Medical gas supplies (Anesthetic machine)

Dr.Mohammad Abdeljawad
Anesthesia Specialist
AL-Bashir Hospital
7/9/2020 1

anesthetic machine consists of the
following components :
1- Supply of medical gases: is either from: - cylinders attached to the
machine,
or - a central pipeline supply.
They are attached to the machine by appropriate unions.
2- Pressure reducing valves (pressure regulators): convert the high
pressure to low pressure suitable tc the anesthetic machine and the
patient.
3- A flowmeter: delivers known flow rates to the vaporizer and
anesthetic breathing system and in the same time reduces pressure of
gases from 4.1 bar (in the pipelines) to 1 bar, which is delivered to
patients.
4- A Vaporizer: converts the liquid anesthetics to a vapor and delivers
known concentrations of the anesthetic vapor to the breathing circuits.
5- A mechanical anesthesia ventilator: maintains mechanical
ventilation to the patient.
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6- An anesthetic breathing system (anesthetic breathing circuit):
delivers the anesthetic gases from the anesthetic machine to the
patient.
7-A humidifier: humidifies inspired gases.
8- Monitoring devices: for the patient and equipment.
9- Alarm systems: warn against fault or failure of equipment.
10- A scavenging system: removes the waste anesthetic gases to out
side the operation room to minimize environmental pollution.
N.B.: Anesthesia delivery system consists of the anesthetic machine,
vaporizer, ventilator, and scavenging ~·system.
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Pressure unit convertion :
ValueUnit
1bar
14.6psig
101kilopaskal
1020Cm H2O
760mm Hg
1.1atm
Example :
atmmm HgH2Okilopaskalpsigbar
4 = 58.4 404 4080 3040 4.4

Medical Gas Supplies
The anesthesiologists must understand both the sources of the medical
gases and the means of their delivery to the operating room to prevent
and detect medical gas depletion or supply line misconnection.
Sources of medical gases
There are many medical gases that are commonly used in the operating
room (oxygen, nitrous oxide carbon dioxide, air, helium, entonox, and
nitrogen).
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Liquefaction of Medical Gases.
Any gas can be liquefied by pressure if its temperature is below a
critical level. This temperature is the critical temperature of the
gas. Above its critical temperature, a gas cannot be liquefied
whatever pressure is applied. Cooling and application of pressure
both are essential for liquefaction of gases (see before in gas laws).
Critical temperature is the temperature above which a gas
cannot be liquefied by pressure
Critical pressure is the pressure required to liquefy a gas below
its critical temperature, or it is the vapor pressure of a substance
at its critical temperature.
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Liquefied Nitrous Oxide:
Because the critical temperature of nitrous oxide (36.5°C) is above
room temperature, it can be kept liquefied by application of critical
pressure (72 bar), without a cooling or refrigeration system.
N2O is stored in cylinders.
Liquefied Carbon Dioxide:
Because the critical temperature of carbon dioxide (31°C) is above room
temperature, it can be kept liquefied by application of critical pressure
(73bar), without a cooling or refrigeration system.
CO2 is stored in cylinders.
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Liquefied Oxygen:
Oxygen can be liquefied by pressure below its critical temperature (-
119°C).
It is stored at a temperature of -160°C in a special giant vacuum-
insulated container to maintain it at this very low temperature,
 No refrigeration system is needed for the storage container because
the liquid oxygen remains cold due to the efficiency of the vacuum
container and loss of latent heat when oxygen vaporizes.
Gaseous oxygen withdrawn from the top of the container is very cold,
so it should be heated to ambient temperature by a super-heater coil,
then passed through a pressure regulator to reduce its pipeline pressure
to 4.1 bar (figure 6-2).
The pressure inside the liquid oxygen container is 7 bar, which is the
vapor pressure (VP) of oxygen at -160 c.
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If the oxygen, from the containers, flows at a fast rate, the
temperature of the liquid oxygen falls due to the removal of latent
heat, and the vapor pressure of oxygen falls below 7 bar.
To provide a source of beat to this system, a pressure raising
vaporizer is used.
There is also a control valve which senses the pressure in the
vacuum-insulated container.
 When the vapor pressure is decreased below 7 bar, the control valve
allows liquid oxygen to be withdrawn from the bottom of the container
to the vaporizer to be warmed and vaporized and then returned back to
the top of the container and pipeline system to mantain vapor pressure
around 7 bar.
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If no oxygen is used, the temperature of the storage container
gradually rises until after 1 week the oxygen vapor pressure increases
above 17 bar.
Therefore, the excess gaseous oxygen is allowed to escape as waste
through a safety valve at the top of the container to maintain the vapor
pressure around 7 bar.
The container rests on a weight balance to measure the mass of
liquid oxygen in the container which is refilled by the gas supplier as
needed.
Even when a hospital has a liquid oxygen plant, it is still
necessary to hold reserve banks of oxygen cilnders in case
of supply failure
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Liquid oxygen is available in some large hospitals because it is more
economical than oxygen gas cilnders.
O2 is stored in either:
• A special giant vacuum-insulated container as a liquid at very low
temperature,
•or A cylinder as a compressed gas at room temperature, .
Liquid oxygen containers should be kept away from the main
hospital building in an open, cool, well_ventilated area and
protected from any heat or ignition source to prevent fire hazard.
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Liquid oxygen can give 842-860 times its volume as gas.

