Anesthesia Machine
Presented by Gil Soto C.R.N.A
Danger
Unpleasant Surprises
Lecture Outline
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The Machine
Gas Supply Systems:
Hospital pipeline
Cylinder
High Pressure System (exposed to cylinder pressure)
Intermediate Pressure System (exposed to pipeline press)
Low Pressure System (distal to flowmeter needle valve)
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Circle System
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CO2 Absorber System
Unidirectional Valves
Ventilator
Scavenger System
Anesthesia Machine Checkout
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General:
Anesthesia Apparatus Checkout Recommendations, 1993 (Taken from the FDA)
This checkout, or a reasonable equivalent, should be conducted before administration
of anesthesia. These recommendations are only valid for an anesthesia system that
conforms to current and relevant standards and includes an ascending bellows
ventilator and at least the following monitors: capnograph, pulse oximeter, oxygen
analyzer, respiratory volume monitor (spirometer) and breathing system pressure
monitor with high and low pressure alarms. This is a guideline which users are
encouraged to modify to accommodate differences in equipment design and
variations in local clinical practice. Such local modifications should have appropriate
peer review. Users should refer to the operator's manual for the manufacturer's
specific procedures and precautions, especially the manufacturer's low pressure leak
test
(step #5).
* If an anesthesia provider uses the same machine in successive cases, these steps
need not be repeated or may be abbreviated after the initial checkout.
Anesthesia Machine Checkout
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Steps 1-3:
Emergency Ventilation Equipment
*1. Verify Backup Ventilation Equipment is Available &
Functioning
High Pressure System
*2. Check Oxygen Cylinder Supply
a. Open 02 cylinder and verify at least half full (about
1000 psi).
b. Close cylinder.
*3. Check Central Pipeline Supplies
a. Check that hoses are connected and pipeline gauges
read about 50 psi.
Anesthesia Machine Checkout
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Steps 4-7:
Low Pressure Systems
*4. Check Initial Status of Low Pressure System
a. Close flow control valves and turn vaporizers off.
b. Check fill level and tighten vaporizers' filler caps.
*5. Perform Leak Check of Machine Low Pressure System
a. Verify that the machine master switch and flow control valves are OFF.
b. Attach "Suction Bulb" to common Fresh gas outlet.
c. Squeeze bulb repeatedly until fully collapsed.
d. Verify bulb stays fully collapsed for at least 10 seconds.
e. Open one vaporizer at a time and repeat 'c' and 'd' as above.
f. Remove suction bulb, and reconnect fresh gas hose.
*6. Turn On Machine Master Switch and all other necessary electrical equipment.
*7. Test Flowmeters
a. Adjust flow of all gases through their full range, checking for smooth operation of
floats and undamaged flowtubes.
b. Attempt to create a hypoxic 02/N20 mixture and verify correct changes in flow
and/or alarm.
Anesthesia Machine Checkout
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Scavenging System
*8. Adjust and Check Scavenging System
a. Ensure proper connections between the scavenging
system and both APL (pop-off) valve and ventilator relief
valve.
b. Adjust waste gas vacuum (if possible).
c. Fully open APL valve and occlude Y-piece.
d. With minimum 02 flow, allow scavenger reservoir
bag to collapse completely and verify that absorber
pressure gauge reads about zero.
e. With the 02 flush activated allow the scavenger
reservoir bag to distend fully, and then verify that
absorber pressure gauge reads <10 cm H20.
Anesthesia Machine Checkout
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Breathing System
*9. Calibrate 02 Monitor
a. Ensure monitor reads 21% in room air.
b. Verify low 02 alarm is enabled and functioning.
c. Reinstall sensor in circuit and flush breathing system with 02.
d. Verify that monitor now reads greater than 90%.
10. Check Initial Status of Breathing System
a. Set selector switch to "Bag" mode.
b. Check that breathing circuit is complete, undamaged and unobstructed.
c. Verify that C02 absorbent is adequate.
d. Install breathing circuit accessory equipment (e.g. humidifier, PEEP valve) to be
used during the case.
