Anaesthesia Breathing Circuits (EORCAPS 2009)

7/24/2019 Anaesthesia Breathing Circuits (EORCAPS 2009)

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Dr. A K Sethis EORCAPS-20

Dr. A K SethisEORCAPS-2009

Dr. Pradeep Jain

Anaesthesia Breathing Circuits


Breathing System

A 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

Link machine to the patient

Eliminate CO2


Component of Breathing system A fresh gas entry port/delivery tube through which the gases

are delivered from the machine to the systems

A port to connect it to the patients airway

A reservoir for gas, in the form of a bag or a corrugated tube

to meet the peak inspiratory flow requirements

An expiratory port/valve through which the expired gas is

vented to the atmosphere

A CO2 absorber if total rebreathing is to be allowed

Corrugated tubes for connecting these components


Requirements of

Breathing SystemEssential:The breathing system must

Have minimal apparatus dead space

Have low resistance

Deliver the gases from the machine to the alveoli in the

same concentration as set and in the shortest possible time

Effectively eliminate CO2


Requirements of

A Breathing SystemDesirable:The desirable requirements are

Economy of fresh gas

Conservation of heat

Adequate humidification of inspired gas

Light weight

Convenience during use

Efficiency during spontaneous as well as controlled ventilation

Adaptability for adults, children and mechanical ventilators

Provision to reduce theatre pollution


History

McMohan 1951 classified them as open, semi closed &

closed - criteria rebreathing

Dripps 1984 - Insufflation, Open, Semi open, Semi closed

& Closed - criteria presence or absence of Reservoir,

Rebreathing, CO2 absorption & Directional valves

Conway 1985 suggested functional classification according

to the method used for CO2 elimination

Breathing systems with CO2 absorber

Breathing systems without CO2 absorber

Miller 1995 new breathing system called Maxima


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Classification of Breathing Systems

Bi-directional flowTo and Fro system.

Bi-directional flow:a) Afferent reservoir systems.

Mapleson A

Mapleson B

Mapleson C

Lacks system.

B) Enclosed afferent reservoir systems

Millers (1988)

c) Efferent reservoir systems

Mapleson D

Mapleson E

Mapleson F

Bains system

d) Combined systems

Humphrey ADE

Unidirectional flow

Circle system with absorber.

Unidirectional flow:

a. Non rebreathing systems.

Breathing Systems With Co2Absorption.Breathing Systems Without Co

2Absorption.


Non Rebreathing System

Non Rebreathing Valves - Unidirectional Flow

FGF has to be constantly adjusted, not economical

No humidification of inspired gas

No conservation of heat

Inconvenient as the bulk of the valve near the patient

Valve malfunction due to condensation of moisture

Eg. Ruben valve, Ambu valve & Laerdal valve


Four Basic Circuits

Open

Semi-open

Semi-closed

Closed


Open System

Insufflation

Blow anesthetic gas over face

No direct contact

No rebreathing of gases

Ventilation cannot be controlled

Unknown amount delivered


Open Systems

Open drop anesthesia

Gauze covered wire mask

Anesthetic dripped

Inhaled air passes through gauze & picks up anesthetic

Concentration varies

Environmental pollution


Semi-open Systems

Reservoir

No rebreathing


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Semi Closed

Mapleson Breathing System Absence of unidirectional value to direct gases to and fro

from the patient No device for absorbing CO2

Flow controlled breathing systems

FGF must wash CO2 out of the circuit

CO2 without circuit

No clear separation of inspired and expired gases -rebreathing will occur when inspiratory flow exceeds FGF

Composition of inspired mixture will depend uponrebreathing


Bi-Directional Flow

Systems extensively used

Depend on the FGF for effective CO2 elimination

Functions can be manipulated by changing

parameters like

Fresh Gas Supply

Elimination of CO2

Apparatus Dead Space


Bi-Directional Flow

Fresh Gas Supply; Low do not eliminate CO2 effectively

High wastage

If the system has to deliver a set concentration in the shortest possible timeto the alveoli, the FGF should be delivered as near the patients airway aspossible

Elimination of CO2 Normal production of CO2 in a 70 kg patient 200 ml/min

End-tidal concentration of CO2 is 5%

For elimination 200ml of of CO2 as a 5% gas mixture, the alveolarventilation has to be: 200 x 100 = 4,000 ml.

