J.J.M MEDICAL COLLEGE, DAVANGEREDEPARTMENT OF ANESTHESIOLOGY

SEMINAR ON BREATHING SYSTEMS OPEN CIRCUIT

CHAIR PERSON PRESENTED BYDR. PRIYADARSHINI M.B DR. SHOEIB M.D P.G IN ANESTHESIAASSISTANT PROFESSORDATE-- 01-06-2010.

“NECESSITY IS MOTHER OF INVENTION”

• Earlier circuits were simple, differing in the type of anesthetic agent administered.

• The purpose of breathing systems that have evolved in anesthetic practice is to deliver Gas & Vapor to the patient in an appropriate, controlled & efficient manner.

• 1846 Sir W.T.G Morton did public demonstration with Ether.

• 1876 Clover`s Inhaler developed by J.T Clover.

• 1907 Barth used it to administer N₂O.

• 1909 Teter`s apparatus developed.

• 1909-13 F.W.Hewitts developed Hewitt`s apparatus.

• 1913 Gwathemy Apparatus developed.

• 1917 Boyle`s Apparatus developed.

• 1928 Magill`s Circuit was developed.

• 1937 Philip Ayre introduced T piece.

• 1972 J.A Bain & W.E Spoerel introduced Bain`s Circuit.

• 1975 Dr Gordon Jackson Rees developed Mapleson F system.

• Humphrey Davy, Brock & Downing developed combined ADE system.

Definition

• A breathing system is defined as an assembly of components, which connects the patient’s airway to the anesthetic machine creating an artificial atmosphere form and into which the patient breathes.

• The breathing system converts a continuous flow from the anaesthesia machine to an intermittent flow;

• In practice the breathing system is usually regarded as extending from the point of fresh gas inlet to the point at which gas escapes to the atmosphere or a scavenging system.

• Rebreathing: in anesthetic systems, it now conventionally refers to the breathing again of some or all of the previously exhaled gases including CO2 & water vapor.

Components of breathing system:

• Formally these were called breathing apparatus or breathing circuits. These names have been abandoned.

It primarily consists ofa) A fresh gas entry port/delivery tube through which

gases are delivered from the machine to the systems.b) A port to connect it to the patients airway.c) A reservoir for a gas in the form of a bag or a

corrugated tube to meet the peak inspiratory flow requirements

d) An expiratory port/valve through which the expired gas is vented to the atmosphere.

e) Corrugated tubes for connecting these components.

f) Flow directing valves may or may not be used.

g) A CO2 absorber if total rebreathing is to be allowed.

h) Connectors & adaptors • A connector is a fitting that joins

together 2 or more similar components.

• An adaptor is a specialized connector that establishes functional continuity between otherwise disparate or incompatible components.

• There sizes are universal & either

male/female, 15/22mm connections. Some incorporate gas sampling ports.

i) Bacterial filters- • they prevent

transmission of infection to the patients or contamination of equipments.

• Generally a new filter

should be used for every patient or in the absence of filter, a disposable system should be used on every patient.

j) Heat & Moisture Exchange (HME Filters)-

• These humidify & warm

the Anesthetic gases being delivered to the patients.

• These devices also help to dehumidify the gases that are been sampled for analysis by the side stream devices

RESERVOIR BAGS• Composition Rubber, synthetic

latex, neoprene.• Ellipsoidal in shape.• Available in size ranging from 0.25L

to 6L.• Types

Closed End.Double end.Kuhn`s bag.

• A normal size adult bag holds a volume exceeding the patients inspiratory capacity.

• Functions i. Reservoir

ii. Provides PIF.

iii. It provides a means whereby ventilation may be assisted or controlled.

iv. It protects the patient from excessive pressure in the breathing system.

v. It can serve through visual & tactile observation as a monitor of patients spontaneous respiration.

• ASTM Standards specifies –

a. For bags < 1.5L, min pressure 30cms. & max pressure 50cms of water.

b. For bags > 1.5L, min pressure more than 35cms & max pressure not exceeding 60cms of water.

Breathing Tubes1. Made of rubber or plastic or

silicone.2. Can be impregnated with silver

to add antimicrobial effect.3. Length is variable.4. Internal diameter

Adults – 22mm. Pediatric – 15mm.

5. Internal volume 400-500ml/m.6. Distensibility 0-5ml/m/mmHg.

7. Resistance to gas flow <1mm of H₂O/litre/min of flow

8. Corrugations prevent kinking & increased flexibility.

9. Backlash seen during spontaneous breathing.10.Wasted ventilation seen during controlled

breathing.