11. Perform Leak Check of the Breathing System
a. Set all gas flows to zero (or minimum).
b. Close APL (pop-off) valve and occlude Y-piece.
c. Pressurize breathing system to about 30 cm H20 with 02 flush.
d. Ensure that pressure remains fixed for at least 10 seconds.
e. Open APL (Pop-off) valve and ensure that pressure decreases.
Anesthesia Machine Checkout
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Manual and Automatic Ventilation Systems
12. Test Ventilation Systems and Unidirectional Valves
a. Place a second breathing bag on Y-piece.
b. Set appropriate ventilator parameters for next patient.
c. Switch to automatic ventilation (Ventilator) mode.
d. Fill bellows and breathing bag with 02 flush and then turn ventilator ON.
e. Set 02 flow to minimum, other gas flows to zero.
f. Verify that during inspiration bellows delivers appropriate tidal volume and that
during expiration bellows fills completely.
g. Set fresh gas flow to about 5 L/min.
h. Verify that the ventilator bellows and simulated lungs fill and empty
appropriately without sustained pressure at end expiration.
i. Check for proper action of unidirectional valves.
j. Exercise breathing circuit accessories to ensure proper function.
k. Turn ventilator OFF and switch to manual ventilation (Bag/APL) mode.
l. Ventilate manually and assure inflation and deflation of artificial lungs and
appropriate feel of system resistance and compliance.
m. Remove second breathing bag from Y-piece.
Anesthesia Machine Checkout
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Monitors
13. Check, Calibrate and/or Set Alarm Limits of all Monitors
Capnometer, Pulse Oximeter, Oxygen Analyzer, Respiratory Volume
Monitor (Spirometer), Pressure Monitor with High and Low Airway
Alarms
Final Position
14. Check Final Status of Machine
a. Vaporizers off
b. AFL valve open
c. Selector switch to "Bag"
d. All flowmeters to zero
e. Patient suction level adequate
f. Breathing system ready to use
The Anesthesia Machine
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The anesthesia gas
machine is a device
which delivers a
precisely-known but
variable gas mixture,
including
anesthetizing and lifesustaining gases.
Ohmeda
The Machine
N.A.Drager (Narkomed)
Anesthesia Machine:
Jackson Memorial Hospital
Manufacturers & Names
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North American Dräger (Telford, PA) is the
manufacturer of the Narkomed 2C,
Narkomed 4, Narkomed GS, Narkomed
6000, Narkomed Julian, Narkomed MRI
and Narkomed Mobile models.
Datex-Ohmeda (Madison WI)
manufactures the AS/3 ADU, Aestiva,
Modulus SE, Excel 210, and Excel 110
Some Numbers to Remember
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The hospital pipeline is the primary gas source at 50 psi (normal
working pressure of most machines).
Cylinders – O2 is supplied at around 2000 psi (regulated to
approximately 45 psi after it enters the machine).
Oxygen flush is a "straight shot" from supply to delivery point, 3575 L/min.
OSHA Fact Sheet (1991) on Waste Anesthetic Gases (WAGs)
occupational exposure should be limited to an eight hour timeweighted average of not more than 2 ppm halogenated agents
(Halothane, Enflurane, Isoflurane, Sevoflurane, Desflurane)
If Halogenated agent is used in combination with nitrous oxide, then
ONLY 0.5 ppm OF THE HALOGENATED AGENT IS ALLOWED
No more than 25 ppm nitrous oxide can be used at all times (with
or without Halogenated Agent)
Minimal Components
O2 Pipeline
N2O Pipeline
O2 Flowmeter
N2O Flowmeter
Container with VAA
Bag-valve-mask device
Patient
Straight-line model
SPDD (Supply/Processing/Delivery/Disposal)
Oxygen has five "tasks”
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It powers the ventilator driving gas
O2 flush
Activation of low pressure alarms
Activation of fail-safe mechanisms
(O2 pressure sensor shut-off )
Proceeding through the flowmeter
“Other gases: One task Only”
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Transported via flowmeter & breathing
circuit to:
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Anesthetize pt (N2O)
Sustain Life (Air)
Basic Schematics
Gas Supply Systems
Hospital Pipeline
DISS
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Pipeline inlets are connected with
DISS (diameter index safety system)
non-interchangeable connections.
