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Chem/Phys Exam 4 > 02 Measurement & CO2 Absorption > Flashcards

02 Measurement & CO2 Absorption Flashcards

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1
Q

Properties of Oxygen

A

1) It can be chemically reduced (adding electrons)
2) It can serve as an oxidant (taking electrons away)
3) It is paramagnetic (attracted to a magnetic field)
4) is selectively permeable to certain membranes

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2
Q

Methods of Oxygen Measurement

A
  • polarographic electrode
  • fuel cell
  • paramagnetic sensor
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3
Q

Reduction

A

to contribute electrons to.

A compound that is “reduced” accepts electrons.
A “reductant” contributes electrons

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4
Q

H202

A

Hydrogen Peroxide - will speed up oxidation

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5
Q

How many electrons are consumed for each molecule of oxygen completely reduced?

A

4 electrons are consumed

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6
Q

Measuring 02 with an electrode

A

In measuring O2 with the O2 electrode, O2 is consumed. Because oxygen is consumed, current is dependent on diffusion of O2 to the electrode

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7
Q

Polarographic electrode

A

differs from the pH electrode in that current flows through the circuit when oxygen is present. A small direct polarizing voltage (0.6-0.7 V) is applied across the electrodes.

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8
Q

Current is produced in proportion to ________ of oxygen to electrode.

A

rate of diffusion

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9
Q

Problems with early oxygen electrodes

A

1) large surface area consumed lots of oxygen
2) protein was deposited on the electrode.
Solution? Clark’s Electrode!

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10
Q

Clark’s Solution

A

cover the electrodes with membranes to prevent protein deposition, but allow oxygen in

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11
Q

Other Clark Improvements:

A

1) limit the surface area of electrode so less O2 is consumed
2) use voltage pulses to reduce 02 consumption.

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12
Q

Oxygen Measurement by a Fuel (Galvanic) Cell

A

Similar to an oxygen battery. It contains a noble metal cathode and a lead (Pb) anode and KOH electrolyte. A semipermeable membrane is exposed to the blood or expired gas.

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13
Q

Errors in Blood Oxygen Measurement: Integrity of specimens

A
  • too much suction
  • too much heparin
  • air in blood
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14
Q

Errors in Blood Oxygen Measurement: Storage Considerations

A
  • Syringe crack free with properly fitting plunger
  • Gases in blood will equilibrate in time with air in polypropylene syringes
  • High white cell count will increase aerobic respiration and decrease blood oxygen content
  • Bubbles, if present, will increase oxygen dissolved in blood at lower temperature, such as 4C in ice.
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15
Q

Errors in Blood Oxygen Measurement: Patient

A

If pt’s temp is different from 37 C, analysis will not be accurate. More gas dissolved in cooler blood than warmer blood.
(all measurements corrected for temp of blood)

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16
Q

Transcutaneous Electrodes

A

noninvasive method to measure blood oxygen and carbon dioxide that use the same electrode technology as the CO2 and O2 electrodes.

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17
Q

Features of transcutaneous electrodes

A
  • airtight seal with skin
  • heating element to bring skin temp to 43-44C
  • blood flow to skin increases and capillary O2 and CO2 diffuse to the surface where they are measured by the electrodes
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18
Q

Paramagnetic Oxygen Sensor

A

makes use of the fact that oxygen molecules are attracted to a magnetic field (Remember that molecular oxygen has two unpaired electrons).
- In one system a stream of gas containing oxygen is put in an oscillating magnetic field. The oscillating magnetic field causes movement of the oxygen molecules. The oxygen movement causes the pressure of the gas to increase as a function of oxygen concentration.

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19
Q

Fluorescence Technology

A

a technology that can be used for measuring oxygen, pH and pCO2.

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20
Q

Fluorescence Definition

A

emission of light or electromagnetic radiation by a substance as the result of absorption of energy of shorter wavelengths. ie: the excitation of a substance by UV light, and emission of visible light.

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21
Q

Why absorb CO2?

A
  • to reuse volatile anesthetics in a circuit, CO2 absorption is required
  • also important in submarines and NASA spacecraft
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22
Q

CO2

A

the end product of metabolism that is kept low in the body by its expiration.

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23
Q

Normal pCO2 levels

A

40mmHg arterial

45mmHg venous

24
Q

Human CO2 production

A

4mL/min/kg of body weight

25
Q

What is the basis of CO2 absorption?

A

its ability to form carbonic acid in water

26
Q

What does CO2 do when reacting with water?

A

Upon reacting with water CO2 goes from a volatile gas to a nonvolatile carbonate form.
** note that CO2 can form TWO different anions

27
Q

Nonvolatile carbonate salts

A

can be formed w various cations
Na2CO3
CaCO3
BaCO3

28
Q

Basis of irreversible CO2 absorption

A

its ability to react with water to ultimately form nonvolatile carbonates.

29
Q

Role of H20 in CO2 absorption

A

Decreased CO2 absorption <12% or >20%.

