anesthesia workstation

1. Anesthesia Workstation
Presenter
Dr. Pooja Lama
1st year Resident
Anesthesiology
NAIHS
Moderator
Associate.Prof. Dr. U. B. Bajracharya
Anesthesiologist

2. Objectives
• History and evolution of anesthesia machines
• Essential safety features
• Functional anatomy
• Minimum anesthesia checklist

3. History
• After anaesthesia was invented and
introduced with the public
demonstration of ether anaesthesia by
WTG Morton in 1846, for many years
an anaesthesia machine was not
required for providing anaesthesia to
the patients until oxygen (O2) and
nitrous oxide (N2O) were introduced as
compressed gases in cylinders by the
late 19th century

4. Evolution
 Handapparat 145 N or Roth-
Dräger of 1902 could be regarded
as the prototype of a long line of
Dräger anaesthetic apparatus.
 Its most important components
were:-
 the pressure-reducer to control
the gas flow from the cylinder and
 the drip-feed device to control the
flow of anaesthetic agent
precisely.

5.  240 N double apparatus in 1903.
 A second drip feed was added.
 It was for second anesthetic agent
that is ether.

6. 1911:
Roth-Dräger-Krönig
This apparatus had a second
oxygen-driven injector.
With this injector and a hand-
operated switching valve, positive
and negative pressure could be
produced.
The anaesthetist could now
discontinue anaesthesia, if
breathing stopped or some other
incident occurred, and reflate or
deflate the lung with oxygen-
enriched air in
breathing rhythm.

7. Gwathmeys apparatus
• 1912
• James Taylor Gwathmey

8. Boyles apparatus
• The Boyles apparatus
was first made by
Coxeter and Sons.
• Presented his invention
at the Royal Society of
Medicine in London in
1918.

9. Boyles machine
• Henry Edmund Gaskin Boyle in
1917.
• It became the best known early
continuous flow anaesthetic
machine.
• It could administer nitrous
oxide, oxygen, cyclopropane and
carbon dioxide gases
• The machine also has sight-feed
vaporizers, called "Boyle
bottles", to administer the
volatile agents ether and
Trilene.

10. • 1920- addition of vapourizing bottle.
• 1921 – Waters to and fro absorption apparatus was
introduced.
• 1926- addition of second bottle and bypass control.
• 1927 – Flow meter for carbon dioxide was included, the
volatile controls were of the lever type and the familiar back
bar made its first appearance.

11. • 1930 – The plunger of the vaporiser appeared in the 1930
model.
• 1930 – Circle absorption system was introduced by Brian
Sword.
• 1933 – Dry bobbin flow meters were introduced.
• 1952 – Pin index safety system (PISS) by Woodbridge.
• 1958 – Introduction of Bodok seal.

12. Anesthesia Workstation
• Anesthesia machine
• Vaporizers
• Ventilator
• Breathing system
• Scavenging system

13. Function of anesthesia machine
• To deliver oxygen to patient
• To deliver mixture of anesthetic gases .
• To provide ventilation to the patient
• Minimises anesthesia related risks to staff and patient.

14. Types of anesthesia machine
A. Intermittent: Gas flows only during inspiration.
eg. Entonox apparatus.
B. Continuous : Gas flows both during inspiration and expiration.
eg. Boyle, Dragger.

15. Safety features of anesthesia workstation

16. Essential safety features on modern anesthesia
workstation
1. Non interchangeable gas specific connections to pipeline
inlets- diameter index safety system
2. Pin index safety system for cylinders
3. Low oxygen pressure alarm or oxygen supply failure alarm
4. Oxygen failure protection devices or fail safe valves
5. Oxygen must enter the common manifold downstream to
other flowmeters
6. Oxygen concentration monitor and alarm
7. Vaporizer interlock device
8. Flowmeter have flourescent screen
9. Flowmeter needle valve are fluted and colour coded
10. Oxygen flush  does not pass through vaporizers

17. 11. Bobbin with its rotatory movement
12. Capnography and anesthetic gas measurement
13. Breathing circuit pressure monitor and alarm
14. Mechanical ventilator
15. Pulse oximetry, blood pressure and ECG monitoring
16. Backup battery
17. Scavenger system
18. Antistatic rubber wheels
19. Transparent CO2 absorber canister

18. Unacceptable features of older anesthesia
machines
1. Flowmeter-controlled vaporizer.
2. More than one flow control valve for a single gas.
3. Vaporizer with a rotary dial that increases concentration
with clockwise rotation
4. Connections in the scavenging system that are the same
size as a breathing circuit connections.