Functions 11.Act as reservoir in certain systems.12.They provide connection from 1part of system to

another.

Adjustable Pressure Limiting Valve (APL Valve)

• Also called as expiratory valve, pressure relief valve, pop off valve, Heidbrink valve, Dump valve, Exhaust valve, Spill valve etc

TYPES OF APL VALVES• Spring Loaded Disc Most commonly

used type. Has 3 ports –

– Inlet, – The Patient & – Exhaust Port.

Exhaust port may be open to atmosphere or scavenging system.

• Stem & Seat type

• Control Knob type

• Collection Device & Exhaust Port

• Humphrey Type valve.

APL Valves with Inbuilt• Overpressure Safety devices

Uses of APL valves in spontaneous & controlled ventilation.

• Spontaneous

Valve is kept fully opened.Partial closing will result in PEEP.Pressure <1cm H₂O needed to open valve.Should have pressure drop 1-3cm of H₂O for airflow of

3L/min & 1-5cms of water at 30L/min.

• Controlled

Valve is partially left open.

Essential/ Principle Criteria

The breathing system musta) Deliver the gases from the machine to the alveoli

in the same concentration as set and in the shortest possible time.

b) Effectively eliminate carbon-dioxide.

c) Have minimal apparatus dead space.

d) Have low resistance.

Desirable/Secondary Criteria The desirable requirements area) economy of fresh gas.

b) conservation of heat.

c) adequate humidification of inspired gas.

d) light weight

e) Convenience during use.

f) Efficiency during spontaneous as well as controlled ventilation (efficiency is determined in terms of CO2 elimination and fresh gas utilization)

g) Adaptability for adults, children and mechanical ventilators

h) Provision to reduce theatre pollution

Dripps classification

• It is based on rebreathing, presence or absence of reservoir, CO2 absorption & directional valves.

• Insufflation system – gases are delivered directly into the patient’s airways, no reservoir bag, no valves, no CO2 absorber – open drop method

• Open type – gases are directed to the patient from anesthesia machine, and valves direct exhaled gases to the atmosphere – intermittent flow machines, systems with non rebreathing valves

• Semiopen type – mixing of inspired and expired gases occur and rebreathing depends on fresh gas flow.

• No CO2 absorber – Mapleson systems• Semiclosed system – part of the exhaled gases go

out to the atmosphere, part of it gets mixed with inspired gases and is rebreathed. CO2 absorber is present

• Closed system – complete rebreathing of expired gas. CO2 absorber is present.

Breathing system without CO₂ absorption Breathing system with CO₂ absorption

Unidirectional flow1. Non-rebreathing Valve.2. Circle Systems.

Unidirectional Flow• Circle system with Absorber

Bi Directional Flowa) Afferent Reservoir Systems

• Mapleson A• Mapleson B• Mapleson C• Lack`s system

b) Enclosed Afferent Reservoir Systems• Millers (1988)

c) Efferent Reservoir Systems• Mapleson D• Mapleson E• Mapleson F &• Bain`s system.

d) Combined Systems• Humphrey ADE

Bi directional flow•To & Fro System

Breathing systems without CO2 absorber

1) Unidirectional flow• non rebreathing system

– They make use of non-rebreathing valves.– To prevent rebreathing FGF =MV.

Though it satisfies all the 4 essential requirements, still not very popular because

1) Fresh gas flow has to be constantly adjusted and is not economical.

2) There is no humidification of inspired gases.

3) There is no conservation of heat

4) The valve is bulky and has to be placed close to the patient.

5) Malfunctioning of the valve can occur due to condensation of moisture.

6) Can be noisy at times.

7) Cleaning and sterilization is somewhat difficult

2. Bidirectional flow• E.g. Water`s canister• These are obsolete

in current anesthetic practice.

MAPLESON BREATHING SYSTEM

• In 1954 – on advice of William Mushin, Mapleson reported on functional analysis of Breathing systems.

For better understanding of functional analysis they have been classified as

1) Afferent Reservoir System (ARS)

2) Enclosed Afferent Reservoir System

3) Efferent Reservoir System

4) Combined System

The efficiency of a system is determined in terms of CO₂ elimination & FGF utilization.

• Afferent limb is that part of the breathing system which delivers the fresh gas from the machine to the patient.

