The document provides information about anesthesia machines and their components. It discusses the key parts and functions of anesthesia machines including: - The high pressure system which receives gases from cylinders and regulates pressure. - The intermediate pressure system which receives gases from regulators and delivers them to flow meters. - The low pressure system which takes gases from flow meters to the machine outlet and contains vaporizers. It describes components like pressure regulators, flow meters, safety devices, and the common gas outlet in detail. The document is an overview of the design and workings of modern anesthesia machines.

1. Mr. Harshad Khade
MSc. Medical Technology (OTA)
Symbiosis International university, Pune.
Anesthesia Machines
And Breathing Systems

2. Introduction
• The anaesthesia gas machine is a device which delivers a precisely-
known but variable gas mixture, including anesthetizing and life-
sustaining gases.
• Original Boyle was made by the firm COXTERS.
• There are several differences between newer and older anesthesia
machines.
• Advanced ventilators are the biggest difference between newer and
older gas machines.

3. • Boyle machine before Henry Edmund Gaskin Boyle in 1917: Gwathmey
(1912) and Geoffrey Marshal (1914-1918)

4. Types Of Anaesthesia Machine
• Intermittent Anaesthesia Machine
-Gas flows only during inspiration
• Ex:-
• Entonox apparatus ,
• Mackessons apparatus
• Continuous Anaesthesia Machine
-Gas flows both during inspiration
and expiration.
• Ex:-
• Boyle Machine
• Forregar
• Dragger

6. The Anesthesia Machine:

7. • The machine performs four essential functions:
• Provides O2,
• Accurately mixes anesthetic gases and vapours,
• Enables patient ventilation and
• Minimises Anaesthesia related risks to patients and staff.

9. • The anaesthesia machine can be conveniently divided into
three parts:
1. The high pressure system, which receives gases at cylinder
pressure, reduces the pressure and makes it more constant,
2. The intermediate pressure system, which receives gases from the
regulator or hospital pipeline and delivers them to the flow
meters or O2 flush valve and
3. The low pressure system, which takes gases from the flow meters
to the machine outlet and also contains the vapourisers

10. The High Pressure System:
• The high pressure system consists of all parts of the machine, which
receive gas at cylinder pressure.These include the following:
• a) The hanger yoke which connects a cylinder to the machine,
• b) The yoke block, used to connect cylinders larger than size E or
pipeline hoses to the machine through the yoke,
• c) The cylinder pressure gauge, which indicates the gas pressure in the
cylinder and
• d) The pressure regulator, which converts a high variable gas pressure
into a lower, more constant pressure, suitable for use in the machine

12. The Hanger Yoke Consists Of:
1.The body, which is the principle framework and supporting structure,
2.The retaining screw, which tightens the cylinder in the yoke,
3.The nipple, through which gas enters the machine,
4.The index pins, which prevent attaching an incorrect cylinder,
5.The Bodok seal, the washer which helps to form a seal between the
cylinder and the yoke,
6. A filter, to remove particulate matter and
7.The check valve assembly which ensures a unidirectional flow of gas
through the yoke

14. Bourdon’s Pressure Gauge:
• ➢ Cylinder pressure is usually measured by a Bourdon’s pressure
gauge,
• which is a flexible tube which straightens when exposed to gas
pressure causing a gear mechanism to move a needle pointer.

16. Pressure Regulators:
• These are the devices which reduce the high pressures in the cylinders
to a lower and more constant pressure to maintain a constant flow.The
reasons for their presence are:
• 1. If there are no pressure regulators, then there will be a necessity for
the anesthesiologist to keep re-adjusting the flow control valves to
maintain a constant flow as the cylinder pressure decreases with use,
decreasing the flow.

17. • 2.The high pressure from the cylinders can produce damage to the
flow control valves.
• 3.The high pressure can also produce barotrauma to the patient’s
lungs.
• 4.With lowered pressure supplied to the flow meters fine adjustments
of the flow is possible.
• The pressure regulators reduce the pressure of the O2 cylinders from
2200 PSIG to 45-60 PSIG and the N2O cylinders from 750 PSIG 45-60
PSIG

18. Master And Slave Regulator:
• The N2O pressure regulator was constructed in such a way that
pressure of the O2 flow was required to release the flow of N2O.
• So, N2O regulator was made to act like a ‘slave’ regulator to O2 as the
‘master’ regulator.
• This was not a fool proof system as still hypoxic mixtures could be
delivered if the O2 is cut off at the flow meters. Hence proportionating
devices had to be introduced at the flow meter assembly in modern
machines

