Here are the key components of a circle system: - Fresh gas inlet downstream of the soda lime canister and upstream of the inspiratory valve - Unidirectional valves - Breathing tubes - Soda lime canister for absorbing CO2 - APL (adjustable pressure limiting) valve - Reservoir bag or ventilator bellows - Patient end connection The circle system allows for maximum reuse of gases by ensuring exhaled gases pass through the soda lime canister before being inhaled again. However, it requires higher fresh gas flows to prevent rebreathing. Placement of the fresh gas inlet is important to direct exhaled gases through the soda lime.

1. Introductory Class
BREATHING
CIRCUITS
Moderator: Dr. Sanjay Jaswal (Faculty)
Dr. Ananya (SR)
Presented by: Dr. Abdur Rahaman (JR)

2. FIRST
RECOLLECT ABOUT TV,
VC, RV

4. WHAT’S ABOUT
DEADSPACE
?

6. DEFINE BREATHING SYSTEM
Breathing system is defined as an
assembly of components which connects
the patients airway to the anaesthetic
machine creating an artificial atmosphere
,from and into which the patient breathes.

8. REQUIREMENTS OF A BREATHING
CIRCUIT
Essential
I. Deliver the gases from
the machine to the
alveoli in the same
concentration as set
II. Shortest possible time .
III. Effectively eliminate
carbon dioxide.
IV. Have minimal
apparatus dead space.
V. Have low resistance.
Desirable
I. Economy of fresh gas.
II. Conservation of heat
III. Adequate humidification
of inspired gas
IV. Light weight & convenient
during use
V. Efficiency during
spontaneous and
controlled ventilation
VI. Adaptability for adults ,
children and mechanical
ventilators
VII. Provision to reduce
theatre pollution.

9. It primarily consists of
o A fresh gas entry
o A port to connect it to patient’s airway
o A reservoir for gas ,in the form of bag or a
corrugated tubing
o An expiratory port/valve
o A carbon dioxide absorber if total rebreathing is
to be allowed
o Corrugated tubes for connecting these

10. Adjustable Pressure Limiting Valve
 Spill valve, pop – off valve, expiratory valve.
 Designed to vent gas during Positive Pressure.
 Pressure of less than 0.1 kPa activates the valve when open.
Components:- 3 Ports
• Inlet, patient & exhaust port-later can be open to atmosphere or
connected to scavenging system
• Lightweight disc sits on a knife edge seating held in place by a
spring
• TENSION in the spring and therefore the valve’s opening
pressure is controlled by the valve dial.

11. Mechanism of Action
• One way , adjustable , spring loaded valve
• Valve allows gases to escape when pressure in the breathing
system exceeds the valve's pressure.
During spontaneous ventilation: the patient generates a
positive pressure during expiration , causing the valve to
open.
During positive pressure ventilation, a controlled leak is
produced in the inspiration by adjusting the valve dial
,allowing control of the patient’s airway pressure.

12. Connector and Adaptor
• A connector is a fitting device.
• An Adaptor is a specialized connector
-Establishes functional continuity between otherwise
disparate or incompatible components.

13. RESERVOIR BAG
 Also known as Rebreathing bag.
 Standard size is 2L (range from 0.5 to 6L) .
 Made up of Rubber and Plastic, ellipsoid in shape.
Functions :-
• Allows gas to accumulate during exhalation.
• Ventilation may be assisted or controlled.
• Serve as a visual and tactile observation .
• Protects patient from excessive pressure in breathing
system.

14. TUBING
• Corrugated or smooth
• Different lengths depending on system being
used
• Allow humidification of inspired air
• Parallel and coaxial arrangements available

18. Mapleson A
• Corrugated rubber or plastic tubing: 110-180 cm in
length
• Reservoir Bag at Machine end
• APL valve at the patient end.
• Tube volume > Tidal volume

19. Mapleson A : Functional Analysis
Spontaneous breathing
 The system is filled fresh gas before connecting to the
patient
 During Inspiration: The FG (machine + reservoir bag) flows to
the patient.
 The expired gas , initial part of which is the dead space gas ,
pushes the FG from the corrugated tube into the reservoir bag and
collects inside the corrugated tube.
 Expiratory pause- Fresh gas washes the expired gas.

