Anaesthetic Equipment Guide

• Medical Gas supply
• Anaesthetic machine
• Breathing systems
• Humidification and filtration
• Airways
• Tracheal intubation equipment
• Masks and oxygen delivery devices
• Ventilators
Anaesthetic Equipment
√
√
1

Breathing systems
Chapter three
Sileshi Abiy (BSc, MSc)
Department of Anaeathesia
2

Breathing systems
• Why is this knowledge relevant?
– There are several different types of breathing circuit.
– Here in Ethiopia circle and Mapleson A/D circuits are used in large.
– There are benefits and disadvantages to any breathing system
– Knowing about the different systems will allow you to make informed
choices about which system is best for a given situation
– Also, it is important to know the limitations of the system you are
using
3

What is the ideal breathing system?
Breathing systems
Simple and safe to use
Delivers the intended gas mixture
Permits spontaneous, manual and controlled ventilation
Suitable for all age groups
Efficient (uses low gas flow rates  saves IAA)
Protects the patient from barotrauma
Compact, lightweight and durable design
Permits easy removal of waste gases
Easy to maintain
4

A few definitions
Breathing systems
Tidal volume
Minute volume
The volume of gas inspired & expired with each breath
Typically ≈7 mL / kg
(or 500 mL for 70 kg patient)
The total volume breathed in a minute
Typically ≈100 mL / kg / min
(or 7000 mL / min for 70 kg patient)
Alveolar minute volume
The volume undergoing gas exchange per minute
( = RR x [tidal vol – dead space] )
Typically ≈70 mL / kg / min
(or 5000 mL / min for 70 kg patient)
5

A few definitions
Breathing systems
Physiological dead space
The volume of inspired gas that does not undergo gas
exchange in the alveoli
Physiological dead space = anatomical dead space + alveolar dead space
Functional residual capacity
The volume of gas in the lungs at the end of expiration
volume of lung which is ventilated with
gas but not perfused with blood 
cannot take part in gas exchange
gas from upper airways, where gas
exchange does not occur
Typically ≈2 mL / kg
or 140 mL for 70 kg patient
6

A few definitions
Breathing systems
Rebreathing
Definition in anaesthesia; re-breathing is the inspiration of
gas which was exhaled and still has pCO2 = 5 kPa
So, if soda lime is used, “re-breathing” does not occur
because the inhaled gas may have been previously exhaled,
but it has had the CO2 removed
What affects rebreathing?
(1) breathing circuit design (e.g. soda lime or different configurations)
(2) the mode of ventilation (spontaneous or controlled)
(3) the fresh gas flow rate
(4) the patient’s respiratory pattern
7

Key components
Breathing systems
Y-piece to patient
Reservoir bag
APL valve
One-way valve
Soda lime
FGF (with volatile agent)
Tubing
8

Key components (cont.)
Breathing systems
The APL valve = the Adjustable Pressure Limiting valve
Also called a Heidbrink valve, spill valve, relief valve, expiratory valve
3 ports;
inlet port
patient port
exhaust port  can be open to atmosphere or to scavenging
system
In open position, < 1 cm H2O (< 0.1 kPa) required to allow gas escape
In closed position, gas can escape at 60 cm H2O (to avoid barotrauma)
10

Fig. APL valve with
spontaneous/manual changeover.
Note the pressures markings.
A: When the lever is in the spontaneous
position, the valve is fully open,
regardless of the set pressure.
B: When the lever it is placed in the
manual position, the knob is rotated to
adjust the opening pressure.
C: In the manual position, the valve can
be fully opened by pressing down on the
lever.
11

Key components (cont.)
Breathing systems
The reservoir bag
Standard adult size is 2L
Smallest paediatric bag is 500 mL
Roles of reservoir bag:
(1) Accommodates fresh gas flow during expiration
(2) Acts as a monitor of respiratory pattern (& “feel” of ventilation)
(3) Can be used to assist ventilation (hand ventilation)
(4) In a Mapleson F (Jackson-Rees modification of an Ayre’s T-piece), the
bag is double ended and acts as the expiratory outflow
(5) As bag expands, it reaches a maximal pressure of 40 cm H2O; protects
the patient from barotrauma 12

Breathing systems
(3) Circle system
(1) Mapleson systems
A
(2) Humphrey ADE breathing system
B
C
D
E & F
vaporiser out of circle (VOC) or
vaporiser in circle (VIC)
13

1. Mapleson breathing systems
Breathing systems
Mapleson introduced a classification for anaesthetic circuits in 1954
It does not include systems with internal valves or soda lime
The circuits are labeled A to F
The order is from most efficient → least efficient for a spontaneously
breathing patient
The efficiency of the circuits is defined as the fresh gas flow required to
AVOID REBREATHING
14