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0xgyen Concentrators:
It is a device which concentrates and extracts oxygen from
atmospheric air.
Atmospheric air is filtered, compressed, and then cooled before
being dried by silica gel.
Then air passes through two cylinders containing zeolite (hydrous
silicate) which has ion-exchange properties and acts as a molecular
sieve or trapper, separating the oxygen from nitrogen and water vapor
in the air and leaving oxygen and other trace inert gases.
The nitrogen and water vapor are drawn off by a vacuum pump as
waste gas while Oxygen and other inert gases pass to a reservoir then
to the patients

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Advantages:
They produce oxygen concentrations of 90-95%which is suitable for
medical uses. There are also small concentrations of nitrogen and inert
gases (especially argon) which have no toxic effect.
• Small oxygen concentrators, which can give a maximum flow of 4
liters/min and pressure of 70 kPa, are available and suitable for use in
homes for long term domiciliary oxygen therapy (i.e., for domestic use).
They are more convenient than oxygen cylinders. The running cost,
which includes electricity and servicing, is much less than that of oxygen
cylinders.
• Large oxygen concentrators, which can give higher flow and pressures
up to 410kPa, are used to operate ventilators and venturis in small
hospitals and military hospitals in remote areas and in developing
countries.

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Disadvantege :
• Larger oxygen concentrators are needed if higher pressure and
flows are needed in hospitals.
• They need regular maintenance.
• They should be protected from fire hazards.

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Compressed Air Supplies (central compressor plants)
They are more economical for larger hospitals than air cylinders.
Idea:
• Apart from the reservoir, the main units are duplicated so that any
item can be serviced or repaired without interrupting the air supply.
• The air intake unit is placed out-of-doors where it is not affected by
rain, snow, dust or fumes The inlets of these pumps must be distant
from vacuum exhaust vents and machinery to minimize
contamination.. The air from the intake unit (Dehumidified ,
unsterile) air then passes through a preliminary filter and a silencer
then to a compressor which incorporates a cooler to cool the
compressed air. Then the air passes through a non-return valve into a
large cylindrical reservoir.
• After leaving the reservoir, the air is cleaned by separators and
filters to remove oil mist as most compressors are oil-lubricated,
otherwise oil pneumonitis occurs.

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• The air is then dried by a silica gel drier to avoid the
increased humidity which increases when the air is compressed.
• The air is then passed through a final bacterial filter to
ensure that air is free of bacteria
The pressure of the air in the pipeline is either:
7 bar, it is used for operation of surgical tools.
4 bar, it is used for anesthetic machines.