• If the reservoir is placed in this limb as in Mapleson A, B, C and Lack’s systems they are called as afferent reservoir system.

• Efferent limb is that part of the breathing system which carries the expired gas from the patient and vents it to the atmosphere through the expiratory valve/port.

• If the reservoir is placed in this limb as in Mapleson D, E, F and Bain systems they are called efferent reservoir system

• For spontaneous ventilation in the order of efficiency – ADCB (All Dogs Can Bite).

• For controlled ventilation – DBCA (Dead Bodies Can’t Argue)

• Here D includes E, F and Bain`s system

Mapleson postulates (1954)

• Mapleson has analyzed these bi-directional flow systems & few basic assumptions have been made which are of historical interest.

• Gases move En-bloc i.e they maintain their identity as fresh gas, dead space gas & alveolar gas. There is no mixing of these gases.

• Reservoir bags continues to fill up, without offering any resistance till it is full.

• The expiratory valve opens as soon as the reservoir bag is full & pressure inside the system goes above the atmospheric pressure.

• The valve remains open throughout the expiratory phase without offering any resistance to gas flow & closes at the start of next inspiration.

Mapleson A/Magill’s system

• Originally described by Evan Magill.

• Length of breathing tube 110-180 cms.

• FGF from machine end.

• APL close to patient.• Sampling ports to be

placed between APL valve & the tube.

• Spontaneous Breathing

3 phases identified

• Inspiratory • Expiratory

• Expiratory Pause.

• To prevent rebreathing FGF=MV is advised.

• FGF = 70 ml/kg/min is recommended.

• Extremely efficient system for spontaneous ventilation.

Function

• mapelsonA.swf

Controlled Ventilation

• These systems are inneficient for controlled ventilation.

• FGF >20L/min required for CO₂ elimination.

• This system cannot be used in patients less than 30kgs.

Lack system

• Co-axial Mapleson A.• Outer tube 30mm in

diameter.• Inner tube 14mm in

diameter.• APL valve placed near

patients end.

Function

Testing for Leaks in Magills & Lacks

Magill – tested for leaks by occluding the patient end & closing valve & pressurizing the system.

• Opening the APL valve will conform proper functioning of the component.

• In addition the user or patient should breathe

through the system to rule out block.

Lack – tested same as for Mapleson A with testing integrity of inner tube.

• ET tube is attached to inner tube & valve is closed. Air is blown. If leak is present, excursions will be seen in the reservoir bag.

• Occlude both the limbs with APL valve open,

squeeze the bag. Any leak is confirmed by release of gas from APL valve.

Mapleson B system

• This circuit functions similarly during both spontaneous & controlled ventilation.

• FGF > 2x Min Volume used for both spontaneous & controlled ventilation.

Mapleson C system

• Also called as Westminster face piece

• FGF > 2 x Min Volume for both Spontaneous & controlled.

• Used for short periods during transportation of patient.

Enclosed Afferent Reservoir System

• Described by Miller & Miller.• Consists of Mapleson A system

enclosed within a non-distensible structure

• Spontaneous ventilation variable orifice kept open, behaves like Mapleson A.

• Controlled ventilation variable orifice partially closed.

• It is more efficient than Bain`s system when FG is > than Alveolar Ventilation.

Efferent Reservoir System

• Mapleson D,E,& F systems, all have a T piece in common.

• T piece is 3 way tubular connector, 1cm in diameter & 5cm in length.

• It has 3 ports 1. To Patient2. The expiratory Port.3. Fresh Gas Port.• FGF = PIFR has been used to

prevent air dilution.

Bain modification of Mapleson D system

• Originally modified by Bain & Sporel in 1972.

• Is co-axial system.• Usual length is 180cm.• Outer tube

– Diameter -22mm.– Carries exhaled gas.

• Inner tube – Diameter-7mm.– Carries fresh gas.

Spontaneous Ventilation

• FGF of atleast 1.5-3 times MV is advised to prevent rebreathing.

• Based on body wt. 200 ml/kg/min flow has been recommended.

Controlled Ventilation

• FGF to maintain normocarbia is advised to be around 70ml/kg/min.

• Most efficient among the Mapleson Systems.

Recommendations by Bain & Sporel

• 2L/min FGF in patients <10kg.

• 3.5L/min FGF in patients between 10-50 kg.

• 70ml/kg/min FGF in patients more than 60kg.

• Tidal volume to be set at 10ml/kg.

• Respiratory rate at 12-16 breaths/min.