20. Mapleson A : Functional Analysis
Spontaneous breathing

21.  To facilitate IPPV the expiratory valve has to be partly closed.
 During inspiration: Ventilated with FG and part of the FG is vented
through the valve.
 During expiration: FG from the machine flows into the reservoir
bag and all the expired gas ( i.e. dead space and alveolar gas)
flows back into the corrugated tube till the system is full.
 During the next inspiration the alveolar gas is pushed back into
the alveoli followed by the fresh gas.
 Part of the expired gas and part of the FG escape through the
valve, when sufficient pressure is developed.
 This leads to considerable rebreathing as well as excessive wastage of fresh gas.
Hence these system are inefficient for controlled ventilation.
Controlled Ventillation

22. Mapleson A : Functional Analysis
Controlled Ventillation

23. Mapleson A – Lack Modification
 Coaxial modification of Magill Mapleson A & functions like
Mapleson A
 1.5m in length
 FGF through outside tube ( 30mm),
 Exhaled gases from inner tube, vented through the valve placed near
the machine end.
 Inner tube wide in diameter (14 mm) to reduce resistance to
expiration(1.6 cm H2O).
 Reservoir bag & APL valve at machine end.
 Better for spontaneous ventilation.
 This facilitates easy scavenging of expired gases.

24. Mapleson A – Lack Modification

25. Mapleson B System
 The FG inlet is near the patient, distal to the expiratory valve.
 The expiratory valve open when pressure in the circuit rises.
 Inhaled mixture of retained fresh gas and alveolar gas.
 Rebreathing is avoided with fresh gas flow rates of >2MV for
both spontaneous and controlled ventilation.

26. Mapleson C system
 This circuit is also known as Water’s circuit.
 Similar to Mapleson B , but the main tube is shorter.
 A FGF equal to 2MV is required to prevent rebreathing.
 CO₂ builds up slowly with this circuit.
 This allows a complete mixing of FG and expired gas.
 The end result is that these system are not efficient.

27. Mapleson D System
 It consists of fresh gas inlet nearer the patient end.
 Expiratory valve and reservoir bag are away from patient end.
 It is mainly used for assisted or controlled vent.
 The FGF which enters during expiratory pause accumulates in the
patient end and pushes the exp gases towards valve end.
 In spontaneous breathing during inspiration the patient will inhale
the fresh gas from corrugated tube depending on FGF, TV, length
of expiratory pause & volume of corrugated tube.
 Rebreathing can be minimized by increasing FGF 2-3 times the
MV.
For an adult 15L/min FGF.
In some cases 250 ml/kg/min required to prevent rebreathing

29. Bain circuit
 It is a modification of Mapleson D system and is a co-axial circuit.
 It functions like T-piece except that tube supplying FG to the patient is
located inside the reservoir tube.
 Most commonly used. And known as Universal circuit.
 The reservoir bag may be removed and replaced by a ventilator.
 Has a pressure manometer and PEEP valve.
 Dead space of the circuit is the volume from the patient end up to the
point of separation of the gases.
 Entire volume of the tubing becomes the dead space If there is a leak in
either tubing.

30. Specifications:-
 Length-1.8 meters.
 Diameter of Outer tube-22mm (transparent,carries expiratory
gases)
 Diameter of Inner tubing-7 mm (inspiratory) and GREEN in
colour.
 Resistance-Less than 0.7 cmH2O
 Dead space- Outer tube upto expiratory valve( around
500ml=TV)
 Flow rates- 100-150 ml/kg/min for controlled ventilation.
Average 200-300 ml/kg/min for spontaneous ventilation

31. Bain system (Mapleson D)
Functional Analysis
SPONTANEOUS RESPIRATION
 Filled with FG
 First inspires: FG.
 During expiration: The expired gas gets mixed with the FG.
 During expiratory pause: FG continues to flow and fill while the
mixed gas is vented out through the valve.
 Second inspiration: Breaths FG as well as the mixed gas.
 Composition of the inspired mixture: determined by FGF, respiratory
rate, tidal volume, end expiratory pause and CO2 production in
the body.
 To minimize rebreathing FGF should be at least 1.5 to 2x MV.

33. CONTROLLED VENTILATION
• First inspires: FG.
• During expiration: the expired gas gets mixed.
• During the expiratory pause: the FG pushes the mixed gas towards
the reservoir.
• Second inspiration ventilated: with mixture of FG, alveolar gas and
dead space gas.
• When the pressure in the system increases, the expiratory valve
opens.
• The degree of rebreathing that occurs depends on the FGF.
• This system causes less rebreathing that Mapleson B and C.
• This system functions more efficiently when used for controlled
ventilation

34. BAIN CIRCUIT AND IT’S FUNCTION

35. Flow Settings
Controlled ventilation:
2 L/min < 10 kg
3.5 L/min = 10–50 kg
70 mL/kg > 60 kg
Spontaneous ventilation:
200–300 mL/kg

36. BAIN Circuit
ADVANTAGES
I. Can be used for adult and pediatric patient.
II. Spontaneous and controlled ventilation
III. Best Mapleson system for controlled
ventilation
IV. Light weight.
V. Long length.
VI. Coaxial arrangement makes it convenient to
use Long length of the circuit.
VII. Disposable circuit, however can be easily
sterilized and reused
VIII. Warmth added to the inhaled gases by
exhaled gas passing through the outer
tubing.
DISADVANTAGES
I. Disconnection, kinking or
leak of inner tubing.
II. If such, the entire corrugated
tubing becomes dead space.
III. This can result in hypercarbia
from inadequate gas flow.