The check valve, located down
stream from the pipeline inlet,
prevents reverse flow of gases (from
machine to pipeline, or to
atmosphere), which allows use of the
gas machine when pipeline gas
sources are unavailable.
PISS
PISS (pin-index safety system) prevents misconnection of a
cylinder to the wrong yoke. Keep cylinders closed except
when checking machine, or while in use (if O2 from pipeline
is unavailable)
Gas Supply Systems
Cylinder
Pin Index Safety System:
O2 2,5
N2O 3,5
High Pressure System
(parts which receive gas at cylinder pressure)
hanger yoke (including filter and unidirectional
valve)
 yoke block (with check valves)
 cylinder pressure gauge
 cylinder pressure regulators
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Hanger Yoke & Check Valve
Hanger Yoke
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orients cylinders
provides
unidirectional flow
ensures gas-tight
seal.
Check Valve
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minimize trans-filling
allows change of
cylinders during use
minimize leaks to
atmosphere if a yoke
is empty.
Check Valve
More on Cylinders
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The cylinder pressure regulator converts
high, variable cylinder pressure to a constant
pressure of approximately 45 psi downstream of
the regulator.
This is intentionally slightly less than pipeline
pressure, to prevent silent depletion of cylinder
contents if a cylinder is inadvertently left open
after checking its pressure.
Cylinder pressure gauge indicates pressure in
the higher-pressure cylinder only (if two are
opened simultaneously).
E cylinder Characteristics
Gas
O2
N2O
Air
US (International)
Green
(white)
Blue
(blue)
Yellow (B & W)
PSI
1900
745
1900
Capacity (L)
660
1590
625
PISS
3-5
**** We’ll use 2000psi for O2 instead of 1900psi****
2-5
1-5
Intermediate Pressure System
Hospital Pipeline
Outlets
Machine piping “guts”
Hospital Pipeline
Inlets
Gauges-pipeline (intermediate press. )
Intermediate Pressure System
(receives
gases at low, relatively constant
pressures (37-55 psi, = pipeline pressure)
(*For consistency we’ll use 50 psi)
 pipeline inlets and pressure gauges
 ventilator power inlet
 Oxygen pressure-failure device (fail-safe)
and alarm
 flowmeter valves
 oxygen second-stage regulator
 oxygen flush valve
Oxygen pressure-failure device
(fail-safe) and alarm
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What happens if you lose oxygen pipeline
pressure?
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The fail safe device ensures that "Whenever oxygen pressure
is reduced and until flow ceases, the set oxygen concentration
shall not decrease at the common gas outlet" (from ASTM
F1161).
The loss of oxygen pressure results in alarms, audible and
visible, at 30 psi pipeline pressure.
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Fail-safe systems don't prevent hypoxic
mixtures.
Fail-safe systems don't prevent
hypoxic mixtures
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as long as there is pressure in the O2 line, nothing in the
fail safe system prevents you from turning on a gas
mixture of 100% nitrous oxide (however, this should be
prevented by the hypoxic guard system)
or 100% helium (which wouldn’t be prevented by the
hypoxic guard).
Datex-Ohmeda terms their fail safe a "pressure sensor
shut off valve"- at 20 psi oxygen, the flow of all other
gases are shut off. Dräger's, "oxygen failure protection
device" (OFPD) threshold is proportional, unlike
Ohmeda's which is off-or-on.
Fail-safe systems don't prevent
hypoxic mixtures (Cont…)
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Ohmeda uses a second-stage O2
pressure regulator (ensures constant
oxygen flowmeter input until supply
pressure is less than 12-16 psi). The
oxygen ratio monitor controller (ORM
[newer] or ORMC, both by Dräger) shuts
off nitrous oxide when oxygen pressure is
less than 10 psi
Pipeline Trouble
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Pipeline sources are not trouble free:
contamination (particles, bacteria, viral,
moisture), inadequate pressure, excessive
pressures, and accidental crossover
(switch between oxygen and some other
gas such as nitrous oxide or nitrogen) are
all reported.
