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I&M I > I. The Anesthesia Machine & Vaporizers/Circuits & Ventilators (Duke’s CH 18) > Flashcards

I. The Anesthesia Machine & Vaporizers/Circuits & Ventilators (Duke’s CH 18) Flashcards

1
Q

What is the more proper technical name for an anesthesia machine?

A

Anesthesia delivery system

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2
Q

What are the three general functions of an anesthesia machine?

A
  1. Supply, a mixture of anesthetizing and life-sustaining gas.
  2. Ventilate the patient.
  3. Provide monitoring functions.
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3
Q

What are the three most important purposes an anesthesia machine is used?

A

To keep the patient, alive, safe, and adequately anesthetized

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4
Q

What are the two major manufacturers of Anesthesia machines in the United States?

A

Drager & Datex-Ohmeda

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5
Q

What are the three sections (systems) of an anesthesia machine?

A
  1. Gas delivery system.
  2. Patient breathing system.
  3. Scavenging system.
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6
Q

Which system supplies at its outlet a defined mixture of gases, chosen by the anesthetist?

A

The gas delivery system

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7
Q

What does the patient breathing system include?

A
  1. Patient breathing circuit.
  2. Absorber head.
  3. Ventilator.
  4. Gas pressure and flow monitors.
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8
Q

What does the scavenging system do?

A

Collects excess gas and expels the gas outside the hospital, reducing the exposure of operating room personnel to anesthetic gases

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9
Q

What are the three most common gases ordinarily available on all anesthesia machines?

A
  1. Oxygen.
  2. Nitrous oxide (N2O)
  3. Air.
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10
Q

What are some other gases that may be found on the anesthesia machine?

A
  1. Helium.
  2. Heliox (a mixture of helium and oxygen.)
  3. Carbon dioxide. (CO2)
  4. Nitrogen. (N2)
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11
Q

What is the major concern if the third gas does not contain oxygen?

A

It is possible to deliver a dangerous hypoxic mixture to the patient

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12
Q

What are the common sources of gas for Anesthesia machines?

A

Most typically a centralized wall or pipeline supply. An emergency back up supply of gases is stored in E-cylinders attached to the rear of Anesthesia machines (check Supply daily)

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13
Q

What does ORMC stand for?

A

Oxygen ratio, monitor and controller (Drager)

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14
Q

What does the ORMC do? (Drager)

A

It senses the oxygen flow rate and controls nitrous oxide flow pneumatically

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15
Q

Which anesthesia machine possesses the Link-25 system?

A

Datex-Ohmeda

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16
Q

What does the Link-25 system do?

A

This feature mechanically links the oxygen and nitrous oxide flow knobs to ensure that the proportion of nitrous oxide to oxygen remains in a safe range as the nitrous oxide flow is increased

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17
Q

What is the maximum pressure contained in an E cylinder?

A

2200 psig

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18
Q

What is the initial pressure the anesthesia machine requires the gas to be delivered?

A

50 psig

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19
Q

What component of the anesthesia machine reduces the excessively high pressure gases to appropriate pressures required by the anesthesia machine?

A

The regulator (each gas is regulated separately)

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20
Q

What are wall gas pressures typically regulated (by first stage regulator) at?

A

55 psig

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21
Q

What pressure are E cylinder tanks typically regulated (by the first stage regulator) at?

A

45 psi

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22
Q

As long as everything is working correctly, which gas supply is used by the anesthesia machine?

A

The anesthesia machine preferentially chooses the source with the highest pressure, therefore wall supplies are preferentially used because they have the higher pressure. However, if wall gas pressures fall below 45 psi, backup tank supplies will be used.

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23
Q

A full green, a cylinder of oxygen possesses, approximately what psi of gas, and contains how many liters of oxygen?

A
  • 2000 psi
  • 625 L O2
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24
Q

Since oxygen is a compressed, gas, the volume in the tank correlates linearly with the pressure on the gauge. Therefore a pressure of 1000 psi means there are how many liters of oxygen left in the tank.?

A

312 L O2

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25
Q

How can the remaining supply of oxygen in an E tank be estimated?

A

Oxygen usage is calculated based on two measurements:
1. The O2 flow rate.
2. Minute ventilation rate.

For example, if a patient is receiving O2 flow of 2 L per minute and has a minute ventilation of 8 L per minute, a total of 10 L of oxygen will be drained from the oxygen tank every minute.

Therefore, a tank with 312 L remaining will last for 31 minutes

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26
Q

In addition to providing oxygen for cellular respiration, oxygen is also used for what task on the anesthesia machine?

A

Driving the Bellows

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27
Q

What can be done to reduce the consumption of Tank oxygen?

