BREATHING_CIRCUITS POTC 2022 march.pptx

BREATHING
CIRCUITS
Dr.Sanjot Ninave

INTRODUCTION
Anaesthetic breathing systems
•link the patient to the common gas outlet of the
anaesthetic machine,
• thereby supplying a source of oxygen, anaesthetic gas /
vapour,
•and a means of removing exhaled carbon dioxide.

Ideal properties of a breathing system/circuit
• Ability to deliver a targeted
anaesthetic concentration
• Remove carbon dioxide
• Minimal apparatus dead
space
• Low resistance
• Suitable for spontaneous and
assisted ventilation
• Minimise gas flow
• Efficient (save volatile agent)
• Humidify and warm gases
• Easy to use and lightweight
• Allow scavenging of
anaesthetic gases.
• Suitable for adults and
childrens

Components of breathing system:

Components of breathing system:
It primarily consists of
a) 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 bag to meet peak
inspiratory flow requirements

RESERVOIR BAGS
• Composition: Rubber, synthetic latex, neoprene.
• Ellipsoidal in shape.
• Available in sizes 0.5L to 3L.
• A normal size adult bag holds a volume exceeding the
patients inspiratory capacity.

Functions :
As Reservoir
i. It allows gas to accumulate during exhalation.
This provides a reservoir of gas for next inspiration.
This permits rebreating which allows more economical
use of gases,
ii. It provides a means whereby ventilation may be
assisted or controlled.
iii. It can serve through visual & tactile observation as a
monitor of patients spontaneous respiration.

Breathing Tubes
1. Made of plastic or rubber or
silicone.
2. It may be coaxial or side by side.
3. Can be impregnated with silver
to add antimicrobial effect.
4. Corrugations increase flexibility
and helps to prevent kinking.

5. Internal diameter : Adults – 22mm & Pediatric –
15mm.
6. Internal volume : 400-500ml/metre.
7. Resistance to gas flow <1mm of H₂O/liter/min
of flow.
Functions:
1. Act as reservoir in certain systems.
2. They provide connection from 1 part of system
to another

APL valve
• Expiratory valve, pressure relief valve,pop
offvalve Heidbrink valve,dumpvalve ,spill valve.
• ex- spring loaded disc and stem and seat type of
valve
• Spring loaded disc- most commonly used
• Three port – Inlet port, to patient ,Exhaust port
• Exhaust port may be open to atmosphere or to
scavenging system.

Adjustable pressure-limiting valve
Spill valve, pop-off valve, expiratory valve, relief
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 and exhaust port- latter can be
open to atmosphere or connected to the
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

Use of APL valve in spontaneous and
Controlled ventillation.
• Use
Spontaneous ventilation –
• valve is kept fully open
• Partial closing will result in CPAP
• Pressure <1cm of H2o required to open valve
Controlled ventilation
• valve is kept fully open

Classification of Breathing
Systems

• Classifications by Conway and Dripps using
the terms
• open,
• closed,
• semi-open and
• semi-closed - differed in definition, are
confusing, and are not discussed further.
Classification of Breathing Systems

Dripp etal classified as insuffulation ,open semiopen,
semiclosed, closed
taking into account presence of
• Reservoir,
• Rebreathing,
• Co2 absorption and
• Directional valves
Collin divided breathing circuits in 4 broad groups-whether
• The ambient (atmospheric ) air is allowed to enter the
system - open or semi open
• And /Or the system allows gases from it to enter the
ambient atmosphere- semiclosed and closed

Functional classification (Miller)
Breathing System with CO2 absorber
• 1.Unidirectional flow- EX circle system with absorber
• 2. Bidirectional flow ex To and fro system
Breathing System without CO2 absorber
• 1.Unidirectional flow
• a. Non rebreathing system
• b. Circle system.
• 2.Bi directional flow
• A. afferent reservoir system
• Ex Mapelson A,B,C
• Lack,s system
• B.Enclosed afferent reservoir system
• Miller”s 1988
• C. Efferent Reservoir system Ex Mapelson D E, F and Bains circuit
• D. Combined systems Ex- Humphery ADE multi circuit system

Classification of breathing systems
after Miller
1. Systems with absorption of carbon dioxide
(i) Unidirectional flow – circle system
(ii) Bidirectional flow – To-and-fro cannister

2. Systems without absorption of carbon dioxide
(i)Unidirectional flow
(a) Non rebreathing Circle system
(ii) Bidirectional flow no
(a) Simple afferent reservoir system Mapelson A
Junctional reservoir (Mapleson B and C)
(b) Enclosed afferent reservoir Millers 1988
(c) Efferent reservoir ( Mapleson D, E, F and Bains)
(d) Combined system-Humphery ADE

1.Unidirectional -NONREBREATHING
SYSTEM
• Uses non rebreathing valve
• No mixing of fresh gas and expired gas
• FGF =/> minute volume
• Disadv- FGF has to be constantly adjusted so
uneconomical
• No humidification
• Not convinient bcos- bulk of valve
• Valve malfunctioning due to codensation of
moisture

2.Bidirectional Flow system
• Extensively used
• Depend on the FGF for effective elimination of
CO2
• FGF
-No FGF-> suffocation
-Low FGF->does not eliminate CO2
-High FGF- wastage
• FGF should be delivered as near the patients
airway as possible.

• Open system: no reservoir and no rebreathing
• Ex Nasal canula , open ether mask held away from pts face
• Semi-open system: has a reservoir but no rebreathing
• Ex open ether mask held near patients face
• Semi-closed system: has a reservoir and partial rebreathing
• Ex Mapelson breathing circuits,circle obsorber with APL valve
open
• Closed system: has a reservoir and complete rebreathing.
• Ex circle system with APL valve complete closed.

