Anesthesia breathing systems

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Anesthesia Breathing Systems
Prof. Karen Haddock, CRNA

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 Purpose
 To deliver anesthetic gases and oxygen
 Offer a means to deliver anesthesia without significant increase in
airway resistance
 To offer a convenient and safe method of delivering inhaled
anesthetic agents

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 Basic Principles
All anesthesia breathing systems have 2
fundamental purposes
 Delivery of O2/Anesthetic gases
 Elimination of CO2 (either by washout with
adequate fresh gas flow (FGF) or by soda lime
absorption)

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Resistance to flow can be minimized by:
 Reducing the circuit’s length
 Increasing the diameter
 Avoiding the use of sharp bends
 Eliminating unnecessary valves
 Maintaining laminar flow

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Classifications (controversial)
Traditional attempts to classify circuits combine functional aspects (eg,
extent of rebreathing) with physical characteristics (eg, presence of
valves)
Based on the presence or absence of
A gas reservoir bag
Rebreathing of exhaled gases
Means to chemically neutralize CO2
Unidirectional valves

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Classifications
Open
Semiopen
Semiclosed
Closed

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Classifications
Open
No reservoir
No rebreathing
No neutralization of CO2
No unidirectional valves

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Classifications
Open
Nasal cannula
Open drop ether
Think of it as anything where there is NO
rebreathing and NO scavenging

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Classifications
Semiopen
Gas reservoir bad present
NO rebreathing
No neutralization of CO2
No unidirectional valves
Fresh gas flow exceeds minute ventilation
Examples include
 Mapleson A, B, C, D
 Bain
 Jackson-Rees

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Non-rebreathing circuits
 Mapleson – 1954
 Mapleson D still commonly used
 Mapleson F is better known as Jackson-Rees
 Modified Mapleson D is also called Bain
 Used almost exclusively in children
 Very low resistance to breathing
 The degree of rebreathing is influenced by method of ventilation
 Adjustable overflow valve
 Delivery of FGF should be at least 2x the minute volume

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Non-rebreathing Circuits
 All non-rebreathing (NRB) circuits lack unidirectional valves
and soda lime CO2 absorption
 Amount of rebreathing is highly dependent on fresh gas
flow (FGF)
 Work of breathing is low (no unidirectional valves or soda
lime granules to create resistance)

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How do NRB’s work?
During expiration, fresh gas flow (FGF) pushes
exhaled gas down the expiratory limb, where it
collects in the reservoir (breathing) bag and opens
the expiratory valve (pop-off or APL).
The next inspiration draws on the gas in the
expiratory limb. The expiratory limb will have less
carbon dioxide (less rebreathing) if FGF inflow is
high, tidal volume (VT) is low, and the duration of the
expiratory pause is long (a long expiratory pause is
desirable as exhaled gas will be flushed more
thoroughly).
All NRB circuits are convenient, lightweight, easily
scavenged.

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 Mapleson
 Used during transport of children
 Minimal dead space, low resistance to breathing
 Disadvantages
 Scavenging (variable ability)
 High flows
 Lack of humidification/heat
 Possibility of high airway pressures and barotrauma

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FGF
FGF
FGF
FGF
FGF
FGF
Mapleson Circuits
MaskBreathing
Bag
Press-relief
valve
Press-relief valve
Press-relief
valve
Breathing
Bag
Press-relief valve

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Mapleson Components
 Breathing Tubes
Corrugated tubes connect components of
Mapleson to pt
Large diameter (22mm) creates low-resistance
pathway for gases & potential reservoir for
gases
Volume = or > TV to minimize FGF requirements
 Fresh Gas Inlet (position will determine type of Mapleson performance)

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Mapleson Components
 Pressure-Relief Valve (Pop-Off Valve, APL)
If gas inflow > pt’s uptake & circuit uptake =
press buildup (out via scavenger)
APL fully open during spontaneous ventilation
APL partial closure while squeezing breathing
bag
 Breathing Bag
Reservoir Bag of gases
Method of generating positive pressure
ventilation

Mapleson A
Mapleson A
 Since No gas is vented during expiration, high
unpredictable FGF (> 3 times minute ventilation) needed
to prevent rebreathing during mechanical ventilation
 Most efficient design during spontAneous ventilation
since a FGF = minute ventilation will be enough to
prevent rebreathing)

Mapleson A (Magill) System
 The Mapleson A or Magill system is good for
spontaneous breathing patients, so the fresh gas flow
can be lower. However as the APL valve is close to
the patient, it is regarded by many as difficult to use.
1950’s

Mapleson A (Lack) System
 The Mapleson A or Lack system is a modification of
the Magill where the valve is moved to the machine
end of the system using another length of tubing. This
adds volume to the system and makes it rather heavy
at the patient end.
1976

