Chapter 12 Anesthesia Delivery Systems
Anesthesia workstation
1. What are some components of an anesthesia workstation?
2. What is the purpose of the fail-safe valve? What triggers the fail-safe valve on the anesthesia machine?
3. Can a hypoxic mixture be delivered from the anesthesia machine with an intact fail-safe valve? Explain.
4. How are oxygen, nitrous oxide, and air gases that are used in anesthesia typically delivered to the anesthesia machine? At what pressure must these gases be delivered for proper function of the anesthesia machine?
5. How is the delivery of erroneous gases to the anesthesia machine minimized?
6. What is the purpose of the cylinders of oxygen and nitrous oxide that are found on the back of the anesthesia machine?
7. How is an erroneous hookup of a gas cylinder to the anesthesia machine minimized?
8. Please complete the following table illustrating the characteristics of compressed gases stored in E-sized cylinders:
9. How is the pressure of oxygen related to the volume of oxygen in an oxygen gas cylinder? What does this mean with regard to calculating the volume of oxygen remaining in a used oxygen cylinder?
10. How is the pressure of nitrous oxide related to the volume of nitrous oxide in a nitrous oxide gas cylinder?
11. Why does atmospheric water vapor accumulate as frost on the outside surface of oxygen tanks and nitrous oxide tanks in use?
12. What is the purpose of flowmeters on an anesthesia machine?
13. How do flowmeters on an anesthesia machine work?
14. Are flowmeters for various gases interchangeable?
15. Why is the oxygen flowmeter the last flowmeter in a series on the anesthesia machine with respect to the direction in which the gas flows?
16. What is the purpose of the oxygen flush valve?
17. What is the flow of oxygen delivered to the patient when the oxygen flush valve is depressed?
18. What is the risk of activating the oxygen flush valve during a mechanically delivered inspiration?
Vaporizers
19. Why do volatile anesthetics require placement in a vaporizer for their inhaled delivery to patients via the anesthesia machine?
20. What is the heat of vaporization?
21. What is vapor pressure? What influence does temperature have on vapor pressure?
22. Why are contemporary vaporizers unsuitable for use with desflurane?
23. Describe how contemporary vaporizers for volatile anesthetics are classified.
24. What does the term agent-specific refer to?
25. What do the terms variable-bypass and flow-over refer to?
26. What does the term temperature-compensated refer to? Between what temperatures is vaporizer output reliably constant?
27. What does the term out of circuit refer to?
28. How does tipping of a vaporizer affect vaporizer output?
29. How is the delivery of two different volatile anesthetics to the same patient via the same anesthesia machine prevented?
30. How is the potential risk of filling the agent-specific vaporizer with the erroneous volatile anesthetic minimized?
Anesthetic breathing systems
31. What is the function of anesthetic breathing systems?
32. How do anesthetic breathing systems impart resistance to the spontaneously ventilating patient?
33. What are some features of an anesthetic breathing system that enable them to be classified as either open, semiopen, closed, or semiclosed?
34. What are the most commonly used anesthetic breathing systems?
35. What characterizes the Mapleson systems?
36. Describe the Mapleson F anesthetic breathing system. What is another name for this anesthetic breathing system?
37. When is the Mapleson F system commonly used?
38. What are some advantages of the Mapleson F anesthetic breathing system?
39. What are some disadvantages of the Mapleson F anesthetic breathing system?
40. Describe the Bain circuit anesthetic breathing system.
41. What are some advantages of the Bain circuit anesthetic breathing system?
42. What are some disadvantages of the Bain circuit anesthetic breathing system?
43. How does the circle anesthetic breathing system get its name?
44. How does the circle system prevent rebreathing of carbon dioxide?
45. What are the classifications of a circle system and on what does this depend?
46. What is the most commonly used circle breathing system used in the United States?
47. What are some advantages of the semiclosed and closed circle systems?
48. What are some disadvantages of the circle anesthetic breathing system?
49. What is the impact of the rebreathing of anesthetic gases in a semiclosed circle system?
50. What are the components of a circle system?
51. What is the purpose of unidirectional valves in the circle system? What would occur if one of the unidirectional valves should become incompetent?
52. Where is the dead space in the circle system?
53. What is advantageous about the corrugated tubing in the circle system?
54. What is disadvantageous about the corrugated tubing in the circle system?
55. Describe the Y-piece connector in the circle system circuit.
56. What are other names for the adjustable pressure-limiting (APL) valve?
57. Describe the function of the APL valve when the “bag/vent” selector switch is set to “bag.”
58. What are the advantages of the reservoir bag on the circle system?
59. Describe a closed anesthetic breathing system. What is the inflow volume of fresh gases in a closed anesthetic breathing system?
