Anaesthesia Machine and Breathing Systems [BME]

Anesthesia Machine

Dr Umesh G

Associate Professor

Department of Anaesthesiology

KMC, Manipal

Components • Source of supply

• Yoke assembly

• Pressure gauge

• Pressure regulators

• Oxygen pressure failure safety / warning devices

• Flow meters

• Oxygen ratio control devices

• Vaporisers

• Common gas outlet

• Breathing systems

Source of supply

• Central supply – Oxygen, Nitrous oxide,

Vacuum

– Quick couplers

– Diameter index safety systems

• Cylinder – Oxygen, Nitrous oxide,

air

– Pin index

• Body

• Retaining screw

• Index pins

• Gas seal

• Filter

• Check valve

assembly

Yoke assembly

Pin index

Pressure gauge

• Bourdon type

Pressure regulators• Convert high variable pressure

from cylinder to a constant

working pressure

• Frequent adjustments not

needed

• Fine adjustment of flow possible

• Less chance of bursting of tube

and blowing up of connections

Pressure regulators

Functioning principle – Pressure regulators

A large pressure acting over a small area is balanced by a smaller pressure acting over a large area. The relative sizes of the arrows represent the magnitudes of the pressures

High pressure system

• Cylinder,

• Hanger yoke assembly (including pin

indices)

• Pressure gauge

• Pressure regulators

Intermediate pressure system

• Pipeline

• Its connections (quick couplers, diameter

index safety systems)

• Pressure gauge

• Oxygen failure safety devices

• Oxygen flush

• Second stage pressure regulators

Oxygen pressure failure safety / warning devices

• Alarm to failing O2 supply

• Cut off further N2O supply

• Slave regulators

Oxygen failure safety valve

Oxygen flush

Low pressure system - Flow meters

• Measure the flow of

gas – Thorpe tube

• Float / Bobbin

• Flow control knob

• Variable orifice type

• High flows – Density dependent,

Graham’s law

• Low flows – Viscosity dependent,

Poisseulle’s law

Oxygen ratio control device

• Link 25

Scan 182 Miller

Video clip

No 32

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Vaporisers

Breathing systems

They are the technical elements of anaesthetic machines by means of which anaesthetic gas is administered to the patient

REQUIREMENTS OF A BREATHING SYSTEM:

Essential:

The breathing system must

a) deliver the same concentration of gases to

the alveoli as set in the shortest possible time

b) effectively eliminate carbon-dioxide

c) have minimal apparatus dead space

d) have low resistance

Desirable:

The desirable requirements are

a) economy of fresh gas

b) conservation of heat

c) adequate humidification of inspired gas

d) light weight

e) convenience during use

REQUIREMENTS OF A BREATHING SYSTEM:

REQUIREMENTS OF A BREATHING SYSTEM:

f) efficiency during spontaneous as well as

controlled ventilation (in terms of CO2

elimination and fresh gas utilisation)

g) adaptability for adults, children and

mechanical ventilators

h) provision to reduce theatre pollution

Unidirectional flow

Apparatus dead space

Types of Circuits

• Mapleson systems

• Basic circle system

Components of Mapleson systems

• Reservoir bag

• Airway pressure relief valve

• Fresh gas flow

• Patient end

• Breathing conduit

Mapleson systems

Fresh gas flows ≥ minute volume

Mapleson A• FGI near bag

• Breathing tubing

• Expiratory valve near mask

• Volume of breathing tube should be as great as the tidal volume

• Spontaneous ventilation

• High FGF flushes tubing between breaths

Mapleson B

• Similar to A with FGI near expiratory valve

• System fills with FGF

• Exhaled gas forced out through expiratory

valve

Mapleson C• Similar to Mapleson B

• Shorter breathing tubing– less dead space

Mapleson D• Long breathing tube

• FGI near mask

• Exhalation valve at distal end of breathing tubing

Bain Breathing Circuit• Modified Mapleson D

• Tube within a tube– FGF tube within larger tube

• Mounts on anesthesia machine

• APL valve

• Connects to scavenger

Bain System• Advantages

– compact, easy to handle

– warming of inspired gases

– partial rebreathing improves humidification

– APL controls system pressure

– ability of scavenging

Mapleson E• Exhalation tube is reservoir

– no bag

• FGI near mask

• Current use?

Mapleson F• FGI near mask

• Breathing tubing/bag

• Expiratory valve at end of bag

• Current use?

Fresh Gas Flow

Inspiratory & Expiratory limbs

Unidirectional valves

Reservoir bag

Airway pressure relief valve

CO2 absorbent

Essential components (Circle system)

Circle System• Allows rebreathing of anaesthetic gases

– lower FGF rates– Less pollution

• Requires CO2 absorption

• Conserves heat and humidity

Advantages of Circle System• Highly efficient

• Minimal dead space

• Conserves heat and moisture

• Minimal pollution

• Disadvantage - many places to leak

CO2 Absorption

• Soda lime– 94% calcium hydroxide– 5% sodium hydroxide– 1% potassium hydroxide– silica to harden granules– ethyl violet as an indicator

CO2 Absorption

• Baralime

– 80% calcium hydroxide

– 20% barium hydroxide

– ethyl violet as an indicator

CO2 Absorption

• pH is extremely high

• Granule size

– 4 8 mesh

• Water is required for chemical reactions to

occur