5

4 litres is the normal alveolar ventilation.

Apparatus Dead Space

It is the volume of the breathing system from the patient-end to the point upto which, to and fro movement of expired gas takes place


Classification

Five Basic types

A through E

F added by willis in 1975


Mapleson Classification

Reservoir bag

Corrugated tubing

APL valve

FGI

Patient connection


Mapleson A

Magill Circuit

Popularized by Sir Ivan Magill in 1920s

It differs from the other Mapleson systems in that fresh gas does notenter the system near the patient connection but enters at the other

end of the system near the reservoir bag.

A corrugated tubing connects the bag to the adjustable pressure

limiting (APL) valve at the patient end of the system

Length of corrugated breathing tube 110 cm with an internal volume

of 550 ml


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Mapleson A

Most efficient for spontaneous respiration

Resistance 2.5cm of H2O when expiratory valve is fully open

No rebreathing if FGF equal to minute volume

Rebreathing occurs if FGF less than alveolar ventilation


Functional Analysis

Mapleson A with Spontaneous Breathing


Functional Analysis

Mapleson A with Control Ventilation

a = at the end of inspiration

b = at the end of expiration

c = during subsequent inspiration

d = at the end of subsequent inspiration


Mapleson B & C systems

In order to reduce the rebreathing of alveolar gas and to

improve the utilization of FG during controlled

ventilation, the FG entry was shifted near the patient.

This allows a complete mixing of FG and expired gas.

The end result is that these systems are neither efficient

during spontaneous nor during controlled ventilation.


Modifications of Mapleson A Circuit

Lack Circuit Added expiratory limb which runs from pt end to APL

valve at machine end

This limb is coaxially placed inside the affarent limb

Length 1.5 m, resistance 1.63 cm H2O Advantage

Facilitates easy scavenging

Easy adjustment of APL valve

Disadvantage

Increased resistance to breathing


Enclosed Afferent Reservoir System

Miller & Miller 1988

Mapleson A system enclosed within a non

distensible structure

It may also be constructed by enclosing the

reservoir bag alone in a bottle and connecting

the expiratory port to the bottle with a

corrugated tube and a one way valve

To the bottle is also attached a reservoir bag

and a variable orifice for providing positive

pressure ventilation.


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Enclosed Afferent Reservoir System

Functional analysis:

During spontaneous ventilation it is identical to the Mapleson A system

In this mode the variable orificeis kept widely open to allow free communicationto the atmosphere

In controlled ventilation the reservoir bag B is squeezed intermittently & the

variable orificeis partly closed to allow building up of pressure in the bottle

The pressure thus developed closes the expiratory valve squeezes the enclosed

afferent reservoir and the patient gets ventilated

Hence this system should function efficiently during spontaneous and

controlled ventilation with a FGF equivalent to alveolar ventilation


Efferent Reservoir Systems

Mapleson DEF All have a T-piece near the patient and

function similarly

The T-piece is a three-way tubular

connector with a patient connection port,

a FGF port & a port for connection to a

corrugated tubing

Light metal tube 1cm in diameter ,5cm in

length with a side arm

6 mm tube as the affarent limb that supplies

the FG from the machine


Mapleson D

A length of tubing connects the T-piece at the patient end

to the APL valve and the reservoir bag adjacent to it

The length of the tubing determines the distance the user

can be from the patient but has minimal effects on

ventilation

Popular because excess gas scavenging is relatively easy

Most efficient of the Mapleson systems during controlled

ventilation


Mapleson D Functional Analysis

Spontaneous Ventilation


Mapleson D Functional Analysis

Controlled Ventilation


Bain Breathing Circuit

Modified Mapleson D

Bain 1972

The fresh gas supply tube runs coaxially inside the corrugated tubing

and ends at the point where the fresh gas would enter if the classicMapleson D form were used