OPEN SYSTEM
• Now obsolete technique.
• Anaesthetic gases are delivered directly into
patients airway.
• Inhalational agent is directly poured mask -
Schimmelbush mask ,
• Atmospheric air acts as diluent.
• Layers of guage pieces
• Inhalational Agent (Ether)
• Open drop anaesthesia

Open System
• Disadv
• lot of wastage ,uncontrolled Pollution
• Accurate conc. -can not be delivered
• Time consuming
• Guage pieces may become sodden and
increases the dead space
• Fire hazards
• Skin and eye irritation

• If a folded towel is placd over Schimmelbush mask to prevent
early escape of inhalation agent it constitutes semi open
system.
• Other gases used- Chloroform,and ethyl chloride.

SEMICLOSED CIRCUITS
• Described by by Professor W W Mapleson
• 1954
• TYPES - 6
• Type A,B,C,D,E(T piece),F (jackson-Rees
modification of the T piece)
• Because of similarity in charecteristics some
authers have classified them in 3 groups A,
BC,DEF

Non-rebreathing Circuits
• Mapleson's Classification of Non-rebreathing
Circuits

MAPLESON SYSTEM
• William Wellesley Mapleson

Functional Classification
A. Afferent reservoir system
• Ex Mapelson A,B,C
• Lacks system
B.Enclosed afferent reservoir system
• Millers 1988
C. Efferent Reservoir sysytem
• Ex Mapelson D E, F and Bains circuit
D. Combined systems Ex- Humphery ADE
multi circuit system

AFFERENT LIMB –
• Delivers the fresh gas from the machine to the patient.
• 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 –
• Expired gas from the patient and vents it to the
atmosphere through the expiratory valve/port.
• The reservoir is placed in this limb as in Mapleson D, E, F and
Bain systems they are called Efferent reservoir system

MAPLESON SYSTEM -1954 by Professor W W Mapleson.

Ex -
• The expiratory valve is separated from the
reservoir bag. (FGF – away to the expiratory
valve – Mapelson A
• FGF atleast one MV
• Aparatus dead space is minimal
• Not efficient –controlled ventilation
• FGF –close to the expiratory valve (Mapelson B,
C),the system is inefficient both during
spontaneous and controlled ventillation.

Mapleson A (Magill‘s) System
• Best for spontaneous ventillation
• Depends on FGF for CO2 washout also known as FLOW
CONTROLLED BREATHING SYSTEM
• FGF= MV
• FGF OF 51-85 ml/kg/min -no rebreathing
• No separation of inspired and expired gases.
• ETCO2 monitoring is must.
• Work of breathing is less.

Mapleson A (Magill‘s) System
• It consist of -
1. a three-way T-tube connected to the
fresh gas outlet,2. a reservoir bag and
3.a corrugated tube.
• Corrugated rubber or plastic tubing:
110-130 cm in length.
• Volume = 550 ml
• Reservoir Bag at Machine end.
• APL valve (spring loaded) at the
patient end.
Therefore usually FGF should be
equal to or greater than MV.
~ 80ml/kg -70kg = ~6l/min.

During Spontaneous Ventilation: Magills Circuit -Type A
• Inspiration -The valve closes and the patient inspires fresh
gas from the reservoir tube.
• FG flushes the dead space gas towards patients
Expiration - The patient expires into the reservoir tube.
• The initial part of the expired gas is the dead space followed
by alveolar gas.
• Toward the end of expiration, the bag fills and positive
pressure opens the valve, allowing expired gas to escape.
Expiratory pause - FGF flushes Dead space Gas (DSG)
out of valve.
• Rebreathing-The expiratory gases which has gone back in
the tubings may be reinhaled by the patient in next breath.

During Spontaneous Ventilation:
Magills Circuit -Type A

During Controlled ventilation (IPPV)
• Inspiration - Need valve to be closed during inspiration to
stop reservoir gases leaving circuit
• Expiration - The patient expires into the reservoir bag, these
expired gases mix with the FGF and partially fill the
reservoir bag, some are vented.
• Expiratory pause - FGF mixes, mixed gases leave
• Next Inspiration - rebreathing
• It therefore requires a much high fresh gas flow in order to
prevent rebreathing. >20 l/min
• Needs FGF = 2.5 X MV to avoid rebreathing i.e. 12-
15l/min, highly inefficient

 Advantages:
• Best among all Mapleson’s
systems for spontaneous
ventilation
• Minimal wastage of gases
during spontaneous ventilation
 Disadvantages:
• Not efficient for controlled
ventilation.
• Wastage of gases & operation
theatre pollution.
• Expiratory valve required –
produces slight resistance during
expiration.
• Expiratory valve is heavy
(Heidbrink valve).
• Expiratory valve is near patient
and inconvenient to use.
• Not suitable for paediatric
use(because of increased dead
space)

Test for Mapelson A
• Occlude patient end, close APL valve,
pressurize system- maintaining pressure
confirms integrity

LACK’S MODIFICATION
• In 1976; Lack modified the mapelson A.
A co-axial modification of the Mapleson A system, designed to
facilitate scavenging of expired gas.
- APL valve at machine end
-Added expiratory limb so no mixing of gas.
- Two arrangement;
-Dual arrangement (parellel)
-Tube within tube (co-axial)
• Tube length 1.5 m
• Outer tube diameter – 30 mm
• Inner tube diameter - 14 mm
• Inspiratory capacity - 500 ml

Tube within tube (co-axial)
• A four-way block is attached to the
fresh gas outlet (F).
• This block is connected to an outer
reservoir tube (R) attached to the
patient (P), an inner exhaust tube
(E), a breathing bag (B) and a
spring-loaded expiratory valve (V).
• similar in appearance to the
modified Bain, except that the inner
exhaust tube has a greater
diameter than the fresh gas supply
tube in the modified Bain.