What if you lose oxygen pipeline
pressure?
Open the emergency oxygen cylinder fully (not just
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the three or four turns used for checking)
Disconnect the pipeline connection at the wall
Why? Something is wrong with the oxygen pipeline.
What if the supply problem evolves into a nonoxygen gas in the oxygen pipeline? If so, it will flow
to the patient (pipeline pressure 50 psi) rather than
your oxygen cylinder source (down-regulated to 45
psi).
 If you are lucky, the oxygen alarm will sound to
warn you of the change (you do set your alarms,
don't you?).
 If for some reason the oxygen analyzer does not
warn of the crossover, the pulse oximeter will- but
only after the oxygen has been washed out by
ventilation from the patient's functional residual
capacity and vessel-rich group.
Reinforcement!!!!
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Disconnect the pipeline connection at the wall if
oxygen pipeline pressure is lost. It's also easier
to remember one strategy which works for any
problem with the pipeline, rather than to
remember that sometimes you must, and
sometimes it is optional, to disconnect. And use
that oxygen analyzer always!
Ventilate by hand rather than with the
mechanical ventilator (which uses cylinder
oxygen for the driving gas if the pipeline is
unavailable)
HOW LONG BEFORE
O2 TANK IS EXHAUSTED???
-The time to exhaustion is calculated by dividing
the remaining O2 volume in the cylinder by the
rate of consumption of O2.
-Remaining volume in liters (L) in an E-cylinder
is calculated by dividing the cylinder pressure in
psig by 2000 psig and multiplying by 660 L.
EXAMPLE
If cylinder gauge reads 1,000 psig, this represents
(1000/2000) X 660 = 330 L left in that tank. The rate of
consumption of O2 during mechanical ventilation is the
sum of the O2 flow meter setting and the patient’s
minute ventilation (VT in L x RR in breaths/min).
 If FGF is 0.5 L/min O2 and 1.0 L/min N2O and VT is 0.7
L and RR is 10 bpm, then the minute ventilation is
7 L/min (0.7L x 10 bpm)
* The total O2 consumption is 7.5 L/min. The expected
time to exhaustion is thus approximately 330 L divided
by 7.5 L/min = 44 min (ignoring the gas sampled by the
gas analyzer and leaks)
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The Low-pressure system
(distal to flowmeter needle valve)
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flowmeter tubes
vaporizers
check valves (if present)
common gas outlet
Flowmeters
-Thorpe tube is an older term for flowmeters.
-Components: needle valve, indicator float, knobs, valve
stops.
-Flow increases when the knob is turned counterclockwise
(same as vaporizers).
-At low flows, the annular-shaped orifice around the float is
(relatively) tubular so (according to Poiseuille's Law) flow is
governed by viscosity. (laminar flow)
-At high flows (indicated on the wider top part of the float
tube), the annular opening is more like an orifice, and
density governs flows. (turbulent flow)
Low Pressure System
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Distal to Flowmeter Needdle Valve
Flow Meters- measures and indicates the rate of gas flowing through
it. Variable orifice/Thorpe tube-constant press. flow meters.
Rate of flow r/t: 1) pressure drop across the constriction
2) size of annular opening
3) Physical properties of the gas
(viscosity and density) FLOW
Indicator, float or bobbin-
1) rotometers
2) non-rotating floats
3) ball floats
Sequence of flowmeters tubes is very important
to decrease chance of hypoxic mixture.,
Gas flow is from left to right, O2 on right side.
Any leak in flowmeters will vent other gas out or
entrain air before O2 is added to gas mixture decreasing
chance that O2 will be lost or diluted.
More on Flowmeters
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Needle valve can be damaged if it is
closed with force
Flowtube (Thorpe tube) is tapered
(narrower at bottom) and gas-specific
If gas has 2 tubes, they are connected in
series with a single control valve
Did anyone say Flowmeters??