• Even though the components and component arrangement are
simple, functional analysis of the Mapleson systems can be complex
15
• The amount of CO2 rebreathing associated with each system is multifactorial,
and variables that dictate the ultimate CO2 concentration include :-
1. The fresh gas inflow rate,
2. The minute ventilation,
3. The mode of ventilation
(spontaneous or controlled),
4. The tidal volume,
5. The respiratory rate,
6. The inspiratory to expiratory time
ratio,
7. The duration of the expiratory pause
8. The peak inspiratory flow rate
9. The volume of the reservoir tube
10. The volume of the breathing bag
11. Ventilation by mask
12. Ventilation through an endotracheal
tube, and
13. The CO2 sampling site.

Mapleson breathing systems (cont.)
Breathing systems
Most efficient for
spontaneously
breathing patient
Least efficient for
spontaneously
breathing patient
Fresh gas flow
(FGF)
16
APL
Facemask
Reservoir bag

Breathing systems
Reservoir bag on
inspiratory limb
Transitional position of
reservoir bag
Reservoir bag on expiratory
limb
17

Breathing systems Alternative
name
Co-axial
design
Lack
Ayer’s T-
piece
Jackson-Rees
modification of an
Ayer’s T-piece
Bain
Magill
Water’s
(not used)
(not used)
(not used)
(not used)
18

Mapleson A (Magill) circuit
Breathing systems
Components:
Reservoir bag at the machine end (inspiratory limb)
Corrugated tubing (generally 110 cm or 180 cm)
APL valve at patient end
19

Breathing systems
Mode of action during
spontaneous ventilation (APL
open)
During inspiration:
• Gas inhaled from the two litre
reservoir (breathing) bag
• Bag partially collapses = visual
confirmation that breathing is
occurring
20

During expiration:
• Bag and tubing initially refilled with
combination of exhaled dead space
gas and fresh gas from machine
• Once bag is full, pressure within the
breathing system rises and APL valve
near the patient releases alveolar gas
(containing CO2)
Breathing systems
open)
21

During the expiratory pause:
• More fresh gas enters the system
driving any remaining alveolar gas out
through the valve
Breathing systems
open)
22

Breathing systems
spontaneous ventilation
• If FGF is sufficiently high, all the
alveolar gas is vented from the circuit
before the next inspiration  no
rebreathing will take place
• With careful adjustment the fresh
gas flow can be reduced until there is
only fresh gas and dead space gas in
the breathing system at the start of
inspiration.
23

Breathing systems
So, a Mapleson A is very efficient for spontaneous ventilation
In theory, FGF equal to the patient’s alveolar minute ventilation is sufficient to
prevent re-breathing
So,
a sensible FGF = 85 mL / kg / minute
or, ≈ 6 L / min for a 70 kg man
In practice, FGF closer to the patient’s total minute ventilation is usually selected (
to increase margin of safety)
for
spontaneous
ventilation
24

Breathing systems
• Inspiratory pressure is provided by
the anaesthetist squeezing the
reservoir bag after partly closing the
APL valve next to the patient
• During lung inflation some of the gas
is vented from the circuit
• At the end of inspiration the
reservoir bag is less than half full
CONTROLLED ventilation (APL?)
25

Breathing systems
CONTROLLED ventilation
• During expiration, dead space and
alveolar gas pass down the system
tubing and may reach the bag which
will then contain some carbon dioxide
• During the next inspiration, when
the bag is squeezed, alveolar gas re-
enters the patient’s lungs followed by
a mixture of fresh, and dead space gas
26
Breathing of CO2
containing gas

A FGF of two and a half times the patient’s minute volume is required to vent
enough alveolar gas to minimise rebreathing
Breathing systems
So, a Mapleson A is very inefficient for CONTROLLED ventilation
In practice, the Magill circuit should not be used for positive pressure ventilation
except for short periods of a few minutes
In theory, this would be 2.5 x 100 mL / kg / min
= 250 mL / kg / min
or 17 L / min for a 70 kg patient
27

Breathing systems
Summary:
• Efficient for spontaneous ventilation
• Very inefficient for controlled ventilation
• APL is at patient end; bulky, heavy and awkward
• Not suitable for paediatrics < 25 kg due to excessive dead
space in circuit
28

