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I&M Final > Oximetry > Flashcards

Oximetry Flashcards

1
Q

Hypoxemia

A

Oxygen deficiency in arterial blood

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2
Q

Hypoxia

A

The body or a region of the body is deprived of adequate oxygen supply

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3
Q

Causes of Hypoxemia

A

Decreased inspired oxygen, hypoventilation, shunt, or V/Q mismatch

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4
Q

Reasons for Hypoventilation

A

Respiratory center depression, neuromuscular disease, or respiratory failure

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5
Q

Reasons for Shunt

A

Pulmonary - Atelectasis, pneumonia, pulmonary edema, acute respiratory distress syndrome.
Cardiac - Patent foramen ovale

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6
Q

Reasons for V/Q Mismatch

A

Airway secretions, bronchospasm

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7
Q

Types of Hypoxia

A

Hypoxemic hypoxia, Anemic hypoxia, circulatory hypoxia, affinity hypoxia, and histotoxic hypoxia

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8
Q

Hypoxemic Hypoxia

A

Lower than normal PaO2

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9
Q

Anemic Hypoxia

A

Decreased red blood cell count, carboxyhemogobin, methemoglobin, or hemoglobinopathy

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10
Q

Circulatory Hypoxia

A

Decreased cardiac output or decreased local perfusion

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11
Q

Affinity Hypoxia

A

Decreased release of oxygen from hemoglobin to the tissues

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12
Q

Histotoxic Hypoxia

A

Cyanide poisoning

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13
Q

Oxyhemoglobin Dissociation Curve - Shift Left

A

Increases oxygen saturation for a given PO2 (increased affinity)

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14
Q

Oxyhemoglobin Dissociation Curve - Shift Right

A

Decreases oxygen saturation for a given PO2 (decreased affinity)

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15
Q

Oxyhemoglobin Dissociation Curve - Causes for Left Shift

A

Alkalosis, Hypocarbia, Hypothermia, Decreased DPG, Cabocyhemoglobin, and Fetal Hb

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16
Q

Oxyhemoglobin Dissociation Curve - Causes for Right Shift

A

CADET face Right!

Hypercarbia, Acidosis, Increased DPG, Exercise, and Hyperthermia

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17
Q

Content Equation

A

CO2 = 0.0031 * PO2 + 1.31 * O2Hb * SO2

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18
Q

Carboxyhemoglobin

A

Hemoglobin and carbon monoxide

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19
Q

Methemoglobin

A

The iron heme is Fe3+ instead of Fe 2+

Cannot bind to oxygen

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20
Q

Spectrophotometry

A

Technology that performs quantitative measurement about the transmission of light using various wavelengths of light

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21
Q

Lambert-Beer Law

A

The concentration of substances absorbing light can be determined by measuring the amount of light entering and exiting the system

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22
Q

CO-Oximetry

A

Uses arterial blood gases to determine the amounts of each form of hemoglobin including oxyhemoglobin, deoxyhemoglobin, methemoglobin, carboxyhemoglobin, fetal hemoglobin, sickle cell hemoglobin, and sulfhemoglobin

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23
Q

*Fractional SaO2 equation

A

Fractional SaO2 = O2Hb / (O2Hb + Hb + COHb + MetHb + HbF)

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24
Q

*Functional SaO2 equation

A

Functional SaO2 = O2Hb / (O2Hb + Hb)

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25
Q

Pulse Oximeter

A

A specialized spectrophotometer that uses two wavelengths of light to measure HbO2 saturation

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26
Q

*Pulse Oximeter wavelengths

A

660nm - 940nm

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27
Q

*What two form of hemoglobin are read as SaO2 on a conventional pulse oximeter? At what wavelength are they absorbed equally?

A

Oxyhemoglobin and Carboxyhemoglobin

660nm

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28
Q

Transmission vs. Reflectance Oximetry

A

Transmission - LED and photodetector on opposite sides

Reflectance - LED and photodetector on the same side; Light reflects off of the bone underneath the perfused tissue

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29
Q

Possible protuberances used for pulse oximetry. Which is the most common?

A

Finger!

Ear, tongue, nose, toes, lips, penis

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30
Q

Why is pulsatile flow necessary for pulse oximetry?

A

Pulsatile flow allows the pulse oximeter to account for the effects of absorption of light by tissue and venous blood

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31
Q

AC vs. DC blood flow

A

AC: ‘Alternating current’ - Arterial blood flow
DC: ‘Direct current’ - venous, capillary, and non pulsatile arterial blood flow

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32
Q

Pulse oximetry utilizes what spectrum of light?