A
  1. Reduce oxygen flow rate.
  2. Switch from mechanical ventilation to bag ventilation.
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28
Q

PSI vs PSIG

A

PSI is a unit of pressure that can be used to measure gauge pressure, absolute pressure, or vacuum pressure, while PSIG specifically refers to gauge pressure

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29
Q

A new tank of nitrous oxide contains what PSIG?

A

750

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30
Q

Why cannot air and oxygen be compressed to liquids at room temperature?

A

Because the critical temperature of air and oxygen, the temperature, at which a gas can be compressed into a liquid, is exceeded at room temperature

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31
Q

At room, temperature nitrous oxide condenses into a liquid at what psi?

A

747

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32
Q

E cylinders of nitrous oxide contain the equivalent of how many liters of gas?

A

About 1600 L (whereas E cylinders of oxygen in air hold only about 600 L)

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33
Q

Once the pressure of a nitrous oxide cylinder begins to drop how much nitrous oxide gas remains in the cylinder?

A

Approximately 1/4

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34
Q

List the uses of oxygen in an anesthesia machine

A
  1. Contributes to the fresh gas flow.
  2. Provides gas for the O2 flush.
  3. Powers, the low oxygen alarm.
  4. Controls the flow of nitrous oxide.
  5. Power of the failsafe valves
  6. Is the driving gas for the ventilator Bellows
35
Q

What is the safety system used for wall? Gas supply connectors?

A

Diameter index safety system (DISS)

36
Q

What is the safety system for gas cylinders?

A

Pin index safety system (PISS)

37
Q

The safety systems should be backed up by what in order to prevent delivery of a hypoxic gas mixture?

A

A monitor that measures the delivered concentration of oxygen in a mixed gas

38
Q

What is different about the oxygen flow knob compared to other knobs for other gases?

A

The oxygen knob is distinctively fluted, while other gases are knurled

39
Q

What is the color code for oxygen air and nitrous oxide in the United States?

A

Oxygen is Green, air is yellow and nitrous oxide is blue

40
Q

Why are two flow tubes (meters) essential for each gas on an anesthesia machine?

A

In order to measure flows accurately in the range is used for low flow or even closed circuit Anesthesia (200 - 1000 ml/min)

41
Q

What is the other name for flow meters?

A

Thorpe tubes

42
Q

Why must the oxygen flow meter always be on the right just proximal to the anesthesia vaporizers?

A

Because this is the closest point of egress into the common gas manifold. With the oxygen flow meter in that position, most leaks will involve gases other than oxygen. This configuration is least likely to deliver a hypoxic gas mixture.

43
Q

What is meant by a failsafe valve?

A

The failsafe valve device is designed to cut off the flow of all gases, except oxygen, when the oxygen pressure falls below a set value, usually 25 psig.

44
Q

How long can a full oxygen E cylinder last at 2 L/min flow rate if mechanical ventilation is not in use?

A

Approximately five hours (600 L total O2/2 L per min = 300 min of O2 supply)

45
Q

What physical principles are involved in the process of vaporization?

A
  1. Saturated vapor pressure.
  2. Heat of vaporization.
46
Q

What is saturated vapor pressure?

A

This determines the concentration of vapor molecules above the liquid anesthetic. This principle is influenced by temperature.

Saturated vapor pressure specifically refers to the pressure of a vapor when it is in equilibrium with its condensed phase at a particular temperature.

↑ Saturated Vapor Pressure: more of substance will exist in vapor phase.

↓Saturated Vapor Pressure: less of a substance will exist in vapor pressure.

↑T° = ↑ Vapor Pressure (↑KE)
↓T° = ↓ Vapor Pressure (↓KE)

47
Q

What is heat of vaporization?

A

This is the energy required to release molecules of a liquid into the gaseous phase

48
Q

What material are vaporizers constructed of and why?

A

Vaporizers are constructed of metals with high thermal conductivity. High thermal conductivity, ensures that there is a conduit of heat, so the heat required for vaporization is constantly restored from the environment, and the rate of vaporization of the volatile anesthetic is independent of changes in the temperature of the vaporizer.

As the vaporizer liquid volume decreases, the temperature of the liquid decreases as well. Because the construction materials possess high thermal conductivity, sufficient heat is still delivered in order to sustain the necessary saturated vapor pressure.

Also, some machines have compensation mechanisms that automatically increase the rate of gas flow as vaporizer volume (∴ T°) decreases (less gas particles are available for delivery) IOT deliver sufficient vaporizer/anesthetic gas to pt.

49
Q

what takes place during the liquid phase with regard to vaporization?