Because water is critical to absorption, decreased CO2 absorption occurs below a water content of 12%. Decreased absorption also occurs above a 20% water content.

30
Q

Temperature of Soda Lime Canister

A

40-45C. The sides are cooler

31
Q

Composition of Soda Lime

A 
Ca(OH)2 - 79%
H2O - 13.6%
KOH - 2.3% (activator)
NaOH  - 1.2%
Indicator (ethyl violet) - 0.06%

Plus small amounts of silica to form Ca++ and Na+ silicates for hardness and binding.

32
Q

Composition of Baralyme

A 
Ca(OH)2 - 69%
Ba(OH)2 - 10.4%
H2O - 13.7%
KOH 4.6%
Indicator (ethyl violet) - 0.15%

Also contains silicates for hardness.

33
Q

Baralyme vs Soda Lime

A

Baralyme is more dense than sodalime and 15% less efficient, releases more water.

34
Q

In a properly packed canister, how many L of CO2 will be absorbed per 100g of Soda Lime before exit gas exceeds 1% CO2?

A

15 L will be absorbed per 100g.

For an 8 hour operation, 1kg of Soda Lime is needed.

35
Q

Factors that can reduce absorption efficiency of Soda Lime

A
  • Channeling (uneven flow through soda lime)
  • High gas flows, decreased CO2 residency time
  • Caking (particles stick together)
  • Decreased moisture
36
Q

Amsorb

A

a newer absorbent that greatly decreases sevoflurane and desflurane breakdown.

It accomplishes this by not containing the strong bases NaOH and KOH

37
Q

Amsorb composition

A

It consists of calcium hydroxide with a compatible humectant, namely, calcium chloride. The absorbent mixture does not contain sodium or potassium hydroxide, but includes two setting agents (calcium sulfate and polyvinylpyrrolidine) to improve hardness and porosity.

Others: Sodasorb LF (LF for low flow) also does not contain NaOH.

38
Q

Size of Soda Lime and Baralyme Granules

A

between 4 and 8 Mesh.

Size is a function of resistance to air flow and absorptive efficiency

39
Q

Mesh

A

Number of openings per linear inch in a sieve through which the particle can pass.

40
Q

4-mesh

A

four 1/4” openings per inch

41
Q

8-mesh

A

eight 1/8” openings per inch

42
Q

Shape of granules

A

To increase surface area, and thus absorption efficiency, granules are made porous and irregular shaped.

Newer granules are cylindrical in shape.

43
Q

Silica in Sodalime

A

Silica is added to sodalime to make granules harder and to reduce dust formation.
(we don’t want our patient inhaling dust!)

44
Q

Dye Indicator

A

Ethyl Violet used in sodalime and baralyme

45
Q

Critical pH of Ethyl Violet

A

10.3

>10.3 = colorless
<10.3 = turns purple
46
Q

When does pH of sodalime drop?

A

pH drops as the soda lime is exhausted because the very basic NaOH is depleted

47
Q

Color Change: CO2 absorption is a chemical reaction

A
  • removes CO2 from the gas flowing around granules in the container
  • reaction produces HEAT and MOISTURE
48
Q

Color Change: Exhaustion of CO2 absorber capacity indicators

A
  • color change to violet

- increasing ETCO2 monitoring level (>0.5% ERCO2 or 4mmHg)

49
Q

Color change requires moisture. What makes absorbent dry out?

A
  • exposure to constant gas flows for long periods of time
  • heat

** beware: color change can also reverse, making it appear like absorbent is unused!

50
Q

Why do circuits get wet?

A

Average adult exhaled CO2 is 200 mL/min at rest.
When absorbed, this CO2 produces 8mL of h2O/hr
8 hours = 70mL H2O!

51
Q

Causes of potential deactivation of ethyl violet dye indicator:

A

a. Fluorescent lights
b. Intense UV light
c. long periods of time (oxygen flushes = oxidation of dye).
d. severe moisture loss

52
Q

Oxygen flush impact on ethyl violet dye

A

Oxygen flushes will allow oxidation and dehydration of the dye absorbant

53
Q

Color Reversion of Ethyl Violet

A

After setting for several hours following use, subsurface Ca(OH)2 may allow dye to revert to colorless due to pH increasing to > 10.3. This may occur when soda lime is near exhaustion. Soda lime does not regenerate.

54
Q

Color Change duration

A

intensit fades, but color visible for 12 hours to months

55
Q

Canister temperature

A

absorption accompanied by HEAT but heat of canister is NOT an indicator of soda lime effectiveness!
Heat depends on gas flow rate, temp of OR, etc and canister may be warm even after soda lime is exhausted.

56
Q

Volatile fluorinated anesthetics can react w CO2 absorbents to result in several unwanted reactions including:

A

1) Carbon monoxide formation (des)
2) degradation products from sevo (Compound A-E but mostly A)
3) extreme heat and fire (sevo + baralyme)

Avoid this w Amsorb which doesn’t contain strong bases NaOH or KOH

Chem/Phys Exam 4 (10 decks)

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