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Basics > Pulse Ox > Flashcards

Pulse Ox Flashcards

1
Q

oxyhemoglobin disassociation curve

A

describes relationship between SaO2, and PaO2

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2
Q

4 species of Hgb

A
  • Oxyhemoglobin (O2Hb): hgb with O2
  • Reduced Hemoglobin (Rhb): deoxygenated hgb
  • Methemoglobin (MetHb)
  • Carboxyhemoglobin ( COHb)
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3
Q

MetHb

COHb

A

dont transport O2, called dysfunctional Hgb

- very low concentrations

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4
Q

SaO2

A

functional hgb (ABG, measured in cooximeter)

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5
Q

SpO2

A

measured by pulse ox

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6
Q

Spectrophotometry

A

Lambert Beers Law

- relates the conc of a solute to the intensity of the light transmitted through a solution

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7
Q

Lambert Ber Law

A

at a constant light intensity and Hgb concentration the intensity of light transmitted through a tissue is a logarithmic function of the oxygen saturation of Hgb

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8
Q

Cooximeter

A

uses 4 wave lengths of light. 1 for each hgb

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9
Q

Spectrophotometry - pulse ox

Hgb absorbs light at ________

A

characteristic wavelengths

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10
Q

oxygenated hemoglobin absorbs

A

more infra red light (940nm) than red light

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11
Q

Deoxygenated hemoglobin absorbs

A

more red light (660nm) than infrared

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12
Q

The ratio btw _____ and _____ determine Sp O2

A
  • Oxygenated hemoglobin (O2Hb)

- reduced hemoglobin (Rh B)

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13
Q

Pulse ox wavelengths

A

2

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14
Q

Plethysmography

A

used to identify arterial wavelengths, detects pulsations.

venous- constant flow

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15
Q

Pulse ox diotes

A

2 diotes - 940 nm and 660 nm to differentiate btw O2hgb and RHgb

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16
Q

oxyhemoglobin dissociation curve

A

non linear relationship btw SaO2 and Pa O2

Hgb release O2 –> plasma —> o2 leaves plasma –> tissues

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17
Q

Shift to the left

A
  • holds O2 longer
  • greater affinity to bind to O2
  • decreased O2 to tissues
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18
Q

Leftward shift caused by

A 
alkalosis 
fetal Hgb 
methomoglobinemia and carboxyhemoglobinemia
hypothermia 
decreased 2,3, DPG (holding O2) 
- hyperventilating
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19
Q

Shift to right

A

gives up O2
Hgb less affinity to bind with O2
displaces O2 from Hgb
makes more O2 available to tissues

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20
Q

Rightward shift caused by

A 
acidosis 
volatile anesthetics 
hyperthermia 
preganancy 
increased 2, 3, DPG - releasing O2.. Starved for O2 
abnormal Hgb 
metabolic
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21
Q

DPG

A

enzyme made in RBC by chronic hypoxia. Bonds Hgb and O2, helps Hgb release O2 more.

22
Q

SpO2 95%

A

PaO2 - 80

23
Q

SpO2 90%

A

PaO2 - 60

24
Q

SpO2 <90%

A

subtract 30

25
Q

SpO2 90, 80, 70

A

Pa O2 = 60,50,40.. w/o fever, DPG you can predict

26
Q

Accuracy of pulse ox

A

70-100% = +/- 2%
50-70% = 3%
<50% not specified

27
Q

response

A

detection and calculation may take up to 40 seconds

28
Q

Dysfunctional hemoglobin

A

COHb and MetHb absorb light at one or 2 of the wavelengths used by standard pulse ox and may give false SpO2 readings
- accurate measurement requires 4 wavelengths oximetry (Co Oximeter)

29
Q

Carboxyhemoglobin COHb

A

normally <2%, smokers 6%

  • similar light absorbance properties as oxyhemoglobin resulting in false pulse ox
  • has carbon monoxide which binds to hgb more than O2
  • measured by ABG
  • seen in burn inj or poisoning
30
Q

Patho for COHb

- Carbon monoxide

A

limits O2 transport

greater affinity for Hgb 210x than O2

31
Q

Patho for COHb

- inhibits O2 _____

A

transfer

- interferes with unloading to tissues

32
Q

Patho for COHb

- binds with ______

A

myoglobin (muscle)

- interferes with heart and skeletal muscle fnx

33
Q

Patho for COHb

- binds with _________ oxidases

A

cytochrome

- induces anerobic metabolism (cellular and tissue)

34
Q

Patho for COHb

- increases _______ formation

A

N2O

  • accelerates free radical formation
  • significant vasodilation (hypotension)
35
Q

Methemoglobin

A

normally less than 1% of total hgb

  • congenital or acquired (drugs)
  • congenital: problems with enzyme B5 reductase) hgb cant metabolize Methgb
36
Q

MetHgb Fe3+

A 
Fe2+ = ferrous - hgb can bind 
Fe3+ = ferrate- hgb cannot bind... MetHgb stays in Fe3+
37
Q

MetHgb >/= 35%

A

pulse ox will read 85%
causing - falsely low sat reading with SaO2 is >85
- falsely high reading when SaO2 <85%

38
Q

MetHgb common causative drugs

A

LA- prilocaine, lidocaine, benzocaine

Metroclopramide, Nitric Oxide, Nitro, and sodium prusside

39
Q

Fetal hgb (HbF)

A

acts like adult hgb (HbA) has little effect on accuracy of pulse ox

40
Q

Sickle cell anemia (HbS)

A

believed to have little effect on Pulse ox

41
Q

IV dyes

A 
methylene blue
indigo carmine 
indocyanine green, 
isosulfan blue (Lymphazurin)
nitrobenzene 
- all can cause sudden decrease in saturation
42
Q

Which dyes decrease sats for a few minutes

A

methylene blue

indigo carmine

43
Q

Which dye will give false low sat for a few hours

A

isosulfan blue (Lymphazurin)
6-8 hours.
if your pt looks blue - get ABG

44
Q

Artifact on pulse ox

A
  • nail polish and acrylic nails - false low
  • ambient light- erratic reading (cover probe)
  • motion- erratic reading (moving causes veins to pulsate, pulse ox reads veins instead of arteries)
  • low perfusion (cold) can prevent detection (warm the fingers)
45
Q

adequate SpO2

A

does NOT mean good ventilation

maybe hypercarbic - hypoventilating

46
Q

ventilation

A

always measure CO2 not Sp02

47
Q

Normal ETCO2

A

does not mean good oxygenation

- ARDS

48
Q

Pulse ox Does not give___

A

info about delivery to tissues

SV02- better for delivery to tissue

49
Q

Cyanosis

A

not good indicator of hypoxia

  • anemic pt can be hypoxic without cyanosis
  • 5g of reduced hgb in capillary bed to = cyanotic… anemic pt wont reach 5
50
Q

polycythemic and cyanotic

A

not hypoxic, still have enough hgb to carry O2

Basics (9 decks)

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