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DR:- IMRAN
PAEDIATRIC BREATHING CIRCUIT’s
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DEFINITION: Assembly of components which
connects the patient’s airway to the anaesthetic machine creating an artificial atmosphere, from and into which the patient breathes.
A breathing system converts continuous flow from the machine to a intermittent flow.
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INTRODUCTION
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 Bain Circuit was introduced in 1972
by Bain and Spoerel.
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CRITERIA FOR IDEAL SYSTEM
ESSENTIAL:- 1.Delivery of gas from machine to the alveoli in same concentration as set and in shortest possible time
2.Effective elimination of CO2 3.Minimal dead space 4.Minimal resistance
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DESIRABLE:- 1.Economy of fresh gas 2.Conservation of heat 3. Adequate humidification 4. Efficient during spontaneous and controlled ventilation 5. Efficient for adult, pediatrics and with mechanical ventilators 6. Light weight 7. Less theater pollution 8. Convenient during use.
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COMPONENTS
1.Bushings(mount)
2.Sleeves
3.Connectors & Adaptors
4.FGF inlet
5.Breathing tube
6.Reservoir Bag
7.Valve’s 8.Filters
9.CO2 absorber
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CLASSIFICATION OF BREATHING
SYSTEMS McMohan in 1951 Open - no rebreathing Semiclosed - partial rebreathing Closed - total rebreathing
Dripps et al have classified them as Insufflation, Open, Semi-open,
Semi-closed and Closed
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Conway suggested a functional classification
1. Breathing systems with CO2 absorber
2. Breathing systems without CO2 absorber.
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BREATHING SYSTEMS WITHOUT CO2 ABSORPTION
BREATHING SYSTEMS WITH CO2 ABSORPTION
Unidirectional flow
A) Non rebreathing systems.B) Circle systems.
Unidirectional flow Circle system with absorber.
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BREATHING SYSTEMS WITHOUT CO2 ABSORPTION
BREATHING SYSTEMS WITH CO2 ABSORPTION
Bi-directional flow A) Afferent reservoir systems. - Mapleson A,B,C - Lack’s system.B) Enclosed afferent reservoir systems Miller’s (1988)
Bi-directional flow To and Fro system.
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BREATHING SYSTEMS WITHOUT CO2 ABSORPTION
c) Efferent reservoir systemsMapleson DMapleson EMapleson FBain’s systemd) Combined systemsHumphrey ADEMulti circuit system
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NONREBREATHING SYSTEM(Uni-directional)
Uses non-rebreathing valve
No mixing of fresh gas and expired gas
Fresh gas flow =/> Minute volume
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Disadvantage:
● FGF has to be constantly adjusted so uneconomical ● No humidification
● No conservation of heat
● Not convenient because of bulk of valve
● Valve malfunctioning due to condensation of moisture
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Bi-Directional Flow system extensively used depend on the FGF for effective
elimination of CO2 FGF - No FGF - suffocated - Low FGF - does not eliminate CO2 - High FGF – wastage FGF should be delivered as near the
patient’s airway as possible.
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Mapleson systems 1954 by Professor W W Mapleson
- Maplesons A-(magills ) - Maplesons B- Maplesons C- Maplesons D- Maplesons E (T-piece) - Maplesons F (Jackson-Rees modification of
the T-piece)
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MAPLESON SYSTEM
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Functional classification
Afferent reservoir system (ARS). Enclosed afferent reservoir systems
(EARS). Efferent reservoir systems (ERS). Combined systems.
Enclosed afferent reservoir system has been described by Miller and Miller.
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afferent limb - delivers the fresh gas from the machine to the patient.
efferent limb - expired gas from the patient and vents it to the atmosphere through the expiratory valve/port
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AFFERENT RESERVOIR (AR) SYSTEMS
- Mapleson A, B and C systems have the reservoir in the afferent limb
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AR systems - spontaneous breathing
- the expiratory valve is separated from the reservoir bag
- FGF should be atleast one MV - apparatus dead space is minimal.
Not efficient - controlled ventilation
FGF close to the expiratory valve (Mapleson B & C) , the system is inefficient both during spontaneous and controlled ventilation
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Mapleson A (Magill’s)
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MAPLESON A Also known as “MAGILLS SYSTEM”
Best for spontaneous ventilation
Depend on FGF for CO2 washout so also known as “FLOW CONTROLLED BREATHING SYSTEM”
No rebreathing if FGF=minute volume
No separation of inspired and expired gases
Monitoring of ETCO2 is must.
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APL valve at patient end. FGF and RB at other end of system Only one tubing so mixing of gases Work of breathing is less Length of corrugated tube 110cm /
volume=550ml
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FGF requirements
SpontaneousFGF = Minute volumeFGF of 51-85ml/kg/min advised to prevent re-breathing
ControlledFGF = 2.5 x MV
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Mapleson A Inspiration
The valve closesPatient inspires FG from
the reservoir barFG flushes the dead
space gas towards patient
ExpirationThe pt expires into the
reservoir bagThe initial part of the
expired gas is the dead space followed by alveolar gas
Meets up with FG,pressure in the circuit increases forces the APL open
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Mapleson A Controlled Ventilation
The Mapleson A is inefficient during controlled ventilation.