Co-axial Mapleson A (Lack) circuit
Breathing systems
• This is a Mapleson A system in which the exhaled gases travel down a
central tube located within an outer corrugated tube towards the expiratory
valve
• APL valve is placed next to the reservoir bag, by the common gas outlet
• FGF requirements are the same as for the Magills circuit (in spontaneous
and controlled ventilation)
29

Mapleson B & C
circuits
Breathing systems
B & C are similar to each
other;
FGF entry and
the expiratory valves are
located at the patient
end of the circuit
They are not commonly used in anaesthetic practice
High flows of gases are needed to prevent rebreathing of CO2
Mapleson C (Water’s) circuit is used in intensive care units, for augmenting patients’
spontaneous breaths during intubation and extubation
 typically 1.5 x minute volume, or 150 mL/kg/min
30

Mapleson D circuit
Breathing systems
Components:
Reservoir bag on the expiratory limb
Connection to FGF near to patient
APL valve away from patient on the expiratory limb
31

Mapleson D
Breathing systems
• During expiration, exhaled gas and
fresh gas mix in the corrugated tubing
and travel towards the reservoir bag
• When the bag is full the pressure in
the system rises and the expiratory
valve opens
• A mixture of fresh and exhaled gas
is vented to the atmosphere
32

Mapleson D
Breathing systems
• During the expiratory pause, fresh
gas continues to push exhaled
alveolar gas down the tubing towards
the valve
• Unless the FGF is at least twice the
patient’s minute volume, re-breathing
of alveolar gas occurs
33

Mapleson D circuit
Breathing systems
So, a Mapleson D is very inefficient for spontaneous ventilation
A FGF of two times the patient’s minute volume is required to minimise
rebreathing
This would be 2 x 100 mL / kg / min
= 200 mL / kg / min
34

Mapleson D
Breathing systems
Mode of action during CONTROLLED ventilation
• During expiration the corrugated tubing and reservoir bag fill with a
mixture of fresh and exhaled gas
• Fresh gas fills the distal part of the corrugated tube during the expiratory
pause prior to inspiration
• When the bag is compressed this fresh gas enters the lungs and when the
expiratory valve opens a mixture of fresh and exhaled gas is vented
• A FGF of about the alveolar minute volume is usually adequate for
controlled ventilation
35

Mapleson D circuit
Breathing systems
So, a Mapleson D is very efficient for CONTROLLED ventilation
A FGF of just above the patient’s alveolar minute volume is required
(the alveolar minute volume is about 70 mL / kg / min)
The FGF required is about 85 mL / kg / min
A FGF of 100ml/kg/min will result in a degree of hypocapnia (too low CO2
level in the blood)
36

Co-axial Mapleson D (Bains) circuit
Breathing systems
• Most commonly used form of the Mapleson D system
• Fresh gas flows down the central narrow bore tubing (7mm internal
diameter) to the patient
• Exhaled gases travel in the outer corrugated tubing (22mm internal diameter)
compact at
patient end; APL
valve and bag
near to machine
Functionally, the FGF is by the
patient
37

Co-axial Mapleson D (Bains) circuit (cont.)
Breathing systems
• Before use, the bain circuit should be carefully checked
• The outer tubing of a Bain circuit is made of clear plastic and the inner green
or black
• If a leak develops in the inner tubing or it becomes detached from the fresh
gas port, a huge increase in apparatus dead space occurs
• In order to check for this, the lumen of the inner tubing should be occluded
with a finger or the plunger of a 2ml syringe, demonstrating a rise in gas
pressure within the anaesthetic circuit
38

Mapleson E (Ayre’s T-piece)
Breathing systems
• Performs in a similar way to the mapleson D, but there is no APL
valve and very little resistance to breathing
• Very suitable for use with children
• Typically for kids under 25 kg
• Spontaneous ventilation only
• Requires FGF of 2 ½ x minute volume 39

Mapleson F (Jackson-Rees modification of an Ayre’s T-piece)
Breathing systems
• Jackson-rees modification is the most commonly used version of a T-piece
• An open (double-ended) bag is attached to the expiratory limb
• Movement of the bag can be seen during spontaneous breathing
• The bag can be compressed to provide manual ventilation
• Suitable for children under 25 kg
open
bag
40

Mapleson F (Jackson-Rees modification of an Ayre’s T-piece)
Breathing systems
• Fresh gas flows of 2-3 times the minute volume should be used to prevent
rebreathing during spontaneous ventilation, with a minimum flow of 3 L/min
• During controlled ventilation, normocapnia can be maintained with FGF of
(1000 ml + 100 ml/kg)/min
41

