Aspectos elementales y constitutivos de la Máquina de Anestesia.

1. THE ANESTHESIA MACHINE:
INTRODUCTION
Lucie Filteau (2013), Real GE Aisys Anesthesia Machine
[photograpgh]. Retrieved from
https://www.flickr.com/photos/luciefilteau/19843830788/i
n/album-72157654569908142/

2. Objectives
• Know the definition of an Anesthesia Machine
• Know the different parts of an Anesthesia
Machine and their use.
• Set up and use of anesthetic machine
• System check out
• Common Problems and repairs

3. What is an Anesthetic Machine?
• At the minimum an anesthesia machine administers anesthetic gases to a
patient in a controlled manner
• A medical equipment used to administer anesthesia to patients.
• monitors patient and allows the anesthetist/anesthesiologist (user) to make
necessary adjustment in order to keep patients under stable state of
anesthesia.
• gives the patient a mixture of anesthetic gas
• Has incorporated devices that monitors vital signs (HR,BP, Temp,
SPO2…)
• Has alarm systems to allow failsafe operations.
• Has a protection system that prevents the surgeons, anesthetists… to inhale
anesthetic gases.(scavenging system)

4. What is Anesthetic Gas?
 Gas used to temporarily keep the patient in total unconsciousness.
(General anesthesia)
 2 types of anesthetic gases are common:
1. Ether Halogenated (most common):e.g. ISOFLURANE,SEVOFLURANE
2. Non-Ether Halogenated hydrocarbons: e.g. HALOTHANE, CHOLOROFORM
 Non-Ether Halogenated hydrocarbons are no longer used in
developed countries because they are toxic, but are very common in
Third World. E.g. HALOTHANE is very common in Rwanda.
 Other types of anesthetic gases: XENON (costly)
 The Anesthetic gases are stored in liquid state at room temperature
but are very volatile.
 A vaporizer is used to administer the anesthetic gases to patients

5. Source: Malkin, “Medical Instrumentation in the Developing World”
Corrugated tube
Ventilator bag
Scavenging system
cabinet
Vaporizer
Flow meter
Oxygen flush valve
Adapted from: DiverDave (2013), Flow-I anesthesia machine [photograph]. Retrieved from
https://commons.wikimedia.org/wiki/File:Maquet_Flow-I_anesthesia_machine.jpg

6.  APL (Adjustable Pressure Limiting) valve: Pressure limiting valve
which releases gas over an adjustable range of pressures on purpose
to control system pressure and thus intrapulmonary pressure.
 Scavenging System: An assembly of specific components that
collect excessive exhaled gases and exhausts them out of the
operating room to avoid accidental anesthesia of staff.
 Soda lime: A mixture of sodium and calcium hydroxides that absorbs
liquids and gases, especially CO2 from patient exhaled gases
 Vaporizer: Used to produce an accurate amount of gas from a
volatile liquid anesthetic gas. It has a dial or knob to know and to
regulate the percentage of anesthetic gases given to the patient.
System Components

7. Homeostasis Control
– Manual (bag) or assisted (automatic) ventilation
– Circulation (Blood volume, vasopressor drugs)
– Neurologic (Autonomous reflex; Anesthetic drugs,
relaxant)
– Thermal regulation (physical; cover, room
temperature)

8. Side effects
• Drug Toxicity
• Drug interactions with therapeutic, herbal,
abused substances
• Post-operation Nausea and vomiting

9. The Anesthesia Machine
Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013),
p. 472-480.

10. High Pressure System
• Gas from the high pressure cylinders or
from a compressor and an O2 plant is
supplied via the back of the anesthesia
machine (2200 psig for O2)
• The high pressure side consists of:
– Hanger Yolk (reserve gas cylinder
holder) and seal
– Check valve (prevent reverse flow of
gas)
– Cylinder Pressure Indicator (Gauge)
– Pressure Reducing Device (Regulator)
• Cylinders are not used if there is wall-
mounted gas supply.
Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.”
Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

11. Pressure Reducing Device
• Reduces the high and variable pressures found in a cylinder to
a lower and more constant pressure found in the anesthesia
machine (45 psig)
• Reducing devices are preset so that the machine uses only gas
from the pipeline (wall gas), when the pipeline inlet pressure is
50 psig.
This prevents gas use from the cylinder even if the cylinder is
left open (i.e. saves the cylinder for backup if the wall gas
pipeline fails)

12. Intermediate Pressure System
 Gets gas from the cylinder
regulator or the hospital
pipeline at pressures of 40-55
psig
 Consists of:
 Pipeline inlet connections
 Pressure gauges
 Pipes
 Common gas outlet
 Master switch
 Oxygen pressure failure
devices
 Oxygen flush
 Additional reducing devices
 Flow control valves
Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.”
Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.

