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pmi > 8. Pulse Oximetry > Flashcards

8. Pulse Oximetry Flashcards

1
Q

how many hemoglobin per RBC

A

300 million

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2
Q

hemoglobin subunits

A

4 subunits
each subunit contains a heme group

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3
Q

heme group

A

porphyrin ring
iron (site of oxygen binding)

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4
Q

how may oxygen molecules can 1 hemoglobin bind?

A

4 subunits
each bind 1 oxygen

= 4 total oxygen per hemoglobin

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5
Q

how many oxygen molecules per RBC

A

over 1 billion oxygen molecules

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6
Q

hematocrit
(Hct)

A

percentage of blood that is red blood cells

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7
Q

blood components

A

plasma
white blood cells (thrombocytes)
red blood cells (RBCs)

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8
Q

normal male hematocrit

A

45%

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9
Q

normal female hematocrit

A

39%

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10
Q

hematocrit vs hemoglobin lab values

A

Hct = 3xHb

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11
Q

hematocrit units

A

percentage

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12
Q

hemoglobin units

A

concentration (g/dL)

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13
Q

anemia

A

decrease in hemoglobin and/or hematocrit

  • decr Hct will result in decr Hb (directly proportional)
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14
Q

anemia Hb

A

<6.5 g/dL
<65 g/L

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15
Q

anemia Hct

A

<20%

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16
Q

Causes of anemia

A

fluid administration
- dilutes [Hb]
blood loss
- decr Hb
lysed RBCs
- destroyed Hb
renal insufficiency/failure
-decr erythropoietin (EPO) production. –> less RBCs

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17
Q

PAO2

A

partial pressure of O2 in the alveoli

cannot measure
can calculate

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18
Q

PAO2 factors

A

primarily determined by pt FiO2
- incr FiO2 = incr PAO2
- decr FiO2 = decr PAO2

barometric pressure
- higher alt: decr press = decr FiO2

minute ventilation (minimally)
- changing breathing rate does not really help

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19
Q

PaO2

A

partial pressure of O2 in the arteries

portion of O2 that dissolves in blood

1.5% of all O2 in body

measured by blood sample

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20
Q

what percentage of O2 in the body is bound to hemoglobin?

A

98.5%

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21
Q

PaO2 factors

A

determined by PAO2
- decr PAO2 = decr PaO2 (room air)
- incr PAO2 = incr PaO2 (supp O2)

not affected by Hct (RBC levels) or SaO2

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22
Q

normal PaO2

A

80-100 mmHg (room air)

decreases w/age

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23
Q

normal PaO2 for healthy pts calculation

A

PaO2 ~ 5x FiO2

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24
Q

low PaO2 causes

A

lung disease
problems w/alveolar capillary gas exchange

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25
Q

PaO2 can be a quick indicator of

A

if the pt has healthy or unhealthy lungs

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26
Q

SaO2

A

% of Hb that is saturated w/O2

directly measured: blood sample
indirect measure: pulse ox

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27
Q

SaO2 factors

A

Primarily determined by PaO2
- lower PaO2 = lower SaO2
- higher PaO2 = higher SaO2

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28
Q

supplementary O2 impacts to SaO2

A

supp O2 incr PAO2
(incr FiO2)
incr PAO2 = incr PaO2
(incr diffusion of O2 into blood)
incr PaO2 = incr SaO2
( Hb can soak up more O2)

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29
Q

Other factors that impact SaO2

A

pH
Co2
Temp
Anemia
2,3 DPG
Carboxyhemoglobin levels
Methemoglobin levels

these alter the way Hb soaks up O2

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30
Q

A-a Gradient

A

difference in PAO2 and PaO2
- PAO2 (lungs) vs PaO2 (blood)

should be small in healthy pts w/good lung diffusion

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31
Q

normal A-a Gradient

A

room air: 5-15mmHg
100% FiO2: 10-110mmHg

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32
Q

widened A-a Gradient

A

expected w/lung disease
-impaired alveolar/capillary diffusion

PAO2 = normal
- O2 can still get into alveoli
PaO2 = decreased
- more difficult to get O2 into blood

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33
Q

Oxyhemoglobin Dissociate Curve
(HbO2)

A

shows how PaO2 determines SaO2

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34
Q

PaO2 = 60 mmHg

A

SaO2 = 90%

35
Q

PaO2 = 27 mmHg

A

SaO2 = 50%

36
Q

Right Shift HbO2

A

Hb less affinitive f/O2
- wants to release O2 to tissues
- better tissue perfusion

Same level of O2 in blood
– Pa O2 no change
Hb unable to saturate as much w/O2
– SaO2 lower

If you want to incr SaO2 with a right shift, you need to increase PaO2

37
Q

Right Shift HbO2 causes

A

acidosis (decr pH)
hypventilation (incr CO2)
incr 2,3-DPG
anemia
hyperthermia

when you want better O2 delivery to tissues

38
Q

Bohr effect

A

right shift

PaCo2 incr
O2 displaced from Hb

39
Q

Left Shift HbO2

A

Hb more affinitive f/O2
- worse tissue perfusion

Same level of O2 in blood
– PaO2 no change
It does not take much O2 to achieve same SaO2

40
Q

Left Shift HbO2 causes

A

alkalosis (incr pH)
hyperventialtion (decr CO2)
decr 2,3-DPG
hypothermia
CO poisoning (carboxy Hb)
CN poisoning (cyano Hb)
methemoglobinemia (metheoglobin)