An overview of circuit efficiency
Breathing systems
Circuit
FGF for
spontaneous
ventilation
FGF for
spontaneous
lybreathing
70kg patient
FGF for
controlled
ventilation
FGF for 70 kg
patient with
controlled
ventilation
A
>alveolar minute
ventilation
(85mL/kg/min)
6 L/min
2.5 x minute
ventilation
(250mL/kg/min)
17 L/min
B 1.5 x minute
ventilation
(150mL/kg/min)
10 L/min
1.5 x minute
ventilation
(150mL/kg/min
10 L/min
C
D
2 x minute
ventilation
(200mL/kg/min)
14 L/min
>alveolar minute
ventilation
(85mL/kg/min)
6 L/min
E
2-3 x minute
ventilation
Always > 3 L
_ _
F
1000mL +100
mL/kg
n/a
42

2. Humphrey ADE breathing systems
Breathing systems
The Mapleson A circuit is inefficient for controlled ventilation
The Mapleson D circuit is inefficient for spontaneous ventilation
A Humphrey ADE circuit allows the advantages of both to be
used
A Humphrey ADE takes advantage of the properties of a
Mapleson A for spontaneous ventilation and a Mapleson D for
43

Humphrey ADE breathing systems
Breathing systems
44

Breathing systems
• Reservoir bag is situated at the fresh gas inlet end of the circuit
• Gas is conducted to and from the patient down the inspiratory and
expiratory limbs of the circuit
• Depending on the position of the control lever at the humphrey block,
gases either pass through the expiratory valve or the ventilator port
• When the lever is ‘up’ the reservoir bag and the expiratory valve are used,
creating a mapleson A type circuit
• When the lever is in the ‘down’ position the bag and valve are bypassed
and the ventilator port is opened, creating a mapleson D system for
• If no ventilator is attached and the port is left open, the system functions
like an Ayre’s T piece 45

Breathing systems
46

Breathing systems
So, the FGF rate with the Humphrey ADE are typically;
Spontaneous  Mapleson A  85 mL/kg/min
(or 6 L/min for 70 kg patient)
Controlled  Mapleson D  85 mL/kg/min
(or 6 L/min for 70 kg patient)
47

Breathing systems
• It is essential that the anaesthetist fully understands the function of this
circuit
• If the lever on the humphrey block is moved from ‘up’ to ‘down’ while gases
are flowing, the breathing bag will remain full of gas but manual ventilation of
the patient’s lungs by compressing the bag will be impossible and may
resemble complete obstruction of the breathing circuit
48

3. The circle breathing system
Breathing systems
• An alternative to using high flow circuits is to absorb CO2 from the
expired gases which are then recirculated to the patient
• This saves on gases and also on volatile anaesthetic agent
• The reaction of co2 with soda lime generates some water and
considerable heat  the gases are warmed and humidified prior to
inspiration
circle circuits are potentially very efficient and cause minimal pollution
(however, they are expensive to buy and require soda lime)
49

The circle breathing system
Breathing systems
Y-piece to patient
Reservoir bag
APL valve
One-way valve
(inspiratory limb)
One-way valve
(expiratory limb)
Soda lime
The components
PATIENT
Bag
APL valve
One-way valve
(inspiratory limb)
One-way valve
(expiratory limb)
Soda lime
50

Breathing systems
The soda lime
• CO2 is removed from the expired gas by passage through soda lime
• Mixture of 94% calcium hydroxide, 5% sodium hydroxide, and 1%
potassium hydroxide, plus silica and dye.
• It reacts with CO2 to form calcium carbonate:
CO2 + H2O → H+ + HCO3
-
Ca(OH)2 + H+ + HCO3
- → CaCO3 + 2H2O + heat
• The silica makes the granules less likely to disintegrate into powder
• The chemical dye changes colour with PH
• As CO2 is absorbed the PH decreases and the colour of the dye changes
from pink to yellow/white. 52

Breathing systems
The soda lime (cont.)
• When around 75% of the soda lime has changed colour it should be
replaced
• The soda lime canister should be mounted vertically on the anaesthetic
machine to prevent the gases passing only through a part of the soda lime
(streaming)
• Barium (barium lime) is a commercially available CO2 absorber which
contains 5% barium hydroxide instead of sodium hydroxide.
53

Breathing systems
Vaporizer position
• Placed either outside the circle (VOC) on the anaesthetic machine or (rarely) within
the circle itself (VIC)
• Normal plenum vaporisers, with high internal resistance, cannot be used within the
circle  low internal resistance type vaporiser is required
• Draw-over vaporisers are not recommended for VIC because of the risk of achieving
dangerously high levels of inhalational agent
• This is a particular danger during controlled ventilation
• VIC should only be used when inspired volatile anaesthetic agent monitoring is
available
• It is safest to use VOC with a conventional plenum vaporiser
• With VOC, the maximum volatile anaesthetic agent concentration achievable within
the circle cannot exceed that set on the vaporiser
54