TESTING FOR LEAKS
A) To attach a tracheal tube to the inner tubing at the patient end of the system.
Blowing down the tube with APL Valve closed will produce movement of the
bag, if there is a leak between the two limbs.
B) To occlude both limbs at the patient end with the APL Valve open & then
squeeze the bag.
If Leak in the inner tube, gas will escape through the APL Valve & the bag will
collapse.

• Advantage:-
• Location of APL valve – facilitates IPPV/scavenging
• Disadvantages:-
• Slight increase in work of breathing.
• Break /disconnectionof inner tube- entire reservoir
tube becomes dead pace.

MAPLESON B SYSTEM
The Mapleson B system features
• The fresh gas inlet near the patient, distal to
the expiratory valve.
• The APL expiratory valve opens when pressure in
the circuit increases, and a mixture of alveolar gas
and FG is discharged.
• During the next inspiration, a mixture of retained
fresh gas and alveolar gas is inhaled.
• Rebreathing is avoided with FGF>2×MV,
•For spontaneous and controlled ventilation -Not
very efficient

MAPELSON- C SYSTEM
• Also known as Water to and fro
(Water’s Circuit)
• Similar in construction to the
Mapleson B but corrugated tubing
shorter
• FGF is equal to 2×MV 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
neither efficient during spontaneous
nor during controlled ventilation
• offers no advantage - no more used

• The Waters bag, developed by Ralph Waters, comprises a C
system with an attached soda lime absorption canister to
remove exhaled carbon dioxide, meaning that exhaled gases
can safely be rebreathed.
• Waters to-and-fro canister modified by Samson

• Afferent limb 6mm tube that supplies the FG from the
machine.
• ER systems are modifications of Ayres T piece.
• Works efficiently and economically for controlled
ventilation.

MAPLESON D SYSTEM
• Incorporates T piece at patient
• It consists of fresh gas inlet
nearer the patient end ,
• a corrugated rubber tubing one
end which is connected with
expiratory valve and
then reservoir bag.
• It is mainly used for assisted or
controlled ventilation.
• FGF required to prevent
rebreathing is 1.5-2 times M.V

Bain system (Mapleson D)
Described by Bain & Spoerel in 1972
• Modification of Mapelson D system
• Added one more tube; arranged coaxially
• Inner tube inspiratory;outer tube expiratory+inspiratory

Specifications :-
• Length-1.8 meters.
• Diameter of outer tube- 22mm
(transparent, carries expiratory gases
• Diameter of inner tubing-7 mm
(inspiratory)
• Resistance- Less than 0.7 cm H2O
• Dead space- Outer tube upto expiratory
valve( around 500ml=TV)

• For controlled ventillatiom
• 1.6 times MV
Weight
For Infants < 10kg =
2L/min
For 10-50 kg =3.5L/min
For Adults >60kg =70ml/kg
For spontaneous ventilation
2.5 times MV
200-300ml/kg/min

ADVANTAGES
• Light weight -Useful for pediatric and adult.
•less resistance
• Allows warming & humidification of gases
• Useful for spontaneous as well as controlled ventilation
• Easily dismantled; sterilised; so useful in infected cases.
• Facilitates scavenging
• Corrugated tubing is long- head and neck surgeries
• outer tube is transparent
less fire hazards as exhaled gases escapes away from machine

DISADVANTAGES
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

Checking the Bain’s circuit
1)Pethicks test - To check the integrity of the inner tube
• Flush high flow into the circuit and occlude the patient end until
the reservoir bag is filled
• The patient end is then opened and circuit is then flushed with
oxygen.
• If inner tubing is intact, the venturi effect occurs at the patient
end, causingdecrease in pressure within the circuit and bag will
deflate.
• If there is leak in inner tubing, fresh gas will escape in the
expiratory limb and the bag will inflate

• 2. If fresh gas flow is established, and the inner
tube is occluded, the flowmeter bobbins (if
present) should dip (due to back pressure) if the
inner tube is patent.
• Dorsch & Dorsch (Understanding Anesthesia Equipment 5th
ed. 2008:942)

2.Foex Crempton Smith Test
• For checking integrity of inner tube of Bain’s system, a test is performed
• by setting a low flow on the oxygen flowmeter and close APL valve
• occluding the inner tube with a finger or barrel of a small syringe at the
patient end
• while observing the flow meter indicator.
• If the inner tube is intact and correctly connected,
the indicator will fall due to back pressure.
•

For checking integrity of outer tube of Bain’s system
• By occluding the patient end and closing the APL valve the
system is pressurized.
• If no leak - Pressure will be maintained
1. Integrity of APL valve and scavenging system: - The APL
valve is then opened. The bag should deflate easily if the valve is
working properly.
2. Integrity of outer tubing: Wet the hands with spirit. Blow air
through the tube. Wipe the tube with wet hands. Leak will
produce chillness in the hands.

• Hazard of the use of the Bain circuit
• occult disconnection or kinking of the inner, fresh gas delivery hose.
• If this occurs, the entire corrugated limb becomes dead space.
• results in respiratory acidosis which is unresponsive to increased minute
ventilation.