The outer tube is clear so that the inner tube can be inspected

The outer tubing of most commercially available versions of the

Bain system is narrower than conventional corrugated tubing

A long version of the Bain system may be used for remote

anesthesia in locations such as MRI


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Bain System

Depends on fresh gas flow to flush out CO2

Spontaneous ventilation

200 - 300 ml / kg / min

Controlled ventilation

infants 60 kg 70 ml/kg/min


Bain Circuit

Coaxial length 1.8m

Inner inspiratory tubing - 7 mm diameter

Outer expiratory tubing - 22 mm diameter

Resistance - < 0.7 cm H2O


Relation Between Alveolar

Ventilation and FGF


Bain System Advantages

Light-weight, Compact, easy to handle

Warming of inspired gases

Partial rebreathing improves humidification

Ability of scavenging

Can be used with ventilator


Disadvantage

Accidental disconnection of inner tube, kinking & twisting of

inner tube converts entire exhalation limb into dead space

FGF may be connected to outer tube

Lower FGF may result in re-breathing

Tests-visual inspection for damage, disconnection

Pethicks test, occlusion test


Mapleson E

Ayres T Piece, 1937

Low resistance, low dead space

Simple piece of metal with 3 limbs & a port at the end of

each limb Exhalation tube is a reservoir

No bag

FGF near mask


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Mapleson E

Hazards

Over inflation and barotrauma by prolonged occlusion

and no feel of inflation

Also pressure buffering effect of bag absent


Mapleson F

Jackson Rees Modification

Addition of a bag with an opening to exhalation limb of T- piece

Corrugated hose 15cm X 11 mm

Reservoir bag 0.5 1 L

Green tube for FGF 1.5m in length

Advantage

Early to assist / Controlled ventilation

Easy to monitor ventilation


Advantage of the Mapleson Systems

Simple, inexpensive, light weight. With the exception of the APL

valve, there are no moving parts

In coaxial systems (Lack, Bain), the inspiratory limb is heated by the

warm exhaled gas in the coaxial expiratory tubing

Resistance is usually low at flows likely to be experienced in practice

Easy to position conveniently. A long Mapleson D system may be

used to ventilate a patient in the MRI unit

Compression & compliance volume losses are less than with the circle

system

Changes in fresh gas concentrations result in rapid changes in

inspiratory gas composition


Disadvantage of the Mapleson Systems

Require high gas flows - results in higher costs, increased

atmospheric pollution, and difficulty assessing spontaneous

ventilation

Inspired heat and humidity tend to be low because of high FGF

In the Mapleson A, B, and C systems the APL valve is located close

to the patient, where it may be inaccessible to the user.

The Mapleson E and F systems are difficult to scavenge

Air dilution can occur with the Mapleson E system.

Mapleson systems are not suitable for patients with malignant

hyperthermia


Combined System

Humphrey ADE To over come the difficulties of changing the breathing system for

different modes of ventilation

Humphery designed a system called Humphery ADE in 1983

Two reservoirs, one in the afferent limb and the other in the

efferent limb

Only one reservoir will be in operation and the system can be

changed from ARS to ERS by changing the position of a lever

Can be used for adults as well as children

Functional analysis is the same as Mapleson A in ARS mode and

as Bain in ERS mode

Not yet widely used


Paediatric Circuit

work of breathing

Prevent rebreathing

Volume of the non rebreathing circuit is small as

compared with that of circuit system, the compression

and compliance volume will be significantly less. This

improves the ability to observe respiratory effect as

reflected by movement of the anaesthesia bag

Mapleson D recommended for use in children < 10 kg wt


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Questions ?


Which system have the FGF

near the reservoir bag

A


Apparatus Dead Space extend

upto

In ARS Expiratory valve

In ERS Fresh Gas entry


F circuit was introduced by

Whom & When?

Willis 1975


Bain Circuit

Coaxial length 1.8 meter

Inner inspiratory tubing diameter 7 mm

Outer expiratory tubing diameter 22 mm

Resistance


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The efficiency of the circuit

is determined in terms of

CO2 elimination

FGF utilization


Which system is most efficient with

respect to prevention of rebreathing

during Spontaneous Respiratory

A > DEF > BC


Which system is most efficient with

respect to prevention of rebreathing

during Controlled ventilation

DEF > BC > A


To prevent rebreathing of CO2

system DEF require a FGF of

2.5 times the minute volume


In spontaneous respiration to

prevent rebreathing the

Mapleson A requires flow rate

Equal to minute volume

Documents

Anaesthesia Breathing Circuits (EORCAPS 2009)