The most common type of anaesthetic machine in use in the developed world is the continuous flow anaesthetic machine, which is designed to provide an accurate & continuous supply of medical gases(such as O2 & NO2)mixed with an accurate concentration of anaesthetic vapour(such as halothane,isoflurane)& deliver this to the patient at a safe pressure & flow. Modern machine incorporate a ventilator,suction unit & patient monitoring devices.

1. Anaesthesia Machine
Dr. Shamsun Nahar Shanta
DA Student
Department of Anaesthesia Intensive Care and Pain Medicine
Shaheed Suhrawardy Medical college & Hospital

2. • NO EQUIPMENT IS MORE INTIMATELY ASSOCIATED
WITH THE PRACTICE OF ANAESTHESIOLOGY
THAN THE
ANAESTHESIA MACHINE

3. Introduction
• The most common type of anaesthetic machine in use in the
developed world is the continuous flow anaesthetic machine,
which is designed to provide an accurate & continuous supply
of medical gases(such as O2 & NO2)mixed with an accurate
concentration of anaesthetic vapour(such as
halothane,isoflurane)& deliver this to the patient at a safe
pressure & flow.
• Modern machine incorporate a ventilator,suction unit &
patient monitoring devices.

4. Importance of Anesthesia
machine
• Anesthesia machine use to control patient’s ventilation &
oxygen delivery & to administer inhalational anaesthetics.
• Proper functioning of the machine is crucial for patient safety.
• Much progress has been made in reducing the number of
adverse outcome arising from anaesthetic gas delivery
equipment,through redesign of equipment & machine.
• Misuse of anesthesia gas delivery system is three times more
likely than failure of the device to cause equipment related
adverse outcome.

5. Anaesthesia Workstation
• 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 life-sustaining gases.
• Consists of:
• The anesthesia machine
• Ventilator
• Breathing system
• Scavenging system
• Monitors Added to this may be drug delivery systems, suction
equipment, and a data management system

6. History
• The original concept of Boyle's machine was invented by
the British anaesthetist Henry Boyle in 1917
• 1920 – A vaporizing 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
• vaporizing bottle.
• 1933 – A dry-bobbin type of flow meter is
• introduced.
• 1937 – Rota meters displayed dry-bobbin
• type of flowmeters
• 1952- Pin index safety system
• 1958-introduction of Bodok seal

7. Why should we know about
anaesthesia machine ?
• For proper & familiar operation of machine.
• If the machine get any trouble during anaesthesia of a patient
we cannot wait for the engineer to come. Because it may
endanger the patient’s life.
• For rapid detection of any trouble.
• For quick correction of the trouble & continuing the
anaesthesia.

8. Safety features of modern
anaesthesia machine
To ensure the delivery of safe gas mixture should include the
following :
1. colour-coded pressure gauges
2. colour-coded flow meters
3. An oxygen flow meter controlled by a coded knob.
4.Oxygen is the last gas to be added to the mixture.
5. Oxygen conc. analyzer

9. Contd….safety features
6. N2O is cut-off when oxygen pressure is low.
7. O2 : N2O ratio monitor and controller
8. Pin index safety system for cylinders
9. Non-interchangeable screw thread (NIST) for pipelines.
10. Alarm for failure of Oxygen supply.
11. At least one reserve oxygen cylinder should be available on
machine that use pipeline supply.

10. Types of Anesthesia Machine
• Intermittent- Gas flows only during
inspiration
Egs: Entonox apparatus, Mackessons apparatus
• Continuous- Gas flows both during inspiration
and expiration. Egs :
• Boyle Machine
• Forregar
• Dragger

12. Basic Schematics

13. SyStem componentS
Electrical Pneumatic
1.Master Switch
2.Power Failure Indicator
3.Reserve Power
4.Electrical Outlet
5.Circuit Breakers
6.Data Communication Port
1.High Pressure System
2.Intermediate System
3.Low Pressure System

14. Electrical Components
• Master Switch
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
quickly
Computer-driven machines should be
turned OFF and restarted with a
full checkout at least every 24
hours.
STANDBY mode is not used for an
extended period.