+Mapleson D
FGF forces alveolar gas away from pt toward APL
valve
It requires very high fresh gas flows to prevent
rebreathing of CO2
Efficient during ControlleD Ventilation
FGIAPL
valve

+Mapleson F (Jackson Rees Modification)
 The Mapleson F or Jackson
Rees modification of the Ayres
T Piece is a basic system for
use with very small patients. It
is a big disadvantage that you
cannot remove waste gases
safely.
 Because this has a bag with an
open tail, it is technically a
Jackson-Rees Modification
system
Ayres – 1937
JR - 1950

Mapleson C Bagging System
 The Mapleson C is more
than an anesthesia
system. It can be found all
over the hospital for use
as an emergency bagging
system for resuscitation or
manual ventilation using
oxygen, as well as being a
standard induction system
in some countries.

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Bain system
 Coaxial version of Mapleson D
 Fresh gas enters through narrow inner
tube
 Exhaled gas exits through corrugated
outer tube
 FGF required to prevent rebreathing:
 200-300ml/kg/min with spontaneous
breathing (2 times VE)
 70ml/kg/min with controlled
ventilation
1972

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Bain at work (spontaneous)
 Spontaneous: The breathing system should be filled with
FG before connecting to pt. During inspiration, the FG
from the machine, the reservoir bag and the corrugated
tube flow to the pt.
 During expiration, there is a continuous FGF into the
system at the pt end. The expired gas gets continuously
mixed with the FG as it flows back into the corrugated
tube and the reservoir bag. Once the system is full, the
excess gas is vented to the scavenger.
 During the expiratory pause the FG continues to flow
and fill the proximal portion of the corrugated tube while
the mixed gas is vented through the valve.

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Bain at work (spontaneous)
 During the next inspiration, the pt breaths FG as well as the
mixed gas from the corrugated tube. Many factors influence
the composition of the inspired mixture (FGF, resp rate,
expiratory pause, TV and CO2 production in the body). Factors
other than FGF cannot be manipulated in a spontaneously
breathing pt.
 It has been mathematically calculated and clinically proved
that the FGF should be at least 1.5 to 2 times the patient’s
minute ventilation in order to minimize rebreathing to
acceptable levels.

Bain at work (controlled)
 Controlled: To facilitate intermittent positive pressure ventilation,
the APL has to be partly closed so that it opens only after sufficient
pressure has developed in the system. When the system is filled
with fresh gas, the patient gets ventilated with the FGF from the
machine, the corrugated tube and the reservoir bag.
 During expiration, the expired gas continuously gets mixed with the
fresh gas that is flowing into the system at the patient end.
 During the expiratory pause the FG continues to enter the system
and pushes the mixed gas towards the reservoir.

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Bain at work (controlled)
 When the next inspiration is initiated, the patient gets ventilated
with the gas in the corrugated tube (a mixture of FG, alveolar
gas and dead space gas).
 As the pressure in the system increases, the APL valve opens
and the contents of the reservoir bag are discharged into the
scavenger.

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Bain
Advantages
 Warming of fresh gas inflow by surrounding
exhaled gases (countercurrent exchange)
 Improved humidification with partial rebreathing
 Ease of scavenging waste gases
 Overflow/pressure valve (APL valve)
 Disposable/sterile

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Bain
Disadvantages
 Unrecognized disconnection
 Kinking of inner fresh gas flow tubing
 Requires high flows
 Not easily converted to portable when commercially used
anesthesia machine adapter Bain circuit used

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Bain is a Modified Mapleson D

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Classifications
Semiclosed
A type of “circle system”
Always has a gas reservoir bag
Allows for PARTIAL rebreathing of exhaled
gases
Always provides for chemical neutralization of
CO2
Always contains 3 unidirectional valves
Fresh gas flow is less than minute ventilation
Examples: The machine we use everyday!

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Classifications
Closed
 Always has a gas reservoir bag
 Allows for TOTAL rebreathing of exhaled gases
 Always provides for chemical neutralization of CO2
 Always contains unidirectional valves
 We don’t use these….Suffice to say you can do this
with the machines we have now if you keep your
fresh gas flow to metabolic requirements around
150ml/min

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Optimization of Circle Design
 Unidirectional Valves
 Close to pt to prevent backflow into inspiratory limb if circuit leak
develops.
 Fresh Gas Inlet
 Placed between absorber & inspiratory valve. If placed downstream
from insp valve, it would allow FG to bypass pt during exhalation
and be wasted. FG placed between expiration valve and absorber
would be diluted by recirculating gas

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Optimization of Circle Design
 APL valve
 Placed immediately before absorber to conserve absorption
capacity and to minimize venting of FG
 Breathing Bag
 Placed in expiratory limb to decrease resistance to exhalation. Bag
compression during controlled ventilation will vent alveolar gas thru
APL valve, conserving absorbent