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The anesthesia machine has 2 medical gas supply sources: -
A-cylinder supply source, and
B- pipeline supply source.
By some hospitals e.g., military hospitals, oxygen is also
derived from oxygen concentrators
Cylinders Cylinder bank Liquid oxygen

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A-Medical Gas Cylinders
Synthesis: Medical gas cylinders are made of a strong metal alloy
(thin walled) as molybdenum steel, high carbon steel, or manganese
steel. There are cylinders made of aluminum (non-ferromagnetic)
which are suitable for magnetic resonance imaging (MRI)rooms.
Test: Medical gas cylinders should be tested by the manufacturer at
regular intervals (usually every 5 years for the presence of defects to
ensure that cylinders can withstand higher pressures (about 65-70%)
greater than those they are subjected to in normal use.
One cylinder in every 100 is cut into strips to test the metal for
tensile strength, flattening impact, bend tests, and even internal
examinations with an endoscope are performed. The tests are
marked by a mark stamped on the neck of the cylinders.

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NOTE: In UK O2 cylider presented with white sholder and black body,
many question depend on this answer
‫لونين‬ ‫من‬ ‫تتكون‬ ‫االوكسجين‬ ‫اسطوانه‬ ‫بريطانيا‬ ‫في‬(‫اسود‬ ‫و‬ ‫االسطوانه‬ ‫اعلى‬ ‫ابيض‬
‫االسطوانه‬ ‫جسم‬)

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Color : Medical gas cylinders have a color code system specific for
each gas. This color code is different in each country

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The size of the cylinders is classified according to their height in
an alphabetical letter
 code starting with the letter "A" being the smallest (10 inches
height) up to the letter "H'' (57 inches height) being the largest
 "E" (31inches height) is used in anesthesia machines, for
patient's transport and for resuscitation.
 size "H'' is the largest and connected by a manifold to form a
bank for the pipeline systems.
Capacity: The capacity of the cylinders differs according to the size
of the cylinder and the type of th gas or liquid inside them.
anesthesiologist must always have an emergency (E-cylinder) supply
of oxygen available during anesthesia.

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Filling ratio:
As above, the cylinders contain either gaseous form or liquid form
according to the critical temperature of the gas
Cylinders of liquefied gases (as N20 and C02) are never filled to the
point where they only contain liquic because any slight increase in
temperature will cause a dangerous rise in cylinder pressure because
temperature will cause N20 or C02 liquid to expand, as liquid is not as
compressible as gases.
 The degretof filling of cylinders is expressed by the filling ratio;
The filling ratio of N20 or COi cylinder is 75% in temperate climate
and 65% in tropical climates

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Cylinders are attached either:
• Directly to the anesthetic machine especially E cylinders of
02 or N20 which serve as a backup if the pipeline system fails or
•To a manifold.
Types of connections:
1- A Pin Index Safety System (PISS): This system of connection is
present in cylinders from size A to E to prevent incorrect
attachment c cylinders to anesthesia machine (figure 6-5).
connections:

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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.

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BODY:
Threaded into frame of
machine
Supports cylinder
Hinged Swinging gate
RETAINING SCREW:
Threaded into the distal end of yoke
Tightening the screw – gas tight seal
Conical point fits into conical
depression on cylinder
NIPPLE:
Projects from yoke and fits into cylinder
port
Entrance of gas into machine INDEX PINS
Component of pin index safety system
4mm in diameter and 6mm long (except pin
7 which is slightl thicker) .
Fit into the corresponding holes
on the cylinder

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Each gas cylinder has two holes in the cylinder valve, which mate
with two corresponding pins in the yoke (connecting structure) of the
anesthesia machine.
A flush connection is only achieved if the holes an pins fit correctly.
The relative positioning of the pins and holes is unique for each gas.
This design makes it impossible to attach an oxygen cylinder to any
yoke other than that designed for oxygen.

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

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2- Direction of the internal thread:
In large cylinders, there is another type of protection.
In 02, air, helium, and nitrogen cylinders, the internal thread on the
cylinder outlet is right handed
while in hydrogen and other flammable gases; the internal thread on
the cylinder outlet is left handed. This system gives only partial
protection against wrong connections (figure 6-6).