Mapleson E OR Ayre's T- PIECE
• Ayre's T-piece Designed as a no
valve circuit for paediatrics in
1937 by Philip Ayre. (Later
classified as Mapleson E).
• Available as metallic / plastic.
• Length-5cm and Diameter-1cm.
Side arm – 6 mm
• Parts – inlet, outlet, side tube.
Flow rate : Spontaneous - 2 X MV
Controlled - 3 X MV

Mapleson E OR Ayre's T- PIECE
• Not a complete circuit as no Bag
• Hence only for spontaneous ventilation
• Controlled Ventilation-By occluding the expiratory Limb.
• Uses have decreased because of difficulties in scavenging.

T- Piece System
• The Mapelson 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

Functioning
• Fresh gas enters the system
through side arm.
• One end of the body is connected
to the patient (apparatus dead
space) and other end is connected
to the tubing which acts as
reservoir.
• System is suitable for neonates
and infants in whom expiratory
valve would produce significant
resistance.

Mapelson E or Ayre's T- PIECE
• For spontaneous ventilation,the
expiratory limb is left open.
• For controlled ventilation,the
expiratory limb is intermittently
occluded and fresh gas flow inflate the
lungs.
• Rebreathing will depend on
• the FGF,
• the volume of the expiratory limb,
• the patients minute vent.
• And the type of ventilation,i.e.spont
verses controlled.

• Spontaneous Breathing
• Inspiration-
• Since the peak inspiratory
flow rate are higher than
the FGF ,gases are drawn
from the reservoir limb.
• If the reservoir limb
capacity is less than the
tidal volume of the patient
then air dilution
occurs,converting
semiclosed system into
semiopen system (Collins
classification)
• Exhalation-
• Both exhaled and FGF passes
into reservoir limb and then to
the atmospher.
• End Expiratory Pause-FGF
flushes out and fill the reservoir
limb with fresh gases pushing
out the exhaled gases
• If the reservoir limb capacity is
more than the tital volume of
the patient and FGF are less
then rebreathing occur

SPONTANEOUS BREATHING
• Diameter of reservoir must be
sufficient to have lowest possible
resistance.
• Vol. Of reservoir limb should not be
less than the patients tidal volume.
• If RV=TV then FGF =2.5 times the
MV is required to prevent
rebreating
• If RV is less the TV then FGF is
required to be increased further .
• If Rv = 0 (no expiratory limb) than
TV then FGF must be equal to the
peak inspiratory flow rateof the
patient to prevent air dilution
CONTROLLED VENTILATION.
• Done by intermittent occluding
the resarvoir limb by thumb.
• No rebreathing and air dilution
can occur

• ADVANTAGE
• Low resistance
• Low dead space
• No valves so easy to use
• DISADVANTAGES
• Barotrauma
• No feel of bag
• No APL VALVE so no
presure buffering effect
of the bag
• Difficult for scavanging

Mapelson F
Modification of Mapleson E
by Jackson Rees -known as Jackson
Rees modification of the Ayre's T-
piece
• Two-ended bag connected to the
expiratory limb of the circuit, gas
escaping via the `tail' of the bag
• This bag helps in respiratory
monitoring

Mapleson F (OR) Jackson-Rees Modification of ayre's T- PIECE
• 500 ml bag- allows both spontaneous and controlled
ventilation,
• allows respiratory movements to be more easily seen and
• permits intermittent positive ventilation - may be performed
by occluding the tail of the bag between a finger and thumb
and squeezing the bag.
• Bags with valve are also available - To prevent over
pressurising, scavenging can be done.
• bag-tail valve', may be attached to the bag tail - which
employs an adjustable resistance to gas flow,
• This causes the bag to remain partially inflated and so
facilitates one-handed performance of IPPV.
• Use in neonates, infants, and paediatric patients less than 20 kg

Different designs of T-piece
Modern T-pieces incorporate 15 mm
fittings for the reservoir tube and
endotracheal adapter

Technique of use:
• It also functions like Mapleson D system.
FGF Requirement:
• The flows required to prevent rebreathing are 2 .5 to 3 times
minute volume during spontaneous ventilation.
• The flows required to prevent rebreathing are 1000 + 100ml/kg or
1.6 times MV during controlled ventilation.

Mapleson F (or) Jackson-Rees Modification of ayre's T- Piece
• For spontaneous
respiration.
• Relief mechanism is
completely left fully
open.
• Small movement of bag
demonstrate the pattern
and rate of breathing.
• For controlled
respirationor assisted
ventilation
• Inspiration -The hole in
the bag can be occluded
partially or completly by
user during inspiration
and ventillation is done by
sqeezing the bag.
• Expiration- the open end
is released to allow the
gas in system to escape.

Mapleson F (or) Jackson-Rees Modification of ayre's T- Piece
• Advantages of T-piece systems
• Simple and easy to assemble
(compact)
• Light weight
• Portable
• No valves
• Low resistance to breathing
• Suitable for pediatric
• Minimal dead space.
• Effective for both controlled and
spontaneous ventillation
• Inexpensive and Economical
• DISADVANTAGE
• High gas flow required.
• Wastage of gases
• It lacks humidification
• Barotrauma – occlusion of relief
valve can increase airway
pressure producing barotrauma.
• Some T-pieces are rather heavy
and difficult to keep connected to
the endo-tracheal tube
• The bag may get twisted and
impede breathing.

