Safety feature of the anesthesia machine

1. DR. ZIKRULLAH

2. BOYLE’S ANAESTHETIC MACHINE
 continuous-flow anaesthetic
machine
 Pressurised gases - cylinders or
pipelines- anaesthetic
machine - controls the flow –
vaporiser -resulting mixture
delivered to the patient

3. WHY SAFETY FEATURES?
 safeguard from unknown human errors &
equipment failures.
alert the anesthesist to high risk condition .
 prevent delivery of hypoxic mixture
 prevent excessive pressure - traumatic to
patient.

4. COMPONENTS
High pressure system
Intermediate system
Low pressure system
Alternative oxygen control

5. HIGH PRESSURE SYSTEM
Gas Cylinder
Hanger Yoke
Bourdon’s pressure
gauge
Bodok seal
Pressure regulator
 Safety relief device
Check valve
assembly

6. Gas Cylinders Are Color Coded
 Colour - nonfading, durable water insoluble
 O2 : black body, white shoulders (in
USA green, in UK white)
 N2O : blue CO2 : gray
 Air : white and black
 Helium : brown
 Entonox : black , blue shoulders

7. PIN INDEX SAFETY SYSTEM
Hanger yoke assembly
Air : 1,5
O2 : 2,5 N2O : 3,5
CO2 : 1,6
Cyclopropane : 3,6
Heliox : 2,4 Entonox : 7

9. BOURDON’S PRESSURE GAUGE
Indication of incoming gas supply
In O2 cylinder – indicates amount of gas
N2O cylinder – pressure is
not indicative of amount - liquified form.
Curved tube can rupture with High
pressure - gauge has vent on its back .

10. PRESSURE REGULATOR
Present in the cylinder supply source
 reduces the high & variable storage pressure in
cylinder to a lower, more constant pressure
Oxygen: reduced from 2000 psig to 45 psig
N2O: reduced from 760 psig to 45 psig
Pipeline pressure is pre-regulated to 50 psig

11. SAFETY RELIEF DEVICE
It is composed of atleast one of
Frangible disc [bursts under extreme pressure]
Fusible plug [wood’s metal - low melting Point ]
WOOD’S METAL is a fusible alloy
50% bismuth, 25% lead, 12.5% tin,
12.5% cadmium: melts at 158°F (70-72°C);.
Safety relief valve [ opens at extreme pressure ]

12. BODOK SEAL
 A cylinder is fitted with a yoke
with a sealing called bodok seal .
 Composed of noncombustible material(neoprene
rubber)
 Metal periphery which makes it long lasting .
 Gas tight seal between cylinder and yoke.

13.  Allows gas from a cylinder to enter
but prevents gas from exiting machine
when there is no cylinder .
If double yoke – prevents transfer of gas
between cylinders.
 Empty cylinder can be replaced without
turning off the “in -use”cylinder.
CHECK VALVE ASSEMBLY

14. INTERMEDIATE SYSTEM
Pipeline system
Pipeline pressure
indicators (gauges)
Oxygen flush valve
Pressure regulators –
second stage
Pressure relief valve
Oxygen pressure
failure device
Oxygen supply failure
alarm [ Richter alarm]
Flow control valve

15. PIPELINE SYSTEM
Flexible and colour coded from the
anaesthetic machine to outlet.
Made of high quality copper - withstand
4 times the intended service pressure .
Utilize diameters index safety system(DISS)
or non-interchangable quick couplers

16. Separate shut off valves needed for
each gas in every operating room
Shutoff valve permit isolation of specific
areas of the piping system in
the event of fire .

17. PIPELINE INLET CONNECTION
Inlets are fitted with Diameter
Index Safety System fittings .
Each inlet contain check valve
(shraders valve) to prevent
flow of gas from the machine
into the piping system .

18.  The DISS is designed to prevent
misconnection of the medical gases.
 The end of the hose for each gas is
assigned a unique diameter and
thread that is used to connect the
pipeline gas supplies to the machine
Diameter index safety
system[DISS]

19. NON INTERCHANGEBLE SCREW
THREAD

20. OXYGEN FLUSH VALVE
 High unmetered flow to common gas outlet.
 Flow of 35-75 lit/min at 400 kPa expected.
 In modern anaesthesia machine ,oxygen flush
button painted green , in front for easy access.
 Surrounded by protective rim ,protects from
accidental damage & serves as tactile signal

21. OXYGEN PRESSURE FAILURE
DEVICE
• N2O cut-off or OFPD: the flow of
N2O is dependent on O2 pressure.
• This is done at the regulator level.
• In essence, the N2Oregulator is a
'slave' of the O2 regulator. i.e., if
O2 pressure is lost then the other
gases can not flow past their
regulators.

