13a- Clinical Correlations: Hypoxemia Flashcards

1
Q

What is hypoxemia? How do we measure it?

A

Reduced oxygen tension (partial pressure) below that normally experienced by that organism-low pO2

measured by pulse ox or arterial blood gas (ABG)

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2
Q

What is hypoxia? How is it diagnosed?

A

when low oxygen levels cause end organ/tissue dysfunction

**just like how it is azotemia until there are symptoms and then it is uremia**

Diagnosed clinically

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3
Q

Anoxia

A

total lack of oxygen at the tissue level which causes end organ dysfunction

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4
Q

What is:

A

a

FIO2

How many mmHg is 1 Torr?

A

A: alveolar

a-arterial

FIO2- fraction of inspired oxygen

1 Torr-1mmHmg

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5
Q

What are the PaO2 values for the different classifications of hypoxemia?

Normal

Mild hypoxemia

Moderate hypoxemia

Severe hypoxemia

A

Normal 80-11 mmHg

Mild hypoxemia 60-80mmHg

Moderate hypoxemia 40-60 mmHg

Severe hypoxemia <40 mmHg

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6
Q

What are the 4 types of hypoxia?

A

Hypoxemic

Anemic

Stagnant

Histotoxic

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7
Q

What are the 4 causes of hypoxemia?

A
  • decreased partial pressure of oxygen in atmosphere
  • decreased diffusion across the alveolar or capillary membrane
  • slow or absent blood flow in the capillaries that afects ability of oxygen to travel into the blood
  • metabolic derangements as acidosis or fever
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8
Q

What is Dalton’s Law?

A

each of the gases present in a space contribute to the total pressure in proportion to it’s relative abundance

760mmHg= PO2 + PCO2 + PN2

760mmHg x .21(FIO2) about 150 mmHg

total pressure= sum of individual gads pressures

partial pressure= pressure that each gas would exert if it were alone

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9
Q

What is Henry’s Law of Gases?

A

At a constant temperature, the amount of gas that dissolved in a certain type/ amount of liquid is directly proportional to the partial pressure of that gas when in equilibrium with that liquid

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10
Q

What things can cause left shift on the hemoglobin dissociation curve?

WHat things cause a right shift?

A

left: increased pH, decreased DPG, decreased temp

Right: decrease pH, increase DPG, increase temp

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11
Q

How pO2 change as you move from the air to the alveoli and then into the blood?

A

PO2 in the air is 150

PAO2 is 100

PVO2 is 40 and then PaO2

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12
Q

What is the A-a gradient?

A
  • PAO2-PaO2
  • used to help define the mechanism hypoxemia
  • assesses the integrity of the alveolar-capillary unit
  • alveolar oxygen partial pressure

PAO2- FIO2 (Pb-Ph20) -PACO2 (FIO2 + (1-FIO2/R))

simplified on room air at seal level with 100% water vapor in alveolus becomes

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13
Q

Calculate the A-a gradient. Compare it to a normal gradient:

pH=7.35

pCO2=60

pO2= 65

HCO3=30

A

A-agradient= 150-5/4(PaCO2)-PaO2

A-a gradient=150-5/4(60)-65

A-a gradient=10

This is normal! normal is 5-10.

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14
Q

What is Dalton’s Law of Partial Pressure?

A

total pressure=sum of individual gas pressures

partial pressure=pressure that each gas would exert if it were alone

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15
Q

If the A-a gradient is 10, and pCo2=60 and pO2=65, why are they hypoxemic?

A

Not a diffusion problem because gradieent is normal

They are hypoxemic becasue they have high CO2 so according to Dalton’s law pO2 must decrease

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16
Q

What are the 3 pathologic causes of an elevated A-agradient? What is one physiologic cause?

A

Pathologic:

  • diffusion defects
  • V/Q mismatch
  • Systemic shunts (right to left shunt)

Physiologic: increases with age!

17
Q

What is this picture demonstrating? In what disease is it often found?

A

Clubbing of fingers often found in interstitial lung disease

18
Q

What usually happens to the DLCO during interstitial lung disease? Why does it change?

A

it decreases! Sometimes all the way down to 50%

Increased thickness of the interstitium