Relative Efficiency of rebreathing among various
Mapleson circuits
• Spontaneous Ventilation- A>D>F>E>C>B
• Controlled Ventilation- D>F>E>B>C>A
• Mapleson A - efficient during spontaneous
ventilation, but it is the worst for controlled
ventilation
• Mapleson D is most efficient during controlled
ventilation

INSUFFLATION
• The blowing of anaesthesia gas across a patients
face.
• Avoid direct connectionbet a breathing circuits
and a patients airway.
• Because children resist the placement of a
facemask or an IV line insufflation is valuable.
• CO2 accumulation is avoided with insufflation of
oxygen and air at highnflow rate (>10 L/m) under
H &H drapes at opthalmic surgery.
• Maintain arterial oxygenation during brief period
of apnea.

OPEN DROP ANESTHESIA
• open-drop anesthesia is not used in mod-ern medicine,
• its historic significance
• highly volatile anesthetic— historically, ether or chloroform—was dripped onto a
gauze-covered mask (Schimmelbusch mask) applied to the patient’s face.
• As the patient inhales, air passes through the gauze, vaporizing the liquid agent,
and carrying high concentrations of anes-thetic to the patient.
• The vaporization lowers mask temperature, resulting in moisture condensation
and a drop in anesthetic vapor pressure (vapor pres-sure is proportional to
temperature).
• A modern derivative of open-drop anesthe-sia utilizes draw-over vaporizers that
depend on the patient’s inspiratory efforts to draw ambient air through a
vaporization chamber.
• This tech-nique may be used in locations or situations in which compressed
medical gases are unavailable (eg, battlefields).

• Draw-Over Apparatus
• Draw-over systems refer to those breathing systems
in which an inhalation anesthetic is vaporized by the
patient's breathing.
• These include the original methods of administration
of inhalation anesthetics, where the agent is poured
over a pad or gauze which is then applied to the
patient's face. Such methods are obsolete,

Draw over Anaesthesia
• Nonrebreathing circuits
• Use ambient air as carrier gas.
• devices can be fitted with connections and equip-ment that allow
intermittent positive-pressure ven-tilation (IPPV) and passive
scavenging,as well as continuous positive airway pressure (CPAP) and
positive end-expiratory pressure (PEEP).
• Inspired vapor and oxygen concentrations are predictable &
controllable.
• Advantage- simple , portable.
• Disadvantage- absence of reservoir bag- not able to appreciate the
depth of TV during spontaneous ventillation.

Modern Draw-Over Systems
• The most simple form of modern
drawover system consists of two
reservoir tubes, a vaporizer and a
non-rebreathing valve:
• The patient (P) inspires and
expires via the non-rebreathing
valve (V). Air (A) enters the
system from the atmosphere and
may be supplemented with
oxygen. The tubes provide
reservoirs of oxygen (if it is being
used) and anesthetic-containing
gas.
• Most systems incorporate a
self-inflating bag (e.g. Ambu bag)
so that ventilation can be
controlled or assisted if necessary:

• Disadvantage of insufflation and drawover
system-
• Poor control of inspired gas concentration& depth
og anaesthesia.
• Inability to assist or controll ventilation.
• No conservation of exhaled heat or humidity.
• Difficult to manage airway during head and neck
surgery.
• Pollution of the operating room with large volumes
of waste gas.

COMBINED SYSTEM- HUMPREY” ADE
system
• to overcome the difficulties of changing breathing system for a
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
positionof lever.
• Use- Adult and children.
• Functional Analysis same as -MAPELSON A in ARS and as
BAIN in ERS

COMBINED SYSTEM- HUMPREY” ADE
system
• Construction
• The circuit consists of a block
with a fresh gas inlet (FG), two
breathing bag connectors (B1
and B2), an adjustable
expiratory valve (V),
connectors for the patient (P)
tubing (which may be parallel,
as shown above, or co-axial),
and a rotary selector valve,
shown here schematically in
red. Smooth-bore tubing is
used in order to reduce
resistance compared with the
normal corrugated tubing.

• The circuit to be used (i.e.
Mapleson A, D or E) is
determined by the position of
the selector valve and which
bag connector is used.
• Here, the selector valve is set
to connect the bag connector
B1 and disconnect B2. It will
be seen that the circuit is now
identical to the Magill or Lack,
except that the expiratory
valve is connected to the
patient via the expiratory limb
of the circuit.

• The selector valve is set
to connect the bag
connector B2 and
disconnect B1. The
inspiratory limb of the
patient circuit acts as
the fresh gas supply
tube, and the circuit is
now functionally a
Mapleson D.

• The selector valve is set
as above, but the bag is
removed and the
expiratory valve is
closed. The circuit is
now a Mapleson E. A
ventilator may be
attached to the bag
port in order to perform
intermittent positive
pressure ventilation.

• Function
• In each of its configurations, the circuit functions in the same way as
the conventional circuits of each type.
• Uses
• This circuit provides a convenient method of switching between
the Mapleson A and D/E arrangements.
• This makes it particularly easy to perform IPPV, making use of the
economy of fresh gas flow provided by the Mapleson A in
spontaneous breathing and the Mapleson E during IPPV.

