugated tube and dilutes and
pushes the exhaled gases to be vented to the outside from the end
of the tube especially if FGF is 2-3 x MV (with a minimum 4 L/min)
and so that the rebreathing does not occur

72. 8/20/2020 72
During Inspiration :
At first, the patient inhales gas from the FG coming from the inlet.
When the patient's inspiratory flow becomes greater than the flow of
fresh gas from the inlet of the T-piece, the patient may in addition
draw and inhale from the gas in the proximal end of the reservoir
tubing (area C).
provided there is an expiratory pause (where the FG fills larger area of
the corrugated tube), the possibility of rebreathing is decreased
- If the FGF is too low e.g.,< 2 x MV, the patient will draw upon the gases
at area Band C, and rebreathing occurs
.if the corrugated tube is too small, the patient will inhale room air,
thus the volume of the corrugated tube which acts as a reservoir limb)
should exceed the patient's tidal volume

73. 8/20/2020 73
During Spontaneous Ventilation :
There is no indication of the presence or the adequacy of ventilation.
Some anesthesiologists attach a +isual indicator such as a piece of
tissue paper or a feather, at the end of the corrugated tube, but this
is not satisfactory enough
During controlled Ventilation :
Controlled ventilation is done by occlusion of the end of the
corrugated tube with a finger. However, there is no way of assessing
the pressure in the system and there is a possibility of exposing the
patient's .ungs to excessive volumes and barotrauma.

74. 8/20/2020 74
Mapleson F System (Jackson Rees Modification of the Ayres
T-Piece)
The Ayre's T-piece (Mapleson E) was modified by Jackson Rees, where
a small bag (0.5 L) with an open end was attached to the outlet of
the reservoir limb (there was no valve present). Later on, a valve was
added as a further modification (figure 6-63).It is suitable for
children up to 25–30 kg body weight.

75. 8/20/2020 75

76. 8/20/2020 76
Advantages :
1- The bag's movement indicates that the child is breathing during
spontaneous respiration i.e., it acts as visual monitor for
spontaneous breathing.
2- By occluding the open end of the bag temporarily, it is possible to
confirm that fresh gas is entering the system.
3- It provides a degree of continuous positive airway pressure (CPAP)
during spontaneous ventilatior and positive end expiratory
pressure (PEEP) during mechanical ventilation.

77. 8/20/2020 77
4- It provides a convenient method of assisted or controlled ventilation.
The open end of the reservoir bag is occluded between the 4th and the 5th
fingers and the bag squeezed between the thumb and index fingers;
the 4th and 5th fingers are relaxed during expiration to allow gas to
escape from the bag.
It is possible for an experienced anesthesiologist to assess
(approximately) the inflation pressure and to detect changes in the lung
and chest wall compliance.

78. 8/20/2020 78

79. 8/20/2020 79
Mapleson ADE System

80. 8/20/2020 80
This system consists of :
• Two parallel corrugated tubing of 15-mm diameters.
• The Humphrey block consists of an APL valve, a lever to select
spontaneous or controlled ventilation, a reservoir bag, a port to
connect a ventilator, and safety pressure relief valve which opens
at a pressure above 6-kPa
• The tubes are connected from one end to a Y-piece
connection and from the other end to the Humphrey block
This system carries the properties of the Mapleson A, D, and
E systems:

81. 8/20/2020 81
• When the lever is in the "A" mode (up), the system behaves as the
Mapleson "A" and become connected to the bag where one tube acts
for inspiration while the other for expiration (connected to APL and
scavenging system). Now it can be effiently used for spontaneous
ventilation.
• When the lever is in the D/E mode (down), the inspiratory limb
delivers gas to the patient while the expiratory limb returns it back
The Humphrey block acts as a reservoir and is open to atmosphere or
connected to the ventilator such as Penlon. The bag and APL valve
are now isolated from the system. It can be used now efficiently for
mechanical ventilation.

82. 8/20/2020 82
In adults, FGF is 50-60mL/kg for spontaneous ventilation,
and 70 mL/kg/min for mechanical ventilation.
Can be used in both adult and paediatric anaesthetic practice
(the recommended initial FGF for children weighing
less than 25 kg body weight is 3 L/min This offers a considerable
margin for safety.)

83. 8/20/2020 83
To-and-Fro (Waters') System
It is one phase rebreathing system. It is rarely used nowadays.
Compnents :
A Mapleson C breathing system.
• A canister of soda lime; interposed between the spill valve and
reservoir bag .

