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Fall 2013 Anesthesia Concepts > Scavenging systems and CO2 absorbers > Flashcards

Scavenging systems and CO2 absorbers Flashcards

1
Q

What is the purpose of the scavenging system?

A

To collect excess gases from anesthesia equipment or exhaled by patients and remove them to an appropriate place outside the work envirnoment

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2
Q

The scavenging system has the added benefit of removing __________ from the machine and preventing build up.

A

pressure, especially where high flows are used

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3
Q

What is NIOSH?

A

National Institute of Safety and Health; they set the recommendations for anesthetic gas levels in the OR.

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4
Q

How much volatile anesthetic gas alone is permitted in the OR according to NIOSH?

A

**2ppm ** (note:without nitrous you can tolerate more volatile anesthetic in the envirnoment, with nitrous is it is much less)

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5
Q

How much nitrous oxide is permitted in the OR according to NIOSH?

A

25 ppm

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6
Q

If you have both volatile anesthetic and nitrous, how much does NIOSH permit in the OR?

A

0.5 ppm

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7
Q

Name some things that might increase or decrease the amount of anesthetic gas in the OR?

A

Delivering anesthesia by mask, taking mask on and off, increases anesthetic in the air. But, because the air in the OR is turned over about 20x an hour, the anesthetic is quickly diluted out. Scavenging of gases also limits our exposure. Care providers can experience symptoms of the anesthetic when exposed, and miscarriage, liver damage, neurological symptoms and other adverse events in the provider have occurred.

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8
Q

The scavenger system alarm will alert you when the system is malfunctioning, (T or F)

A

F. There is not alarm on the scavenging system. This must be checked with your daily machine check.

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9
Q

What is this?

A

This picture shows a basic scavenging system using a reservoir bag.

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10
Q

What are the 5 basic components of the scavenging system?

A

Gas collecting assembly, transfer means, scavenging interface, gas disposal tubing, gas disposal assembly

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11
Q

Label the 5 components of the scavenging system

A
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12
Q

Describe the gas collecting assembly portion of the scavenging system.

A

It captures excess gases at the site of emission. From the APL valve if manually ventilating or from the Ventilator relief valve (excess gas from the vent/ driving gas can be part of this). They are then delivered to the transfer means tubing.

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13
Q

What size are the connections in the gas collecting assembly of the scavenging system and why is their size important?

A

The outlet connection is 30mm (19 mm in older machines) (male-fitting). It is important to to have connection sizes that are incompatible with any other part of the breathing system to prevent an accidental misconnection of lines.

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14
Q

Describe the transfer means portion of the scavenging system.

A

Also called exhaust tubing or hose and transfer system. It conveys gas from the collecting assembly to the interface. It us usually a tube with female fitting connectors on both ends. The tubing is short with a wide diameter to carry a high flow of gas w/o a significant increase in pressure. It must be kink resistant. It must be different from breathing tubes. (usually stiffer and colored yellow)

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15
Q

The scavenging interface prevents ___________ changes from being transferred to the breathing system.

A

pressure

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16
Q

The scavenging interface is also called the?

A

balancing valve or device

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17
Q

The scavenging interface limits pressures immediately downstream of the gas collecting assembly to between:

A

-0.5 to +5 cmH2O

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18
Q

The scavenging interface inlet should be what size?

A

30mm male connector

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19
Q

The scavening interface should be positioned where?

A

as close to the gas collecting assembly as possible.

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20
Q

What are the 3 basic elements of the scavenging interface?

A
  • positive pressure relief protects patient and equipment in case of occlusion of system -negative pressure relief-limit subatmospheric pressure -reservoir capacity matches the intermittent gas flow from gas collecting assembly to the continuous flow of disposal system
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21
Q

The scavenging interface comes in two types, they are:

A

Open or Closed

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22
Q

Does the open interface have valves?

A

No. It is open to the atomosphere via holes in the reservoir, avoiding buildup of positive or negative pressure. If pressure builds up, pressure will be released out via the holes, if vacuum is powerful, the reservoir will not crush/ collapse, it will pull air through the holes in to relieve pressure

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23
Q

Does the open interface require a vacuum?

A

Yes, it requires a central vacuum and a reservoir that is an open cansiter, large enough to accomodate high waste gas flows. (Envision a metal coke can- gases sit in the reservoir until they can be sucked away by the vacuum. When the vacuum is on, the canister does not collapse, it pulls atmospheric air into it via the holes and flushes the anesthetic gases through) Make sure there are no surgical drapes, or other things blocking the relief holes.

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24
Q

How much vacuum pressure should be on in an open interface?

A

It can be adjusted. It must be higher than the excess gas flow, otherwise you will get spill out through the relief holes into the OR atmosphere.

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25
Q

In an open interface, gas enters the system at the _______ and travels through ________

A

enters at the top of the canister and travels through a narrow inner tube to the base.

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26
Q

There are 2 different types of closed interface systems, they are?

A
  1. positive pressure relief only system and 2. positive pressure and negative pressure relief
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27
Q

Describe the positive pressure relief only closed interface system.