A

Red and infrared

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33
Q

Ratio of Ratios

A

R = (AC 660/DC 660)/(AC 940/DC940)

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34
Q

What are the R values for oxyhemoglobin and deoxyhemoglobin?

A

OxyHb - 0.4

DeoxyHb - 3.0

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35
Q

When the R value is 1.0, the displayed SpO2 is what?

A

85%

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36
Q

The Isobestic Point is at what wavelength?

A

800nm

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37
Q

*Normal Value for Hb P50

A

26.8mmHg

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38
Q

Causes of Low Perfusion

A

Intense vasoconstriction, severe peripheral vascular disease, hypothermia and hypovolemia

39
Q

Causes of Ambient Light Interference

A

Excessive sunlight, infrared warming devices, lights (fluorescent, phototherapy, surgical)

40
Q

Effects of Anemia on Pulse Oximetry

A

The pulse oximetry values stay the same despite the low hemoglobin content in the blood because the oxygen saturation of that hemoglobin is still the same

41
Q

Effects of Venous Pulsations on Pulse Oximetry

A

Venous pulsation will cause the pulse oximeter to record the venous oxygen saturation instead of the arterial oxygen saturation

42
Q

Effects of Carboxyhemoglobin on Pulse Oximetry

A

Carboxyhemoglobin in the blood will cause the pulse oximeter to show artificially high SpO2 values
The difference between the actual SpO2 and the measures SpO2 is approximately equal to the amount of COHb

43
Q

Effects of Methemoglobin on Pulse Oximetry

A

High levels of MetHb results in SpO2 readings of approximately 85%
Low levels of MetHb (<10%) will reduce a high SpO2 by approximately half of the amount of MetHb

44
Q

Masimo SET

A

Reduces motion artifact

45
Q

*Dyes in order of defending effect on SpO2

A

Methylene Blue, Lymphazurine Blue, Indocyanine Green, Indigo Carmine, Fluoresceine (no effect)

46
Q

Effects of nail polish on SpO2

A

Blues and blacks can absorb extra light and reduce the SpO2 reading by up to 6%
(Just turn the probe 90 deg.)

47
Q

Hazards of Pulse Oximetry

A

Pressure necrosis and thermal burns

Thermal burns happened as a result of incorrect probe connects and are no longer likely to occur

48
Q

Response times for Pulse Oximetry on the finger

A

Shortest delays: 25-35 seconds (cold, hypovolemic vasoconstriction)
Longest delays: 1 minute (hypotension)

49
Q

Accuracy of Pulse Oximetry

A

+/- 2% for 70%-100% saturation
+/- 3% for 50%-70% saturation
(one standard deviation)

50
Q

Disadvantages of Pulse Oximetry

A

Easy to misinterpret

Response too late for many catastrophic events

51
Q

Sudden sympathetic stimulation results in what effect on the pulse oximeter?

A

Vasoconstriction on the pulse oximeter waveform

52
Q

The asterisks in the top left corner of the SpO2 display box indicate what?

A

Pulse signal strength

53
Q

How do pulse oximeter failure rates relate to ASA physical status?

A

As ASA physical status increases so to do the failure rates
ASA 1 ~1% failure rate
ASA 4 ~7% failure rate

54
Q

Multi Wavelength Pulse Oximetry

A

Employs more wavelengths of light in addition to 660nm and 940nm
Able to distinguish more forms of hemoglobin, including COHb and MetHb

55
Q

Masimo Multi Wavelength Pulse Oximeter

A

Rainbow Rad-57

Radical-7

56
Q

*What is the Perfusion Index (PI)?

A

A numerical value that indicates the strength of the infrared signal returning from the monitoring site

57
Q

PI is a ______ number and varies between what?

A

Relative

Monitoring sites and patients

58
Q

What is Pleth Variability Index (PVI) and how do you calculate it?

A

PVI is a measurement of the dynamic change in PI that occurs during the respiratory cycle
PVI = (PImax - PImin) / PImax * 100

59
Q

Noninvasive continuous hemoglobin monitoring (SpHb) enables what?

A

More efficient blood transfusion management and early detection of bleeding

60
Q

A tactile ridge is used on which pulse-ox devices?