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 Is present before the cylinder is connected to the flowmeter of
the anesthetic machine,
to reduce the pressure from the high pressure inside the cylinder
to the low pressure (4 bar) at the anesthetic machine.
- Cyclopropane cylinders do not require a pressure reducing valve
because the pressure inside the ...d..er is 5 bar. It is only provided
with a fine adjustment valve.
-Is present to measure the gas pressure inside the cylinder.
-The pressure in an oxygen cylinder and other gaseus contents is directly
proportional to the content of the cylinder, so the pressure gauge can indicate
olurne of oxygen (and other gases) remaining in the cylinder.

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As oxygen is expended, the cylinder’s pressure falls in proportion to its
content. A pressure of 1000 psig indicates an E-cylinder that is
approximately half full and represents 330 L of oxygen at atmospheric
pressure and a temperature of 20°C. If the oxygen is exhausted at a
rate of 3 L/min, a cylinder that is half full will be empty in 110 min.
Oxygen cylinder pressure should be assessed prior to use and
periodically during use.

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-On the other hand, the pressure gauge of N20 cylinder will
indicate a steady pressure as long as any liquid nitrous oxide
remains in the cilendier.
-When all the liquid is vaporized, the gauge pressure falls steadily
until the cylinder becomes emptey
- The pressure gauge of a N20 cylinder should not exceed 750 psi
at 20°C. A higher reading indicates ze malfunction, liquid
overfilling, or faulty presence of a gas other than N20
Vaporization of a liquefied gas (e.g., nitrous oxide) and expansion of
a compressed gas (e.g., oxygen)
reguire heat, which is extracted from the metal cylinder and the
surrounding atmosphere.
For this reason, atmocpheric water vapor accumulates as a frost on
gas cylinders.
Heat should be applied locally e.g., by sorrunding the valve by a
towel soaked in warm water to keep it above the freezing point.

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 All gas cylinders are equipped with an emergency pressure relief valve
(rupture disk) to prevent explosion under conditions of unexpectedly high
gas pressure (e.g., unintentional overfilling). The pressure relief valve is
designed to rupture at 3300 psi. The E-cylinder walls can withstand more
than 5000, so the pressure-relief valve protects against cylinder explosion.
 Full cylinders are supplied usually with a plastic dust cover to
prevent contamination by dirt. The cover should .be removed just
before usage. The cylinder valve should be opened momentarily before
attaching clinder to the anesthesia machine to blow out any dust which
might be lodged in its outlet.
Precautions:
The valve should be opened slowly when attached to the
anesthetic machine or regulator . This prevent the rapid rise in
pressure and the associated rise in temperature of the gas in the
machine’s piplines.

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Heating cylinders is dangerous because it increases the pressure
inside them. A moderate rise in temprature as occurs in summer,
however, is not important because the cylinders are made to
withstand presures well above their normal working range. The
cylinders can usually withstand pressure 65-70% above the working
pressure.
 Most large gas cylinders are stored in the upright position, while
some smaller ones and Entonox clindaers are stored horizontally
cylinders should be stored indoors, protected from the weather
and should not be subjected to extemes of heat or cold.
Gas from N2O and O2 cylinders enters the anesthesia
machine through a pressure regulator that reduce the
pressure to 45 psig
The gases and vapours should be free of water vapour when stored
in cylinders . Water vapour freezes and blocks the exit port when the
temperature of the cylinder decreases on opening

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If the cylinder supply valves are left open, the reserve cylinder
supply can be silently depleted if pressure inside the machine
decreases to a value lower than the regulated cylinder pressure.
For example, oxygen pressure within the machine can decrease to less
than 45 psig with oxygen flushing or possibly even during use of a
pneumatically driven ventilator, particularly at high inspiratory flow
rates. Additionally, the pipeline supply pressures of all gases can fall to
less than 45 psig if problems exist in the central piping system
Moreover, the yoke hanger seal is vulnerable to leakage

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N20 cylinders:
Nitrous oxide is almost always stored by hospitals in large H-cylinders
connected by a manifold with an automatic crossover feature.
Because the critical temperature of nitrous oxide (36.5°C) is
above room temperature, it can be kept liquefied without an
elaborate refrigeration system.
If the liquefied nitrous oxide rises above its critical temperature, it will
revert to its gaseous phase
Because nitrous oxide is not an ideal gas and is easily
compressible, this transformation into a gaseous phase is not accompanied
by a great rise in tank pressure.