19. Intermediate-pressure System:
• 1. Pneumatic part of the master switch,
• 2. Pipeline inlet connections,
• 3. Pipeline pressure indicators,
• 4. Piping,
• 5.The gas power outlet,
• 6. Oxygen Supply Failure Alarm.
• 7. Oxygen pressure failure devices,
• 8.The oxygen flush,
• 9. Additional pressure regulators (if so
equipped),
• 10.The alternate oxygen control (if so
equipped), and
• 11.The flow control valves.
• The intermediate-pressure system receives gases from the pressure
regulator or the pipeline inlet. Components in this system include the

20. Master Switch (Pneumatic Component)
• 1.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.When the
master switch is turned OFF, the pressure in the intermediate-pressure
system will drop to zero.

21. Pipeline Inlet Connections
• . a) The pipeline inlet connections are the entry points for gases
from the pipelines.There are usually connections for air, oxygen,
and nitrous oxide.
• b) The pipeline inlets are fitted with threaded noninterchangeable
Diameter Index Safety System (DISS) connectors.
• c) Each inlet contains a unidirectional (check) valve to prevent
reverse gas flow from the machine into the piping system (or to
atmosphere if no hose is connecte
• d) and a filter to prevent debris from the pipeline entering the
anesthesia machine.

22. Pipeline Pressure Gauges
• a) Gauges are present to monitor the pipeline pressure of each gas.
They are usually on a panel on the front of the machine (or the
information screen, if present) and color coded for the gases they
monitor.
• b) Some machines have digital pressure gauges that display pressure
either continuously or on demand. Some use light-emitting diodes
(LEDs) to indicate adequate pipeline pressure.

23. • c) The sensing point for the pipeline pressure gauge is located on the
pipeline side of the check valve. In this location 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.
• d) 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.

25. Oxygen Supply Failure Alarm
• ➢ whenever the oxygen supply pressure falls below a manufacturer-
specified threshold (usually 30 psig (205 kPa)), at least a medium
priority alarm shall be enunciated within 5 seconds.
• ➢ It shall not be possible to disable this alarm.
• ➢ The whistle sounds continuously until the oxygen pressure has fallen
to approximately 40.5 kPa (6 psi).

27. Oxygen Pressure Failure Devices
• A Fail-Safe valve is present in the gas line supplying each of the
flowmeters except O2.
• This valve is controlled by the O2 supply pressure and shuts off or
proportionately decreases the supply pressure of all other gasses as
the O2 supply pressure decreases.
• Historically there are 2 kinds of fail-safe valves
• ✓ Pressure sensor shut-off valve (Ohmeda)
• ✓ Oxygen failure protection device (Drager) – OFPD

28. Oxygen Failure Safety Valve-
• When oxygen pressure in the machine is normal, it will push the
diaphragm and stem downward, opening the valve.
• The anesthetic gas flows in at the inlet around the stem and through the
outlet to the flowmeter.
• When the oxygen pressure falls, the stem moves upward, closing the
valve.
• The middle chamber is vented to atmosphere to prevent mixing of
anesthetic gas and oxygen in the event that the diaphragm ruptures or
the packing leaks.

30. Second-stage Pressure Regulator
• . Second-Stage Pressure Regulator Some machines have additional
pressure regulators in the intermediate pressure system just upstream
of the flow adjustment controls.
• The second-stage regulator receives gas from either the pipeline or
the cylinder pressure regulator and reduces it further to around 26 psi
(177 kPa) for nitrous oxide and 14 psi (95 kPa) for oxygen.
• Not all anesthesia machines incorporate this device.

31. Oxygen Flush
• a) The oxygen flush (oxygen bypass, emergency oxygen bypass)
receives oxygen from the pipeline inlet or cylinder pressure regulator
and directs a high (35 to 75 L/minute) unmetered flow directly to the
common gas outlet.
• It is commonly labeled “O2+.” on most anesthesia machines,
• the oxygen flush can be activated regardless of whether the master
switch is turned ON or OFF.

32. • b) Oxygen flush activation may or may not result in other gas flows
being shut OFF and may result in either a positive or negative pressure
in the machine circuitry, depending on the design of the inlet and the
flush line into the common gas line.
• This pressure may be transmitted backward on other structures in the
machine, such as flow indicators and vaporizers, and may change the
vaporizer output and the flow indicator readings.
• The effect will depend on the pressure generated, the presence or
absence of check valves in the machine, and the relationship of the
oxygen flush valve to other components.

