The Anaesthesia Machine - 1
Presented by- Dr. Vineet Chowdhary
Moderator- Dr. Avnish Bharadwaj
NO EQUIPMENT IS MORE INTIMATELY
ASSOCIATED WITH THE PRACTICE OF
ANAESTHESIOLOGY THAN THE
An anesthesia workstation integrates most of the
components necessary for administration of anesthesia
into one unit
It is a device which delivers a precisely-known but
variable gas mixture, including anaesthetizing and
The anesthesia machine
Added to this may be drug delivery systems,
suction equipment, and a data management system
The original concept of Boyle's machine was invented
by the British anaesthetist H.E.G. Boyle in 1917
1920 – A vapourizing bottle is incorporated
to the machine.
1926 – A 2nd vaporizing bottle and by-pass
controls are incorporated.
1930 – A Plunger device is added to the
1933 – A dry-bobbin type of flowmeter is
1937 – Rotameters displayed dry-bobbin
type of flowmeters
Types of Anesthesia Machine
Intermittent-Gas flows only during inspiration
Egs: Entonox apparatus, Mackessons apparatus
Continuous-Gas flows both during inspiration and
expiration. Egs :
Standards for Anesthesia Machines and
Standards for anesthesia machines and workstations
provide guidelines to manufacturers regarding their
minimum performance, design characteristics, and
safety requirements. During the past 2 decades, the
progression of anesthesia machine standards has been
1979: American National Standards Institute
1988: American Society for Testing and Materials,
1994: ASTM F1161-94 (reapproved in 1994 and
discontinued in 2000)
2005: International Electrical Commission (IEC)
2005: ASTM (reapproved)F1850
European standard is EN740
To comply with the 2005 ASTM F1850-00 standard, newly
manufactured workstations must have monitors that
measure the following parameters:
continuous breathing system pressure,
exhaled tidal volume,
ventilatory CO2 concentration,
anesthetic vapor concentration,
inspired oxygen concentration,
oxygen supply pressure,
arterial hemoglobin oxygen saturation
arterial blood pressure,
and continuous electrocardiogram.
The anesthesia workstation must have a
prioritized alarm system that groups the
alarms into three categories: high, medium,
These monitors and alarms may be enabled
automatically and made to function by turning
on the anesthesia workstation, or the
monitors and alarms can be enabled manually
and made functional by following a pre-use
2.Power Failure Indicator
6.Data Communication Port
1.High Pressure System
3.Low Pressure System
Master (main power) switch activates both the pneumatic
and electrical functions . On most machines, when the
master switch is in the OFF position, the only
electrical components that are active are the battery
charger and the electrical outlets
Standby position - allows the
system to be powered up
Computer-driven machines should be
turned OFF and restarted with a
full checkout at least every 24
STANDBY mode is not used for an
Most machines are equipped with a visual
and/or audible indicator to alert the
anesthesia provider to the loss of mains
The machine will usually give an indication
when mains power is lost.
Power Failure Indicator
Backup source of power for the occasional outage is
The anesthesia provider should check the battery
status during the preuse checkout procedure.
While some older anesthesia machines used replaceable
batteries, most new machines use rechargeable
It usually takes a number of hours to fully recharge a
battery after it has completely discharged.
Most modern anesthesia machines have electrical
These are intended to power monitors and other
As a general rule, these outlets should only be used
for anesthesia monitors.
Other appliances should be connected directly to mains
Next to each outlet is a circuit breaker.
There are circuit breakers for both the anesthesia
machine and the outlets .
When a circuit breaker is activated, the electrical
load should be reduced and the circuit breaker reset
Data Communication Ports
Most modern anesthesia machines have
data communications ports.
These are used to communicate between
the anesthesia machine, monitors, and
the data management system
Gases are supplied under tremendous pressure for the
convenience of storage and transport.
The anaesthesia machine receives medical gases from a
gas supply; controls the flow of desired gases
reducing their pressure, to a safe level.
