This document discusses breathing systems used during anesthesia. It begins with definitions and a brief history of breathing systems. It then classifies different breathing systems and describes the working principles and components of various systems, including Mapleson systems and the circle system. Key points covered include how fresh gas flow rates impact carbon dioxide levels, components of the circle system like the reservoir bag and carbon dioxide absorbers, and factors that influence the absorptive capacity of different carbon dioxide absorbents.

1. Circuits
Presenter Moderator
Dr. Pooja Lama Associate Prof. Dr. U. B. Bajracharya
Resident
Anesthesiology

2. Objectives
• Definitions
• History of breathing system
• Classification of breathing systems
• Working principles of breathing systems
• Components of breathing system
• Conclusion

3. Definition
Assembly of components which connects the patient
airway to the anaesthetic machine creating an artificial
atmosphere ,from and into which the patients breathes.

4. Function
• To deliver oxygen and other gases to the patient and
to eliminate carbon dioxide.

5. History
• Any resemblance to a breathing system was developed by
Barth (1907)
• The Mapleson A (Magill) system was designed by Sir Ivan
Magill in the 1930’s
• In 1926, Brian Sword introduced the circle system.
• Ayre’s T piece was introduced in 1937 by Phillip Ayre
• Modified by Jackson Rees into Mapleson F in 1950 by adding
500ml of reservoir bag
• Bain circuit was introduced in 1972 by Bain and Spoerel.

6. Classification
 McMohan in 1951
 Open  no rebreathing
 Semi closed  partial rebreathing
 Closed  total rebreathing

7.  Dripps classification
• Insufflation
• Open
• Semi open
• Semi closed
• Closed
Schimmelbush mask
Yankeur mask

8.  Conway classification
• Breathing systems with CO2 absorber
• Breathing systems without CO2 absorber
 Miller Classification
Breathing system without CO2
absorber
Breathing system with CO2
absorber
Unidirectional flow:
Non-rebreathing valve
Unidirectional flow:
Circle system with absorber
Bi-directional flow:
a) Afferent Reservoir systems
Mapleson A, B, C and Lack
b) Efferent Reservoir system
Mapleson D, E , F and Bain
c) Combined system
Humphrey ADE
Bi-directional flow:
To & Fro system

9. Disadvantages of insufflation and open
• Poor control of inspired gas concentration
poor control of depth of anesthesia
• Pollution of operating room with large volumes of waste gas
• Mechanical drawbacks during head and neck surgery.

10. Anesthetic breathing circuit classification:
• On the basis of use of carbon-dioxide absorber:-
do not use an absorber use an absorber
MAPLESON SYSTEM CIRCLE SYSTEM
Circle system is the most common breathing
circuits used for anesthetic delivery

11. Criteria for anesthetic breathing circuit
1. Low resistance conduit for gas flow
2. A reservoir for gas that can meet the patient’s inspiratory
flow demand
3. An expiratory port or valve to vent excess gas.
4. Have minimal apparatus dead space.

12. Mapleson’s classification of breathing
system
• Mapleson in 1954 described and analyzed five different
breathing circuits. (A, B, C, D, E)
• Willis in 1975 described the F system.
• Similar to circle breathing system that they accept a fresh gas
flow, supply sufficient volume of gas and eliminate carbon-
dioxide.
• Differ from circle system that they have bidirectional flow and
do not use an absorber.

13. Components of Mapleson
• Patient end to a facemask or endotracheal tube
• Breathing corrugated tubes
• Fresh gas inlet
• Adjustable pressure limiting valve
• Reservoir bag

14. Different types of Mapleson

15. Three distinct functional groups can be seen:
Functional groups Gas stored in
reservoir bag
Named as
A Fresh Gas Afferent reservoir
system
BC Mixed inspired
and expired gas
Junctional
reservoir system
DEF Mixed expired gas Efferent reservoir
system

16. Relative efficacy of Mapleson system
 During spontaneous ventilation:
A>DFE>CB
 During controlled ventilation:
DFE>BC>A

17. Mapleson A
• Mapleson A is also called as Magill circuit
• It is best for spontaneous ventilation.
• Modification of Magill circuit is called as Lack’s circuit.
• Mapleson A has a corrugated breathing hose of length 110 cm
with an internal volume of 550ml.