A

single positive pressure relief valve opens when a maximum pressure is reached. There is passive disposal, no vacuum, no reservoir bag.

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28
Q

Describe the positive pressure and negative pressure relief closed interface system.

A

Has both positive pressure relief valve, negative pressure relief valve and a reservoir bag. It is used with an active disposal system with vacuum control valve adjusted so that the reservoir bag is over distended or completely deflated.

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29
Q

If the pressure in the system exceeds +5cm H2O, what happens?

A

Gas will be vented into the atmosphere

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30
Q

If the system pressure is less than -0.5 cm H2O what will happen?

A

Entrainment of room air into the system, prevents the crushing of the reservoir canister.

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31
Q

What would happen if the primary negative pressure relief valve becomes occluded?

A

A backup negative pressure relief valve opens at -1.8 cm H2O

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32
Q

Describe the gas disposal tubing portion of the scavenging system.

A

It can deliver up to 75 L/min to the gas disposal assembly. It connects the scavenging interface to the disposal system. Should be a different size and color than the breathing system. With a passive system the hose should be short and wide. Having the tubing run overhead is ideal to prevent accidental obstruction and kinking.

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33
Q

What are the 2 types of gas disposal assembly found in the scavenging system?

A

Active and Passive

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34
Q

Describe an active gas disposal assembly.

A

The gases are moved by a mechanical, flow- inducing device. It produces negative pressure in the disposal tubing so it must have a negative pressure relief.

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35
Q

Describe a passive gas disposal assembly.

A

The waste gas is directed out of the building via an open window, a pipe passing through an outside wall, an extractor fan vented to the outside air.

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36
Q

What is the advantage of a passive gas disposal assembly?

A

It’s inexpensive to set up and simple to operate.

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37
Q

What is the disadvantage of a passive gas disposal assembly?

A

It may be impractical in some buildings.

38
Q

Describe the active sytem of gas disposal.

A

This connects the exhaust of the breathing system to the hospital vacuum system by an interface controlled by a needle valve.

39
Q

What are the advantages of an active system of gas disposal?

A

It is convenient in large hospitals where many machines are in use in different locations.

40
Q

What are the disadvantages of an active system of gas disposal?

A

The vacuum system and pipework is a major expense. The needle valve may need continual adjustment.

41
Q

Which is more commonly used in hospitals, passive or active gas disposal systems?

A

active

42
Q

What are the 4 steps to conducting a scavenging system check?

A
  1. Ensure proper connections between the scavenging system and the APL valve and the Ventilator relief valve and waste-gas vacuum. 2. Fully occlude the APL and occlude the Y-piece 3.With minimal O2 flow, allow the scavenger bag to collapse completely and verify that the pressure gauge reads zero. 4. With the O2 flush activated, allow the scavenger reservoir bag to distend fully and then verify that the pressure gauge reads less than 10 cmH2O pressure.
43
Q

What does the CO2 absorber do?

A

It chemically neutralizes CO2. It is a base that neutralizes the acid.

44
Q

What is the acid that must be neutralized with the base in the CO2 absorber?

A

CO2 combines with H2O (on the surface of the pellets) and forms H2CO3 (carbonic acid).

45
Q

What sorts of bases are used in CO2 absorbers?

A

Hydroxide or an alkali or alkaline earth metal

46
Q

What is the end product of the reaction that takes place in the CO2 absorber?

A

End product is water, a carbonate, and heat.

47
Q

What are the 2 common absorbants used in CO2 absorbers?

A

Soda lime and Amsorb Plus (Calcium Hydroxide Lime)

48
Q

What are the 5 ‘ingredients’ of soda lime?

A

4% sodium hydroxide, 1% potassium hydroxide, 15% H2O, 0.2% silica, 80% calcium hydroxide.

49
Q

Why is silica added to soda lime?

A

To add hardness and prevent dust that could get into the patient’s lungs.

50
Q

How much CO2 can soda lime absorb?

A

It is capable of absorbing 26 liters of CO2 per 100g of absorbant granules.

51
Q

Water is present as a thin film on the granule surface, why is this important?

A

Moisture is essential. The reaction takes place between ions that only exist in the presence of water.

52
Q

What happens in the soda lime reaction?

A

CO2 combines with H2O to form H2CO3. Then the H2CO3 reacts with the hydroxides to form Na2CO3 or K2CO3 (sodium carbonate or potassium carbonate), water (2H2O) and heat.

53
Q

How much CO2 does the average person expel each hour?

A

12-17 liters. So if granules can absorb 26 liters/ 100grams of CO2 it gives you an idea of how long they will last.

54
Q

In the soda lime reaction, does the carbonic acid bind with the NaOH or the CaOH?

A

Most commonly the NaOH, and then the NaOH can bind further with the CaOH. It is possible for the H2CO3 to bind directly to the CaOH it takes longer. The Na route is quicker.

55
Q

What are the ingredients for Calcium Hydroxide Lime (Amsorb Plus)?