So the pressure inside a source ( cylinder or pipeline
) must be brought to a certain level before it can be
used for the purpose of ventilation.
And it needs to be supplied in a constant pressure,
otherwise the flow meter would need continous
This is achieved by bringing down the pressure of a
gas supply in a graded manner with the help of three
pressure reducing zones .
Thus the pneumatic part of the machine can be
conveniently divided into three parts- high
,intermediate and low pressure systems
• Consists of:
– Hanger Yolk
– Check valve
• Usually not
supply is off
Hanger Yoke Assembly
The Hanger yoke assembly
1) Orients and supports the cylinder
2) Provides a gas-tight seal
3) Ensures uni-directional gas flow
The workstation standard recommends that
there be at least one yoke each for
oxygen and nitrous oxide.
If the machine is likely to be used in
locations that do not have piped gases,
it is advisable to have a double yoke,
especially for oxygen.
It is threaded into the frame of the machine.
It provides support for the cylinder(s).
Commonly the swinging gate type is used.
When a cylinder is mounted onto or removed from a
yoke, the hinged part can be swung to side.
It is threaded into the distal end of the yoke.
Tightening the screw presses the outlet of the
cylinder valve against the washer and the nipple so
that a gas tight seal is obtained.
The cylinder is then supported by the retaining screw,
the nipple, and the index pins.
The conical point of the retaining screw is shaped to
fit the conical depression on the cylinder valve.
It is a part of the yoke
through which the gas
enters the machine.
It fits into the port of
the cylinder valve.
If it is damaged, it may
be impossible to obtain a
tight seal with the
These are situated below the nipple.
These help to prevent mounting of incorrect cylinder
The holes into which the pins are fitted must be of a
If they extend too far into the body of the yoke, it
may be possible to mount a incorrect cylinder.
-cylinders are fitted with
yoke with a sealing washer
called BODOK SEAL
-it is made up of non
combustible material and
has a metal periphery which
make it long lasting.
-it should be less than
2.4mm thick prior to
-only one seal should be
use between the valve &
The wrong Cylinder may be fitted by:
1. Using extra sealing washers
2. Removing of/ Wearing of the Index Pins
3. Placing an inverted gas cylinder
It is used to prevent particulate matter from entering
It is to be placed between the cylinder and the
pressure reducing device.
Placing a Cylinder in a Yoke
1.Cylinder valves and yokes not
be contaminated with oil or
2. Persons placing a cylinder in
a yoke should always wash their
3. Pin Index Safety System pins
4.Retract the retaining screw
5. The washer is placed over the
6.The cylinder is supported by
the foot and guided into place
7. The port on the cylinder valve is guided over the nipple
and the index pins engaged in the appropriate holes
8. The retaining screw is tightened
9. Do not insert the screw in the safety relief device
10. Make certain that the cylinder is full and that there is no leak
It allows gas from a cylinder to enter the machine but
prevents gas from exiting the machine when there is no
cylinder in the yoke.
It allows an empty cylinder to be replaced with a full
one without having to turn off the `in–use` cylinder.
Prevents transfer of gas from one cylinder to the
other with a lower pressure in a double yoke.
It consists of a plunger that slides away from the
side of the greater pressure.
It is not designed to act as a permanent seal for
empty yoke and may allow small amount of gas to
As soon as a cylinder is exhausted it should be
replaced by a full one or a dummy plug.
In order to minimize losses –
Yokes should not be left vacant for extended periods
An empty cylinder should be replaced as soon as possible
An yoke plug can be used to prevent gas leak or
An empty cylinder can be left behind after closing the
A Bourdon tube is a hollow metal tube(copper alloy) bent into a
curve, then sealed on one side and linked to a clock
Safety features in Cylinder Pressure
Gauge is usually color coded.
Name and symbol of gas are written over dial.
If bourdon tube ruptures gas is vented from back side
Gauges are angled and placed in such a way that it can
be easily read by anesthetist.