84. 8/20/2020 84
Disadvantages:
1-The soda lime granules nearest to the patient become exhausted
first, increasing the dead space of the system .
2- The canister is positioned horizontally and gas may be
channelled above the soda lime unless the canister is tightly
packed.
3- The system is cumbersome.
4-There is a possibility of inhalation of soda lime dust from
the canister by the patient.

85. 8/20/2020 85

86. 8/20/2020 86
The Circle System

87. 8/20/2020 87
Note: Over 80% of the anaesthetic gases/ vapours are
wasted when FGF of 5.0 L/min is used. Typically, the
reduction of FGF from 3.0 L/min to 1.0 L/min results in a
saving of about 50% of the total consumption of any volatile
anaesthetic agent.
In this breathing system, soda lime is used to absorb
the patient’s exhaled carbon dioxide.

88. 8/20/2020 88

89. 8/20/2020 89
Several additional components are added to enhance patient
safety :
 a circuit pressure sensor,
 a pressure gauge,
 an expiratory (and possibly an inspiratory) flow sensor,
 an inspired oxygen concentration sensor.
A separate positive end-expiratory pressure (PEEP) valve may be
present.

90. 8/20/2020 90
Arrangement of the Components :
There are many arrangements but the following arrangement is preferred.
1- A Y-piece connector.
It is connected, so closely, to the patient's endotracheal tube to
decrease the dead space (where tl apparatus dead space is the
common channel of the Y-piece only).
Unlike Mapleson circuits, the breathing-tube length does not affect
the dead space due to presence unidirectional flow in them.
2- unidirectional valves.
They should be relatively close to the patient, but not on the Y-piece,
as this makes the circuit heavier when it is connected to the
endotracheal tube intraoperatively.
NOTE: The dead space in the circle breathing system begins at the
Y-piece and continues to the patient

91. 8/20/2020 91

92. 8/20/2020 92
3-A fresh gas flow (FGF) Inlet .
It is placed between the canisters and the inspiratory valve.
If it is positioned downstream from the inspiratory valve, FG may
bypass the patient during exhalation and become wasted
If it is positioned between the expiratory valve and the canisters,
FG may be diluted by re-circulating gas and the volatile anesthetics
may be more absorbed or released by soda lime granules, thus
slowir.z induction and emergence .

93. 8/20/2020 93
4-An adjustable pressure limiting valve (APL)valve.
It is placed immediately before the FG inlet and after the canister to
minimize venting of FG.( placed between the absorber and the
expiratory valve and close to the reservoir bag ) It can be placed also
before the canister, thus allowing the expired gas (containing C02) to
be ventec before reaching the canister, conserving the soda lime and
decreasing its exhaustion
Switching the workstation to a ventilator mode excludes or closes
the valve
.
The two basic types of APL valves are :
1-the variable-orifice (or variable-resistor) type
2- the pressure-regulating type.

94. 8/20/2020 94
1-variable-orifice (or variable-resistor)
The variable-orifice 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 any given adjustment
is directly related to the fresh gas flow rate.

95. 8/20/2020 95
2-Pressure-regulating type
This type of APL valve has an adjustable internal spring and an external
scale indicating the approximate opening pressure. When the pressure
in the system exceeds spring tension, a disk opens and gas is vented

96. 8/20/2020 96
Waste gas is prevented from returning from the scavenging system
by a downstream check valve.
By adjusting spring tension, the operator can choose the desired
maximal circuit pressure in manual mode
Unlike variable-orifice type valves, the pressure-regulating APL
valves are designed to maintain stable circuit pressure even as
fresh gas flow is increased.
Continuous positive airway pressure (CPAP)
can be more reliably controlled using this type of APL valve.
A comparison of two modern anesthesia machines demonstrated
that not all APL valves have equivalent linear behavior, and with
certain valves the PIPs may routinely exceed set values.
 This serves as a reminder that the operator must vigilantly
monitor circuit pressure during manual ventilation

97. 8/20/2020 97
5- The canister (soda lime or baralyme). And the Reservoir bag
They should be placed in the expiratory limb so that they do not
increase the apparatus dead space even · the canisters are empty
6-:The vaporizer position is either VIC or VOC

98. 8/20/2020 98
However, to prevent rebreathing of CO2 in a traditional circle
system, three rules must be followed:
(1) a unidirectional valve must be located between the patient
and the reservoir bag on both the inspiratory and expiratory
limbs,
(2) the fresh gas inflow cannot enter the circuit
between the expiratory valve and the patient,
(3) The APL valve cannot be located between the patient and the
inspiratory valve.
 .If these rules are followed, any arrangement of the other
components will prevent rebreathing of CO2.