37. TEST TO CHECK BAIN CIRCUIT
The Pethick test
 Fill Reservoir Bag
 Flush high flow oxygen into the circuit.
 Occlude the patient’s end of the circuit until the.
 The patient end is then opened and
 The circuit flushed with oxygen.
Interpretation 1
 Bag will deflate -If the inner tube is intact
 Reason: the venturi effect occurs at the patient end, causing decrease in
pressure within the circuit.
Interpretation 2
 Bag will inflate -If there is a leak in the inner tube.
 Reason: FG will escape into the expiratory limb and inflate the bag.
BackPressure Test
• Block the inner tube at the patient end and flush the circuit.
• No leak in the inner tube.
• The flow meter bobbins will dip due to the back pressure.

38. Mapleson E and F
o Valveless breathing system used for children
upto 20 kg.
o Suitable for spontaneous and controlled
ventilation.
Components:-
 T shaped tubing with 3 ports.
 FGF delivered to one port
 2 nd port goes to patient & 3rd to reservoir tube.

39. Ayre’s T- PIECE
 Belongs to Mapleson E.
 Available as meatllic / plastic.
 Length – 2 inches.
 Parts – inlet, outlet, side tube.
 Inlet size-10 mm, outlet size-10mm metallic & 15 mm
plastic

40. Advantages
 Simple to use , Light weight.
 No dead space , no resistance.
 For pediatric pts. Less than 20 kgs
.
 Expiratory limb is attached to the outlet
of T piece.
 It should accommodate air space equal
to 1/3 rd of TV.
 If too short – air dilution in spont.
Breathing & pts become light.
 1 inch of expiratory tube can
accommodate 2-3 ml of gas.
 Gas Flows – 2- 3 times MV
Disadvantages
 High flow rates are
required.
 Loss of heat & humidity.
 Risk of accidental
occlusion of expiratory
limb- risk of increased
airway pressure &
barotrauma to lungs.

41. Mapleson F
 The most commonly used T –piece system is the
Jackson-Rees’ modification of Ayre’s.
 This system connects a two ended bag to the expiratory
limb of the circuit.
 Gas escapes via the tail of the bag.

42. It comprise of-
 Plastic angle mount
 Plastic Ayre’s T-piece
 Corrugated rubber hose.
 Reservoir bag of 0.5- 1 lit capacity.
 Green PVC 1.5 meter long tube with plug that fits into the
fresh gas outlet of the Boyle’s apparatus.
 Gas flows required -2-3 times MV.
 Dead spce-1 ml/lb( 1KG=2.2LBS)
 Tidal volume- 3 times dead space.

43.  The internal volume of the tube between the patient and the bag
should exceed the patient’s tidal volume.
 FGF flushes expiratory limb during the pause.
 Expiratory limb should be more than TV to prevent air dilution &
rebreathing in spon. Breathing child.
 This allows respiratory movements to be more easily seen and
permits intermittent positive ventilation if necessary.
 Alternatively , a ‘bag-tail valve’,which employs an adjustable
resistance to gas flow, may be attached to the bag tail
 To prevent rebreathing , system requires a minimal flow of 3
litre/minute, with a FGF of 2 to 3 times the patient MV.
CONT…

44. FRESH GAS FLOW
Spontaneous ventilation
• Fresh gas flows of 2–3 x MV to prevent
rebreathing,
• (with a minimum flow of 3 L/min)
Mechanical Ventilation
• Fresh gas flow of 1L + 100 mL/kg/ min to maintain
normocapnia.
• It can be used in adult patients with controlled

45. Mapleson – F Circuit
Advantage
• Simple
• Easy to assemble
• Light weight
• Portable
• No valves
• Least resistance
• Suitable for pediatric anesthesia,
especially head and neck surgery
(due to the above factors)
• Equally effective for both
controlled and spontaneous
ventilation.
• Easy to scavenge Inexpensive
Disadvantage
• Wastage of gases—FGF 3 times
minute volume
• Required Lack’s humidification
(can be overcome by allowing FG
to pass through a humidifier)
• Occlusion of the relief valve can
increase airway pressure
producing barotrauma.