A

Fetal and esophageal reflectance oximetry

61
Q

T/F Transmission and Reflectance oximetry devices may be used in the manor of one another

A

False

62
Q

T/F Reducing the ambient light may help when a pulse-ox device is having difficulty obtaining a satisfactory reading

A

True

63
Q

The ASA standards for basic monitoring require what when a pulse oximeter is in use?

A

A variable pitch tone be audible

64
Q

Occasionally, poor function may occur with probe attachment on the same extremity as an intravenous infusion due to what?

A

Local hypothermia and vasoconstriction

65
Q

Which finger should be avoided for pulse-ox placement during patient recovery from anethesia?

A

The index finger

66
Q

A satisfactory pulse-ox waveform indicates what?

A

Reliable readings

67
Q

A discrepancy between pulse and EKG pulse rates indicates what?

A

Probe malposition or malfunction

Certain dysrhythmias

68
Q

Downside of preoxygenation when using pulse-ox

A

By the time desaturation occurs the clinician may not be thinking about incorrect tracheal tube placement

69
Q

T/F The absence of desaturation rules out bronchial intubation

A

False

70
Q

T/F Pulse oximetry is not reliable in diagnosing impaired perfusion with increased intracompartmental pressures

A

True

71
Q

T/F Pulse oximetry provides sufficient indication of hypoventilation in sedated patients receiving supplemental oxygen

A

False

72
Q

T/F Pulse oximetry is a reliable method of detecting leaks, disconnections and esophageal intubations

A

False

73
Q

If the pulse oximeter signal appears to be weak, the site should be checked for what?

A

Increased pressure

74
Q

Cardiac changes that can affect plethysmography variability

A

Cardiogenic shock, pericardial tamponade, pericardial effusion, constrictive pericarditis, restrictive cardiomyopathy, acute myocardial infarction

75
Q

Pulmonary changes that can affect plethysmography variability

A

Asthma, tension pneumothorax, pulmonary embolism, bronchospasm, airway obstruction

76
Q

Non-cardiac and non-pulmonary changes that can affect plethysmography variability

A

Hypovolemia, septic shock, anaphylactic shock, diaphragmatic hernia, superior vena cava obstruction, extreme obesity

77
Q

Cerebral Oximetry (rSO2) utilizes…

A

Utilizes Near-Infrared Spectroscopy (NIRS)

Utilizes two lengths of light to distinguish between tissue layers

78
Q

Near-Infrared Spectroscopy (NIRS)

A

Used in cerebral oximetry
Penetrates human tissues to a depth of several centimeters
710nm and 830nm are commonly used

79
Q

What does cerebral oximetry measure? What are the typical values?

A

Average saturation of arterial and venous compartments

55%-75%

80
Q

Problems with cerebral oximetry

A

Dependance on venous and arterial saturation and contaminants
Dependance of partition of arterial and venous blood (BP, PaCO2, hypoxia, pH, cerebral edema)

81
Q

Interventions to improve rSO2

A

Mechanical - Head position and cannula position
Decrease Demand - Increase anesthetic and increase temperature
Increase Supply - Increase FiO2, increase cerebral blood flow, increase CO2 to physiologic level, increase blood pressure, increase hematocrit

82
Q

Carodid Endarterectomy effect on cerebral oximetry

A

Clamping, shunt opening, shunt closing, and unclamping all cause significant differences in readings between the left and right hemispheres

83
Q

Tissue Oximetry (StO2)

A

Detects oxygenated and deoxygenated levels in the microcirculation

84
Q

What StO2 level indicates adequate perfusion?

A

75%

85
Q

StO2 is an early indicator of what?

A

Hypoperfusion

86
Q

Mixed Venous Oxygen Saturation (SvO2)

A

Functional mixed venous oxygen saturation using a fiberoptic pulmonary artery or venous catheter

87
Q

SvO2 indicates what?

A

The amount of oxygen returning to the pulmonary capillaries because it was not needed to support metabolic function

88
Q

What variables effect SvO2?

A

Blood flow, hemoglobin concentration, arterial oxygenation, and oxygen uptake (metabolic rate/perfusion)

89
Q

High CO and High SvO2 indicate

A

Sepsis, excessive blood flow

90
Q

High CO and Low SvO2 indicate

A

Anemia, hypoxia, high VO2

91
Q

Low CO and High SvO2 indicate

A

Low VO2

92
Q

Low CO and Low SvO2 indicate

A

Low output syndrome

93
Q

Jugular Venous Saturation (SjvO2) normal range

A

55%-75%

I&M Final (5 decks)

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