99. 8/20/2020 99

100. 8/20/2020 100

101. 8/20/2020 101

102. 8/20/2020 102

103. 8/20/2020 103
Advantages of the Circle System

104. 8/20/2020 104
Unlike Mapleson circuits, the circle system tube
length does not affect dead space. Like Mapleson
circuits, length does affect circuit compliance and thus
the amount of tidal volume lost to the circuit during
positive-pressure ventilation.
The unidirectional valves and absorber increase circle system
resistance, especially at high respiratory rates and large tidal
volumes. Nonetheless, even premature neonates can be
successfully ventilated using a circle system

105. 8/20/2020 105

106. 8/20/2020 106

107. 8/20/2020 107

108. 8/20/2020 108
Disadvantages of the Low Fresh Gas Flow (FGF):
1- FGF produces unpredictable concentrations of 02 and volatile
anesthetics to be inspired by the patient as follows:
• Low FGF at the induction of anesthesia (in the early period of
administration within 10-15 minutes); The system is filled with air (80%
nitrogen) initially.
If low flow rates of the anesthetic gases (preset by the anesthesiologists)
are used, the anesthetic gases are diluted by the air (and nitrogen) in
the circuit (due to their large volume) and lungs; therefore, light
anesthesia may occur.

109. 8/20/2020 109
Even if the system is primed with a mixture of anesthetic gases at a low
flow rate for the first 10-15 minutes, the initial rapid uptake of
anesthetics by the patient results in a marked decrease in concentrations
of anesthetic agents in the system, resulting in light anesthesia also.
 Therefore, it is usually necessary to provide a higher total fresh gas
flow rate (e.g., 3-4 l/min) initially (for 15 minutes) at the beginning of
the use of the circuit to allow denitrogenation of the circuit and lungs.
This high flow rate may be reduced subsequently by theanesthesiologist
 Low FGF is unable to produce rapid changes in the concentrations
of inhaled anesthetic gases i.e., slow changes in depth of
anesthesia.

110. 8/20/2020 110
• Low FGF during maintenance of anesthesia:
If the FGF, coming from the fresh gas inlet, is low, it will be markedly
affected by the exhaled gas coming from the canister. Therefore, the
gas in the inspiratory limb (a mixture of the FGF and exhaled gas
coming from the canister) will have very unpredictable concentrations
of 02 and anesthetics. Thus, if N20 is used the risk of hypoxia is very
high with low FGF, unless an 02 analyzer is used.
The higher the fresh gas flow rate, the less the effect of the gas,
coming from the canister, on the anesthetic concentrations of the
FGF; therefore, the patient will receive the same concentrations of 02
and anesthetic present in FGF

111. 8/20/2020 111
2- Low FGF produces accumulation of foreign trace gases within the
circuit because they are not washed out by the low FGF. These gases
include:
methane from the intestine,
acetone from the liver, in prolonged starvation or diabetes,
ethanol in alcoholic patients,
 carbon monoxide in heavy smokers.
Therefore, it is recommended to use intermittent periods of high FGF
rates to washout these gases

112. 8/20/2020 112
3- Low FGF does not compensate for leaks in the circuits.
4- Low FGF produces a greater degree of humidity than high flow
rates.
Generally higher FGF rates:
 speed induction and recovery,
 decrease the marked variations in the gas mixture,
 decrease the accumulation of foreign gases, and
 compensate for leaks in the circuit,
 but produce relatively lower degrees of humidity.

113. 8/20/2020 113

114. 8/20/2020 114
Potential Circle System Problems
leaks and disconnections.
No matter the size, all leaks should be investigated.

115. 8/20/2020 115
misconnections.
obstruction.

116. 8/20/2020 116
. Adequate monitoring of inspired oxygen, end-tidal carbon
dioxide and inhalational agent concentrations is essential and
mandatory. Expired gas has lower concentrations of oxygen and
inhalational agent than the inspired gas due to the uptake by
patient. At low FGF flows, due to the progressive dilution by the
recycled expired gases, the inspired concentration drifts
downwards. This can be prevented by setting high concentrations
of oxygen (at flowmeter) and agent (at vaporizer).
Continue ….