7/9/2020 45
Below 36.5°C (the critical temperature of nitrous oxide), nitrous oxide
cylinders contain both gas (vapor) and liquid at a pressure of 750 psi.
This pressure remains steady as long as any liquid nitrous oxide .remain
in the cylinder.
 When all the liquid is vaporized, the pressure falls steadily until the
cylinder becomes empty and the pressure gauge reads zero.
The pressure within the cylinder
will being to fall when 400L of gas
remain in the cylinder.(
approximatly ¾ of the gas has left
the cylinder )

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If liquid nitrous oxide is kept at a constant
temperature (20°C), it will vaporize at the same rate at which
it is consumed and will maintain a constant pressure (745 psig)
until the liquid is exhausted.
The only reliable way to determine residual volume of
nitrous oxide is to weigh the cylinder. For this reason, the
tare weight (TW), or empty weight, of cylinders containing a
liquefied compressed gas (eg, nitrous oxide) is often
stamped on the shoulder of the cylinder.

7/9/2020 47
The pressure gauge of a nitrous oxide cylinder should not exceed
745 psig at 20°C. A higher reading implies gauge malfunction, tank
overfill (liquid fill), or a cylinder containing a gas other than
nitrous oxide.
Because energy is consumed in the conversion of a liquid to a gas
(the latent heat of vaporization), liquid nitrous oxide cools during
this process. The drop in temperature results in a lower vapor
pressure and lower cylinder pressure
The cooling is so pronounced at high flow rates that there is often
frost on the tank, and the pressure regulator may freeze in such
circumstances.
Frost develops on the outside of the cylinder during general
anesthesia because of the flow of N2O from the cylinder into the
anesthesia machine is rapid.

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‘ENTONOX is the trade name for a premixed gaseous mixture of 50%
N20 and 50% 02. It is prepared by ~ 02 gas in liquid N10 (Poynting
Effect). . by volume (not by weight) .
When the temperature is above the pseudo-critical temperature (-
7°C), Entonox mixture remains in the gaseous state.
Below -7°C, the mixture separates into 02 and some N10 gas (above)
and 80% N10 and 20% 02 liquid (below) · due to liquefaction of N20).
This is a very dangerous situation, because 02 is drawn off first and the
gas mixture at first has a high %of 02, then the gas mixture becomes
progressively anoxic, until at last N2O' is drawn off and inhaled by the
patient.
At room temperature Entonox cylinders contain only gas.

7/9/2020 49
To prevevt this hazard:
•The cylinders should be warmed above 10°C.
• The small cooled cylinders should be inverted repeatedly
before use to reconstitute the gaseous mixture.
• Large cylinders have a dip tube which draws off any liquid
phase first. This prevents the delivered 02 concentrations from
falling below 20% at any time (figure 6-7).
• The Entonox cylinder has a special pressure reducing valve which
regulates the output pressure to a subatmospheric level for self
administration by the patient.
• The Entonox cylinder is widely used in the United Kingdom to produce
inhalation analgesia for labor, trauma, dental and minor surgical
procedures e.g., removal of chest tubes.
• Entonox is not a single gas but a mixture of two gases; therefore, it is
said to have a pseudo-critical temperature rather than a critical
temperature.

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Carbon Dioxide
Many surgical procedures are performed using laparoscopic or
robotic-assisted techniques requiring insufflation of body cavities
with carbon dioxide,
 an odorless, colorless, nonflammable and slightly acidic gas.
 Large cylinders containing carbon dioxide, such as M-cylinders or
LK-cylinders, are frequently found in the operating room; these
cylinders share a common size orifice and thread with oxygen
cylinders and can be inadvertently interchanged

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B) Medical Gas Pipeline System
In many modern hospitals, a central pipeline system for distribution of
medical gases has replaced the use of compressed gas cylinders in the
operating room (OR),post-anesthetic care units (PACU), and intensive
care units (ICU).
Advantage of Pipeline System:
• It decreases the cost.
• It allows more space as there is no need for the presence of
large numbers of cylinders in the OR, PACU or ICU.
• It is more convenient and safe to the personnel and patients
Internal contamination of the pipelines with dust, grease, or
water must be avoided

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The hospital’s gas delivery system appears in the operating room
as hose drops, gas columns, or elaborate articulating arms
(Figure 2–3)

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Quick connector (Quick-coupler)
-The outlets are colour-and shape- coded . They accept matching
quick connect / disconnect probes.