Rebreathing Circuits
• The exhaled gases of patient through expiratory limb reaches sodalime
canister -sodalime absorb carbondioxide and the same gasas can be
reused. since same gases are in circulationthey are called as circle system.

after Miller
Types of Closed Circuit
1. Breathing System with CO2 absorber
(i) Unidirectional flow – CIRCLE SYSTEM with absorber
(ii) Bidirectional flow – TO & FRO SYSTEM-
no more used
Brian C. Sword introduced the circle (CO2 absorption) system in the
1930s

Closed Circuit
• Water’s 1923 – used in human being
• No gas escaped to atmosphere (Closed Circuit )
• Exhaled gases after absorption of Carbon dioxide are
re -inhaled by the patient.
• Same gases can be re used ,very low flows are
sufficient (low flow anaesthesia)
• Advantage – very economical
• Canister- made up of Transparent plastic material and
have capacity of 4 lb

Soda-lime
• 94% calcium hydroxide -provides
the main capacity for carbon
dioxide of soda lime,
• 5% sodium hydroxide and 1%
potassium hydroxide. - added to
accelerate the rate of
absorption.
• Moisture:14-19%-contains water
(since the carbon dioxide must be
dissolved before it can react),
• silica to preserve its
granularity.harness to prevent dust
formation
• pH sensitive dye which
indicates when exhaustion of
the soda lime is taking place,
and
• Size:4-8 mesh (or 3-6mm)
• CO2 absorption: heat generting
process .lot of Water and
Calories is produced
• 1lb canister last for 2 hours -
continous use
• 100 gm of sodalime absorb- 24-
26 liters of CO2.

Carbon dioxide absorption occurs by the following
chemical reactions:oda lime
• H2O + CO2 H2CO3 H+ + HCO3-
• NaOH + H2CO3 NaHCO3 + H2O
• 2NaHCO3 + Ca(OH)2 2NaOH + CaCO3 + H2O
• two types of soda lime in use,
• 1. turns from white to purple when it is exhausted,
• 2. changing from pink to white upon exhaustion, which may result in
confusion.
• Since the color change disappears when soda lime is left to stand, it should
be changed immediately exhaustion occurs.

Baralyme
• Baralyme may be used as an alternative to soda-
lime, containing 20% barium hydroxide and little
alkali.
• It is less dusty and the dust is less alkaline than that of
soda-lime.
• The contents of a typical soda lime canister will
provide around 8 hours of use
• and it should then be changed whether or not it has
changed color.

• Advantages of non-rebreathing systems
• Economy of anesthetic consumption.
• Warming and humidification of the inspired gases.
• Reduced atmospheric pollution.
• Disadvantages
• Poor control of the inspired anesthetic concentration, since fresh
gas delivered from the anesthetic machine is diluted by the gas
already contained within the circuit.

Circle Absorber-Construction
• essential features :
• Carbon dioxide absorber canister (C), transparent plastic
material , capacity 4lb
• Resrvoir bag (B),
• Unidirectional inspiratory (Vi) and expiratory (Ve) valves,
• Fresh gas supply (F) and
• Pressure-relief valve (V).
• absorber is connected to the patient via corrugated hoses
(Low resistance interconnecting tubing )
• Y-piece (not shown) attached to the inspiratory and expiratory
valves (Vi and Ve).
• Reservoir bag,
• The position of the breathing bag and pressure-relief valve
may vary in relation to the absorber,

Function Circle Absorber Function
• Inspiration:
• Inspiration causes the expiratory
valve to close and gas flows from
the breathing bag to the patient
via the inspiratory limb of the
circuit. Anesthetic is taken up
from the in-circuit vaporizer
(VIC), if fitted.
• Expiration:
• The inspiratory valve closes and
gas flows into the breathing bag
via the expiratory limb. Carbon
dioxide is absorbed by the soda
lime canister. Excess gas is vented
when necessary via the pressure-
relief valve.

The circle absorber may be used as a closed or semi-
closed system:
• Closed systems:
• the pressure relief
valve is closed so that
no gas escapes from the
system.
• Oxygen flows into the
system to replace that
consumed by the
patient and exhaled
carbon dioxide is
absorbed by the soda
lime.
http://www.asevet.com/res
ources/circuits/images/circf
un0.gif

• Semi- Closed systems:
• the pressure relief valve is
opened allowing excess
gas to escape from the
system. This allows higher
fresh gas flow rates to be
used.
http://www.asev
et.com/resource
s/circuits/images
/circfun1.gif

Closed systems
Advantage
anesthetic and oxygen consumption, and atmopsheric pollution, are
minimized.
Disadvantages :
• (a) the system is inherently unstable, in that if the fresh gas flow is
not matched exactly to the patient's oxygen consumption, the system
will over-fill or empty, and the patient will be unable to breathe.
• (b) the fresh gas flow rate is usually too small to allow use of a
precision, out of circuit vaporizer.

• Modern circle systems also
• have a bag/ventilator switch
• and a ventilator that is usually either a piston
driven ventilator (Dräger) or an ascending
bellows.

• For optimal function the following configuration is most
satisfactory:
• Fresh gas inlet -placed between the absorber and the inspiratory valve.
• APL valve - situated between the expiratory valve and the absorber
• Bag/ventilator switch - in the expiratory limb so that during IPPV exhaled
gas will be vented through the APL valve.
• Unidirectional valves - close to the patient to prevent backflow into the
inspiratory limb in the event of a leak in the circuit.
• Unidirectional valves not placed in the Y-piece - difficult to observe
during surgery.
• Valve malfunction - occur due to water condensation on the expiratory
valve resulting in partial obstruction to expiration and rebreathing.
• Valve malfunction - occur due to wearing of the valve seat.

• Important facts to note about circle systems:
• The one-way valves can become stuck by water vapour within the
system leading to an increase in dead space.
• The one-way valves increase the resistance to breathing in the
system.
• The lower the fresh gas flow rate, the longer it takes for changes
made to the anaesthetic gas mixture to occur.
• Monitoring the gas composition within the circle is essential.
• Use of sevoflurane at low flow rates below 1 litre/minute can
generate Compound A by reaction with soda lime.
• Nephrotoxic in rat models , no evidence of harm in humans.
• One must be familiar which the colour of the pH-sensitive dye as
different manufacturers use different colours to indicate that the soda
lime is exhausted.
• Uneven distribution of soda lime granules in the canister causes gas
to flow unevenly and reduces the efficiency of the soda lime.