117. 8/20/2020 117
. The unidirectional valves may stick and fail to close because of
water vapour condensation. This leads to an enormous increase in dead
space.
. The resistance to breathing is increased especially during
spontaneous ventilation. The main cause of resistance to breathing
is due to the unidirectional valves. Dust formation can increase
resistance to breathing further. It can also lead to clogging and
channelling, so reducing efficiency. Newer soda lime designs claim
less dust formation
. The circle system is bulkier, less portable and more
difficult to clean.
. Because of the many connections, there is an
increased potential for leaks and disconnection.

118. 8/20/2020 118
• Breathing tubes should be:
made of silicon (autoclavable) or plastic (disposable) to avoid cross-
infection,
 corrugated to avoid its closure during kinking,
wide (usually 22mm) to create a low-resistance pathway, at least
equal to the patient's tidal volume, to act as a reservoir for anesthetic
gases,
 with suitable compliance.
• Adjustable pressure-limiting valve (APL valve) should be present to
prevent damage of the patient's airway and lungs.

119. 8/20/2020 119
• Reservoir bag (breathing bag) should be present to act as:
a reservoir of anesthetic gases,
 a method of generating positive pressure ventilation,
 have high compliance which generates a pressure rarely exceeds
above 60 cm H20
• A bag/ventilator switch should be present.
•The canister (the absorber) should have:
Transparent walls to allow clear inspection of the color of the
indicator dye.
 A baffle system to allow direction of flow and uniform dispersion
of exhaled gases, to minimize channelling.
A dust trap at the bottom of the canister to collect alkaline dust
and moisture.
 A large sized canister with less frequent changing of the
exhausted soda lime, because the canisters are not part of the
apparatus dead space, as they are present on the expiratory limb
of the circuit.

120. 8/20/2020 120
• Amsorb is a newly introduced C02 absorbent. It is safe to be used
with volatile anesthetics.
• Monitors for low-flow and closed circuits should be available as:
- An 02 analyzer: to measure inspired 02 concentrations.
- A capnography: to measure end-tidal C02.
- A multi-gas analyzer: to measure anesthetic agent concentration
e.g., Raman spectroscopy.
• Pressure relief valve (Safety valve).

121. 8/20/2020 121
N.B.: Safety features to prevent delivery of hypoxic gas
mixture to the patient:
1-An oxygen analyzer to measure the inspired 02 concentration
(the most preferred).
2- An alarm device to give signals when 02 supply fails.
3- Fail-safes valves to shut off or decrease the supply of N20.
4- A proportioning system to control a safe ratio of N20: 02.

122. 8/20/2020 122
If you are struggling to ventilate a patient and are unsure why, do
not delay in switching to a self-inflating resuscitation bag.
Ventilate the patient first, troubleshoot later.

123. 8/20/2020 123
The Unidirectional Valves:
• They contain a ceramic or mica disk resting horizontally on an
annular valve seat. They are mounted normally in a transparent glass
dome so that they can be observed to be functioning correctly

124. 8/20/2020 124

125. 8/20/2020 125
• Forward flow displaces the disc upwards, allowing the gas to pass
through the circuit. Reverse flow pushes the disc against its seat,
preventing return of the gas.
• The expiratory valve (placed on the expiratory limb) is exposed
to the humidity of alveolar gas, so it car be differentiated easily
from the inspiratory valve.
• Valve incompetence is usually due to disc or seat irregularities.
This can cause rebreathing of CO: resulting in hypercarbia.
•They are constructed to resist the humidity that sometimes
accumulates in the breathing system.
•If the valves are stuck shut, total occlusion of the circuit can result.
An expiratory valve stuck in the closed position can lead to
barotrauma

126. 8/20/2020 126
Anesthesia Reservoir Bag or “Breathing Bag.”
functions,
(1) serving as a reservoir for exhaled gas and excess fresh gas,
(2) Providing a means of delivering manual ventilation or assisting
spontaneous breathing,
(3) serving as a visual or tactile means of monitoring a patient’s
spontaneous breathing efforts,
(4) partially protecting the patient from excessive positive pressure in
the breathing system, such as in the case of inadvertent closure of the
APL valve or an obstruction of the scavenge line

127. 8/20/2020 127
Standard adult breathing bags have a nominal volume of 3 L;
pediatric bags are available as small as 0.5 L.
The reservoir bag is the most compliant part of the breathing
system.
Anesthesia reservoir bags must adhere to pressure standards, which
mandate a minimum pressure of approximately 30 cm
H2O and a maximum pressure of approximately 60 cm
H2O when the bag is filled to four times its stated capacity.
Classically, the reservoir bag was excluded from
the breathing circuit when the ventilator was in use.

128. 8/20/2020 128

129. 8/20/2020 129