Instructions like “use no oil’’ “open the valve
slowly’’ are written on the gauge
Electronic Cylinder Pressure Indicator
Light emitting diodes(LED’S)in electronic
pressure gauge indicate
Cylinder valve is close –Dark color
Cylinder valve is open –
Pressure adequate –Green
The pressure in a cylinder varies. The anesthesia
machine is fitted with devices (reducing valves,
regulators, reducing regulators, reduction valves,
regulator valves) to maintain constant flow with
changing supply pressure.
These reduce the high and variable pressure found in a
cylinder to a lower (40 to 48 psig, 272 to 336 kPa)
and more constant pressure suitable for use in an
The machine standard requires reducing devices for
each gas supplied to the machine from cylinders.
Physical Principle- A large pressure acting over a
small area is balanced by a small pressure over a
Pressure regulators have safety relief
If due to any reason there is build up of
pressure in pressure regulator then the
safety valve blow off at a set pressure of
525 k pa(70psi)
Safety features on pressure regulator
Begins at the regulated
cylinder supply source
at 45 psig includes the
pipeline sources at 50
to 55 psig and extends
to the flow control
Gas power outlet
Oxygen pressure failure
Flow control valves
MASTER SWITCH (PNEUMATIC COMPONENT )
The pneumatic portion of the master switch is located
in the intermediate pressure system downstream of the
inlets for the cylinder and pipeline supplies
The oxygen flush is usually independent of this
The master switch may be a totally electronic switch
that when activated controls the various pneumatic
components in the anesthesia machine.
When the master switch is turned off ,the pressure in
the intermediate system will drop to zero
PIPELINE INLET CONNECTIONS
It is the entry point for gases from the pipelines.
The anesthesia workstation standard requires pipeline
inlet connections for oxygen and nitrous oxide.
Most machines also have an inlet connector for air.
These inlets are fitted with threaded non
interchangeable Diameter Index Safety System (DISS)
A unidirectional (check) valve prevents reversed gas
flow from the machine into the piping system
Each pipeline inlet is required to have a filter with
a pore size of 100μm or less. The filter may become
clogged, resulting in a reduction in gas flow.
PIPELINE PRESSURE INDICATORS
Indicators to monitor the pipeline pressure of each
gas are required by the anesthesia workstation
They are usually found on a panel on the front of the
machine and may be color coded for the gases that they
The workstation standard requires that the indicator
be on the pipeline side of the check valve in the
If the indicator is on the pipeline side of the check
valve, it will monitor pipeline pressure only. If the
hose is disconnected or improperly connected, it
will read “0” even if a cylinder valve is open
If the indicator were on the machine (downstream) side
of the check valve, it would not give a true
indication of the pipeline supply pressure unless the
cylinder valves were closed. If a cylinder valve is
open and the pipeline supply fails, there will be no
change in the pressure on the indicator until the
cylinder is nearly empty.
Pipeline pressure indicators should always be checked
before the machine is used. The pressure should be
between 50 and 55 psig (345 and 380 kPa). The
indicators should be scanned repeatedly during use.
Piping is used to connect components inside the
It must be able to withstand four times the intended
Leaks between the pipeline inlet or cylinder pressure
reducing system and the flow control valve not exceed
If the yoke and pressure reducing system are included,
the leakage may not exceed 150 mL/minute.
Some machines have a gas selector switch that
prevents air and nitrous oxide from being
GAS SELECTOR SWITCH
GAS POWER OUTLET
One or more gas power (auxiliary gas) outlets may be
present on an anesthesia machine. It may serve as the
source of driving gas for the anesthesia ventilator or
to supply gas for a jet ventilator. Either oxygen or
air may be used.
The ventilator is an integral part of the modern
machine and the breathing system and is connected to
the ventilator with internal piping. Therefore, the
power outlet is not found in many anesthesia machines
One of the most serious mishaps that occurred with
early machines was depletion of the oxygen supply
(usually from a cylinder) without the user awareness.
