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
ORMC
Oxy
gen
rat
io m
on
ito
rin
g c
on
tro
l d
evic
e
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