About high pressure system, intermediate pressure system and low pressure system

1. The Anaesthesia Machine
Moderated by Dr. Mahadevaiah
Presented by Dr. Vijay khodifad

2. INTRODUCTION
• The anesthesia machine is a complex piece
of equipment consisting of many com-
ponents.
• It is usually part of the anesthesia
workstation which also includes devices such
as vaporizers, a ventilator, breathing and
scavenging systems, and monitors.
• There are two general systems comprising
the anesthesia machine: the electrical sys-
tem and the pneumatic system.

3. CLINICAL MOMENT
• When being introduced to a new machine,
especially one of the electronically controlled
models, the user manual must be studied
carefully.

4. HISTORY
• In 1917, Boyle developed his anesthetic
machine from Gwathmey’s basic model and
presented it in London, at the Royal Society of
Medicine, in 1918.
• The original design was composed of a wooden
structure in the form of a box, which acted as a
frame, with two transverse bars from which
hung the cylinders of compressed gas (two of
oxygen and two of nitrous oxide), an ether
vaporizer and a water flow meter (the bubble
bottle from the Cotton & Boothby apparatus).

5. • In addition, the machine had a manometer to
measure the pressure in the cylinders, sensitive
pressure-reducing valves and an alcohol lamp
(to prevent the nitrous oxide from freezing and
thus obstructing the cylinder).
• Boyle’s anaesthesia device, originally
manufactured by Coxeter & Sons, and
subsequently acquired by the British Oxygen
Company, is considered the standard design for
the physical composition of anesthesia stations
today, although it has undergone numerous
modifications since its first appearance.

6. Boyle ‘s Machine. Left: First model, wvith wooden frame
1917 Right: 1958 model, with metal structure. Gas cylinders and
pressure regulators are fixed to the frame of the table. In the upper
part is the block of rotamers and vaporisers. Reproduced from Watt
OM. The evolution of the Boyle apparatus, 1917-67.

8. • contemporary of the first version of Boyle’s
apparatus was the anesthetic machine
proposed by the English barge.
• commander Geoffrey Marshall, who in 1917
presented the Coxeter company with his
own design for a sequential machine
(inspired by Gwathmey’s device) supplying
nitrous oxide, oxygen and ether.

9. • The Coxeter company decided to manufacture
the machine, and it became the standard
anesthesia device of the Royal Army Medical
Corps during the
• final stages of the First World War.
However, Marshall did not publish his invention,
and Boyle, who had attended the presentation
of Marshall’s machine, made some slight
modifications, and presented it as his own
device.49

11. The early Boyle’s machine had five elements
which are still present in all modern machines.
(i) A high-pressure supply of gases. It housed
two oxygen and two nitrous oxide cylinders in a
wooden box.
(ii) Pressure gauges on oxygen cylinders and
fine-adjustment reducing valves. These produce
a manageable breathing system pressure. It had
a spirit flame to warm these and prevent
obstruction of gas flow from ice.

12. (iii) Flowmeters to control gas flow rate and
adjust proportions of gas delivered.
(iv) A metal and glass vaporizer bottle for ether.
(v) A breathing system comprising a Cattlin bag,
three-way stopcock and facemask.
Modifications (e.g. Dry bobbin flowmeters
in 1933, pin-index system in 1952) were driven
by a consideration for greater safety.

13. The modern anaesthetic machine
Anaesthetic machines have six basic subsystems:
(i) gas supplies: pipelines and cylinders;
(ii) gas flow measurement and control(flowmeters):
(iii) vaporizers;
(iv) Gas delivery: breathing system and ventilator;
(v) scavenging;
(vi) monitoring.