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Machine’s pipeline inlet
-Flexible colour-coded hoses connect the outlets to the anesthetic
machine . With non-interchangeable diameter index safety system DISS
(valve) to prevent incorrect pipeline attachments .
Diameter-Index Safety

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System Components:
It consists of 5 parts:
1- Pipeline central supply: includes gas store, valves, and alarm
systems.
2- Pipeline distribution network.
3- Pipeline terminal outlets.
4- Flexible color-coded hoses connecting the terminal outlets to the
anesthetic machines.
5- Connections between flexible hoses and anesthetic machines.
Responsibility for items 1-3 lies on the Engineering and Pharmacy
Departments.
 Responsibility for items 4 and 5 within the OR, PACU, or ICU lies
partly on the anesthesiologists to check the correct functioning of
which;
therefore, anesthesiologists should be acquainted with the system
in the hospital to be able to deal with emergencies that may arise.

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1- Pipeline Central Supply:
Gas Store :
Gases as oxygen, nitrous oxide, air, and entonox are stored in large
stored cylinders (size H) connected together by a manifold.
A manifold is a tube with several outlets which connect several
cylinders of the same type of gas to give a continuous supply.
 Each manifold system consists of two groups of cylinder on each
side. Each group is called a cylinder bank.
 For each gas there are two banks, one in use at one time and the
other as a reserve.
 The number of cylinders in each bank depends on the anticipated
daily demand.
When one bank is exhausted, the other reserve bank will work either
by a manual or an autmatic (safer) switch allowing time to replace the
empty cylinders in the first bank (figure 6-8).

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B-Valve
Check valve
This a non-return or unidirectional valve, which allows gases to pass
from the cylinders to the manifold and not the reverse.
 It is placed between each cylinder lead and the manifold.
 It prevents loss of gas from the manifold if there is a leak in an
individual cylinder or lead.
pressure reducing valve
This valve reduces the high variable pressure issuing from the gas
cylinder banks (e.g., 137 bar for 02) to about 10 bar
then a 2nd stage reducing valve decreases the pressure from 10 bar
to a low steady and safe working pressure in the pipelines (4bar).
Pressure relief valve:
This valve is open to the atmosphere to vent excess gases if the
pressure in the central pipeline exceeds a present value.
 It is usually set at 50% above normal pipeline pressure and closes
automatically when the excess pressure has been relieved.
 This valve protects the anesthetic machines or ventilators from damage
by the high pressure.

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Alarm Systems(O2 Failure Safety Devices ):
 Alarm systerns give audible and visual signals if the pipeline pressure
increases (e.g., pressure regulator malfunction) or decreases from a
preset value which is usually 20-35 psi. (e.g., supply depletion).
 The master (central) system monitors the central supply.
The area (local) systems monitor each specific area of use i.e the OR,
PACU, and ICU.

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2-Pipeline Distribution Network:
 This pipeline network is formed of pipelines which deliver the
gases to the site of use e.g., OR, PACU, and icu
Pipes are sized such that the pressure drop across the whole
system never exceeds 5 psi.
Each local has a manual shut-off and a local alarm system.
Pipes are made of copper and are color-coded.
3-Pipeline Terminal Outlets:
The pipelines terminate at terminal outlets which are situated usually
on the walls, ceilings, or artuclating arms at the site of use.