19. Undesirable features of older anesthesia
machines
1. Adjustable pressure-limiting valve that is not isolated during
mechanical ventilation.
2. Oxygen flow control knob that is not fluted or not larger than
other flow control knobs
3. Oxygen flush control that is unprotected from accidental
activation
4. Lack of main on/off switch for electrical power to integral
monitors and alarms
5. Lack of antidisconnect device on the fresh gas hose (common
gas outlet)
6. Lack of airway pressure alarms

20. Functional Anatomy

21. Functional anatomy
High pressure
system
Intermediate pressure
system
Low pressure
system
o Auxillary
E-cylinder inlet
with yoke
assembly
o High pressure
regulator
o Cylinder check
valve
o Pressure
regulator
From pressure regulator to
flow control needle valve.
o Pipeline supply with DISS
o Pipeline pressure gauge.
o Oxygen flush valve
o Pneumatic safety systems
o Oxygen supply failure
alarm
o Fail safe valve
o Auxillary oxygen
Flowmeter
o Second-stage pressure
regulators
From flow control
valve till common
gas outlet.
o Flow control
valves
o Flowmeters
o Proportioning
systems
o Vaporizers
o Common gas
outlet

22. High pressure system

23. Auxillary E-cylinder inlet
• Needed as a backup source in case of failure of hospital supply
source.
• Hanger yoke assemble with PISS is a safety feature.
 provides a gas tight seal
 ensures unidirectional flow of gases
• Pressure in E-cylinders for:-
 N2O is 750 psig
 O2 and air ~ 2000 psig.

24. Pin index safety system
 is a safeguard to reduce the risk of medical gas cylinder error
caused by interchanging cylinders.
 Each has specific pin arrangement. Air 1,5
Oxygen 2,5
Nitrous oxide 3,5

25. Conditions in which failure of PISS
has occurred
 Excessive seating or jamming of pins
 Presence of broken or bent pins
 Excessive use of washers between the cylinder and the yoke

26. High pressure regulator
• E-cylinders have high pressure.
• Each cylinder supply source line have a pressure reducing
mechanism known as high pressure regulator.
• This reduces the variable high pressures present in the
cylinder to a lower, nearly constant pressure suitable for use
in anesthesia machine.
• The pressure should be reduced to as low as 35 to 45 psig.
• The principle is to keep the high-pressure regulator output
pressure lower than the normal pipeline supply pressures 50-
55psig).

27. Cylinder check valve
• After the high pressure regulator
cylinder gas now flows through one-way valve called as the
cylinder check valve.
 Function:- it prevents any backflow of machine gas out
through an empty yoke or back into a nearly empty cylinder.

28. Intermediate- Pressure system fig

29. Pipeline inlet with DISS
• Hospital central gas supply source.
• Source is usually from a cryogenic bulk oxygen storage system
or large H-type oxygen cylinders.
• Pipeline pressure for oxygen, air and nitrous oxide is 50-55
psig.
 DISS – Diameter index safety system
it works by matching the shoulders of stem assembly on the
end of the supply hose to the bores of appropriate inlet .
• Gas passes from pipeline to the one way check valve.

30. DISS

31. Oxygen flush valve
• Is one of the oldest safety features.
• It provides manual delivery of a high flow rate of 100%
oxygen at the rate of 35 – 75 L/min directly to the
patient’s breathing circuit.
• Flow from oxygen flush valve bypasses the anesthetic
vaporizers.
Q. Oxygen flush is placed in
intermediate system

32. Hazards of oxygen flush valve
Defective or damaged valve Improper use of normally
functioning valve
can get stuck
in fully open
position
barotrauma
Can get stuck in
partially open
position
Results in patient
awareness because
of oxygen flow
from the
incompetent valve
dilutes the
anesthetic agents
o Overzealous intraoperative use
of oxygen flush can dilute
inhaled anesthetic agents.
o Oxygen flush during inspiratory
phase of positive-pressure
ventilation barotrauma

33. Pneumatic safety systems
• They help in delivery of hypoxemic gas mixture to the patient.
• ASTM standards state that:-
“ The anesthesia gas supply device shall be designed so that
whenever oxygen supply pressure is reduced to below the
manufacturer specified minimum,
the oxygen concentration shall not decrease below 19% at
the common gas outlet.”

34. Oxygen supply failure alarm sensors
• It senses the oxygen pressure if its drops below the
manufacturer-specified minimum
provide an audible and visual warning to the clinician.
• The alarm is an ASTM requirement and it cannot be silenced
until the pressure is restored to the minimum value.
• Sensors:- pneumatic or electronic

35. Oxygen failure protection device
• Aka fail safe valve or nitrous oxide cut off valve.
• Controlled by oxygen supply pressure .
• The fail safe valves shut off or proportionally decrease the
flow of the other breathing gases as the oxygen supply
pressure decreases.
• Drawback:-
if a gas other than oxygen adequately pressurizes the oxygen
circuit  the fail safe valve will remain open.

36. Auxillary oxygen flowmeter
• Not mandatory.
• But is a convenient feature that allows the use of low-flow
oxygen to the patient.
• It is accesible even the machine is not turned on.

37. Second stage pressure regulator
• These regulators supply constant pressure to the flow control
valves.
• Adjusted to lower pressure level than the pipeline supply that
is usually between 14 – 35 psig.