PATIENT
Bag
APL valve One-way valve
(inspiratory limb)
One-way valve
(expiratory limb)
Soda lime
Consider this as a simple model:
Consider a circle circuit:
FGF in excess gas out
Volume of circle
circuit
APL
Why the Fi(volatile) is NOT the same as the concentration dialled up on
the vaporiser
55

5 L in 5 L out
5 L volume
Let the FGF = 5 L / min
and the circle circuit volume = 5 L
In one minute:
This is like diluting the circle circuit (5 L) with a further 5 L every minute
Suppose the dialed [halothane] = 1 % (the vaporiser setting)
5 L in
(1 % Hal)
5 L out
(0.5%Hal)
5 L volume + 5L
FGF
These are approximately
correct
the vaporiser
56

5 L in 5 L out
0.5% hal
So, after 1 minute:
and after 2 minutes:
5 L in 5 L out
0.75% hal
and after 3 minutes:
5 L in 5 L out
0.875% hal
the vaporiser
57

What kind of relationship is this?
Exponential ‘wash-in’ curve
So, at a FGF of 5 L/min, the halothane conc. gets to only half the
dialed conc. after 1 min…
In theory, it NEVER reaches the dialed concentration!!
1 %
time / min
Halothane
conc.
1 2 3 4 5
Why the Fi(volatile) is NOT the same as the concentration dialled up on the
vaporiser
58

NOTE:
The concentration reaching the patient will double only every 5
min at a FGF of 1 L / min
1 %
time / min
Halothane
conc.
5 10 15 20 25
the vaporiser
59

Finally:
The model above has various assumptions…
• The vaporiser is working
• The vaporiser dial is accurately calibrated
• The rotameter is accurate
• There is no significant leak from the system
So, if these are wrong…
The halothane concentration in the circuit may be even
further away from that dialed on the vaporiser…
NOTE: the above is a model – it indicates the way the system
works, but it is only an approximation
the vaporiser
60

Breathing systems
“De-nitrogenation” (getting rid of N2)
• In the same way that there is a ‘wash-in’ curve for the volatile agent,
there is a ‘wash-out’ curve for the air (mainly N2) in the circuit
• This means that the FiO2 will not be 100% for some time after the start of
an anaesthetic with 100% O2 in the FGF.
• This has practical implications for use of a circle circuit…
61

Breathing systems
Practical use
• During the first five to ten minutes of anaesthesia using a volatile anaesthetic agent
in oxygen, a large amount of the agent is taken up by the patient, causing a reduction
in the agent concentration within the system
• In addition, the total volume of the circle system (tubing and soda lime canister) is a
reservoir of air that needs to be replaced with anaesthetic agent and fresh gas
• High fresh gas flows (roughly equivalent to the patient’s minute volume) ensure that
this wash-out of air from the system and the patient’s functional residual capacity
occurs rapidly (i.E. 6-8 L/min)
62

Breathing systems
Practical use
• After 10 to 15 minutes, the fresh gas flow can be reduced
• Inspired anaesthetic gases should contain no carbon dioxide and a minimum of
30% oxygen
• Exhaled alveolar gas contains a lower concentration of oxygen and around 5%
carbon dioxide which is removed from the exhaled gas on passage through the
soda lime
• A small amount of fresh gas is added before the next breath
63

Breathing systems
Practical use
• At low fresh gas flow rates (<1000ml/min) the oxygen concentration within the circle is
unpredictable
• Circle systems should not be used at low flow rates without an oxygen analyser in the
inspiratory limb
• The lowest fresh gas flow rate of oxygen and nitrous oxide which can be used, (ensuring
that the FiO2 remains safe) is 2000ml/min (nitrous oxide 1200ml/min and oxygen
800ml/min)
• The margin of safety is far greater if only oxygen and a volatile agent is used in the circle
system  flows may be reduced to 1500ml/min under these circumstances
• With flows of ≥1500ml/min the inspired concentration of volatile agent will be similar to
that set on the vaporiser (this is not the case with flows <1500ml/min) 64

• Medical Gas supply
• Anaesthetic machine
• Humidification and filtration
• Breathing systems
• Airways
• Tracheal intubation equipment
• Masks and oxygen delivery devices
• Ventilators
Anaesthetic Equipment
√
√
√
√
65

Anaesthetic Equipment Guide

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