22. PRESSURE RELIEF VALVE
 Downstream of all pressure regulators
 Valves set at 50% above the pressure
regulator setting.
 Function: Fully relieving the pressure at
the set point in case failure of regulator.
 Connections to allow release of gas to
outside facility.

24. LOW PRESSURE SYSTEM
Flowmeters
Hypoxia prevention safety devices
Vaporizers
Vaporizers Back pressure relief valve [opens
when the pressure exceeds 200 cm H2O]
Oxygen analyzers

25. FLOWMETERS
 Measures & indicates rate of
flow of gas passing through it
 The knobs are colour coded as
well as touch coded.
 Designed to be read vertical
position - change in the position
-inaccuracy.

26.  Bobbin rotates on flow - prevents sticking.
Bobbin is antistatic - prevent sticking to the wall.
 Fluorescent coating on the back of flowmeter
panel and on the dot of bobbins
 Flow control knob of N2O is smaller,
rounded & inward in comparison to O2 knob.

28. Arrangement of flow meter tubes
with oxygen upstream
A leak in the middle tube with oxygen
flowing out resulting in delivery of
hypoxic mixture

29. Arrangement of flow meters with
nitrous oxide (N2O) upstream, leak
in the middle tube resulting in N2O
flowing out but oxygen flow intact.
(b) A wedge in the manifold
creating oxygen to be downstream

30.  oxygen leak from flow tube - hypoxic mixture,
regardless of the arrangement of flow tubes
 To prevent this, oxygen flowmeters are
always positioned downstream to other flowmeters.
 Floats rotate constantly - minimize friction between
tube wall and gases.

31. HYPOXIA PREVENTION SAFETY
DEVICES:
 Mandatory minimum
oxygen flow
a minimum flow of
oxygen required
before other gases will
flow(150 ml/min)

32. OXYGEN FAILURE SAFETY VALVE
O2 line pressure falls below 25 psi-
the spring tension engages the valve on
valve seat & shutoff all N2O flow.
Some designs make it impossible for
N2O to be delivered without the
addition of a fixed O2 %.

33. OXYGEN SUPPLY FAILURE ALARM
 Activated when O2 supply falls to 30psig.
 medium priority alarm enunciated within 5 s.
 Power supply from O2 supply pressure
 Can’t be switched off/reset until O2 supply
restored.
 Coupled to gas cut off valve –
opens machine circuitry to air

34. POP OFF VALVE
 Non return pressure relief safety valve
 Relief valve also called as pop off valve
 Opens at a pressure of 35 kpa(300 cm of H2O)
 Prevent the risk of damage to the vapourisers
and flow meters if the outlet is obstructed.

35. COMMON GAS OUTLET –
 A check valve - proximal to outlet
 prevent retrograde gas flow from
flush valve or breathing system into the
lower pressure system .

36. ESSENTIAL SAFETY
FEATURES
 Pin index safety system for color
coded cylinders with pressure gauges &
at least one oxygen cylinder backup
Prevent incorrect cylinder attachments; backup
gas supply; detect depletion

37.  Noninterchangeable gas-specific connections
to pipeline inlets (DISS) with pressure
gauges, filter, and check valve Prevent
incorrect pipeline attachments; detect
failure, depletion, fluctuation.

38.  Minimum O2/N2O ratio controller device
(hypoxic guard) & Oxygen failure safety device
(shut-off or proportioning device)
Prevent delivery of less than 21% O2
& administration of N2O or other gases
when the O2 supply fails

39.  Oxygen flush mechanism that does not
pass through vaporizers Rapidly refill
or flush the breathing circuit
 Oxygen must enter the common manifold
downstream to other gases Prevent hypoxia
in event of proximal gas leak

40.  Oxygen concentration monitor and alarm
Prevent administration of hypoxic gas mixtures in
event of a low-pressure system leak
 Low oxygen pressure alarm Detect oxygen
supply failure at the common gas inlet

41.  Capnography and anesthetic gas
measurement Guide ventilation; prevent
anesthetic overdose; help reduce awareness
 Pulse oximetry, blood pressure, and ECG
monitoring Provide minimal standard
monitoring