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Circle system can be:
 closed (fresh gas inflow exactly equal to patient uptake,
complete rebreathing after carbon dioxide absorbed, and
pop-off closed)
 semi-closed (some rebreathing occurs, FGF and pop-off
settings at intermediate values), or
 semi-open (no rebreathing, high fresh gas flow)

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 Circle systems
 Unidirectional valves
 Prevent inhalation of exhaled gases until they have passed
through the CO2 absorber (enforced pattern of flow)
 Incompetent valve will allow rebreathing of CO2
 Hypercarbia and failure of ETCO2 wave to return to baseline
 Pop off (APL) Valve
 Allows pressure control of inspiratory controlled ventilation
 Allows for manual and assisted ventilation with mask, LMA, or
ETT

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Circle systems
Most commonly used
Adult and child appropriate sizes
Can be semiopen, semiclosed, or closed
dependent solely on fresh gas flow (FGF)
Uses chemical neutralization of CO2
Conservation of moisture and body heat

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Circle system
Allows for mechanical ventilation of the
lungs using the attached ventilator
Allows for adjustment of ventilatory
pressure
Is easily scavenged to avoid pollution of OR
environment
Low FGF’s saves money

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 Advantages of rebreathing
 Cost reduction (use less agent and O2)
 Increased tracheal warmth and humidity
 Decreased exposure of OR personnel to waste gases
 Decreased pollution of the environment
 REMEMBER that the degree of rebreathing in an anesthesia
circuit is increased as the fresh gas flow (FGF) supplied to the
circuit is decreased

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Dead space
 Increases with the use of any anesthesia system
 Unlike Mapleson circuits, the length of the breathing tube of
a circle system DOES NOT directly affect dead space
 Like Mapleson’s, length DOES affect circuit compliance
(affecting amount of TV lost to the circuit during mech vent)
 Increasing dead space increases rebreathing of CO2
 To avoid hypercarbia in the face of an acute increase in dead
space, a patient must increase minute ventilation
 Dead space ends where the inspiratory and expiratory gas
streams converge

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Carbon dioxide neutralization
 Influenced by
 Size of granules
 Presence or absence of channeling in the canister (areas of loosely
packed granules, minimized by baffle system)
 Tidal volume in comparison to void space of the canister
 Ph sensitive dye
 Ethyl violet indicator turns purple when soda lime exhausted (change
when 50-70% has changed color)
 Regeneration: Exhausted granules may revert to original color if
rested, no significant recovery of absorptive capacity occurs

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 Carbon dioxide neutralization
 Maximum absorbent capacity 23-26L of CO2/100g granules
 Granules designated by Mesh size (4-8 mesh)
 A compromise between higher absorptive surface area of small
granules & the lower resistance to gas flow of larger granules
 Toxic byproducts
 The drier the soda lime, the more likely it will absorb & degrade
volatile anesthetics

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Disadvantages of Circle System
 Greater size, less portability
 Increased complexity
 Higher risk of disconnection or malfunction
 Increased resistance
 Dissuading use in Pediatrics
 Difficulty of predicting inspired gas concentration during low
fresh gas flow

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Airway Humidity Concerns
 Anesthesia machine FGF dry and cold
 Medical gas delivery systems supply dehumidified gases at room
temp.
 Exhaled gas is saturated with H2O at body temp
 High flows (5 L/min)  low humidity
 Low flows (<0.5 L/min)  allow greater H2O saturation
 Absorbent granules: significant source of heat/moisture
(soda lime 14-19% water content)
 Normal upper airway humidification bypassed under
General Anesthesia
 Passive heat and humidity (“Artificial Nose”)
 Active heat and humidity (electrically heated humidifier)

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Bacterial Contamination
 Slight risk of microorganism retention in Circle system that
could (theoretically) lead to respiratory infections in subsequent
pts
 Bacterial filters are incorporated into EXPIRATORY LIMB of the
circuit

Mode Reservoir Rebreathing Example
Open No No Open drop
Semi-open Yes No Nonrebreathing
circuit or
Circle at high
FGF (>VE)
Semi-closed Yes Yes, partial Circle at low FGF
(<VE)
Closed Yes Yes, complete Circle (if APL
valve closed)

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Reference
Morgan, G. E., Mikhail, M. S.,
Murray, M. J., & Larson, P. C. ,
(2013). Clinical anesthesiology (4rd
ed.). New York: The McGraw-Hill
Companies, Inc..
Stoelting, R. K., Miller, R. D. ,(2007).
Basic of Anesthesia (5th ed.). New
York: Churchill Livingstone Elsevier,
Inc.
(2011). MemoryMaster. Des
Moines:

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