Pulse Ox

Question 1

oxyhemoglobin disassociation curve

Answer 1

describes relationship between SaO2, and PaO2

Question 2

4 species of Hgb

Answer 2

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

Question 3

MetHb

COHb

Answer 3

dont transport O2, called dysfunctional Hgb

- very low concentrations

Question 4

SaO2

Answer 4

functional hgb (ABG, measured in cooximeter)

Question 5

SpO2

Answer 5

measured by pulse ox

Question 6

Spectrophotometry

Answer 6

Lambert Beers Law

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

Question 7

Lambert Ber Law

Answer 7

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

Question 8

Cooximeter

Answer 8

uses 4 wave lengths of light. 1 for each hgb

Question 9

Spectrophotometry - pulse ox

Hgb absorbs light at ________

Answer 9

characteristic wavelengths

Question 10

oxygenated hemoglobin absorbs

Answer 10

more infra red light (940nm) than red light

Question 11

Deoxygenated hemoglobin absorbs

Answer 11

more red light (660nm) than infrared

Question 12

The ratio btw _____ and _____ determine Sp O2

Answer 12

• Oxygenated hemoglobin (O2Hb)

- reduced hemoglobin (Rh B)

Question 13

Pulse ox wavelengths

Answer 13

2

Question 14

Plethysmography

Answer 14

used to identify arterial wavelengths, detects pulsations.

venous- constant flow

Question 15

Pulse ox diotes

Answer 15

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

Question 16

oxyhemoglobin dissociation curve

Answer 16

non linear relationship btw SaO2 and Pa O2

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

Question 17

Shift to the left

Answer 17

• holds O2 longer
• greater affinity to bind to O2
• decreased O2 to tissues

Question 18

Leftward shift caused by

Answer 18

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

Question 19

Shift to right

Answer 19

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

Question 20

Rightward shift caused by

Answer 20

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

Question 21

DPG

Answer 21

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

Question 22

SpO2 95%

Answer 22

PaO2 - 80

Question 23

SpO2 90%

Answer 23

PaO2 - 60

Question 24

SpO2 <90%

Answer 24

subtract 30

Question 25

SpO2 90, 80, 70

Answer 25

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

Question 26

Accuracy of pulse ox

Answer 26

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

Question 27

response

Answer 27

detection and calculation may take up to 40 seconds

Question 28

Dysfunctional hemoglobin

Answer 28

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)

Question 29

Carboxyhemoglobin COHb

Answer 29

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

Question 30

Patho for COHb | - Carbon monoxide

Answer 30

limits O2 transport | greater affinity for Hgb 210x than O2

Question 31

Patho for COHb | - inhibits O2 _____

Answer 31

transfer | - interferes with unloading to tissues

Question 32

Patho for COHb | - binds with ______

Answer 32

myoglobin (muscle) | - interferes with heart and skeletal muscle fnx

Question 33

Patho for COHb | - binds with _________ oxidases

Answer 33

cytochrome | - induces anerobic metabolism (cellular and tissue)

Question 34

Patho for COHb | - increases _______ formation

Answer 34

N2O - accelerates free radical formation - significant vasodilation (hypotension)

Question 35

Methemoglobin

Answer 35

normally less than 1% of total hgb - congenital or acquired (drugs) - congenital: problems with enzyme B5 reductase) hgb cant metabolize Methgb

Question 36

MetHgb Fe3+

Answer 36

``` Fe2+ = ferrous - hgb can bind Fe3+ = ferrate- hgb cannot bind... MetHgb stays in Fe3+ ```

Question 37

MetHgb >/= 35%

Answer 37

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

Question 38

MetHgb common causative drugs

Answer 38

LA- prilocaine, lidocaine, benzocaine | Metroclopramide, Nitric Oxide, Nitro, and sodium prusside

Question 39

Fetal hgb (HbF)

Answer 39

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

Question 40

Sickle cell anemia (HbS)

Answer 40

believed to have little effect on Pulse ox

Question 41

IV dyes

Answer 41

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

Question 42

Which dyes decrease sats for a few minutes

Answer 42

methylene blue | indigo carmine

Question 43

Which dye will give false low sat for a few hours

Answer 43

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

Question 44

Artifact on pulse ox

Answer 44

- 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)

Question 45

adequate SpO2

Answer 45

does NOT mean good ventilation | maybe hypercarbic - hypoventilating

Question 46

ventilation

Answer 46

always measure CO2 not Sp02

Question 47

Normal ETCO2

Answer 47

does not mean good oxygenation | - ARDS

Question 48

Pulse ox Does not give___

Answer 48

info about delivery to tissues | SV02- better for delivery to tissue

Question 49

Cyanosis

Answer 49

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

Question 50

polycythemic and cyanotic

Answer 50

not hypoxic, still have enough hgb to carry O2