A

80% CaOH, 16% water, 1-4% CaCl, Calcium suflate and polyvinylpyrrolidine (added hardness)

56
Q

How much CO2 can Calcium Hydroxide Lime absorb?

A

10 Liters of CO2/ 100mg of absorbent granules.

57
Q

Why does the calcium hydroxide lime absorb less CO2 than soda lime?

A

Calcium Hyroxide lime only has one hydroxide in the form of CaOH, soda lime has 3 available as NaOH and KOH and CaOH.

58
Q

What are the disadvantages of Amsorb?

A

It absorbs less CO2, it is costly, NaOH and KOH are strong bases that lead to forming compounds that could cause nephrotoxicity. It can also lead to the formation of CO and if it loses some it’s moisture, it poses a fire risk.

59
Q

What is the Calcium Hydroxide Lime reaction?

A

CO2 + H2O = H2CO3 Then H2CO3 reactis with Ca(OH)2 and yields CaCO3, 2H2O and heat

60
Q

What is an indicator?

A

An acid or base whose color depends on pH.

61
Q

When the color changes, what does this signal?

A

the absorber is exhausted.

62
Q

Once the indicator turns purple, it stays purple. T or F.

A

False. The indicator will revert back to white when at rest.

63
Q

When should you replace the absorbent?

A

With 50-70% color change.

64
Q

What is the most common color indicator used in anesthesia?

A

Ethyl violet

65
Q

When the indicator Phenophthalein is used, what color is it when it is fresh? When exhausted?

A

Fresh= white; Exhausted= Pink

66
Q

When the indicator Ethyl Violet is used, what color is it when it is fresh? When it is exhausted?

A

Fresh= white; exhausted= purple.

67
Q

When Clayton Yellow indicator is used, what color is it when it is fresh? When it is exhausted?

A

Fresh= red; Exhausted= Yellow

68
Q

When Ethyl Orange indicator is used, what color is it when it is fresh? When it is exhausted?

A

Fresh= Orange; Exhausted= Yellow.

69
Q

When Mimosa 2 indicator is used, what color is it when it is fresh? When it is exhausted?

A

Fresh= red; Exhausted= White

70
Q

What size are the absorbent granules?

A

4-8 mesh.

71
Q

Why would you want granules with an irregular shape?

A

It increases surface area.

72
Q

Why would you want small absorbent granules?

A

provides greater surface area.

73
Q

Do you want to blend large and small absorbent granules?

A

Yes, the blend of large and small minimizes resistance with little sacrifice in absorbent capacity.

74
Q

What hardness # should the absorbent granules be?

A

Hardness number should be > 75

75
Q

Why do we want the granules to be hard?

A

Excessive powder will causes channeling, resistance, and caking.

76
Q

What do we add to soda lime to make it hard?

A

silica

77
Q

How do we test granules for hardness?

A

They are tested with stell ball bearings and a screen pan. The % of orginal remaining = the hardness number.

78
Q

What is channeling?

A

Preferential passage of exhaled gas flow through the absorber via pathways of low resistance.

79
Q

How does channeling happen?

A

It results from loosely packed granules.

80
Q

How much air space is in the absorbent canister with the granules?

A

48-55% of the volume is air space

81
Q

Why is channeling a problem?

A

CO2 may filter through exhausted channels and may not be visible. It is important to monitor CO2 to ensure CO2 is not being delivered to the patient.

82
Q

Does the CO2 absorber affect our anesthetic gases?

A

Yes. Desicated (dry) soda lime may degrade sevoflurane, isoflurane, enflurane, and desflurane to CO. Sevoflurane and halothane may also degrade to unsaturated nephrotoxic compounds (compound A). There is also risk of fires.

83
Q

What happens to gas flow through the absorber during inhalation?

A

During inhalation, gas is pulled from the reservoir bag and the common gas outlet, through the absorber, then to the breathing system out the inspiratory limb.

84
Q

What happens to gas through the absorber during exhalation?

A

Exhaled gases flow through the mask, into the rebreathing bag and out the APL valve. Fresh gas continues to flow from the common gas outlet at the machine into the common gas inlet at the absorber.

85
Q

Label the components of the CO2 absorber.

A
86
Q

At the bottom of the absorber is a trap for ________ and _______ that will need to be emptied periodically.

A

moisture and dust.

87
Q

To preserve the life of the CO2 absorbent, what should you do when the machine is not in use?

A

Turn off gas flow to the machine

88
Q

How often should you change the absorbent?

A

It should be changed regularly and whenever the color change indicates exhaustion.

89
Q

If one canister of absorbent is exhausted, just change that one. T or F.

A

False, if one canister is exhausted, change them both.

90
Q

What could happen to the absorber if you are using high gas flows?

A

High gas flows will dry out the aborbent faster. IF you are uncertain about the state of hydration. When in doubt of moisture status, change the granules.

91
Q

What sorts of gas flows help preserve the life of the absorbent granules?

A

Low flows preserve the humidity.

Fall 2013 Anesthesia Concepts (8 decks)

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