13a- Clinical Correlations: Hypoxemia Flashcards
What is hypoxemia? How do we measure it?
Reduced oxygen tension (partial pressure) below that normally experienced by that organism-low pO2
measured by pulse ox or arterial blood gas (ABG)
What is hypoxia? How is it diagnosed?
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
Anoxia
total lack of oxygen at the tissue level which causes end organ dysfunction
What is:
A
a
FIO2
How many mmHg is 1 Torr?
A: alveolar
a-arterial
FIO2- fraction of inspired oxygen
1 Torr-1mmHmg
What are the PaO2 values for the different classifications of hypoxemia?
Normal
Mild hypoxemia
Moderate hypoxemia
Severe hypoxemia
Normal 80-11 mmHg
Mild hypoxemia 60-80mmHg
Moderate hypoxemia 40-60 mmHg
Severe hypoxemia <40 mmHg
What are the 4 types of hypoxia?
Hypoxemic
Anemic
Stagnant
Histotoxic
What are the 4 causes of hypoxemia?
- 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
What is Dalton’s Law?
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
What is Henry’s Law of Gases?
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
What things can cause left shift on the hemoglobin dissociation curve?
WHat things cause a right shift?
left: increased pH, decreased DPG, decreased temp
Right: decrease pH, increase DPG, increase temp
How pO2 change as you move from the air to the alveoli and then into the blood?
PO2 in the air is 150
PAO2 is 100
PVO2 is 40 and then PaO2
What is the A-a gradient? What is the equation? In a perfect world what should it be?
- PAO2-PaO2
- used to help define the mechanism of hypoxemia
- assesses the integrity of the alveolar-capillary unit
- alveolar oxygen partial pressure
simplified on room air at seal level with 100% water vapor in alveolus equation is:
A-a gradient: 150-5/4(PaCO2)-PaO2
A typical gradient is 5-10mmHg (but in a perfect worl it would be 0)
Calculate the A-a gradient. Compare it to a normal gradient:
pH=7.35
pCO2=60
pO2= 65
HCO3=30
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.
What is Dalton’s Law of Partial Pressure?
total pressure=sum of individual gas pressures
partial pressure=pressure that each gas would exert if it were alone
If the A-a gradient is 10, and pCo2=60 and pO2=65, why are they hypoxemic?
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
What is this picture demonstrating? In what disease is it often found?
Clubbing of fingers often found in interstitial lung disease
What usually happens to the DLCO during interstitial lung disease? Why does it change?
it decreases! Sometimes all the way down to 50%
Increased thickness of the interstitium