Venting of gas in the circuit occurs during the inspiratory phase, and the alveolar gases are retained in the tubing during expiration phase
Hence the alveolar gas is rebreathed before the pressure in the system increases sufficiently enough to force the expiratory valve open
A Fresh gas flow of >20l/min is required to prevent rebreathing during controlled ventilation
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This system differs from other circuits in that the fresh gas does not enter the system near the patient but near the reservoir bag.
Hazard:- should not be used with mechanical ventilator coz entire system becomes dead space
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Test for Mapelson “A”
Occlude patient end, close APL valve, pressurize system – maintaining pressure confirms integritiy
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LACK’S MODIFICATION
In 1976; Lack modified the mapelson A. APL valve at other end Added expiratory limb so no mixing of gas Two arrangement; Dual arrangement(parellel) Tube within tube(co-axial)
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Tube length 1.5m
Outer tube diameter; 30mm
Inner tube diameter ; 14mm
Inspiratory capacity ; 500ml
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TESTING
1)Attach tracheal tube to inner tube at patient end ; blowing down the tube with APL valve closed will produce bag movement if there is leak between two tubes
2) Occlude both limbs at patient end with APL valve open; squeeze the bag; if there is leak in inner tube; gas will escape from APL valve and bag will collapse
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Advantages:-
Location of APL valve- facilitates IPPV / scavenging.
Disadvantages:-
Slight increase in work of breathing.
Break / disconnection of inner tube- entire reservoir tube becomes dead pace.
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Mapleson B Fresh gas inlet near pt and
distal to APL APL opens when pressure
in the circuit rises and an admixure of alveolar gas and FG is discharged
During Inspiration,a mixture of alveolar gas and FG is inhaled
Avoid rebreathing with FGF>2×MV,not very efficient
www.anesthesiauk.com
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Mapleson C Also known as Water to
and fro(Water’s Circuit) Similar in construction
to the Mapleson B but main tubing shorter
FGF is equal to 2×MV to prevent rebreathing
CO2 builds up slowly with this circuit,not efficient
www.anesthesiauk.com
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EFFERENT RESERVOIR (ER) SYSTEMs Mapleson’s D, E ,F and bain circuits 6 mm tube as the afferent limb that
supplies the FG from the machine ER systems are modifications of Ayre’s
T-piece work efficiently and economically for controlled ventilation
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MAPELSON D Incorporates T piece at
patient
RB and APL valve at other end
FGF enters the system through side arm of T piece
FGF required to prevent rebreathing is 1.5-2 times minute volume
Used for spontaneous and controlled ventilation
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FUNCTIONAL ANALYSIS
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BAIN’S SYSTEM Described by Bain & Spoerel in 1972
Modification of Mapelson D system
Added one more tube; arranged coaxially Inner tube inspiratory; outer tube expiratory+inspiratory
Length of tube: 1.8m
Outer tube diameter: 22mm
Inner tube diameter :7mm
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Fresh Gas Flow required: SPONTANEOUS:
150 – 200 ml/kg/min
CONTROLLED :
70 ml/kg/min adult >60kgs3.5 L/min for 10 – 50 kgs2L/min for infants < 10kgs
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ADVANTAGE: Useful for pediatric as will as adult patient Allows warming & humidification of gases useful for spontaneous as will as controlled
ventilation Easily dismantled; sterilised; so useful in infected
cases Facilitates scavenging Length of tubing is long so machine can be taken
away from patient ; useful in head & neck & Neurosurgery.
Light weight Can be used with ventilator
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DISADVANTAGE:
High fresh gas flow requirements Cannot be used with intermittent flow machine.
Disconnection ,kink ,break, leak, at inner tube may go unnoticed – entire exhalation limb becomes dead space
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Functional Analysis:- During controlled ventilation-when FGF is high, PaCO2 becomes ventilatory dependent.
-when MV exceeds FGF , PaCO2 becomes dependent on FGF
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TESTING (For inner tube)
A) Foex-Crempton Smith test
Set low flow of O2 on flow meter , close APL valve Occlude the inner tube with a finger or barrel of
syringe at pt end . Observe flow meter indicator If inner tube is intact and correctly connected flow
meter will fall
B) Pathik test Close APL valve, Activate O2 flush Observe the bag Due to venturi effect , Bag will deflate .
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TESTING (for outer tube)
Close APL valve, occlude the patient end & pressurize the system. If no leak pressure will be maintained. When APL valve is opened the bag will deflate easily.
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Ayre's T-piece Designed as a no valve circuit for paediatrics in 1937 by Philip Ayre. (Later classified as Mapleson E).