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Care of flowmeters includes ensuring that:
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floats spin freely
qualified service personnel regularly maintain gas
machines
an O2 analyzer used always (of course, the readings
are erroneous during use of nasal cannula)
one never adjusts a flowmeter without looking at it
one includes flowmeters in visual monitoring sweeps
one turns flowmeters off before opening cylinders,
connecting pipelines, or turning machine "on".
Low Pressure System
Safety Devices-Purpose is to decrease risk of hypoxic mixture
* Mandatory Minimum O2 Flow- factory preset minimum
O2 flow that always flows when machine is on.
* Minimum O2/N2O Ratio– 1:3
Device or proportioning system: Flow valves linked
mechanically or pneumatically so O2 cannot be set below 25%.
Alarm will signal if O2/NO2 ratio falls below preset value
* O2/NO2 Proportioning Device-Automatically mixes O2 and NO2 to
setting selected on dial
Hypoxic breathing is POSSIBLE
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hypoxic guard systems CAN permit
hypoxic breathing mixtures IF:
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wrong supply gas in oxygen pipeline or
cylinder,
defective pneumatic or mechanical
components,
leaks exist downstream of flow control valves,
or
if third inert gas (such as helium) is used.
Low Pressure System
Vaporizers- Classification:
A. Method of regulating output concentration
1. Concentration calibrated
2. Measured flow
B. Method of vaporization
1. Flow over
2. Bubble Through
3. Injection
C. Temperature compensation
1. Thermocompensation
2. Supplied heat
D. Specificity
1. Agent specific
2. Multiple agent
E. Resistance
1. Plenum
2. Low resistance
VAPORIZERS
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Vapor Pressure (VP) Molecules escape from a
volatile liquid to the vapor phase, creating a
“saturated vapor pressure” at equilibrium
VP is independent of Atmospheric Press
VP increases with Temperature
VP depends ONLY on the Physical Characteristics
of the Liquid & on its Temperature
CLASSIFICATION
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Variable bypass
Fresh gas flow from the flowmeters enters the
inlet of any vaporizer which is on. The
concentration control dial setting splits this
stream into bypass gas (which does not enter
the vaporizing chamber), and carrier gas (also
called chamber flow, which flows over the
liquid agent)
CLASSIFICATION
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Flow over
Carrier gas flows over the surface of the liquid
volatile agent in the vaporizing chamber (as
opposed to bubbling up through it (as in the
copper kettle and Vernitrol)
CLASSIFICATION
Temperature compensated
Equipped with automatic devices that ensure
steady vaporizer output over a wide range of
ambient temperatures
Agent-specific
Only calibrated for a single gas, usually with keyed
fillers that decrease the likelihood of filling the
vaporizer with the wrong agent
Out of circuit
As opposed to (much) older models such as the
Ohio #8 (Boyle's bottle) which were inserted
within the circle system.
Vaporizer Interlock Mechanism
Safety mechanism that allows ONLY one vaporizer at a
time to be opened
Circle System
Circle System- CO2 absorber housing and absorber, unidirectional valves,
inspiratory and expiratory ports, fresh gas inlet, APL valve, pressure gauge,
breathing tubes, Y-piece, reservoir bag, bag/vent switch selector, respiratory gas
monitor sensor.
Circle System
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CO2 Absorber System: Housing (canister support), Absorbent, baffles, side tube
Unidirectional Valves-aka Flutter valves, one way valves, check valves, directional
valves, dome valves
Canister-Air space 50%, void space 42%, pore space 8%
 Soda Lime: 4% Sodium Hydroxide, 1% potassium hydroxide, 14-19% H2O,
and calcium hydroxide to make 100%,
Silica and kielselguhr for hardness
Indicator for color change with exhaustion of CO2 absorption capabilities
CO2+H2OH2CO3
2NaOH+2H2CO3+Ca(OH)2 CaCO3+NaCO3+4H2O
heat released 13,700 cal./mole CO2 absorbed
 Barium Hydroxide Lime: 20% Barium hydroxide, 80% calcium hydroxide,
and +/- potassium hydroxide,
Indicator for color change with exhaustion of CO2 absorption capabilities
Ba(OH)2 . 8H2O+CO2BaCO3+9H2O
9H2O+9CO2 9H2CO3
9H2CO3+9Ca(OH) 2  9CaCO3+18H2O
2KOH+H2CO3  K2CO3+2H2O
Ca(OH)2+K2CO3  CaCO3+2KOH
Regeneration (color change loss) with rest can occur. Appears new but is
exhausted Granule size 4-8 mesh- 4 mesh equals strainer with 4
openings/inch
Circle system
CO2 Absorber System
canister locking lever
Removing both canisters
& soda lime
canisters unlocked
Exhausted soda lime
Removing canister & soda
lime
Replacing fresh soda
lime
Circle system
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Unidirectional Valves
Unidirectional valves-aka flutter valves, one way valves, check
valves,
directional valves, dome valves.
