DR:- IMRAN

PAEDIATRIC BREATHING CIRCUIT’s

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.

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.

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

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.

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

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

Conway suggested a functional classification

1. Breathing systems with CO2 absorber

2. Breathing systems without CO2 absorber.

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.

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.

BREATHING SYSTEMS WITHOUT CO2 ABSORPTION

c) Efferent reservoir systemsMapleson DMapleson EMapleson FBain’s systemd) Combined systemsHumphrey ADEMulti circuit system

NONREBREATHING SYSTEM(Uni-directional)

Uses non-rebreathing valve

No mixing of fresh gas and expired gas

Fresh gas flow =/> Minute volume

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

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.

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)

MAPLESON SYSTEM

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.

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

AFFERENT RESERVOIR (AR) SYSTEMS

- Mapleson A, B and C systems have the reservoir in the afferent limb

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

Mapleson A (Magill’s)

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.

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

FGF requirements

SpontaneousFGF = Minute volumeFGF of 51-85ml/kg/min advised to prevent re-breathing

ControlledFGF = 2.5 x MV

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

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

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

Test for Mapelson “A”

Occlude patient end, close APL valve, pressurize system – maintaining pressure confirms integritiy

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)

Tube length 1.5m

Outer tube diameter; 30mm

Inner tube diameter ; 14mm

Inspiratory capacity ; 500ml

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

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.

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

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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

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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

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

FUNCTIONAL ANALYSIS

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

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

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

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

Functional Analysis:- During controlled ventilation-when FGF is high, PaCO2 becomes ventilatory dependent.

-when MV exceeds FGF , PaCO2 becomes dependent on FGF

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 .

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.

Ayre's T-piece Designed as a no valve circuit for paediatrics in 1937 by Philip Ayre. (Later classified as Mapleson E).

Mapleson E (Ayers T-Piece)

Length = 5cm

Diameter = 1cm

Side arms = 6mm

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

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

Our T-Piece

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

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

FGF requirements:-

Spontaneous- 2-3 times MV Minimum flow 3L/min

Controlled- 1000ml + 100ml/kg

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

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

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

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

Draw-over anesthesia

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

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

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

HUMPHREY’S ADE

MAP-A

Map-D

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

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

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