46. Suitable for use in Children
 It is light in weight
 Low resistance
 No valve.
 Suitable for children under 20 kg.
It can be used in adult patients with
controlled ventilation.
FGF ranging from 70–100 ml/kg/min.

48. THE CIRCLE ABSORBER SYSTEM

49. Objectives in a Circle System
• Maximum reuse of dead space.
• Maximum reuse of fresh gases.
• Maximum venting of alveolar gases.
• FGF should join the inspiratory limb.
• For paediatric use, low diameter tubes should be
used.

50. • What are the components?
• What are the advantages and
disadvantages of circle system?
• How CO2is absorbed ? What are the
composition of CO2 absorbents ? What is
the chemical reaction taking place during
CO2 absorption by SODALIME.

51. COMPONENTS
1. Fresh gas Inlet
2. Unidirectional valves
3. Breathing Tubes
4. Sodalime canister
5. APL valve
6. Reservoir bag (Ventilator Bellows)
7. Patient end.

52. 1. FG Inlet:
I. Position: Downstream to Canister but
Upstreram to Inspiratiory valve.
II. Expiratory Pause: FG pushes the expired gas (co2
enriched)
-> sodalime-> APL valve.
I. If FGF is high enough, it might be lost via APL too.
II. Disadvantage if FGF Upstream of Sodalime:
III. If FGF enters between patient and exp valve: risk of
BAROTRAUMA on activation of O2 flush.
A. Its composition may not immediately reflect inspired gas content.
B. Activation of flush may carry dust.
C. Inhaled anaesthetic is absorbed by sodalime.
D. High flow dry up Sodalime

53. 2. Unidirectional valves:
I. Light disc sitting on a knife- edge seat.
II. Gases normally flow under the seat lifting the disc off
the seat and flowing out under the dome.
III. Pressure under the dome firmly seats the disc and
prevents retrograde flow.
3. Reservoir Bag
I. Between the expiratory valve and the canister.
II. Reduces the work of expiration, which is the only work
of the respiratory muscles under IPPV.
III. If it is located between absorber and inspiratory valve,
it reduces the work of inspiration in spontaneous
ventilation.

54. 4. APL Valve:
I. Between the expiratory valve and the canister.
II. Allows exhaled gases to escape before passing through
sodalime.
III. Downstream the canister will lead to loss of gases.
IV. Downstream to the inspiratory valve leads to
rebreathing.

55. Ideal Arrangement of Components in a
Circle System
I. Unidirectional valve should be placed between the
patient and the reservoir valve in each limb.
II. No gases should flow toward the patient via expiratory
limb during inspiration.
III. Reservoir bag should not be located between the
patient and the expiratory valve.
IV. No gases should flow from patient into the inspiratory
limb during expiration.
V. APL valve and bag should not be located between the
patient and the inspiratory valve.
VI. Bag size should be greater than inspiratory capacity
(30mL/kg BW).
VII. Canister should be atleast twice the tidal volume of the
patient (sodalime contains 50- 70% air around the

56. ADVANTAGES
I. Economical –
• Gases and inhalational
anaesthetic agent
• Scavenging volume/ load
decreases.
II. Heat and humidity
preservation.
III. Low dead space
IV. Atmospheric pollution
reduced.
V. Arterial CO₂ tension
depends on MV, not on
FGF
DISADVANTAGES
I. Risk of disconnection and
misconnection.
II. Slow change in the inspired
gas composition particularly
with low flow.
III. Dry sodalime / barylime
absorbs anaesthetic agent
IV. Accumulation of trace gases-
CO, H₂, acetone, methane,
ethanol.
V. acrylic monomer is exhaled
after cementing. Higher FGF
would vent this out.
VI. Greater resistance to
breathing

57. CO2 ABSORBENT

58. Describe the chemical reaction
• CO₂ + H₂O H₂CO₃
• 2NaOH + H₂CO₃ Na₂CO₃ + 2H₂O
• Ca(OH)₂ + Na₂CO₃ CaCO₃ + 2NaOH

59. Advantages of CO₂ Absorber
Neutralization of CO₂
Economical, as low FGF.
Less theatre pollution.
Hazards of explosion is reduced.
Conservation of heat and humidity.

60. Problems with the use of inhalational
anaesthetics with CO₂ Absorbant
 Sodalime + Sevoflurane = Compound A
 Halothane is degraded to form Halokene.
 Production of CO (Des > Iso > Halo = Sevo)
 Compound A and Halokene are nephrotoxic in
rats

63. REFERENCES