A

The liquid phase either draws external heat during vaporization, or else it will become cooler as molecules leave and enter the gaseous phase. The high thermal conductivity properties of metal construction prevents the liquid phase from cooling, allowing for the constant restoration of heat required for vaporization.

50
Q

What does it mean when it is said that a vaporizer has variable bypass?

A

Fresh gas from the flow meters enters the vaporizer, and is divided into two streams. Most of the gas enters the bypass chamber and is not exposed to the volatile agent. The remaining gas enters the vaporizing chamber and becomes saturated with anesthetic. The two streams, then reunite near the vaporizer outlet. The concentration dial determines the proportion of gas flow that enters each of the two streams, thereby determining the concentration of the gas, leaving the vaporizer.

51
Q

What happens if a vaporizer is turned on its side?

A

Liquid anesthetic my spill from the vaporizing chamber to the bypass chamber, effectively creating TWO vaporizing Chambers and increasing vaporizer output. This could create toxic levels of volatile anesthetic being delivered to the patient.

52
Q

What does temperature compensation mean?

A

During vaporization, the liquid anesthetic will cool. As liquid anesthetic cools, the saturated vapor pressure decreases as does vaporizer output. Temperature compensation means the vaporizer as mechanisms for adjusting the output to compensate for temperature.

53
Q

What is the pumping affect?

A

Positive pressure can be transmitted back into the vaporizer during ventilation of the patient. The positive pressure can briefly cause gas to reverse flow within the vaporizer, allowing gas to re-enter the vaporizer. THE RESULT OF THE PUMPING EFFECT IS INCREASED VAPORIZER OUTPUT BEYOND THAT INDICATED ON THE CONCENTRATION DIAL.

54
Q

How do you determine the vaporizer’s output and volume percent at a new altitude?

A

Consider the example: a vaporizer is calibrated at sea level (760 mm Hg) and taken to Denver (630 mm Hg) and set to 1% isoflurane. The actual output is (760/630 = 1.2%).

However, remember, it is the partial pressure of the vapor, Not the concentration in volume percent, that determines the depth of Anesthesia. Therefore 1% at sea level and 1.2% in Denver are both 7.6 mmHg (the clinical effect is unchanged).

- The MAC % is not what determines the delivered anesthetic (1.2% Iso in Denver is different than 1.2% Iso in Miami)
- The Partial Pressure of the vapor (the physical gas particles) is what determines the delivered anesthetic and ∴ the depth of anesthesia. (1.0% in Denver and 1.2% in Miami deliver the same amount of VA particles)

55
Q

What happens if you put the wrong agent in a vaporizer calibrated for another agent?

A

The incorrect agent typically delivers either an overdose or under dose.

56
Q

What will be the output if an agent with a high vapor pressure is put into a vaporizer meant for a less volatile agent?

A

The output will be excessive leading to overdose

57
Q

What will be the output, if an agent with a vapor pressure lower than the agent intended for the vaporizer is accidentally used?

A

The anesthetic output will be lower than anticipated, resulting in an underdose

58
Q

What is different about the desflurane vapor pressure?

A

Desflurane has a very high vapor pressure of 664 mmHg at 20°C. In other words, the boiling point of this agent is approximately at room temperature.

59
Q

Describe Desflurane’s potency, and volume percent.

A

Desflurane has a very low potency (MAC = 6%), and up to 18% volume percent may be delivered. This is a relatively large volume to be vaporized and results in temperature variations that require compensation. Its vaporizer actively heats the liquid agent to 39°C which increases its vapor pressure to approximately 2 atm.

60
Q

What prevents turning onto vaporizer simultaneously?

A

Modern anesthesia machines have an interlock system or an interlocking manifold that allows only one vaporizer to be turned on at a time.

However, in machines that allow for three of vaporizers, the center spot must be occupied, or the interlocking manifold will not be operational .

61
Q

What does it mean to say conventional vaporizers or altitude compensated?

A

Altitude compensation occurs because the diverting valve is functionally located at the outlet of the vaporizer. The output of these vaporizers is a constant partial pressure of agent, not a constant volume percent.

62
Q

How is Desflurane different than conventional vaporizers (halothane, isoflurane, sevoflurane)?

A

Desflurane does not divert a portion of the fresh gas flow through a vaporizing chamber, but rather adds vapor to the gas flow to produce a true volume percent output. Therefore it delivers a set ‘volume percent’ (not partial pressure) regardless of altitude.

In other words, it actively injects vapor into the fresh gas stream, whereas all traditional vaporizers use a passive variable bypass system.

63
Q

Which volatile anesthetic gas must be set to deliver a higher percentage when located at higher altitudes?