18. Working principle: Mapleson A:- Spontaneous ventilation
A. Breathing bag fills with
FGF in first inspiration.
B. Pt inspires the gases so
the reservoir bag
becomes partially empty
C. Exhale:- gases from both
ends enter bag and once
it is full the exhaled gases
pass out through APL
valve
D. End-expiratory pause:
FGF now drives the
exhaled gases out.

19. A. Inspiration: manual squeezing
though APL valve is closed some
of FGF will go out.
B. Since bag is completely empty,
now on expiration the exhaled
gases will reach the bag and get
mixed. But bag is not yet full
enough to open the APL valve.
C. On next inspiration: on
squeezing APL valve opens
and exhaled gases pass out as
well they are inhaled so
rebreathing occurs.
Working principle: Mapleson A:- Controlled ventilation

20. Mapleson B and C
• Mapleson B:- FGF should be 2-
2.5 times the minute
ventilation.
• Mapleson c (Bagging system)

21. A. Inspiration: FGF fills the bag and
hose and as respiratory rate is
higher than FGF rate so the bag
get emptied.
B. Expiration: exhaled gas get mixed
with FGF and reach bag.
C. When bag is full: exhaled gases
pass out of APL valve, first
anatomical dead space then
alveolar gas.
D. Next inspiration: rebreathing
occurs.
Working principle: Mapleson D:- Spontaneous ventilation

22. A. Inspiration: manual squeezing FGF
goes to patient as well pass out of
APL.
B. Expiration: partially emptied bag
gets filled with exhaled gas + FG.
C. Expiratory pause: FGF pushes the
exhaled gases towards bag  gets
full APL opens dead space then
alveolar gas.
D. Next inspiration: pt inspired FGF +
mixed gas and on squeezing the
exhaled gases again pass out of APL.
Working principle: Mapleson D: Controlled ventilation

23. Mapleson E and F
B. During inspiration 
inspiratory drive is
more than FGF rate so
some gases are drawn
from the reservoir limb.
C. During expiration both
the exhaled air and
fresh gas continue to
pass towards limb and
voided to atmosphere
D. D. During end
expiratory pause FGF
fills the limb.

24. Modifications
Lack system
• Modification of Mapleson A
• Inner expiratory and outer
inspiratory.
• length
Bain circuit
• Modification of Mapleson D
• Inner inspiratory and outer
expiratory.
• Pethick test

25. Bain circuit
.
 Coaxial circuit and modification of Mapleson D
 Outer tube 22 mm diameter.
 1.8 m long
 Fresh gas flow to patient end via thinner coaxial inside the
expiratory tube
 Fresh gas inflow rate necessary to prevent rebreathing is
2.5 times minute ventilation

27. Isopleth
• Vf- Fresh gas flow rate
ml/kg/min
• Ve- minute ventilation
ml/kg/min
 When FGF is high
PACO2 becomes
ventilation
dependent.
 When minute
volume exceeds the
FGF PACO2 is
dependent on FGF.

28. Advantages of Bain circuit
• Lightweight, convenient, easily sterilized and reusable.
• Very low resistance to breathing.
• Scavenging of gases from the expiratory valve is facilitated
because the valve is located away from the patient.
• Exhaled gases in the outer reservoir tubing add warmth to the
inspired fresh gases by countercurrent heat exchange.

29. Disadvantages of Bain circuit
o Unrecognized disconnection and kinking of the inner
fresh gas tube.
o An obstructed antimicrobial filter positioned
between the Bain circuit and the endotracheal tube
can result in increased resistance in the circuit.
o High flow gas rate  wastage of gas.
Pethick
test
Outer tube is
transparent

30. Test for Bain’s circuit
Pethick test Foex Crempton Smith test
Close the APL valve and allow
reservoir bag to fill completely
Now press oxygen flush
Reservoir bag collapses if inner
tube is intact
Because oxygen delivered at
high flow through inner tube
will drag all the air present in
the outer tube due to its
venturi effect.
Close the APL valve and turn on
oxygen at 2 L/minute
End of inner tube is occluded
If inner tube is intact then
bobbin will descend slightly
Once released it will ascend to
its original place.