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1-Oxygent outlet: Its color code is white and works with pressure 4
bar.
2-Nitrous oxide outlet: Its color code is blue and works with pressure
4 bar
3- Compressed air outlet: Its color code is black and white and
works with either: 4 bar for anesthetic machine and ventilators
or 7 bar for instrumental use e.g., orthopedic and
neurological instruments.
4- Vacuum outlet: Its color code is yellow. It should be at least 53
kPa (400-500 mm Hg). It is used for surgical suction. Nowadays, it is
an integral part of the medical gas system. This system is called pipe
medical gases and vacuum (PMGV).
5- Scavenging outlet: Its color code is yellow. It should be wider in
diameter than other outlets. There is variety of scavenging outlets.
6- Carbon dioxide outlet: is present in some theaters for use in
laparoscopic surgery.
Types:

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4- Flexible Hoses: They are also color-coded and connect the
terminal outlets to the anesthetic machines or ventilators
5- Terminal Connections:
They are the connections between flexible hoses and anesthetic
machines.

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The functioning of medical gas supply sources and pipeline systems is
constantly monitored by central and area alarm systems. Indicator
lights and audible signals warn of changeover to secondary gas sources
and abnormally high (eg, pressure regulator malfunction) or low (eg,
supply depletion) pipeline pressures (Figure 2–5).

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Suction Apparatus
Suction apparatus is connected to the centralized vacuum pipeline
system. (figure 6-10)
Components
A collecting jar: is present between the patient and the suction
apparatus to collect the suctioned materials.
It contains a float control that floats up and closes the jar when it is
full, to prevent obstruction of the suction apparatus by the suctioned
materials.
Afilter and another float control: provide extra protection to the
suction unit.
A compartment; in which the vacuum inlet is connected.

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Apressure control knob and a diaphragm: The setting of the control
knob at the top alters the pressure in the spring on the diaphragm.
This in turn varies the pressure at which the diaphragm control valve
.open or closes the vacuum inlet, thus adjusting the degree of
vacuum.
A gauge: indicates the suction pressure
Maximum vacuum is usually more than 0.67 bar (500 mmHg) which is
provided when the pressure control knob is fully opened. This is needed
in most general purposes.
Degree vacuum
 Lower vacuum is sometimes needed e.g., during drainage of a
closed cavity which is provided by zringthe flow of suction by the
pressure control knob

7/9/2020 67
Safety Features :
A)Gas Cylinders:
They should have:
A Color code system specific for each gas to avoid misconnection.
pressure regulator to reduce the pressure to 4 bar to avoid damage of
the anesthetic machine.
 pressure relief valve (rupture disk) downstream to the pressure
regulators to prevent explosion under conditions of unexpectedly high
gas pressure (e.g., unintentional overfilling).
-special connection system to avoid misconnection and incorrect
attachment as '!. Pin Index Safety system (PISS) or a special direction
of the internal thread.
Filling ratio i.e., never filled to the point at which they only
contain liquid, because any slight increas in temperature will cause a
dangerous rise in cylinder pressure.

7/9/2020 68
B) Medical Gas Pipeline Systems:
They should have:
• A color code system.
• A pressure regulator.
• A pressure relief valve which is open to the atmosphere to vent
excess gases if the pressure in ·central pipeline exceeds a preset value.
This valve protects the anesthetic machines or ventilators fro damage
due to the high pressure.
• A special connection system to avoid misconnection and incorrect
attachment as a diameter index safety system (DISS).
• Local and central alarm systems (02 failure safety devices).

7/9/2020 69
The Diameter Index Safety System (DISS) is designed to prevent the
misconnection of hospital gas supply lines to the anesthesia
workstation. The Pin Index Safety System (PISS) is designed to prevent
incorrect gas cylinder connections in the anesthesia workstation.
Neither system is immune from failure.
 If the hospital pipeline becomes crossed or contaminated,
two actions must be taken. The backup oxygen cylinder valve
must be opened, and the wall supply sources must be
disconnected. Otherwise, hospital pipeline gas will continue
to flow to the patient.
Therefore, in a case of known or suspected hospital pipeline oxygen
supply contamination or pipeline crossover, in which oxygen is
substituted for another gas but pipeline pressure maintained, only by
disconnection of the oxygen pipeline source hose from the wall outlet
will the machine be able to use E-cylinder
oxygen.

