13a- Clinical Correlations: Hypoxemia

Question 1

What is hypoxemia? How do we measure it?

Answer 1

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

measured by pulse ox or arterial blood gas (ABG)

Question 2

What is hypoxia? How is it diagnosed?

Answer 2

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

Question 3

Anoxia

Answer 3

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

Question 4

What is:

A

a

FIO2

How many mmHg is 1 Torr?

Answer 4

A: alveolar

a-arterial

FIO2- fraction of inspired oxygen

1 Torr-1mmHmg

Question 5

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

Normal

Mild hypoxemia

Moderate hypoxemia

Severe hypoxemia

Answer 5

Normal 80-11 mmHg

Mild hypoxemia 60-80mmHg

Moderate hypoxemia 40-60 mmHg

Severe hypoxemia <40 mmHg

Question 6

What are the 4 types of hypoxia?

Answer 6

Hypoxemic

Anemic

Stagnant

Histotoxic

Question 7

What are the 4 causes of hypoxemia?

Answer 7

• 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

Question 8

What is Dalton’s Law?

Answer 8

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

Question 9

What is Henry’s Law of Gases?

Answer 9

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

Question 10

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

WHat things cause a right shift?

Answer 10

left: increased pH, decreased DPG, decreased temp

Right: decrease pH, increase DPG, increase temp

Question 11

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

Answer 11

PO2 in the air is 150

PAO2 is 100

PVO2 is 40 and then PaO2

Question 12

What is the A-a gradient?

Answer 12

• 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

Question 13

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

pH=7.35

pCO2=60

pO2= 65

HCO3=30

Answer 13

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.

Question 14

What is Dalton’s Law of Partial Pressure?

Answer 14

total pressure=sum of individual gas pressures

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

Question 15

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

Answer 15

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

Question 16

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

Answer 16

Pathologic:

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

Physiologic: increases with age!

Question 17

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

Answer 17

Clubbing of fingers often found in interstitial lung disease

Question 18

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

Answer 18

it decreases! Sometimes all the way down to 50%

Increased thickness of the interstitium