31. Required fresh gas flow

32. Advantages of Mapleson system
 Equipment is simple, inexpensive and rugged.
 Variations in minute volume affect end tidal CO2 less than
circle system.
 Are lightweight and not bulky.
 Easy to position conveniently.
 Changes in fresh gas concentrations result in rapid changes in
inspiratory gas composition.

33. Disadvantages of Mapleson system
 These system require high gas flows.
 Because of high fresh gas flow, inspired heat and humidity
tend to be low.
 In mapleson A, B and C the APL valve is located close to
patient , where it may be inaccessable to the user.
 Mapleson E and F are difficult to scavange.

34. Circle system

35. Circle system
• It is so named because :-
 it allows circular,
 unidirectional gas flows
 Facilitated by unidirectional valves
It must allow for spontaneous ventilation, manual
ventilation and positive pressure ventilation.

36. Circle system

37. Three Essential factors
• There should be:-
 Two unidirectional valves on either side of reservoir bag and
canister.
 Pop off valve or APL valve should be positioned in the
expiratory limb only.
 The Fresh Gas Flow should enter the system proximal to the
inspiratory unidirectional valve.

38. Low Flow Anesthesia
• To enhance oxygen and anaesthetic uptake and the excretion
of nitrogen (N2), a high FGF is recommended at the start of an
anaesthetic.
• When clinically desirable concentrations are reached,
the FGF can be reduced, to a basal metabolic oxygen
consumption rate of approximately 250 ml min−1.
• Hence in circle system, low flow upto 250ml/min to
500ml/min can be administered.

39. Advantage of circle system
1. Maintenance of relatively stable inspired gas concentrations
2. Conservation of respiratory moisture and heat
3. Elimination of carbon dioxide
4. An economy of anesthetic gases resulting:-
 from rebreathing
 as FGF could be reduced to as low as 250-500ml of oxygen
5. Prevention of operating room pollution.

40. Disadvantage of circle system
1. Leaks and disconnections
2. Misconnections
3. Occlusion
4. Malfunction of unidirectional valves

41. Components of circle system
• Fresh gas inflow source
• Inspiratory and expiratory unidirectional valves
• Inspiratory and expiratory corrugated tubes
• Y piece
• Overflow or adjustable pressure limiting valve
• Reservoir or breathing bag
• Canister containing carbon-dioxide absorbent.

42. Unidirectional valves.
• Essential element .
• Incompetence is one the most common problem

43. Adjustable pressure limiting valve
• It is operator-adjustable relief valve that vents excess
breathing circuit gases to the scavenging system.
• Other common names are
 “pop off” valve and
 pressure relief valve.
• Types:- 1. variable- resistor or variable-orifice type
2. pressure-regulating type Modern machines

44. APL valve with inbuilt overpressure safety
devices
A. When unscrewed:- Outer valve
opens when exhaled gases
create a pressure of 1.5cm H20
B. Valve is closed (fully screwed)
C. Valve is fully screwed so an
excess pressure needed to
open the valve.
 At 30 cm H2O valve begins
to open.
 At 60-70 cm H2O valve is fully
open.

45. Anesthetic reservoir bag
 Breathing Bag.
 Capacity:- 500ml, 1L or 2L.
 Pressure standards:-
Minimal pressure 30 cm H2O
Maximal pressure  60 cm H2O

46. Functions of reservoir bag
 Serves as reservoir for exhaled gases and excess fresh gas.
 Means of delivering manual ventilation
 Serves as visual and tactile means of monitoring spontaneous
breathing effort
 Partially protecting the patient from excessive positive
pressure on inadvertent closure of APL valve.

47. Fresh gas decoupling
• During inspiration:- FGF is diverted to reservoir bag by the
decoupling valve

48. Fresh Gas Decoupling
• During Expiratory phase:- decoupling valve opens FG in
reservoir bag is drawn towards circle system to refill piton
chamber ventilator.
• Since ventilator exhaust valve is also open exhaled gases
and excess FG passes to the scavenging system.

49. Corrugated breathing circuit tubing
• The hoses should have a diameter that provided low
resistance to gas flow to provide laminar flow.
 Adults:- 22mm
 Pediatrics:- 15 mm
• Should be flexible so that kinking does not occur.
• Corrugated so as to adjust the length of tube.
• Light weight.