7/9/2020 70
Checking out the Medical Gas SuppIy
System in an operation Room
• Hospitals should have well-defined written policies for
management, testing, and control of their medical gas systems and
appropriate training of personnel.
• Although anesthesiologists are not responsible for the hospital
construction, they are responsible for intraoperative patient safety.
In particular, the anesthesiologists are accountable for the portion of
the medical gas system that extends from the wall outlet to the
patient.
• Checking out the medical gas supply system should be performed
in new operation room before the first anesthesia is delivered, and
after any maintenance or repairs are carried out on a piped medical
gas system.

7/9/2020 71
A) Tests of the Oxygen Cylinders:
Confirm that oxygen cylinders are full (2000psi) or at least half-full
(1000psi).
B) Tests of the Piped Medical Gas Supply:
Each pipeline should be tested separately
Medical air is used, where the whole system (each pipeline is tested
separately) is pressurized and sealed Over a period of 24 hours, there
must be no drop in pressure.
It is performed by connecting medical air to one pipeline system at a
time and ensuring that the test air is delivered from every terminal
outlet bearing the name of the gas pipeline system being tested, and
not delivered from any other terminal outlet.

7/9/2020 72
Particulate contamination in pipes may occur, so purging at each
affected gas outlet is required to remove loose particles in the
pipeline, and to ensure that the pipeline contains only gas from the
supply. Purging involves full opening of the valve at each outlet for a
period of about 4 min. This test may cause a rapid drop in the gas
pressure in the pipeline system which should activate the associated
alarms.
• An oxygen analyzer: checks the identity by giving readings of
0%for nitrous oxide, 21%for air, 50%for Entonox, and 100%for
oxygen.
• A chemical gas detection tube.
• Gas chromatography.
•A mass spectrometer.

7/9/2020 73
This is performed by a suction gauge capable of measuring negative
pressure. Common problems include:
A negative pressure of at least -400 mmHg to -500 mmHg should be
maintained at the outlet.
• Presence of carbon dioxide impurities; as during pipe jointing
procedures, the pipe is filled to a few feet on either side of the joint
with carbon dioxide to decrease oxidation while the pipe is heated.
Therefore, residual carbon dioxide should be removed by purging.
• Presence of residual copper oxide particles inside the pipeline
system.
• Improper joints.
• Inadequate sizing.
• System leaks.
• Components failure e.g., faulty pressure-relief valves

Q1 : concerning cylinders ; one of the following
statements is true : -
A.Oxygen is stored in cylinders as a liquid .
B. The pressure in a half-filled O2 cylinder is 2000 psig
C. N2O is stored in the cylinder in the gas phase.
D. The pressure in a half-full N2O cylinder is 745 psig.
E. The body colour of the O2 cylinder is white . While shoulder colour
is black.

Q2 : About Entonox one is false : -
A. Entonox have cylinders have blue bodies and white and blue
quarters on the shoulders.
B. The pressure in a full-filled O2 cylinder is 1800-2200 psig
C. Entonox is 50:50 mixture by weight of O2 and N2O.
D. Entonox has a critical temperature of -5.5oC .
E. At room temperature, Entonox cylinders contain only gas.

Q3 :Gas from an N2O cylinder enters the anesthesia machine through a
pressure regulator that reduces the pressure to :
A. 1800 psig.
B. 2200 psig.
C. 60 psig.
D. 745 psig.
E. 45 psig.

Q4 : Which of the following systems prevents attachment
of gas-administering equipment to the wrong type of gas line?
A. Pin index safety system
B. Diameter index safety system
C. Fail-safe system
D. check valve
E. Proportion-limiting control system

Q5:True or False :
A. Cylinders are made of thick-walled molybdenum steel to
withstand the high internal pressure .
B. When warmed, liquid O2 can give 860 times its
volume as gas.
False
True
C. Concerning piped medical gas and vacum, the
outlets are shape- and colour coded.
True
D. The pressure within the N2O cylinder will being
to fall when Approximatly ¾ of the gas has left in
the cylinder.
True

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