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Mapleson E (Ayers T-Piece)
Length = 5cm
Diameter = 1cm
Side arms = 6mm
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T-Piece System
The Mapleson E (T-Piece),has a length of tubing attached to the T-piece to form a reservoir
Uses have decreased because of difficulties in scavenging
Still commonly used to administer oxygen or humidified gas to intubated patients breathing spontaneously
There are numerous modifications
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Mapleson E For spontaneous ventilation,the
expiratory limb is left open For controlled ventilation,the expiratory
linmb is intermittently occulded and fresh gas flow inflate the lungs
Rebreathing will depend on the FGF,the volume of the expiratory limb,the patient’s minute vent. And the type of ventilation,i.e. spont versus controlled
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Our T-Piece
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Mapleson F(Jackson-Rees System)
This is a modification of the T-piece with a bag that has a venting mechanism-usually a hole
Adjustable pop-off valve can even be included to prevent over pressuring
Scavenging can be done
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Mapleson F(Jackson Rees) For spontaneous ventilation the relief mechanism is usually left open
For assisted of controlled ventilation, the relief mechanism is occluded sufficient enough to distend the bag, respiration can then be controlled by squeezing the bag
The volume of the reservoir bag should be approximately the patient’s tidal volume, if the volume is too large re-breathing may occur and if too small ambient air may be entrained
To prevent rebreathing the system requires an FGF of 2.5-3 × the patients Minute volume
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FGF requirements:-
Spontaneous- 2-3 times MV Minimum flow 3L/min
Controlled- 1000ml + 100ml/kg
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Advantages Disadvantages
Compact Cheap No valves Minimal dead space Minimal resistance to breathing. Ventilator can be used
The bag may become twisted and impede breathing
High gas flow requirements
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What FGF’s are needed?
Mapleson Systems Uses FGF SV FGF IPPV
A MagillLack
SpontaneousGen Anaesthesia
70-100 ml/kg/min Min 3 x MV
B Very uncommon, not in use today
C ResuscitationBagging
Min 15 lpm
D Bain SpontaneousIPPV, Gen. Anaes
150-200 ml/kg/min
70-100 ml/kg/min
E Ayres T Piece Very uncommon, not in use today
F Jackson Rees Paediatric <25 Kg
2.5 – 3 x MVMin 4 lpm
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Relative Efficiency of rebreathing among various Mapleson circuits
Spontaneous Ventilation-A>DFE>CB
Controlled Ventilation-DFE>BC>A
Mapleson A is most efficient during spontaneous ventilation,but it is the worst for controlled ventilation
Mapleson D is most efficient during controlled ventilation
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The blowing of anesthetic gases across a patient’s face
Avoids direct connection between a breathing circuit and a patient’s airway
Because children resist the placement of a face mask or an IV line, insufflation is valuable
CO2 accumulation is avoided with insufflation of oxygen & air at high flow rate(>10 L/m) under H & N draping at ophthalmic surgery
Maintain arterial oxygenation during brief periods of apnea
Insufflation
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Draw-over anesthesia
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Nonrebreathing circuits Use ambient air as the carrier gas Inspired vapor and oxygen
concentrations are predictable & controllable
Advantage; simplicity, portability Disadvantage; absence of reservoir bag
-> not well appreciating the depth of TV during spontaneous ventilation
Draw-over anestheaia
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Poor control of inspired gas concentration & depth of anesthesia
Inability to assist or control ventilation No conservation of exhaled heat or
humidity Difficult airway management during
head & neck surgery Pollution of the operating room with
large volumes of waste gas
Disadvantages of the insufflation & draw-over systems
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COMBINED SYSTEM HUMPHREY’S ADE system:
To overcome the difficulties of changing breathing system for different modes of ventilation this system is developed
Two reservoir bag; one in afferent limb; other in efferent limb; only one is in use at a time
System can be changed from ARS to ERS by changing the position of lever
Used for adults as will as children
Functional Analysis same as MAP-A in ARS& as BAIN in ERS
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HUMPHREY’S ADE
MAP-A
Map-D
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CIRCLE SYSTEM
ESSENTIAL CPMPONENT: Soda lime canister Two unidirectional valve FGF entry Y piece Reservoir bag Relief valve
CRITERIA FOR EFFICIENT FUNCTIONING:
Two unidirectional valve on either side of RB
Relief valve on expiratory limb
FGF should enter proximal to inspiratory unidirectional valve
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TESTING
Set all the gas flows to zero. Close APL valve Occlude Y piece Pressurize system to 30cm of with Oxygen
flush Pressure should remain fixed for at least
10 sec. Open APL valve and ensure pressure
decrease
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CIRCLE SYSTEM ctd.
ADVANTAGES
Exhaled gas –co2 used again and again Constant inspired concentration Conservation of heat & humidity Useful for all ages Useful for low flow ;reduces cost of Anaesthesia Low resistance Less OT pollution
DISADVANTAGES:
Increased dead space Malfunctioning of unidirectional valve Exhausted soda lime; danger of hypercarbia