1. Inhaled anesthetic Delivery Systems
Sahmeddini MD
Department of Anesthesia
Shiraz medical university

2. Inhaled anesthetic Delivery Systems

3. Safety Standards ANSI - (American National Standards Institute)
Standards set for all machines sold in the U.S.
ASTM -- (American Society for Testing and Materials 1988
1994: ASTM F
2000: ASTM F

4. To comply with the 2000 ASTM F1850-00 standard
Continuous breathing system pressure
Exhaled tidal volume
Ventilatory carbon dioxide concentration
Anesthetic vapor concentration
Inspired oxygen concentration
Oxygen supply pressure
Arterial oxygen saturation of hemoglobin
Arterial blood pressure
Continuous electrocardiogram.

5. Functions of anesthesia machine
Convert supply gases from high pressure to low pressure
Convert liquid agent to gas
Deliver in a controlled manner
Provide positive pressure for ventilation
Alert the provider to malfunction
Prevent delivery of a hypoxic mixture

7. Testing Specific Components of the Anesthesia Delivery System
1)Calibration of the oxygen analyzer 2) The low-pressure circuit leak test 3) The circle system tests.

8. High Pressure System
Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine. (2200 psig for O2, 745psig for N2O)

9. Usually not used, unless pipeline gas supply is off
High Pressure System
Receives gasses from the high pressure E cylinders attached to the back of the anesthesia machine
2200 psig for O2
745 psig for N2O
Usually not used, unless pipeline gas supply is off

10. High Pressure System

11. Hanger Yoke Hanger Yoke: orients and supports the cylinder
Providing a gas-tight seal
Ensuring a unidirectional gas flow into the machine

12. Pin Index Safety System(PISS)
Prevents tank swaps
Pin positions
Air 1-5
Oxygen 2-5
Nitrous oxide 3-5

13. Pin Index Safety System(PISS)

14. Two sources of gas: Pipeline 50 psig Tanks »Oxygen: 2200 psig
»Nitrous oxide: 745 psig
»Both reduced to 45 psig upon entering the machine

15. Tank
H Tank
E Tank

16. E Size Compressed Gas Cylinders
Cylinder Characteristics
Oxygen
Nitrous Oxide
Air
Colour
White
Blue
Black
State
Gas
Liquid and gas
Contents (L)
625
1590
Empty Weight
(kg)
5.90
Full Weight (kg)
6.76
8.80
6.50
Pressure Full
(psig)
2000
750
1800

17. Approximate remaining time#
Oxygen cylinder pressure(psig)
200 .oxygen flow rate(L/min)

18. Intermediate Pressure System

20. Intermediate Pressure System
Receives gasses
from the regulator
or the hospital
pipeline at pressures of psig

21. Pipeline Inlet Connections
Mandatory N2O and O2,usually have air and suction too
Inlets are non interchangeable due to
specific threading as per the Diameter Index Safety System (DISS)

22. Diameter Index Safety System (DISS)

23. Oxygen Pressure Failure Devices
Machine standard requires that an anesthesia machine be designed so that whenever the oxygen supply pressure is reduced below normal, the oxygen concentration at the common gas outlet does not fall below 19%

24. Oxygen Pressure Failure Devices
A Fail-Safe valve is present in the gas line supplying each of the flow meters except O2.
This valve is controlled by the O2 supply pressure and shuts off or proportionately decreases the supply pressure of all other gasses as the O2 supply pressure decreases

25. Oxygen Pressure Failure Devices
Historically there are 2 kinds of fail-safe valves
Pressure sensor shut-off valve (Ohmeda)
Oxygen failure protection device (Drager)

26. 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

27. Pressure sensor shut-off valve

28. 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

29. Oxygen failure protection device

30. Oxygen Supply Failure Alarm
The machine standard specifies that whenever the oxygen supply pressure falls below a manufacturer specified threshold (usually 30 psig) alarm shall blow within 5 seconds.

31. Limitations of Fail-Safe Devices/Alarms
Fail-safe valves do not prevent administration of a hypoxic mixture because they depend on pressure and not flow.
Do not prevent hypoxia from accidents such as pipeline crossovers or a cylinder containing the wrong gas.

32. OXYGEN FLUSH VALVE By passes vaporizer
Delivers large volumes of oxygen to breathing circuit
Is under high(er) pressure caution!!!

33. 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
The ability to provide jet ventilation
Hazards:
May cause barotraumas
Dilution of inhaled anesthetic

34. 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

36. Low Pressure System Extends from the flow control valves to
the common gas outlet
Consists of:
Flow meters
Vaporizer mounting device
Check valve
Common gas outlet

38. Flow Meter Assembly

39. Flow Meter
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

41. Flow Meter Standards Oxygen flow control knob Physically different
Larger and projects further
Different shape
All knobs are colour coded
Knobs are protected

43. Electronic flow sensors
Some newer anaesthesia workstations have now replaced the conventional glass flow tubes with electronic flow sensors that measure the flow of the individual gases.
These flow rate data are then presented to the anaesthesia care provider in either numerical format, graphic format, or a combination of the two.