13. Pipeline Inlet Connectors
 Mandatory N2O and O2,
usually have medical air and
suction ports as well
 Inlets are non-
interchangeable due to
specific threading as per the
Diameter Index Safety
System (DISS)
 Each inlet must contain a
check valve to prevent
reverse flow (similar to the
cylinder yolk)
Pipeline inlet connectors (Air, N2O, O2)
Ignis (2005), Vaporizer [photograph]. Retrieved from
https://commons.wikimedia.org/wiki/File:Vaporizer.jpg

14. Oxygen Pressure Monitors
• An anesthesia machine is designed such that it
sounds an alarm whenever the oxygen supply
pressure falls below normal range. (O2
concentration should not be below 19%)
• Some machines have and electronic as well as a
mechanical low O2 supply alarm. In this case one
would be a beeper/buzzer and the other would be
an air powered whistle

15. Oxygen Pressure Failure Devices
• A Fail-Safe valve is found in each gas line supplying
the flow meters. This valve shuts off or
proportionately decreases the supply pressure of all
other gasses with the decrease in O2 supply pressure.
• 2 kinds of fail-safe valves exist:
– Pressure sensor shut-off valve (e.g. Ohmeda)
– Oxygen failure protection device (e.g. Drager)

16. Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.”
Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p. 472-480.
Oxygen Pressure Fail Device

17. Pressure Sensor Shut-Off Valve
• Oxygen supply pressure opens the valve as long as
it is above a pre-set minimum value (e.g.. 20 psig).
• If the oxygen supply pressure falls below the
threshold value the valve closes and the gas in that
limb (e.g.. N2O), does not advance to its flow-
control valve.

18. Oxygen Failure Protection Device
(OFPD)
• Based on a proportioning principle rather than a shut-
off principle
• The pressure of all gases controlled by the OFPD will
decrease proportionately with the oxygen pressure

19. Oxygen Flush Valve
• Receives O2 from pipeline inlet or cylinder reducing device and
directs high, unmetered flow directly to the common gas outlet
(downstream of the vaporizer)
• Machine standard requires that the flow be between 35 and 75
L/min in flush mode
• The ability to provide jet ventilation
• Hazards
– May cause barotrauma

20. Source: Developing Anesthesia: Guidelines for Anaesthesia in Developing Countries Version 1.6.
O2/N2O System with CO2 Absorber

21. Second-Stage Reducing Device
• Located just upstream of the flow control
valves
• Receives gas from the pipeline inlet or the
cylinder reducing device and reduces it further
to 26 psig for N2O and 14 psig for O2
• Purpose is to eliminate fluctuations in pressure
supplied to the flow indicators caused by
fluctuations in pipeline pressure

22. Low Pressure System
• It goes from the flow control valves to the gas outlet and
consists of:
– Flow meters
– Vaporizer mounting device
– Check valve
– Common gas outlet

23. Flowmeter assembly
• When the flow control valve is
opened the gas enters at the
bottom and flows up the tube
elevating the indicator
• The indicator floats freely at a
point where the downward
force on it (gravity) equals the
upward force caused by gas
molecules hitting the bottom
of the float
Rschiedon (2007), Flowmeter [drawing]. Retrieved from
https://commons.wikimedia.org/wiki/File:Flowmeter.jpg

24. Proportioning Systems
– Mechanical integration of the N2O and O2 flow-control
valves
– Automatically intercedes to maintain a minimum 25%
concentration of oxygen with a maximum N2O:O2 ratio
of 3:1

25. Limitations of Proportioning Systems
• Machines equipped with proportioning systems can
still deliver a hypoxic mixture under the following
conditions:
– Wrong supply gas
– Defective pneumatics or mechanics
– Leak downstream (e.g. worn/broken o-rings or leaking pipe
fittings)
– Inert gas administration: Proportioning systems generally
link only N2O and O2

26. Vaporizers
• A vaporizer is an instrument designed to
change a liquid anesthetic agent into its
vapor and add a controlled amount of this
vapor to the fresh gas flow
Ignis (2005), Vaporizer [photograph]. Retrieved from
https://commons.wikimedia.org/wiki/File:Vaporizer.jpg

27. Classification of Vaporizers
Methods of regulating output concentration
Concentration calibrated (e.g. variable bypass)
Measured flow
Method of vaporization
Flow-over
Bubble through
Injection
Temperature compensation
Thermocompensation
Supplied heat

28. Generic Bypass Vaporizer
• Flow from the flowmeters
enters the inlet of the
vaporizer
• The function of the
concentration control valve is
to regulate the amount of
flow through the bypass and
vaporizing chambers
Splitting Ratio = flow though vaporizing
chamber/flow through bypass chamber
Virginia Reid (2015), Vaporizer [diagram]

29. Factors That Influence Vaporizer Output
• Flow Rate: The output of the vaporizer is generally
less than the dial setting at very low (< 200 ml/min) or
very high (> 15 L/min) flows
• Temperature: Automatic temperature compensating
mechanisms in bypass chambers maintain a constant
vaporizer output with varying temperatures
• Back Pressure: Intermittent back pressure (e.g.
positive pressure ventilation causes a higher vaporizer
output than the dial setting)

30. Factors That Influence Vaporizer Output
• Atmospheric Pressure: Changes in atmospheric
pressure affect variable bypass vaporizer output as
measured by volume % concentration, but not (or
very little) as measured by partial pressure (lowering
atmospheric pressure increases volume %
concentration and vice versa)
• Carrier Gas: Vaporizers are calibrated for 100%
oxygen. Carrier gases other than this result in
decreased vaporizer output.