38. Low pressure system

39. Flow control valves
• Represents an important
landmark as they separate
intermediate-pressure system
form the low-pressure system
• CONSISTS of:-
 Flow control knob
 Tapered needle valve
 Valve seat
 Pair of valve stops.

40. Safety features of flow control valve
• Fluted.
 Oxygen flow control knob may
project beyond the control knobs
of the other gases.
 Larger in diameter.
• Colour coded.

41. Flowmeter or flow tubes
• It indicates the amount of gas being delivered per minute.
• Two types:
(i)electronic flowmeters (ii) calibrated flowmeters
• Gas at a suitably regulated pressure
from either a pipeline supply or cylinder,
is passed through a flowmeter.
• A mobile indicator float inside the
calibrated flow tube known as bobbin.

42. • Thorpe tube: The glass tubes are narrowest at
the bottom and widen vertically are called as
variable orifice area flow tubes or Thorpe tubes.
• The flowmeters are commonly referred to
constant-pressure flowmeters because the
decrease in pressure across the float remains
constant for all positions in the tube.
• Float or bobbin:- it rotates which indicates that
gas is flowing.

43. Annular space
• Flow through the annular space can be
laminar or turbulent, depending on the gas
flow rate.
• The annular space behaves as:-
 a tube at low flow rates  laminar flow and
viscosity determines the gas flow rate.
 An orifice at high flow rate turbulent flow
and density of gas determines the gas flow
rate.
• Stop:- at the top of the flowmeter tube
prevents the float from occluding the outlet.

44. Problems with flowmeters
1. Leaks:- are the potential hazard because the flowmeters are
located downstream from the antihypoxemia safety devices.
2. Inaccuracy:-
* Dirt or static electricity can cause a float to stick.
* Damaged float
* Backpressure from the breathing circuit can cause a
float to drop.

45. Safety feature of flowmeter
Oxygen flowmeter should be placed in downstream

46. Proportioning systems
• It is the most important pneumatic safety component.
• It prevents the creation and delivery of hypoxic gas mixture.
• ASTM standard states that “ the anesthesia workstation shall
be provided with a device to protect against an operator
selected delivery of a mixture of oxygen and nitrous oxide
having an oxygen concentration below 21% oxygen in the
fresh gas or in the inspiratory gas.”
• This is accomplished by a:-
i. Pneumatic-mechanical interface between oxygen and
nitrous oxide flows
ii. Link-25 system.

47. Pneumatic-mechanical interface
 North American Drager Sensitive Oxygen Ratio Controller
System (SOCR)
o It maintains oxygen-nitrous oxide ratio of no less than 25%
oxygen and 75% nitrous oxide into the breathing circuit.
When oxygen flow is decreased
to less than 200ml/min the
nitrous oxide proportioning valve
gets closed.

48. Link-25
o A mechanical propotioning
system.
o The Link-25 automatically
increases oxygen flow when the
nitrous oxide flow is increased to
more than a certain point relative
to oxygen flow to prevent delivery
of a hypoxic mixture.
o In the ratio of 1:3 for
oxygen:nitrous oxide.
Datex-Ohmeda Link-25 Proportion-Limiting Control System.

49. Limitations of Proportioning system
1) Malfunction:
2) Wrong supply gas: Even if wrong gas is supplied and if the
pressure in circuit in adequate it will continue to supply the
wrong gas.
3) Leaks:
4) Dilution of inspired oxygen concentration by volatile inhaled
anesthetic agents.

50. Outlet check valve
• It is located between the vaporizer and the common gas
outlet.
• Purpose:
to prevent backflow of gases into the vaporizer during
positive-pressure ventilation.

51. Minimum Anesthesia checklist

52. Checking your Anesthesia Workstation
2008 recommendations for preanesthesia checkout procedures
Items to be completed
daily
Items to be completed before each
procedure

53. Items to be completed daily

54. Items to be completed before each procedure

55. Verify no leaks between flowmeters and CGO
• The negative-pressure “universal” low-pressure system leak test.
• This test detects a leak as small as 30ml/min.
• The collapsed bulb should remain in collapsible state for 10
seconds.

56. If leak is
present
then
bulb gets
inflated.

57. Testing the low-oxygen concentration alarm and
calibrating the oxygen sensor
• The oxygen concentration analyzer is one of the most
important monitors on the anesthesia workstation.
• It is the only monitor positioned to detect oxygen delivery
problems downstreams from the flow control valves.

58. Breathing system pressure and leak testing
Machine set in manual mode.
Gas flow set to zero and APL valve is closed
Patient’s Y piece is occluded
Breathing system is pressurized with O2 flush to approximately 30
cm of H2O.
The circuit passes the leak test if it holds this pressure for at least
10 seconds.

59. Verify that gas flows properly through the breathing
circuit during both inspiration and expiration
Flow test

61. References
• Miller’s 8th edition
• Morgan and Mikhails 5th edition
• The History of Anesthesia at Drager volume 1
• The Basic Anesthesia Machine; The Indian Journal of
Anesthesia 2013. doi: 10.4103/0019-5049.120138

62. Thank you.