60. What are some advantages to the closed circle anesthetic breathing system?
61. What is a disadvantage to the closed circle anesthetic breathing system?
62. What are the dangers of the closed circle anesthetic breathing system?
63. Are inspired concentrations of oxygen more or less predictable when nitrous oxide is also being delivered in a closed circle anesthetic breathing system? Why?
64. How can the potential problem of the inadequate delivery of oxygen using a closed circle anesthetic breathing system be minimized?
65. In a closed circle anesthetic breathing system, to what extent is the inhaled concentration of anesthetic dependent on the exhaled concentration of anesthetic? What is the potential problem with this? How can this problem be partially offset?
Anesthesia machine ventilators
66. What parts of a circle system are eliminated in anesthesia machine ventilators when the “bag/vent” selector switch is set to “vent”?
67. What are two different ways in which anesthesia machine ventilators are powered?
68. Describe the mechanics of a conventional anesthesia machine ventilator during inspiration.
69. Why is oxygen preferred over air as the ventilator driving gas?
70. Describe the mechanics of a conventional anesthesia machine ventilator during exhalation.
71. Describe the mechanically driven piston type of ventilators found on some newer anesthesia machines.
72. Why are standing or ascending bellows preferred over hanging or descending bellows?
73. How are inhaled gases normally humidified in awake patients breathing through their native airway?
74. What effect does tracheal intubation or the use of a laryngeal mask airway have on airway humidification? What are the negative consequences of this?
75. Describe anesthetic breathing system humidification. What effect does chemical neutralization of carbon dioxide have on this process?
76. What are three types of humidifiers used for anesthesia and in the intensive care unit?
77. Describe heat and moisture exchanger (HME) humidifiers. What is the difference between an HME and an HMEF?
78. What are the advantages of HME humidifiers over other types of humidifiers?
79. What are the disadvantages of HME humidifiers?
80. What is the advantage of heated water vaporizers and humidifiers over HME humidifiers? When are they used most frequently?
81. What are the risks of heated water vaporizers and humidifiers?
82. Describe nebulizer humidifiers used for anesthesia and in the intensive care unit.
Pollution of the atmosphere with anesthetic gases
83. In the operating room, what are the Occupational Safety and Health Administration (OSHA) recommendations for the maximum concentrations of nitrous oxide and volatile anesthetics in parts per million?
84. What is required to control pollution of the atmosphere with anesthetic gases?
85. Describe operating room scavenging.
86. Describe the two types of scavenging systems used in the operating room.
87. What are the advantages of active scavenging with a waste gas receiver mounted on the side of the anesthesia machine?
88. What are the potential hazards of scavenging systems?
89. What two features do scavenging systems have to minimize their potential hazards?
90. Where might be the source of a high-pressure leak of nitrous oxide?
91. Where might be the source of a low-pressure leak of nitrous oxide?
92. What anesthetic techniques can lead to operating room pollution?
93. How often should the air in the operating room be exchanged?
Elimination of Carbon Dioxide
94. How is carbon dioxide eliminated in open and semiopen breathing systems?
95. How is carbon dioxide eliminated in a semiclosed or closed anesthetic breathing system?
96. What are two types of chemicals that are used to neutralize carbon dioxide? What products are formed? Are the neutralization reactions endothermic or exothermic?
97. What does soda lime consist of?
98. Why is silica added to soda lime?
99. Why is the water in the soda lime carbon dioxide absorbent canister hazardous?
100. What does Amsorb Plus consist of?
101. Why are calcium sulfate and polyvinylpyrrolidine added to Amsorb Plus?
102. Why is the water formed by the neutralization of carbon dioxide useful? What if the carbon dioxide absorbent canister fails to become warm during use?
103. What two factors influence the efficiency of carbon dioxide neutralization?
104. How does the size of the carbon dioxide absorbent granules affect the efficiency of carbon dioxide neutralization?
105. What is the optimal carbon dioxide absorbent granule size? How is this sizing system defined?
106. What does channeling in the carbon dioxide absorbent granule-containing canister refer to? How does channeling in the canister affect the efficiency of carbon dioxide neutralization?
107. What is the most frequent cause of channeling in the carbon dioxide absorbent granule-containing canister? How can it be minimized?