16. 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
continuous adjustment.

17. 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

19. • Consists of:Consists of:
– Hanger YolkHanger Yolk
– Check valveCheck valve
– CylinderCylinder
PressurePressure
IndicatorIndicator
(Gauge)(Gauge)
– PressurePressure
ReducingReducing
DeviceDevice
(Regulator)(Regulator)
• Usually notUsually not
used, unlessused, unless
pipeline gaspipeline gas
supply is offsupply is off

20. 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.

24. •Bodok seal
-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
compression.
-Only one seal should be use
between the valve & yoke

25. It is used to prevent particulate matter from
entering the machine.
It is to be placed between the cylinder and the
pressure reducing device.
FILTER

26. Placing cylinder in
yoke
Placing a Cylinder in a Yoke
1.Cylinder valves and yokes not
be contaminated with oil or
grease
2. Persons placing a cylinder in
a yoke should always wash their
hands first
3. Pin Index Safety System pins
are present
4.Retract the retaining screw
5. The washer is placed over the
nipple
6.The cylinder is supported by
the foot and guided into place
manually
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

28. CHECK VALVE
ASSEMBLY

29. 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.

30. It is not designed to act as a permanent seal
for empty yoke and may allow small amount of
gas to escape.
As soon as a cylinder is exhausted it should
be replaced by a full one or a dummy plug.

31. • 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
valve

33. A Bourdon tube is a hollow metal tube(copper alloy) bent
into a curve, then sealed on one side and linked to a clock
like mechanism

34. PRESSURE REDUCING
DEVICE (REGULATOR)

35. 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
anesthesia machine.
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
larger area

36. • Pressure regulators have safety relief
valves
• 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

37. INTERMEDIATE
PRESSURE
SYSTEM
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
valve.

38. • Consists of:
• Pipeline inlet
connections
• Pipeline pressure
indicators
• Piping
• Gas power outlet
• Master switch
• Oxygen pressure failure
devices
• Oxygen flush
• Additional reducing
devices
• Flow control valves
Check valve

39. 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 switch.
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

40. 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)
fittings
 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 100 m or less. The filter may becomeμ
clogged, resulting in a reduction in gas flow.

41. PIPELINE INLET CONNECTIONS

42. PIPELINE PRESSURE
INDICATORS
Indicators to monitor the pipeline pressure of
each gas are required by the anesthesia
workstation standard.
 They are usually found on a panel on the front
of the machine and may be color coded for the
gases that they monitor
The workstation standard requires that the
indicator be on the pipeline side of the check
valve in the pipeline inlet.
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

43. 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.

44. • Piping is used to connect components inside
the machine
• It must be able to withstand four times the
intended service pressure
• Leaks between the pipeline inlet or cylinder
pressure reducing system and the flow control
valve not exceed 25 mL/minute
• If the yoke and pressure reducing system are
included, the leakage may not exceed 150
mL/minute.
PIPING

45. • Some machines have a gas selector switch
that prevents air and nitrous oxide from
being used together.
GAS SELECTOR SWITCH

46. 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 today.

47. OXYGEN PRESSURE FAILURE
DEVICES

48. 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
Oxygen Failure
Safety Device
Oxygen Supply
Failure Alarm

50. Pressure Sensor Shut-off Valve:Pressure Sensor Shut-off Valve:
Datex OhmedaDatex 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 valve

51. Oxygen Failure Protection Device: Drager
• Based on a proportioning principle rather than
a threshold principle
• Pressure of N2O falls in Proportion of
decrease of Oxygen. Total cutoff seen at
<12psig.
• Seat nozzle assembly connected to a spring
loaded conical tapered piston

52. 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 this alarm
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)