33. • c) Reported hazards associated with the oxygen flush include
accidental activation and internal leakage, which result in an oxygen-
enriched mixture being delivered.
• The flush valve may stick in the ON position.
• It may also stick and obstruct flow from the flowmeters.
• Barotrauma and awareness during anesthesia have resulted from its
activation.

35. Flow Adjustment Control
• The flow adjustment control regulates the flow of oxygen, air, and other
gases to the flowmeters.
• There is one flow adjustment control per gas and it must be adjacent to
or identifiable with its associated flowmeter.
• Flow adjustment control is shown in the closed position.
• Turning the stem creates a leak between the pin and the seat so that
gas flows to the outlet.
• The stop collar prevents overtightening of the pin in the seat.

37. Lazy Tongs
• In Adams valve the pushrod is replaced by a ‘lazy tongs’ toggle
arrangement which reverses the direction of the thrust transmitted
from the diaphragm.
• There are several types of pressure regulator available, the choice
being dependent on
• ✓ The maximum flow rate required
• ✓ The regulated pressure to which it is to be set
• ✓ The maximum input pressure that it is to handle

38. The Low-pressure System:
• The low-pressure system is located between the flow control devices and the
machine outlet.
• Pressure in this section is only slightly above atmospheric, and variable
rather than constant.
• Pressure fluctuations depend on the flow from the flow control valves, the
presence of back-pressure devices (check valves), and back pressure from
the breathing system.
• Components found in this section include
✓ Flowmeters,
✓ Hypoxia prevention safety devices,
✓ Unidirectional valves,
✓ Pressure relief devices, and
✓ The common gas outlet.

40. Auxiliary Oxygen Flowmeter
• An auxiliary (courtesy) oxygen flowmeter is a self-contained flowmeter
with its own flow control valve, flow indicator, and outlet. It is not affected
by computer control.
• It usually has a short tube with a maximum flow of 10 L/minute and a
barbed fitting on the outlet for connection to a face mask or nasal cannula.
• It is used to supply oxygen to the patient without turning ON the
anesthesia machine.
• The tube assembly calibrated for one gas cannot be used for a different
gas.
• If a tube, indicator, and scale calibrated for one gas are used for another
gas, they will deliver an incorrect gas flow.

41. Flow Meters (Rotameters) Not Interchangeable:
• ➢ Flow meters are calibrated for specific gases.
• ➢ Flow rate across a constriction depends on the gas’s viscosity at low
laminar flows and its density at high turbulent flows.
• ➢ Therefore, gases with similar viscosity (oxygen and helium) may
read identically at low flows, while gases with similar densities (nitrous
oxide [N2O] and carbon dioxide) will read the same at high flows.
• ➢ Nitrous and oxygen rotameters would not read the same, having
different density and viscosity.
• ➢ Therefore, for calibration purposes both the density and the
viscosity of the gas are important (i.e., flow meters are not
interchangeable)

42. Hypoxia Prevention Safety Devices
• One of the hazards associated with flowmeters is the possibility that the
operator will set the flows that could deliver a hypoxic mixture.Various
devices have been developed to prevent this problem.
• The hypoxia prevention devices discussed here should not be
confused with the oxygen pressure failure device discussed earlier.
• The oxygen pressure failure device prevents hypoxia due to a loss of
oxygen pressure in the machine, whereas hypoxia prevention devices
prevent the operator from accidentally setting a hypoxic gas mixture.

43. Pressure Relief Device
• Some machines have a pressure relief device near the common gas
outlet to protect the machine from high pressures.
• This valve opens to atmosphere and vents gas if a preset pressure is
exceeded.
• On anaesthetic machines with a regulated pressures of 45-60 PSIG
there may be a relief valve also called as pop off valve which opens at
a pressure of 5 PSIG (300 cm of H2O) to prevent the risk of damage to
the vapourisers and flow meters if the outlet is obstructed.

44. Common (Fresh) Gas Outlet
• a.The common (fresh) gas outlet receives all of the gases and vapors
from the machine and delivers the mixture to the breathing system.
• Some outlets have a 15-mm female slip-joint fitting (that will accept a
tracheal tube connector).
• They may also have a manufacturer-specific fitting.
• There is a mechanism to prevent a disconnection between the machine
and the hose to the breathing system.
• Do not use the common gas outlet to administer supplemental oxygen
to a patient. Use the auxiliary oxygen flowmeter or a separate
flowmeter

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