51. Carbon-dioxide absorbers
• Ideal carbon-dioxide absorbents:-
 Lack of reactivity with common anesthetics
 Absence of toxicity
 Low resistance to airflow
 Minimal dust production
 Small cost
 Ease of handling
 High efficiency carbon dioxide absorption

52. Absorber canister
• Transparent  to monitor the absorbent for its presence and colour.
• The absorbent should be changed when the colour change is about
50 to 70%.

53. Chemistry of Absorbents
• Most commonly used is Soda-Lime
Absorbent Ca(OH)2 H2O NaOH KOH
Soda lime 80% 16% 3% 2%
1. CO2 + H2O H2CO3
2. H2CO3 +2HaOH (KOH) Na2CO3 (K2CO3) +H2O + heat
3. Na2CO3 (K2CO3) + Ca(OH)2 CaCO3 + 2NaOH(KOH) +Heat

54. Some of carbon dioxide abosorbers:
Absorbent Ca(OH)2 % LiOH% H2O% NaOH% KOH% Other%
Classic
soda lime
80 0 16 3 2 --
Baralyme 73 0 11-16 0 5 11 Ba(OH)
New soda
lime
73 0 19 <4 0 --
Spiralith 0 95 0 0 0 <5
Polyethylene

55. Indicators
• Fresh soda lime has pH = 12.
 Decreases as CO2 is absorbed.
 Indicators:-
 White Soda lime contains ethyl violet, critical pH = 10.3;
purple
 Pink Soda lime contains phenolphthalein, critical pH= 7.
colourless.

56. Carbon dioxide removal capacity
• 100 grams of soda lime granules absorb around 14-23 liters of CO2.
• If completely reacted:-
A pound of calcium hydroxide
has the capacity to absorb 0.59
lb of carbon dioxide
A pound of Lithium
hydroxide has the ability to
absorb 0.91 lb of carbon
dioxide.

57. Factors affecting carbon dioxide
removal capacity
1. The amount of surface area of the absorbent to which the
exhaled gas is exposed,
2. The intrinsic capacity of absorbent to remove carbon dioxide,
3. The amount of functionally intact absorbent remaining in the
absorber.
Smaller the granule size greater the surface area so more absorption.
BUT
the airflow resistance is increased

58. Size of granule
• 4-8 mesh size  is the size at which absorptive surface area
and resistance to flow are optimized.
• Mesh size refers to the number of openings per linear inch in
a seive through which the granular particles can pass.

59. Problems with absorbents
A. Formation of potentially harmful products:-
1. Compound A 2. Carbon monoxide 3.Dichloroacetylene
Nephrotoxic Increased
Carboxyhemoglobin
Cranial nerve
neuropathies and
encephalitis
Sevoflurane Desflurane,
enflurane and
isoflurane
Trichloroethylene

60. B. Absorbent Heat Production:-
Rare but potentially life-threatening complication which
leads to fires and explosions due to extreme exothermic
reactions.

61. Summary

62. Scavenging system
• Scavenging is collection and removal of the vented anesthetic
gases from the operation theatre.
• Types: Active Passive
Suction is applied Waste gases proceed passively
down corrugated tubing through
the room ventilation exhaust grill of
operating room

63. Recent advances
• New soda lime does not contain KOH
• Spiralyth  only Lithium hydroxide

64. Conclusion
• Most common used breathing system is circle system.
• Mapleson A for spontaneous ventilation
• Mapleson D for controlled ventilation.
• Modification of Mapleson A is Lack’s system.
Mapleson D is Bain’s system.
Mapleson E is Mapleson F.
• Test for Bain’s circuit Pethick test and Foex Crempton Test

65. Thank you..

66. Reference
• Miller’s anesthesia 8th edition
• Ward’s anesthetic equipments 6th edition
• Morgan 5th edition

67. Role of heat and humidification

68. Filter

69. Physics
• Hagen Pouesille law.

70. Apparatus dead space.

71. Recent advances
• New soda lime
• Limb – O circuit
• King Flex – 2

72. • Humphrey ADE

73. THANK YOU..