14. 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

16. Anesthesia work station
• Integrates most of the components necessary for
administration of anesthesia into single unit.
• Standard guidelines have been given to
manufacturers for minimum
performance, design, characteristics and safety
requirements of machine.
• The current standard for anesthesia workstation
as( promulgated by American society for testing
and materials) (ASTM) is F1850. European
standard is EN740

17. Components of anesthesia machine

18. Pressure units to remember
1 atm pressure = 1 bar = 760 mm Hg =
14.7 psi = 100 kilopascals

19. Components of pressure systems

25. Limitations of check valve assembly
• The check valves are not designed to act as
permanent seals for empty yokes.
• Small amounts of gases can escape if the yoke is
empty or an empty cylinder (or cylinder with low
pressure) and valve open is present in the yoke.

26. • In order to minimize such losses –
• Yokes should not be left vacant for extended periods
• An empty cylinder should be replaced as soon as possible
, if not then,
• An yoke plug can be used to prevent gas leak or
• An empty cylinder can be left behind after closing the valve

27. Yoke Block(Dummy Cylinder plug)
• Yoke block is a solid piece of metal that has a conical
depression on one side to fit into the retaining screw
and a hollow area on the other side to fit over the
nipple.
• They are pin indexed.
• Uses
• Prevents gas leak from the machine when placed in an
empty yoke.
• Connect cylinders larger than size E to the machine.
• Connect pipeline supply to the machine that does not
have pipeline inlet connections.

28. Limitations of yoke block
• Can be responsible for crossover of gases in
the machine.
• Pressure regulators in the machine are
designed to accept gases at cylinder pressure
may not function properly when supplied with
gases at reduced pressure(pipeline supply
through yoke block)

30. Limitations of pin index safety system
• A wrong cylinder can be placed in yoke if-
• 2 washers are placed on the port.
• Pins on the yoke are broken.
• Holes on the cylinder valve are too deep.

33. Pin index safety system

35. Bourdon pressure gauge

37. Safety features in cylinder pressure
indicator
• 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.

38. 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
• Pressure inadequate-Red

41. Types of pressure regulators
• Adam’s pressure regulator valve-
• Used in past
• Working principle is same differs in internal structure
from newer valves(toggle levers instead of push rod)
• Fins on Adam’s regulator for N2O which are not
present in newer regulators.
• Mackesson’s regulator
• Medishield valve
• Endurance valve
• Modern preset type of reducing valve-Direct and
Indirect.

42. Safety features on pressure regulator
• 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)

49. Oxygen failure safety valve
Pressure sensor shut off valve
• Based on threshold
principle
• Cuts off N2O supply when
O2 pressure falls below 25
psi.
• MOA-O2 pressurises and
holds open shut off valve
that interrupts the supply
of N2O and other gases if
O2 pressure<threshold
setting.
oxygen failure protection device
• Based on proportioning
principle
• Gas loaded regulator
• When O2 pressure decreases
there is a proportional
decrease in N2O supply and
complete cut off seen
at<12psi.
• MOA-O2 pressure
regulator(primary regulator)
controls secondary(slave)
regulator located in N2O line

56. Master switch
• Turning the master switch to the ‘on’ position
activates both pneumatic and electrical
functions of the machine as well as certain
alarms and safety devices.

70. Electronic flow meter
• Prefer digital system
• Solenoid valves
• Control flow on or off
valves
• Computer controlled
• .

78. Link-25
• .

79. Oxygen ratio monitor controller
Sensitive oxygen ratio controller
• Linear resistors [3:1 ratio for
N2O & O2)between O2
andN2O flow control valves.
• Ensure 25% O2 by limiting
N2O flow.
• ORMC shuts off N2O if ratio
of O2 flow falls below 30%
• S-ORC-newest hypoxic
guard . installed in Fabius-
GS by Drager.ensures aFiO2
of 23%. O2 flow
<200ml/min.
• .

80. Limitations of proportioning system
• Anti hypoxic device may also deliver hypoxic
mixture under following conditions-
• Wrong supply of gas.
• Defective pneumatics/mechanics.
• Inert gas administration(3rd gas-He,N2,CO2).
• Leaks downstream.