The result was delivery of 100% anesthetic gas.
Numerous inventions have been devised to prevent this
Pressure Sensor Shut-off Valve: Datex Ohmeda
Operates in a threshold manner: either open or shut
Oxygen pressure moves the piston and pin upward and
the valve opens for N2O
When pressure of oxygen falls below preset value,
force of the valve return spring completely closes the
Oxygen Failure Protection Device: Drager
Based on a proportioning principle rather than a
Pressure of N2O falls in Propotion of decrease of
Oxygen.Total cutoff seen at <12psig.
Seat nozzle assembly connected to a spring loaded
conical tapered piston
Oxygen Supply Failure Alarm
ASTM standard specifies that whenever the oxygen
supply pressure falls below a certain threshold
(usually 30 psig), alarm must get activated within 5
seconds. It should not be possible to disable
They aid in preventing hypoxia caused by problems
occurring upstream in the machine circuitry (disconnected
oxygen hose, low oxygen pressure in the pipeline, and
depletion of oxygen cylinders)
These devices do not offer total protection against a
hypoxic mixture being delivered, because they do not
prevent anesthetic gas from flowing if there is no
flow of oxygen.
Equipment problems (such as leaks) or operator errors
(such as a closed or partially closed oxygen flow
control valve) that occur downstream are not prevented
by these devices.
They do not guard against accidents from crossovers in
the pipeline system or a cylinder containing the wrong
Second-stage Pressure Regulator
Some machines have pressure regulators in the
intermediate pressure system just upstream of the flow
Reduce the pressure further to around 26 psi (177 kPa)
for nitrous oxide and 14 psi (95 kPa) for oxygen
The purpose of this pressure regulator is to eliminate
fluctuations in pressure supplied to the flow
By reducing the pressures below the normal fluctuation
range, the flow will remain more constant.
Not all anesthesia machines are equipped with this
The oxygen flush (oxygen bypass, emergency oxygen
bypass) receives oxygen from the pipeline inlet or
cylinder pressure regulator and directs a high
unmetered flow directly to the common gas outlet.
It is commonly labeled “02+.”
On most anesthesia machines, the oxygen flush can be
activated regardless of whether the master switch is
turned ON or OFF.
A flow between 35 and 75 L/minute must be delivered.
The button is commonly recessed or placed in a collar
to prevent accidental activation.
It consists of a button and stem
connected to a spring loaded ball
.The ball is in contact with the seat
.When the button is depressed, the
ball is forced away from the seat ,
allowing the oxygen to flow to the
outlet. A spring opposing the ball
will close the valve when the button
is not depressed . Delivers oxygen
at 60 psig.
Reported hazards associated with the oxygen
Accidental activation – causing oxygen-enriched gas
mixture, anaesthetic dilution
The flush valve stuck in the ON position
Barotrauma and awareness during anesthesia
The anesthesia workstation standard requires that the
connection of the flush valve delivery line to the
common gas outlet be designed so that activation does
not increase or decrease the pressure at the vaporizer
outlet by more than 10 kPa or increase the vapor output
by more than 20%.
FLOW ADJUSTMENT CONTROL
Controls flow of gas through it’s
associated indicator by manual adjustment
of a variable orifice
Current standard requires that there be
only one flow control for each gas. It
must be adjusted or identifiable with its
Touch and colour coded
Joined to stem
Large enough to be turned easily
ROTATORY STYLE KNOBS
Oxygen knob- Fluted Profile, as large/ larger than any
other gas knob
Knobs turned counter clockwise- increase flow
Knobs turned clockwise- decrease flow
All other knobs should be round
Oxygen knobs must look and feel different than other
They should operate smoothly
Knob should not be over turned during closure because
further tightening may damage the pin/seat
Loose or worn knobs may respond to light
touch or accidental brushing
Leakage through open flow control valves
Inability to turn the knob
Failure to allow adequate gas flow
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