ADVANTAGES
• Constant inspired concentration
• Conservation of heat & humidity
• Useful for all ages
• Useful for low flow ;reduces cost of Anaesthesia
• Low resistance
• Less OT pollution
• the ability to easily switch between spontaneous and controlled
ventilation, decreased theatre pollution,
• and a reduction in the risk of fires and explosions when using
inflammable agents such as cyclopropane and ether.

DISADVANTAGES
•Increased dead space
• Malfunctioning of unidirectional valve
• Exhausted soda lime; danger of hypercarbia.
• complexity of the system with multiple components, which
can lead to misconnections, disconnections, and leaks.
• Valves stuck in the open position can cause rebreathing,
• and sticking of the expiratory valve can result in breath
stacking and tension pneumothorax.
• The increased resistance to breathing will lead to increased
work of breathing especially in paediatrics.
• Resistance can be reduced by using circulation fans.
• Cross infection between patients , can be diminished by using
appropriate filters, or abolished by using disposable circuits

Factors affecting carbon dioxide absorption in
closed circuit
• 1. Freshness of sodalime:fresh absorbent .
• 2.Tidal volume of patient:large tidal volume
will pass without CO2 being absorbed .
• 3.High flow: allows less time for CO2
absorption.
• 4.Dead Space.
• 5.Inadequate filling of sodalime

Colour indicators of sodalime
Sr no Name Colour when fresh Colour on
exhaution
1 Ethyl violet white purple
2 Phenolpthalein white pink
3 Clyton red yellow
4 Durasorb pink white

Signs of exhaution
• tachycardia
• hypertention
• increased oozing from wound site
• increased end tidal CO2on capnography.

2.To and fro systems
• bidirectional flow systems with carbon dioxide absorption.[28]
• Waters to and fro system, is valveless and conveniently portable.
• been widely used in the past and now is only of historical importance.
• The canister is placed between the mask (ET tube) and the reservoir bag.
• Fresh gases are introduced near the face mask, so that any alteration is
immediately transferred to the patient.
• The close proximity of canister towards patient ensures minimal temperature and
humidity loss at the cost of its awkward and heavy presence.
•
• A standard canister is cylindrical and measures 8 × 13 cm.
• When filled with soda lime, the air capacity lies between 375 and 425 mL, which
may sometimes be less than the normal tidal volume.
• For the initial 90 min, the canister may perform carbon dioxide elimination
satisfactorily but becomes inefficient later on to add to dead space
• It was useful to conduct infected cases so that it can be disposed but later put to
total disuse[30,31] [Figure 9].
•

Waters to-and-fro canister modified by
Samson

Waters' Canister
Construction
• A carbon dioxide absorber canister (C) is
connected to a breathing bag (B), the fresh gas
supply (F), the patient (P) and a pressure-relief
valve (V).

Function
• Waters' Canister Function -
http://www.asevet.com/resources/circuits/images/watfun.gif
• The patient breathes to-and-fro into the
circuit. Expired carbon dioxide is absorbed
by the soda-lime. Excess gas is vented
when necessary via the pressure-relief
valve.
• One problem with the original horizontal
canister is that, unless it is tightly packed,
the soda-lime tends to settle and allow
channeling of the gas above the granules:
• http://www.asevet.com/resources/circuits/images/watfun1.gif
• This can lead to substantial rebreathing
and can be avoided by ensuring that the
soda-lime is tightly packed using a nylon
pot scrub pad. An alternative, and superior,
approach usually used in large animal
systems is to use a vertical canister so that
channeling cannot occur:

• Advantages
• Inexpensive and portable.
• Economy with low flow of oxygen
• Reduction of op room population
• Convertion of heat and humidity
• Uses
• Little used in small animals, but is still
useful for field anesthesia of large
animals, where portability of the
equipment may be a major concern
• Disadvantages
• Cumbersome
• The position of the canister close to the
patient's head is a major inconvenience.
• The to-and-fro pattern of breathing
causes the soda lime to become more
rapidly exhausted at the patient end of
the canister, leading to inefficiency in
soda-lime use and a progressive
increase in apparatus dead space.
• Channeling of gas can lead to
rebreathing with horizontal canisters.
• Expiratory valve position near the
patient end is major inconvinience
• Risk of patient inhaling sodalime.
• Risk of extubation due to weight and
poximity to patient

Non-Rebreathing Mask
• Provided with one way valves between mask
and bag, exhalation ports
• FiO2 of 95% can be achieved with an oxygen
flow rates of 10 to 15 L/min
• Ideally NRM should not allow entrainment of
air, but because of safety concerns one of the
two exhalation ports is not provided with valve

Non-Rebreathing Mask
• The non-rebreather mask covers both the nose and mouth of the patient and
attaches with the use of an elastic cord around the patient's head.
• The NRB has an attached reservoir bag, typically one liter, that connects to an
external oxygen tank or bulk oxygen supply system.
• Before an NRB is placed on the patient, the reservoir bag is inflated to greater
than two-thirds full of oxygen, at a rate of 15 liters per minute (lpm).
• Approximately ¹⁄₃ of the air from the reservoir is depleted as the patient
inhales, and it is then replaced by the flow from the O2 supply.
• If the bag becomes completely deflated, the patient will no longer have a
source of air to breathe.
• Exhaled air is directed through a one-way valve in the mask, which prevents
the inhalation of room air and the re-inhalation of exhaled air.
• The valve, along with a sufficient seal around the patient's nose and mouth,
allows for the administration of high concentrations of oxygen, approximately
60% - 90% O2.