Found on Inspiratory and Expiratory flow
ports
Ohmeda Machine
Narkomed Machine
Ventilator
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Ventilator Components: Driving gas supply, injector, controls,
alarms, safety-release valve, bellows assembly, exhaust valve,
spill valve, connection for ventilator hose
Bellows assembly
Ventilator controls
Ventilator
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Driving gas supply or power gas supply-O2 pneumatically drives
(compresses) ventilator bellows
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Injector or Venturi mechanism-Increases the flow of driving gas by using the
BERNOULLI Principle- As a gas flow meets a restriction, its lateral pressure
drops. Any opening in the tube at this constriction will entrain air (suck air in)
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Controls-Adjusts Flow, Volume, Timing, and Pressure of the driving gas that
compresses the bellows
Pneumatic-Uses pressure changes to initiate changes in respiratory cycle
Fluidic or fluid logic-Uses gas streams through channels in solid
material. Allow for compact ventilator
Electronic-Electronic control of many addition
ventilation parameters powered
by a driving gas on newer machines. Must
have both power and pnuematics.
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Alarms-ASTM standards group alarms into three levels: High, Medium, Low
Priority
correlates to;operator immediate action, prompt action,or
awareness.
Loss of main power is the only required alarm with a
required duration of at least
2 minutes
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Safety relief valve-aka pressure limiting valve, drving gas pressure relief
valve. Vents
driving gas if factory pre-set pressure is reached (65-80 cm
H2O) or adjustable
set pressure is reached.
Bernoulli’s Principle
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At constriction:
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Flow is higher
Pressure is lower
Ventilator
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Bellows Assembly:
Housing- Usually made of hard rigid clear plastic
Bellows; ASCENDING-standing, upright. Compressed downward
during inspiration. ASCEND DURING EXPIRATION
Pressure is always positive. PEEP 2-4 cm H2O.
DESCENDING-hanging, inverted. Compressed upward during
inspiration. DESCEND DURING EXPIRATION. Weight of bellows
results in negative airway pressure during exhalation until bellow
refilled.
IMPORTANT difference between ascending and descending is
that when there is a major leak or disconnect, the ascending
bellows will collapse (unless prevented by scavenging system).
When a disconnection occurs with a descending bellows
system,
the ventilator will continue it’s upward movement
and downward
movements, drawing in room air and driving gas during it’s
descent and discharging it during the upward movement.
Gas flow during upward movement may generate enough
pressure such that the low pressure alarm is not activated.
Remember that the type is described by how the bellows move
during EXPIRATION
What type is
shown?
Scavenger System
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Scavenger System consists of: 1) gas collecting assembly, 2) a
transfer means, 3) the interface, 4) gas disposal tubing, 5) gas
disposal assembly. (some or all components may be combined).
ASTM standard
fitting size for scavenger hoses 19 mm ( international standard
30mm) to prevent incorrect connection to breathing hoses (22mm).
3
2
4&5
1
4&5
1
REFERENCES
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N&Z pg 247-252
M&M pg 35-49
D&D pg 3-74
http://chico.med.yale.edu/machine/agmpa
rt1.htm#General%20features
http://www.anest.ufl.edu/~eduweb/vam/
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The essence of intelligence is skill in extracting
meaning from everyday experience