A

Desflurane (because it is designed to deliver a set volume percent regardless of altitude, rather than a set partial pressure)

64
Q

What is the term to describe the ‘number of molecules of agent’ that anesthetizes the patient?

A

Partial pressure

65
Q

Which vaporizers our altitude compensated and therefore deliver a constant partial pressure regardless of altitude?

A

Halothane, Sevoflurane, & Isoflurane

66
Q

After the vaporizers are removed from the anesthesia machine in preparation for a malignant hyperthermia patient, what should be done next?

A

Flushing the machine with oxygen for several minutes, in order to remove all the agent (except from rubber parts in the absorber in circle).

67
Q

What components comprise exhaust gas?

A

Exhaust gas is a mixture of expired gas from the patient and fresh gas that exceeded the patient’s needs, but contains anesthetic agent

68
Q

What is the device acts as a Reservoir and is used to capture and expel anesthetic laden exhaust gas from the operating room environment into the hospital vacuum system?

A

Scavenger

69
Q

The scavenger must also prevent excess suction or an occlusion from affecting the patient breathing circuit. How is this accomplished?

A

It does this by providing both positive and negative relief valves.

If the vacuum system fails or is set to too low a rate, back pressure exits through a positive pressure relief valve and enters the operating room. If the vacuum is adjusted to high, a negative pressure relief valve allows room air to mix with the exhaust gas preventing buildup of more than 2.5 mmHg suction at the breathing circuit . 

70
Q

What are the four different types of anesthesia breathing circuits?

A
  1. Open
  2. Semi open.
  3. Semi closed.
  4. Closed.
71
Q

What type of circuit describes the method by which core form was administered over 160 years ago.

A

Open; the depth of anesthesia was controlled by the amount of liquid anesthetic on the cloth, which was then placed over the patient’s face.

72
Q

Which type of circuit is the Mapleson A, B, C, D, E & F circuits and are rarely used today, except for patient transport.

A

Semi open

73
Q

Which type of circuit is commonly found in operating rooms in the United States?

A

Semi closed (circle system)

74
Q

What are the main components of a semi closed circuit?

A
  1. Inspiratory limb.
  2. Expiratory limb.
  3. Unidirectional valves.
  4. CO2 absorber
  5. Gas Reservoir bag.
  6. Pop off valve on the expiratory limb
75
Q

What type of circuit is a circle system adjusted so the inflow of fresh gas just matches the patient’s oxygen consumption and aesthetic agent uptake?

A

Closed

76
Q

How is a breathing circuit disconnection detected during delivery of an anesthetic?

A
  1. Breath sounds are no longer detected with an esophageal or precordial stethoscope.
  2. Airway pressure monitor and tidal volume-minute volume monitor alarms will sound
  3. Capnograph no longer detects carbon dioxide.
  4. SpO2 begins to decline.
    5.
77
Q

What is probably the best monitor to detect breathing circuit disconnection?

A

Exhaled carbon dioxide (a decrease, or absence of carbon dioxide is sensitive, although not specific for disconnection)

78
Q

How is carbon dioxide eliminated from a circle system?

A

Exhaled gases, pass through a canister containing a carbon dioxide absorbent, such as soda, lime or Baralyme.

79
Q

How much carbon dioxide can the absorbent neutralize?

A

Soda lime is the most common absorber and can, at best, absorb 23 L of carbon dioxide per 100 g of absorbent; however, the average absorber illuminates 10 to 15 L of carbon dioxide per 100 g absorbent in a single chamber and 18 to 20 L of carbon dioxide in a dual chamber system.

80
Q

What factors affect the canister’s neutralization of carbon dioxide?

A
  1. Size of the absorbent granule.
  2. Size of the absorbent canister.
  3. Channeling (loose, packing, allowing exhale gases to bypass absorber granules.)
81
Q

How do you know when the absorbent has been exhausted?

A

A pH sensitive dye added to the granules, changes color in the presence of carbonic acid, an intermediary in the carbon dioxide absorption chemical reaction. The most common dye in the US is Ethel violet, which is white when fresh, and turns violet when the absorbent is exhausted.

82
Q

nitrous oxide is ____ useful as altitude increases, why?.

A

it becomes more difficult to supply adequate pO2 using N2O when total atmospheric pressure declines

83
Q

Altitude Formula for Mac % adjustments of volatile agents

A

Required vaporizer setting = (Desired vaporizer setting at sea level x 760 mmHg)/ (barometric pressure in mmHg)

Ex: Sevo in Denver (630mmHg)

(2.1% x 760)/(630) = 2.5%

84
Q
A

I&M I (5 decks)

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