41
Q

P50

A

the PaO2 which will cause a SaO2 of 50%

42
Q

P50 of 27

A

when the PaO2 is 27mmHg
the SaO2 of an adult is 50%

43
Q

High P50

A

right shift
Hb less affinitive for O2
better tissue perfusion

44
Q

Low P50

A

left shift
Hb more affinitive for O2
worse tissue perfusion

45
Q

P50 Sickle Cell anemia (HbS)

A

31 mmHg

want to be less affinitive for O2 to increase tissue perfusion

46
Q

P50 Pregnancy

A

30 mmHg

want mom to be less affinitive for O2 to donate more O2 to the baby

47
Q

P50 fetal

A

19 mmHg

baby is more affinitive for O2 to steal more O2 from mom

48
Q

P50 packed RBC

A

18 mmHg

low due to depleted 2,3-DPG

49
Q

SaO2 Direct Measurement

A

draw arterial blood sample
- blood gas
- ABG

50
Q

SaO2 Indirect Measurement

A

SpO2
pulse oximetry
not always accurate

51
Q

SpO2 monitor

A

plethysmography
- finger volume changes

SpO2
pulse rate

52
Q

what indicates adequate pulse measurement in SpO2?

A

adequate waveform

53
Q

Oxyegenated Hb light absorption

A

absorbs more IR (940 nm)

allows more RED to pass (660nm)

54
Q

De-oxygenated Hb light absorption

A

absorbs more RED (660 nm)

allows more IR to pass (940nm)

55
Q

when is the pulse oximeter accurate?

A

if it has a good waveformc

56
Q

Causes of bad SpO2 waveform

A

blood pressure cuff on same side
- flattens SpO2 wave on inflation
conditions that decr BF to fingers
- hypotension
- vasoconstriction (NE infusion)
- cold extremities (hyperthermia)
- low cardiac output
motion/shivering

57
Q

SpO2 probe placement

A

Best: opposite arm as BP cuff
(same side as IV)

58
Q

NIBP cuff placement

A

opposite side as IV

59
Q

alternative pulse ox placements

A

ear clip

nose clip

closer to heart = respond more quickly to SpO2 changes
(more accurate)

60
Q

SpO2 accuracy

A

95% accurate when SpO2 >70%

(more inaccurate as SpO2 decreases)

61
Q

bad SpO2 waveform treatment

A

ear/nose probe
treat hypotension (if present)
warm up extremities

62
Q

SpO2 HR and ECG HR relationship

A

should be equal

if not equal, look for the bad waveform.

Trust the one with the good waveform.

63
Q

Low SpO2
Normal SaO2 Causes

A

false low reading
bade waveform
diagnostic IV dye (MB,indigo carmine)
dark nail polish

64
Q

Low SaO2
Normal SpO2

A

false normal reading
CO poisoining
CN toxicity

65
Q

CO poisoning

A

CO binds to Hb
- CO is 230x more affinitive for Hb
displaces O2
- decr SaO2
caboxyhemoglobin forms (COHb)

CO absorbs light in same was as O2
- normal SpO2 reading

66
Q

COHb Formation Causes

A

smoking/smoke inhalation
- nonsmokers: 1%
- smokers: 8-10% (SpO2: 90%)
dried out CO2 absorbant (old type)

67
Q

CO2 absorbant old type fun facts

A

degradation of VA can produce CO
risk increases w/dried out absorbant

new CO2 absorbant doesnt degrade VA into CO or compound A

68
Q

CO Poisoning Diagnosis

A

SaO2: decreased (hypoxic)
SpO2: normal or elevated
- COHb absorbs same RED as O2
- SpO2 thinks COHb is O2
PaO2: no change
No cyanosis
- Hb is still bound (skin pink/red)

69
Q

2 methods to confirm CO poisoning

A

arterial blood gas lab
- SaO2
- carboxyhemoglobin saturation
- % methemoglobin

co-oximeter
- special pulse ox for CO detection

69
Q

what has a higher effect on tissue perfusion: SaO2 or PaO2?

A

SaO2

70
Q

CO poisoning treatment

A

administer 100% O2
- awake: mask
- unconscious: intubate (mech)

71
Q

CN- poisoning

A

CN- bind to Hb
displace O2
creates cyanohemoglobin (CNHb)
decreased SaO2 (hypoxia)

72
Q

CN- poisoning diagnosis

A

SaO2: decreased SaO2 (hypoxia)
PaO2: normal
SpO2: normal
No cyanosis

73
Q

2 methods to confirm CN- poisoning

A

arterial blood gas
Co-oximeter

74
Q

causes of CN- poisoning

A

high nitroprusside (nipride)
smoke inhalation

75
Q

CN- poisoning treatment

A

Sodium nitrate
Sodiam thiosulfate

76
Q

Methemoglobinemia

A

formation of methemoglobin
MetHb

iron is oxidized
- Fe2+ to Fe3+

77
Q

Causes of MetHb

A

high dose nitroprusside
high dose nitroglycerine
local anesthetic in pharynx
- benxocaine
- cetacaine
chemical workers
- factory/mine/pesticides

78
Q

nitroprusside

A

extremely potent vasodilator
infusion
light sensitive so covered w/ bag

79
Q

nitroglycerin

A

vasodilator
less potent than nipride
more common
can be bolused

80
Q

MetHb diagnosis

A

SaO2: decreased (hypoxia)
- unable to bind O2
SpO2 reading: 85%
PaO2: no change
cyanosis

81
Q

Why does the SpO2 read 85% for MetHb

A

absorbs identical amounts of Red (660nm) and IR (940nm) light

82
Q

MetHb treatment

A

methylene blue

pmi (18 decks)

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