Advantages of Bains circuit1) light weight2) convenient to use3) easily sterilized and reusable4) scavenging of exhaled gases is facilitated5) exhaled gases in the outer tubing add warmth tothe inspired gases6) a long corrugated tubing with an aluminium APL

valve may be used to ventilate a patient undergoing MRI

Testing –

For the integrity of the inner tube1) Set a low flow of O2 on the flow meter and

occluding the inner tube (with a finger or the barren of a small syringe) at the patient end while observing the flowmeter indicator.

• If the inner tube is intact and correctly connected, the indicator will fall.

2) Pethick’s test – • High flow O2 is fed into the circuit while the

patient end is occluded until the bag is filled.• The patient end is opened and simultaneously

‘O2 flush’ is activated. • If the inner tube is intact, the Venturi effect

occurring at the patient end, causes a decrease in pressure within the circuit and the reservoir bag deflates.

• Conversely if there is a leak in the inner tube, gas escapes into the outer tube and the reservoir bag remains inflated

Mapleson E system

• Modification of Ayre`s T Piece.• Used initially for pediatric patients

undergoing palate repair & intracranial surgery.

• Minimal dead space, no valves, v.little resistance.

• Volume of expiratory limb > Pts tidal volume to prevent air dilution.

• Used in children weighing 25-30kg.

• Sampling port is between expiratory port & tubing.

• FGF > 3 times min. volume

Problems with this system are

1) Air dilution of the expiratory limb is short.

2) High fresh gas flow is required to prevent rebreathing and air dilution.

3) During controlled ventilation feel of the bag is not there and hence hazard of ‘barotrauma’ is a possibility.

• Used to administer O₂ for spontaneously breathing patients in ICU.

Mapleson F system(JACKSON-REES)

• T piece arrangement with a reservoir bag.• Relief mechanism is either an adjustable valve

at end of bag or a hole on side of Bag.• Newer modification incorporates APL valve

before the reservoir bag. • Pressure relief is actuated at 30cms of water.• FGF = 2-3 x MV for spontaneous respiration.• FGF = Bain`s for controlled respiration.

1) light weight 2) simple construction3) inexpensive4) minimal resistance5) minimal dead space6) controlled ventilation is

easily done7) scavenging is easily

facilitated.

Hazards

1) lack of humidification2) need for high fresh gas flows3) occlusion of relief valve can increase the

airway pressure, producing barotraumas

Advantages of Mapleson systems

1) the equipment is simple, inexpensive and rugged.

2) components can be easily disassembled and can be sterilized.

3) the systems provide buffering effect so that variations in minute volume affect end tidal CO2 less than in a circle system

4) rebreathing will result in retention of heat and moisture

5) resistance is within the recommended ranges

6) light weight and not bulky

7) do not cause excessive drag on ET tube

8) easy to position conveniently.

9) compression & compliance losses are less with these systems than with circle systems.

10) Changes in fresh gas concentration result in

rapid changes in inspiratory gas composition

Disadvantages

1) require high gas flows, higher costs, increased atmospheric pollution.

2) optimal fresh gas flow may be difficult to determine. Necessary to change fresh gas flows when changing from spontaneous to controlled mode.

3) anything that causes decreased fresh gas flow can produce dangerous rebreathing

4) in Mapleson A, B and C system the APL valve is close to the patient end and may be inaccessible.

5) Mapleson E and F are difficult to scavenge.

6) These are not suitable for patients with Malignant Hyperthermia because it may not be possible to increase the fresh gas flow enough to remove the increased CO2 load.

Combined systems• Designed by Humphrey D, Brock

& Downing.• Has 2 reservoirs,

– Afferent– Efferent.

• While in use, only 1 reservoir functions.

• Lever helps in switch over function.

• Can be used in adults as well as in children.

• Not yet widely used.

REFERENCES:• Dorsch J.A, Dorsch S.E. Understanding Anesthesia

Equipment; 4th edition• Ward C S. Anaesthetic Equipment; 2nd edition.• Eisenkraft JB, Ehrenwerth J. Anesthesia Equipment. 1st

edition• Ravishankar M. Man and the Machine – Anesthetic

Breathing Systems• Barasch PG, Cullen BF, Stoelting RK. Clinical

Anesthesia. 5th edition.• Wylie and Churchill Davidsons. A practice of

anesthesia. 5th edition.• RACE 2008- Breathing Circuits by Dr M R Shankar.