44. Cracked tubes
In the presence of a flow meter leak (either at the “O” ring or the glass of the flow tube)
a hypoxic mixture is less likely to occur if the O2 flow meter is downstream of all other
flow meters

45. Proportioning Systems
Mechanical integration of the
N2O and O2 flow control valves
Maintain a minimum 25% concentration of oxygen with a maximum N2O:O2 ratio of 3:1

46. Proportioning Systems

47. Proportioning Systems

48. Proportioning Systems

49. 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

50. Vaporizers

51. Classification of Vaporizers
Methods of regulating output concentration
Concentration calibrated
Method of vaporization
Flow-over
Bubble through
Injection
Temperature compensation:
Thermocompensation
Supplied heat

52. Applied Physics Vapor pressure Based on characteristics of agent
Varies with temperature
Boiling point: Vapor pressure equals atmospheric pressure
Latent heat of vaporization: Heat required to change liquid into a vapor
Comes from liquid
environment

53. Ohmeda and Drager Characteristics
Variable bypass
Flow over
Temperature compensated
Agent specific
Out of circuit

54. Basic Design Gas enters vaporizer Flow is split Majority is by passed
Some enters vaporizing chamber
Saturated gas leaves chamber
Diluted by bypass gas
Delivered to patient

56. Generic Bypass Vaporizer
Flow from the flow meters 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

58. Factors that Effect Output
Flow rate
Accurate at most flows
Lower than dial setting at both extremes of flow
Temperature
Vapor pressure varies with temp
Accurate at C

59. Factors that Effect Output
Intermittent back pressure
Retrograde flow
Higher than dial setting
especially at low flows and high
ventilator pressures
Carrier gas composition
N2O causes transient drop

61. Carbon Dioxide Absorbents
Two formulations of carbon dioxide absorbents are commonly available today:
soda lime
calcium hydroxide lime
Baralyme, or barium hydroxide lime

62. CO2 Absorption (con’t) Soda lime –94% calcium hydroxide
–5% sodium hydroxide
–1% potassium hydroxide
–silica to harden granules
–ethyl violet as an indicator

63. CO2 Absorption (con’t)
Ethyl violet is the pH indicator added to both soda lime
Ethyl violet changes from colorless to violet when the pH of the absorbent decreases as a result of carbon dioxide absorption.
Unfortunately, in some circumstances ethyl violet may not always be a reliable indicator of the functional status of absorbent

64. Anesthesia Ventilators
The ventilator on the modern anesthesia workstation serves as a mechanized substitute for the hand of the anesthesia care provider in manipulating the reservoir bag of the circle system, or another breathing system.

65. Ventilators Classified by:
Power source
pneumatic
electric
both
Drive mechanism
double circuit
driven by oxygen

66. Ventilator Problems (con’t)
Leak in bellows assembly
Mechanical problems
Electrical problems

67. Setting the Ventilator
Based on the principle that PaCO2 is directly proportional to alveolar ventilation

68. AV X CO2 = AV X CO2 (what you have) (what you want)
AV = alveolar ventilation
CO2 = carbon dioxide
If you know 3, you can solve for the 4th

69. 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

71. 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
The final three points of the advantages section are meant to contrast with the Bain circuit

72. 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

73. The Adjustable Pressure Limiting (APL) Valve

74. Scavenging Systems
Scavenging is the collection and removal of vented anesthetic gases from the OR
Since the amount of anesthetic gas supplied usually far exceeds the amount necessary for the patient, OR pollution is decreased by scavenging

75. Scavenging Systems
Workers should not be exposed to an eight hour time-weighted average of > 2 ppm halogenated agents (not > 0.5 ppm if nitrous oxide is in use) or > 25 ppm nitrous oxide.

76. Evidence of harm to anesthesia personnel from waste gases is suggestive but unproved (strongest relationship is N2O and reproductive difficulties).

77. Type of Scavenging Systems
Scavenging may be active (suction applied)
passive (waste gases proceed passively down corrugated tubing through the room ventilation exhaust grill of the OR).

78. Hazards of scavenging Obstruction distal to interface
Occupational exposure
Barotrauma or inability to ventilate

79. High-Pressure System Checkout
   Check Oxygen Cylinder Supply.   
   Open the O2 cylinder and verify that it is at least half full (≈1000 psi)   
   Close the cylinder.
Check Central Pipeline Supplies.   
   Check that hoses are connected and pipeline gauges read about 50 psi.

80. Low-Pressure System Check Initial Status of Low-Pressure System.
a.    Close the flow control valves and turn the vaporizers off.   
b.    Check the fill level and tighten the vaporizers’ filler caps.

81. Perform Leak Check of Machine Low-Pressure System.
Verify that the machine master switch and flow control valves are OFF  
Attach a “suction bulb” to the common (fresh) gas outlet   
Squeeze the bulb repeatedly until it is fully collapsed.     
Verify that the bulb stays fully collapsed for at least 10 seconds.       
Open one vaporizer at a time and repeat steps c and d as above.       
Remove the suction bulb and reconnect the fresh gas hose.

83. Turn on Machine Master Switch and All Other Necessary Electrical Equipment.
Test Flow Meters.
  a.    Adjust the flow of all gases through their full range while checking for smooth operation of the floats and undamaged flow tubes.   
b.    Attempt to create a hypoxic O2/N2O mixture and verify correct changes in flow and/or alarm.

84. Calibrate O2 Monitor a. Ensure that the monitor reads 21% in room air.
b.    Verify that the low-O2 alarm is enabled and functioning.   
c.    Reinstall the sensor in the circuit and flush the breathing system with O2.   
d.    Verify that the monitor now reads greater than 90%.

85. Check Initial Status of Breathing System.
a.    Set the selector switch to “Bag” mode.   
b.    Check that the breathing circuit is complete, undamaged, and unobstructed.   
c.    Verify that CO2 absorbent is adequate.   
d.    Install the breathing circuit accessory equipment (e.g., humidifier, positive end-expiratory pressure [PEEP] valve) to be used during the procedure.

86. Perform Leak Check of Breathing System.
Set all gas flows to zero (or minimum).     
Close the APL (pop-off) valve and occlude the Y-piece.     
Pressurize the breathing system to about 30 cm H2O with an O2 flush.     
Ensure that the pressure remains fixed for at least 10 seconds.       
Open the APL (pop-off) valve and ensure that the pressure decreases