54. OXYGEN FLUSH
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.

55. It consists of a button and stem connected to a spring loadedIt consists of a button and stem connected to a spring loaded
ball .The ball is in contact with the seat .When the button isball .The ball is in contact with the seat .When the button is
depressed, the ball is forced away from the seat , allowing thedepressed, the ball is forced away from the seat , allowing the
oxygen to flow to the outlet. A spring opposing the ball willoxygen to flow to the outlet. A spring opposing the ball will
close the valve when the button is not depressed . Deliversclose the valve when the button is not depressed . Delivers
oxygen at 60 psig.oxygen at 60 psig.

56. • Reported hazards associated with the oxygen flush
include
Accidental activation – causing oxygen-enriched gas
mixture, anaesthetic dilution
The flush valve stuck in the ON position
Barotrauma and awareness during anesthesia
Internal leakage
• 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%.

57. The Flow Meter
Assembly
• The flow meter assembly controls, measures & indicate the
rate of flow of gas passing through it. The flow meter
assembly consists of :
1.Flow control valve
2.Flow meter sub assembly
The flow meter control valve control the rate of flow of a gas
through its associated flow meter by manual adjustment of
variable orifice, flow control valve also called needle valve or
pin valve. The valve mainly consists of control knob, stem &
seat.

59. CONTROL KNOBCONTROL KNOB
• Touch and colour coded
• Joined to stem
• Large enough to be turned easily

60. •Flow meter sub assembly:
This consists of the tube through which gas flows, the indicator
or bobbin or float, a stop at the top of the tube and the scale
which indicates the flow. Flow meter tubes are known as
Thrope type & are made of borosilicate glass pyrex. Imdicator
also called as rota meter or bobbin or float is present within the
flow meter tube which moves up & rotate as the gas flows into
the tube. The bobbin is made of allominium & has an upper rim
which is wider than the body. The upper rim contains slanted
flutes which make the bobbin rotate, fluroscent dot 0ver the
bobbin make its rotation obsereved easily. Sometimes the float
get stuck due to static electricity particularly in dry atmosphere,
can be reduced by spraying croxtine.

61. Low pressure system
• The low pressure system is the part of the machine
downstream of the flow meter in which the pressure is slightly
above the atmosphere. The component of this system:
1.Vapourisers
2.Back pressure safety device
3.The common gas outlet

62. Check list for anaesthesia
apparatus
• Check that that the anaesthesia machine and relevant
equipment are connected to the main electrical supply and
switched on.
• Check that all monitoring device are functioning
• Oxygen analyzer , pulse oximeter and capnograph are
functioning correctly.
• Ensure that each gas pipeline is correctly inserted.
• Check that the anaesthesia apparatus is connected to a supply
of oxygen and that an adequate reserve supply of oxygen is
available from a spare cylinder

63. Check list for anaesthesia
apparatus
• Check that adequate supply of any other gases intended
for use are available and connected
• Check the operation of flow meters , ensuring that
bobbin moves freely throughout its range.
• Check that vaporizers are fitted correctly to the
anaesthesia machine with locking mechanism fully
engaged. Check that the vaporizers are adequately filled
and the filling port is tightly closed.

64. Check list for anaesthesia
apparatus
• Check the breathing system visually and manually
• Check that the ventilator tubing is securely attached
• Check that all ancillary equipment
(facemask.LMA,Connector,Laryngoscope etc)
• Check that the suction apparatus is functioning correctly

65. Check list for anaesthesia
apparatus
• Check that the trolley or bed can be tilted head-down
rapidly
• Ensure that an alternative oxygen supply and means of
ventilation are readily available
• Document the fact that the anaesthesia machine and
equipment have been checked.

66. Check list for anaesthesia
apparatus
• Check the scavenging system
• Check the ancillary equipment is present & working
• Ensure the monitoring equipment is present, switched
on & calibrated ready for use

68. THANK YOU