• Ideally, a non-rebreather mask would not permit air from the surrounding
environment to be inhaled.
• However, due to safety concerns regarding anti-suffocation protection in the event
of a source gas failure (i.e. the oxygen cylinder being drained completely), one of
the two one-way valves is normally removed, allowing inhalation of outside air to a
significant degree.
• However, as almost all non-rebreathing masks are disposable, and manufactured
in one adult size, most (from decades of clinical observation) do not provide a
good seal with an individual patient's face, thus permitting the inflow of large
amounts of ambient air (most air follows the path of least resistance), and diluting
the oxygen provided.
• Hence, very few patients receive anything close to 100% oxygen.
• Very high flows (> = 30 LPM) from the oxygen flowmeter are required to partially
overcome room air dilution.
• Further, the larger the patient's inspiratory flow rate, the greater the dilution from
air.
• Very little effort is required by most patients, to inspire at flow rates in excess of 50
LPM (easily seen in the pulmonary function lab with routine spirometric testing).
•

Partial rebreather masks
• Partial rebreather masks are designed to capture
the first 150ml of the exhaled breath into the
reservoir bag for inhalation during the subsequent
breath.
• This portion of the breath was initially delivered at
the end of inhalation and was therefore delivered
to the "deadspace" anatomy where gas exchange
did not occur.
• Therefore, there would be no depletion of oxygen
nor gain of carbon dioxide during the rebreathing
component.

• Use
• The non-rebreather mask is utilized for patients with
• physical trauma,
• chronic airway limitation,
• cluster headache,
• smoke inhalation, and
• carbon monoxide poisoning, or
• any other patients who require high-concentration oxygen, but do not
require breathing assistance.
• Patients uncomfortable with having a mask on their face, such as those
with claustrophobia, or patients with injuries to the mouth are more
likely to benefit from a nasal cannula, or passive ("blow-by") oxygen.
• Patients who are unable to breathe on their own would require
invasive or noninvasive mechanical ventilation.

Advantage:
• Highest possible FiO2
without intubation
• Suitable for
spontaneously breathing
patients with severe
hypoxia
Disadvantage
• Expensive
• Require tight seal,
Uncomfortable
• Interfere with eating and
drinking
• Not suitable for long term
use • Malfunction can cause
CO2 buildup, suffocation

Resuscitation Breathing Systems
• Resuscitation breathing systems (including brand-name AMBU bags
or bag-mask units) are simple and portable systems used in
emergency scenarios or when transporting patients in need of
ventilation.
• ability to deliver nearly 100% oxygen to a patient.
• Components
• contains an inlet nipple (open to the air or connected to an oxygen
source) connected through an intake valve to a ventilation bag.
• The ventilation bag, which is self-inflating based on inherent
material memory, then delivers gas to the patient’s mask or invasive
airway via a patient valve.
• An intake valve attached to the ventilation bag closes when the bag
is compressed, allowing for positive-pressure ventilation.

AMBU
• In 1956 by Ambu
• Resuscitation bag
• Used for emergency ventilation
with or without pressurized gas
supply
• Simple,Portable,ability to deliver
100% oxygen.
• Contains Nonreabreathing valve.

• Permits both spontaneous and controlled ventilation
• Patient valve opens during inspiration
• Rebreathing prevented by venting exhaled gas to the
atmosphere through exhalation port in this valve.
• where an additional PEEP valve can be added to allow for
positive end-expiratory pressure.
• The compressible , self-refilling ventilation bag also contains
an intake valve, this valve closes during bag compression,
permitting positive pressure ventilation.
Disadvantages :
• Little tactile feedback during ventilation
• No visual indication for spontaneous ventilation.
• Requires high fresh gas flow to acheive high Fio2.
AMBU bag

Non Rebreathing Valve
• Non-rebreathing valves (NRV) ensure unidirectional flow of gases.
• During inspiration, gases flow exclusively into the patient port, while
during exhalation, they vent out through the expiratory port.
• Classification:
1.Valves designed for spontaneous respiration, e.g. Stephen Slater valve:
During inspiration, the negative pressure exerted by the patient closes the exhalation port.
During exhalation the pressure in the valve increases and gas escapes through the
exhalation port.
If this valve is to be used for controlled ventilation, it is essential to close the exhalation
port with a finger during inspiration.

2. Valvesdesignedfor controlled respiratione.g.(artificialmandatory
breathing unit) AMBU resuscitation valve:
In this type of valve, a rise in pressure opens the inlet and closes the
exhalation port.
If the patient is allowed to breathe spontaneously, room air through the
exhalation port will be inspired. Hence, it cannot be useful for general
anesthesia.
3.Valves designed for both spontaneous and controlled ventilation Ruben
valve, AMBU E, and Lewis Leigh valve can be used for both spontaneous and
controlled ventilation.
The exhalation port is closed and the inlet opens during inspiration with
either controlled or spontaneous respirations.
Only dual purpose valves are used during anesthesia

REFERENCES
1. Jerry A. Dorsch, Susan E. Dorsch. Lippincott Williams
& Wilkins, 5th edition, 2007, 121-223 pages.
2. Breathing Systems in Anaesthesia ATOTW 333 –
Breathing Systems in Anaesthesia (5th July 2016)
3.Miller DM. (1988). Breathing systems for use in
anaesthesia. BJA 60(5) 555-566.
4.Anesthesia Equipment Resource pages.

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