31. The Circuit: Circle System
• Arrangement is variable, but to prevent re-breathing
of CO2, the following rules must be followed:
– Unidirectional valves between the patient and the
reservoir bag
– Fresh-gas-flow cannot enter the circuit between
the expiratory valve and the patient
– Adjustable pressure-limiting valve (APL) cannot
be located between the patient and the inspiratory
valve

32. Circle System
 Advantages:
 Relative stability of inspired concentration
 Conservation of respiratory moisture and heat
 Prevention of operating room pollution
 PaCO2 depends only on ventilation, not fresh gas
flow
 Low fresh gas flows can be used
 Disadvantages:
 Complex design = potential for malfunction
 High resistance (multiple one-way valves) = higher
work of breathing

33. The Adjustable Pressure Limiting (APL)
Valve
• User adjustable valve that releases gases to the scavenging
system and is intended to provide control of the pressure in the
breathing system
• Bag-mask Ventilation: Valve is usually left partially open.
During inspiration the bag is squeezed pushing gas into the
inspiratory limb until the pressure relief is reached, opening the
APL valve.
• Mechanical Ventilation: The APL valve is excluded from the
circuit when the selector switch is changed from manual to
automatic ventilation

34. • Protects the breathing circuit or ventilator from
excessive positive or negative pressure.
Developing Anesthesia: Guidelines for Anaesthesia in Developing Countries Version 1.6 (2007). Retrieved from linrary.ewh.com
Patient Rebreathing Circuit

35. Patient Rebreathing Circuit with
Scavenger Output
Malkin, R. (2006). Medical instrumentation in the
developing world (p. 65). Memphis, Tenn.: Engineering
World Health.
Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia
Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p.
472-480.

36. Checking Anesthesia Machines
Categories of checks:
• Gas supply/High pressure system
• Low-Pressure system
• APL valve and Scavenging system
• Breathing system
• Manual and automatic ventilation system
• Monitors
• Final configurations
• Any emergency ventilation equipment located in the
OR
• Check any gas analysis found on the machine

37. Patient Monitoring
• Clinical Signs – not automatic measured
– Movement, Pupil dilation, Sweating, Heart and lung sounds
• Anesthesia
– Neuromuscular Relaxation- Evoked response - accelerometers, EMG
– Sedation, Hypnosis
• Blood concentration - Expired inhaled anesthetic agent
concentration
• Spontaneous EEG - Compressed Spectral, BiSpectral analysis;
Entropy
• Evoked EEG responses -- Somatic, Auditory, Optical
– Analgesia (no pain) -- ??

38. Patient Monitoring
• Respiration
– Ventilation - Spirometry
(Respiratory rates, tidal
volumes, minute ventilation),
Airway pressures
– Gas Exchange - FiO2
(inspired oxygen), Pulse
oximetry, FeCO2
(Capnography - expired
carbon dioxide)
Kalumet (2005), Narkosemonitor [photograph]. Retrieved from
https://commons.wikimedia.org/wiki/File:Narkosemonitor.jpg

39. Patient Monitoring
• Circulation
– Electrocardiogram (ECG)
– Blood Pressures
• Non-invasive blood pressures
(NIBP)
• Invasive Blood Pressures
– Arterial, Venous
– Atrial, Ventricle, Pulmonary
Artery, Pulmonary pressures
– Cardiac Output
• Temperature
Pflegewiki-User Würfell (2007)., Medical Monitor [photograph].
Retrieved from
https://commons.wikimedia.org/wiki/File:Monitor_(medical).jpg

40. Patient Safety
• Fail Safe Mechanism against
– Hypoxia
- O2/N2O mechanic connection, O2 monitor, pulse oximetry
– Apnea, Leaks, disconnect, occlusion
- low minute ventilation, high/low pressure, CO2 monitor
– Excessive airway pressure
- redundant pressure relief valves
– Over/Under Anesthetic deliver
-Vaporizer interlock, concentration monitor

41. Patient Safety
• Mandatory preanesthesia checkout
• Alarm System - a dilemma
– Intended for vigilance
– Result: Excessive alarms noise

42. Common Problems
• Power supply
• User error
• Leaks
– Gases leak may affect staff and are
flammable
• Sticky rotameters needle valves
– Flush with alcohol
Mintz I Flow Meter (2013). Retrieved from
https://en.wikipedia.org/wiki/Anaesthetic_machine

43. Preventive Maintenance
•O2 sensor contacts cleaning with alcohol
•Batteries replacement
ClckrFreeVectorImages (2015), Battery [drawing.
Retrieved from Pixabay
Mark.murphy (2005), Diving oxygen analyser
[photograph]. Retrieved from
https://commons.wikimedia.org/wiki/File:Diving_oxygen_a
nalyser.JPG

44. Preventive Maintenance
• CO2 absorber replacement
Przemysław Jahr (2012), Drägersorb® Soda Lime [photograph]. Retrieved
from
https://commons.wikimedia.org/wiki/File:Dr%C3%A4gersorb_Soda_Lime.j
pg