108. Define carbon dioxide absorbent absorptive capacity. What can cause a decrease in absorptive capacity?
109. Why do the carbon dioxide absorbent granules change color?
110. Contrast the color change of soda lime granules with those of Amsorb Plus.
111. Describe the degradation of inhaled anesthetics by soda lime to carbon monoxide.
112. Describe the degradation of inhaled anesthetics by soda lime to compound A.
113. Does Amsorb Plus degrade inhaled anesthetics?
114. What factor contributes to the degradation of inhaled anesthetics by soda lime?
115. Why do most instances of increased blood concentrations of carboxyhemoglobin occur in anesthetized patients on a Monday?
116. What causes the development of fire and extreme heat in the breathing system? How can this be avoided?
117. Complete the following table:
| Feature | Soda Lime | Amsorb Plus |
|---|---|---|
| Mesh size | ||
| Generation of compound A with sevoflurane | ||
| Generation of carbon monoxide with inhaled anesthetics | ||
| Risk of exothermic reactions and fire in the presence of sevoflurane |
Checking the anesthesia machine and circle system function
118. What are the current recommendations for preanesthesia checkout procedures? How do these apply to newer machines with automated checkout procedures?
119. How often should these checkout procedures be performed?
120. What are the most important preoperative checks?
121. Does the presence of a Jackson-Rees circuit along with a full oxygen E-cylinder mounted on the back of the anesthesia machine comply with the current checkout recommendations?
122. What does a leak check of the machine’s low-pressure system evaluate? Why is this so important?
123. Why is calibration of the oxygen monitor so important?
124. Does a manual positive-pressure leak test check the integrity of the unidirectional valves?
Answers*
Anesthesia workstation
1. Components of an anesthesia workstation include what was previously recognized as the anesthesia machine, (the pressure-regulating and gas-mixing components), as well as the vaporizers, anesthesia breathing circuit, ventilator, scavenging system, and respiratory and physiologic monitoring systems (electrocardiogram, arterial blood pressure, temperature, pulse oximeter, and inhaled and exhaled concentrations of oxygen, carbon dioxide, anesthetic gases, and vapors). (198, Table 15-1)
2. The purpose of the fail-safe valve is to prevent the delivery of hypoxic gas mixtures from the anesthesia machine in the event of failure of the oxygen supply. The fail-safe valve is triggered when the pressure in the oxygen delivery line decreases to less than 30 psi. When the fail-safe valve is triggered, it either shuts off or proportionally decreases the flow of all gases. Note that it is only the pressure of oxygen that triggers the fail-safe valve. (199)
3. An intact fail-safe valve is actually only a pressure-sensor valve. A hypoxic mixture may still be delivered to the patient if the fail-safe valve is sensing an adequate gas pressure in the circuit of the anesthesia machine when the oxygen flow is zero. This confirms the importance of the oxygen analyzer on the anesthesia machine. Far superior to the fail-safe valve or an oxygen analyzer is the continuous presence of a vigilant anesthesiologist. (199)
4. The oxygen, nitrous oxide, and air gases that are used in anesthesia are most often delivered to the anesthesia machine as compressed gases from a central supply source located in the hospital. These hospital supplied gases enter the operating room from a central source through pipelines to operating room wall outlets. Pressure hoses then connect the wall outlets to the anesthesia machine. These gases must be delivered at a pressure of about 50 psi for the anesthesia machine to function properly. (199-200).
5. The delivery of erroneous gases from the central supply source to the pipeline inlet connections on the anesthesia machine is minimized in two ways. First, the wall outlets and pressure hoses are color-coded. Second, and more importantly, the pressure hoses are connected to the wall outlet and anesthesia machine by noninterchangeable gas-specific diameter fittings. This diameter index safety system (DISS) is designed to prevent misconnections of pipeline gases. (199-200)
6. The purpose of the cylinders of oxygen and nitrous oxide that are found on the back of the anesthesia machine is for the delivery of those gases should the central gas supply fail. (200)
7. An erroneous hookup of a gas cylinder to the anesthesia machine is minimized in two ways. First, the cylinders are color-coded. Second, and more importantly, the color-coded cylinders are attached to the anesthesia machine by a hanger yoke assembly, which consists of two metal pins that correspond to holes in the valve casing of the gas cylinder. This pin index safety system (PISS) makes it impossible to attach an oxygen cylinder to any yoke on the anesthesia machine other than that designed for oxygen. Otherwise, a cylinder containing nitrous oxide could be attached to the oxygen yoke, which would result in the delivery of nitrous oxide when the oxygen flowmeter was activated. (200)
