1. The Anesthesia Machine: Introduction
Lucie Filteau (2013), Real GE Aisys Anesthesia Machine [photograpgh]. Retrieved from
By : Didier Mukama

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:
Ether Halogenated (most common):e.g. ISOFLURANE,SEVOFLURANE
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. Corrugated tube Oxygen flush valve Ventilator bag Flow meter Vaporizer
Different parts of an anesthesia machine- check with engineer to label
Vaporizer
cabinet
Scavenging system
Source: Malkin, “Medical Instrumentation in the Developing World”
Adapted from: DiverDave (2013), Flow-I anesthesia machine [photograph]. Retrieved from

6. System Components
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.

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
Mention how the machine is divided into high, intermediate, and low pressure systems
Subrahmanyam, M. and Mohan, S. “Safety Features in Anesthesia Machine.” Indian Journal of Anesthesia, Vol. 57, No. 5 (2013), p

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

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 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

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)
Ignis (2005), Vaporizer [photograph]. Retrieved from
Pipeline inlet connectors (Air, N2O, O2)

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

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
Not able to reproduce electronically- draw?

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

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

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
Found source- Universidade Technologica Federal Do Parania- not sure if ok to reproduce, looks like no according to their website.

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

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
The concentration control dial may be located in the bypass chamber of the outlet of the vaporizing chamber
Mention that the machine standard requires that all vaporizers on the anesthesia workstation be concentration calibrated (aka variable bypass, direct reading, dial-controlled, automatic plenium, percentage-type, tec-type vaporizers, and vaporizer chamber bypass arrangements
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)
C’ = concentration at the new atmospheric pressure
C = the concentration at the old atmospheric pressure (i.e. the concentration dialed into the vaporizer)
P’ = the barometric pressure for which c’ is being established
P = the barometric pressure for which the vaporizer is calibrated (i.e. at the old atmospheric pressure)

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: Disadvantages:
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
The final three points of the advantages section are meant to contrast with the Bain circuit

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. Patient Rebreathing Circuit
Protects the breathing circuit or ventilator from excessive positive or negative pressure.
Mention that the ventilator relief valve is the same thing as the overflow valve mentioned in the previous slides
Developing Anesthesia: Guidelines for Anaesthesia in Developing Countries Version 1.6 (2007). Retrieved from linrary.ewh.com

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

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
For more details on checking out the anesthesia machines please visit (copy and paste in web browser):

37. Patient Monitoring Clinical Signs – not automatic measured Anesthesia
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

39. Patient Monitoring Circulation Temperature 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

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 Sticky rotameters needle valves 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

43. Preventive Maintenance
O2 sensor contacts cleaning with alcohol
Batteries replacement
Mark.murphy (2005), Diving oxygen analyser [photograph]. Retrieved from
ClckrFreeVectorImages (2015), Battery [drawing. Retrieved from Pixabay

44. Preventive Maintenance
CO2 absorber replacement
Przemysław Jahr (2012), Drägersorb® Soda Lime [photograph]. Retrieved from